Volume 63 (2011)
List of Contents
Volume 63, Issue 1
- Microstructure and Thermomechanical Behaviour of a SiC-based Refractory
- Strony: 4-10
Refractory materials are commonly used in waste-to-energy plants. They compose part of the wall covering the combustion chamber and protect metallic cooling tubes. Refractories are subjected to severe thermal gradients, to corrosion and to high temperature levels. They also collect part of the thermal energy generated by the waste combustion in order to allow electrical energy production. Such materials must couple a high thermal conductivity and high thermomechanical properties to cope with running solicitations. Nitride-bonded silicon carbides (NBSC) are porous materials with high thermal and mechanical properties. Microstructures and Thermomechanical properties are investigated in order to understand their behaviour in waste-to-energy plants. Specific properties come from their processing route. The resulting microstructure deals with SiC grains bonded with silicon nitride phases. Such bonding phases are characterised by a high complexity degree. Microstructural properties of as-received NBSC refractory are studied. They deal with the crystalline phase identification (by X-ray diffraction) and phase morphology (by SEM). As the material is used at high temperature in oxidizing atmospheres, the oxidation occurs. Long-term oxidation effects are investigated. Phase and morphological changes are considered. Kinetic aspects of oxidation are taken into account, too. Thermomechanical properties are also studied. In the 20-1200°C temperature range, NBSC refractory exhibits a linear elastic behaviour. The effect of long-term oxidation on the thermomechanical behaviour is also investigated.
- Preparation of β-sialon Bonded Al2O3-Refractories in Different Atmospheres
- Strony: 11-15
Six test series of sialon bonded Al2O3-refractories with the same composition have been sintered at different temperatures and indifferent atmospheres. A reasonable phase composition was ascertained. For the sintering, two different electrically heated furnaces were used, one heated with graphite heating elements (furnace G) and one with MoSi2 heating elements (furnace M). The samples were sintered in nitrogen atmosphere at temperatures from 1400 to 1650°C. The oxygen partial pressure in furnace M was partly defined by the use of a carbon bed and partly by the use of N2/CO gas. The results show that β-sialon cannot be prepared at a sintering temperature of 400°C. At 1550°C and 1650°C different atmospheres lead to the formation of different phases in the matrix. These phases are β-sialon, X-sialon, mullite, glassy phase, Si, SiC and carbon besides the main component Al2O3. The occurrence of silicon shows that the control of the atmosphere is also very important to assure a complete nitration, which is necessary for β-sialon formation.
- Characteristics of Refractories Applied in Glass Tanks
- Strony: 16-21
The performance of refractories influences significantly the lifetime of a glass tank and the quality of glass. The main general requirements addressed to the refractory material are: a feasible low level of glass defects and a feasible long service, which are in some cases contrary to each other. Thus, it is necessary to prove several characteristics essential for the behaviour of refractory material in a glass tank prior to its application, especially in the case of melting glasses where the products are subjected to strict specification conditions. The application examples of some testing methods used to characterize refractories, especially the fusion cast, intended to be used in contact with special glass melts and to qualify them for this application are shortly presented; e.g., examination of microstructure, analysis of thermal expansion behaviour, volume changes due to thermal cycling, static plate and dynamic corrosion tests as well as the blistering test with a continuous glass change. Taking into account the relations between parameters of the manufacturing process, the material microstructure and material properties, it is shown that an appropriately designed lab test and correct interpretations validated by the experience gathered during service in similar systems allow the proper choice and the right evaluation of refractories to be executed.
- Physical and Chemical Processes During Firing of ZrSiO4-Al2O3 Powders
- Strony: 22-26
Mullite-zirconia materials are of great interest for their application in filters, catalytic carriers, heat exchangers, as well as coatings in combustion engines and classical refractories. They posses high fi re and heat shock resistance as well as good mechanical and chemical resistance at high temperatures. The microstructure of the material is formed as a result of complex physical and chemical processes taking place at high temperatures. Their course depends on temperature, purity and grain size of the substrates. In this work, the microstructure evolution was studied in the samples composed of ZrSiO4 and α-Al2O3. The samples were prepared from commercially available powders showing various grain size distributions. The oxide composition was specified according to stoichiometry of the reaction: Al2O3+2ZrSiO4 →3Al2O3∙2SiO2 +ZrO2. The final fi ring was carried out at temperatures ranging from 1300°C to 1600°C for the time varying from half an hour up to 60 hours. The changes of chemical and phase compositions were examined with the application of XRD (Rietveld technique), FTIR and EDS analytical methods. The microstructure evolution was traced with SEM for the model samples prepared from ZrSiO4 (of grain size below 150 μm) and Al2O3 (of grain size distribution D90 below 10 μm). The obtained results have been used as a basis for the description of dominant mechanisms responsible for formation of the mullitezirconia material microstructure. It has been found that the decomposition of ZrSiO4 into oxide components takes place at the first stage of fi ring of the ZrSiO4 and α-Al2O3 powder. Then a two way diffusion of Si4+ and Al3+ ions goes on, followed by nucleation and growth of a crystalline mullite.
- Synthesis of Spinel - Calcium Zirconate Materials
- Strony: 27-33
The synthesis of spinel and calcium zirconate, by sintering natural dolomite, zirconia and alumina mixture, has been studied. The evolution of properties and microstructure of spinel-calcium zirconate material at one- or two-step firing process was investigated as a temperature function. The kinetic of the reaction of MgAl2O4 and CaZrO3 at mixes was estimated by XRD analysis. The densification process was investigated by using firing shrinkage, apparent density, average pore diameter and pore size distribution measurements. The microstructure of sintered materials was observed by SEM. The optimum properties of spinel-calcium zirconate material were obtained at the sufficiently low temperature of 1500°C.
- Refractories from the MgO-Al2O3-SnO2 System for Metallurgical Applications
- Strony: 34-39
Due to the excellent corrosion resistance and high durability, chrome containing refractories are broadly used in many branches of modern industry. However, among different types of refractory waste, chrome-containing materials after service are probably the most dangerous, requiring complex and expensive treatment before further processing. Due to the potential hazards from refractory waste and changes in technical preferences of the users, the share of chromium containing materials in the total production of refractories has been systematically decreasing. Searching for the chrome-free alternatives, fundamental properties of materials from the MgO-Al2O3-SnO2 system, i.e., phase composition and thermal stability, were studied. On that basis three different kinds of SnO2-containing refractories were prepared, i.e., fired bricks, chemically bonded and hydraulically bonded materials. The microstructure and basic properties of the developed refractories were investigated. The results obtained so far seem to be promising and confirm the possibility of applying of selected materials in low temperature processes as an alternative to typically used fired magnesia-chromite products.
- Experimental Phase Studies in the TeO2 – CdO System
- Strony: 40-43
In the present study, phase equilibrium in the TeO2–CdO system has been investigated. Different compositions of (1-x)TeO2–xCdO, where x = 0.10, 0.20, 0.25, 0.30 and 0.40 in molar ratio were prepared. The samples waited at 750°C in a platinum crucible for 30 minutes and then quenched in a water bath. DTA studies performed on as-cast samples. According to the DTA results, all samples were heat-treated at 550°C for 24 hours to obtain phase equilibrium. XRD and SEM/EDS studies were performed on the crystallized samples for microstructural analysis.
- Analysis of Nd3+/Yb3+ ions energy transfer in oxyfluoride silicate glass for optical fibre ASE source
- Strony: 44-47
The paper presents optimisation of Nd3+/Yb3+ ratio to enhance the emission bandwidth at 1 μm. Analysis of the energy transfer scheme between Nd3+ and Yb3+ ions incorporated in oxyfluoride glass was performed. The highest efficiency (60 %) was measured for the equalvalues of absorption cross-section (Yb3+) and emission cross-section (Nd3+). The emission spectrum with 100 nm bandwidth of the Nd3+/Yb3+ co-doped glass samples under excitation at 808 nm was determined. The fabricated glass with the highest efficiency of energy transfer Nd3+→Yb3+ was used as a core in helical core double clad optical fibre.
- Behaviour of Nickel Sulphide Inclusions in Glass Melts
- Strony: 48-53
A brief review of the magnitude of the nickel sulphide problem is discussed. Nickel sulphide inclusions have been studied in soda-lime annealed glass and SLS tempered glass. The discussion was meant to clarify the cause for appearing nickel sulphide inclusions in glass, and explain how these inclusions may cause tempered glass to break. Since these inclusions cannot be eliminated, the discussion addresses how to reduce the potential of nickel sulphide inclusion breakage. The glass batches with different source of nickel sulphide were melted in the laboratory conditions, as well as glass with metallic nickel addition was prepared. The possible forming process of nickel sulphide in glass was tested. The DTA/DSC, XRD, SEM studies allowed us to state that the formation of inclusion from nickel and sulphur during the manufacturing process is difficult, moreover in some cases not possible. The nickel sulphide was introduced to SLS float glass and then tempered. The tempered glass samples, which included the NiS stones, were investigated by microscopic (SEM) method and characterized by EDAX analysis. The glass samples were analysed by elastooptic studies. The obtained results will help to solve the problem of forming nickel sulphide inclusions.
- Phenomenon of Moisture Expansion and Its Influence on Mechanical Properties of Brick Clay Products
- Strony: 54-57
The paper considers the moisture expansion phenomenon, as a specific form of corrosion process of brick clay products degradation . The influence of the mineralogical composition of raw materials, firing temperature and environmental parameters on the magnitude of the moisture expansion phenomenon and mechanical properties of brick clay products have also been considered. The study of the moisture expansion phenomenon of brick products was done using two typical raw materials, one with a considerable and the other with a low content of earth-alkaline carbonates. All investigations were carried out at room temperature on the fired samples, on the fired samples after firing and after hydrothermal treatment and reheating of the samples at 550°C. It was found that brick moisture expansion depends on the presence or absence of earth-alkaline carbonates in raw materials, temperature of firing, appearance of amorphous phase as well as on the modulus of elasticity . Brick raw materials with low content of earth alkaline carbonates in the fired state show a higher tendency to moisture expansion and fired brick products with high content of earth alkaline carbonates show a minor tendency to moisture expansion . The experiments have confirmed the influence of the modulus of elasticity on moisture expansion magnitude. Moisture expansion caused the decrease of mechanical properties and small increase of the volume of brick clay products, ranging from 0,001 to 0,7 mm/m.
- The Influence of the Vitreous Phase of Fly Ashes on Sintering Process
- Strony: 58-63
Fly ashes developing from hard bituminous coal burnt in conventional boilers are a precious material used in ceramic production by means of sintering. Depending on their physical and chemical properties, they can be used as a raw material in production of building ceramics with both porous and solid sintered structure. If fly ashes are picked up with the use of a few sections of electrostatic precipitator, the ashes from each of these sections display a large diversity of their physical and chemical properties. These differences affect the kinetics of sintering and forming of the liquid phase. Although the influence of granularity and the amount of alkalis on the sintering process of the fly ashes is rather obvious, the influence of vitreous phase is not so clear. In this paper, the extensive research was carried out on a dozen different fly ashes focusing on the properties of their vitreous phase. The differences in the chemical composition of the vitreous phase in ashes were also pointed out and to what extent it is organized: the number of broken Si–O–Si bridges, the degree of Si4+↔Al3+ isomorphous replacements in tetrahedral positions. The achieved results together with the tests of fly ashes sintering gave grounds for putting forward a hypothesis concerning the role of the vitreous phase in sintering of fl y ashes. To examine the vitreous phase the following methods were used: FTIR, NMR, XRD/Rietveld and classic chemical analysis.
- Characteristic Features of Ceramic Materials Containing Waste Moulding Sand
- Strony: 64-73
This study summarises the properties of ceramic materials containing waste moulding sands, obtained from processing of used moulding and core mix. The sand preparation involved the crushing processes and separation of metallic parts. Thus prepared substance acted as a substitute for natural quartz sand, which is widely used as a leaning agent in ceramic plastic mass to be formed into ceramic-based construction materials. The issues addressed include the basic functional parameters, selected structural aspects and microstructure of ceramic materials made from plastic bodies varying in the qualitative and quantitative proportion of mould sand contents. Other aspects include the potential threats associated with manufacturing and utilisation of these type of materials. Potential hazards include atmospheric emissions of hazardous gaseous substances, particularly in the form of polycyclic aromatic hydrocarbons (PAHs) as derivatives of organic binders used in manufacturing of moulding and core mix. These substances can originate in the process of burning of ceramic products or might be produced when heavy metals are released from the ceramic matrix. This process might occur throughout the whole service life of ceramic products in the given conditions. Applicability of waste sands in this utilisation scheme is well proved by good parameters of thus obtained ceramic materials and positive results evidencing the absence of atmospheric emissions of hazardous substances and low-level leaching of heavy metals.
- Influence of Firing Conditions on Properties of Ceramic Materials Made of Carbon Slate
- Strony: 74-79
The results of investigations on ceramic materials properties are presented in this paper. The ceramics were obtained by mixing carbon slate from Lublin Coal Basin (LCB) and clays with addition of melaphyre (M) and quartz sand (QS). Subsequently the samples were fired according to three different firing cycles. The maximum temperature of fi ring was 1100°C and the cycles differed in the heating rate and soaking time. The firing cycles were modified in order to obtain a ceramic material with the limited number or even without defects, aiming also to meet the quality characteristics of clinker ceramics. The results show that the best properties were obtained for the ceramics fired according to the cycle with the longest duration. An addition of melaphyre and other plastic clays to the carbon slate ceramic masses improves the properties of the so-obtained ceramics. In most cases, the ceramics from carbon slate are characterized by satisfactory compression strength (about 40-65 MPa), required for clinker ceramics, low water absorption (about 8.5-12 %) and full resistance in the freeze-thaw test.
- Investigations of Chrysotile Asbestos Application for Sintered Ceramics Obtaining
- Strony: 80-84
Asbestos is a serious health hazardous substance and its removal is a priority for pollution prevention. The destruction of the tubular structure of asbestos can be achieved by means of thermal treatment. In order to characterize the changes accompanying thermal treatment, both natural chrysotile asbestos and calcined asbestos were subjected to the thermogravimetric and differential thermal analysis, X–ray diffraction phase analysis and examination by scanning electron microscopy. The results of laboratory investigations of using calcinated chrysotile asbestos to production of sintered ceramics (stoneware) are presented.
- The Effect of Cellulose Ethers on Water Retention in Freshly-Mixed Mortars
- Strony: 85-87
Cellulose ethers are polymers frequently introduced into mortar formulations in order to improve water retention capacity and workability of the freshly-mixed materials. Physico-chemical parameters of these admixtures (molecular weight, granulometry, substitution degrees, etc) seem to have a strong influence on mortar water retention capacity. In this paper, the influence of cellulose ether molecular weight on mortar water retention and its consistency was studied. Moreover, a new method was used to evaluate mortar consistency, named Consistor Baronnie method. This method was confirmed with rheological measurements.
- Influence of Fly Ashes Generated at Burning Hard and Brown Coal in Fluidized Boilers on AAC Phase Composition
- Strony: 88-92
Properties of fly ashes coming from the fluidized combustion of brown and hard coal, combined with desulphurization, are totally different as compared to the properties of conventional ashes. The fluidized process runs at about 850°C and calcium carbonate is used as a sorbent. Such an ash, when compared to conventional ashes, contains no glassy phase. It contains a considerable amount of an amorphous phase in the form of dehydrated silty minerals and crystalline phases in the form of quartz, free CaO, CaCO3 and CaSO4 II. The ash coming from fluidal combustion has totally different phases, as compared to conventional ashes. It results in alteration of both the structure and microstructure of autoclaved aerated concrete (AAC). PGS (foamed gas silicate) is an autoclaved aerated concrete manufacturing technology, commonly used in Poland. Its main raw materials comprise siliceous fly ashes from hard coal combustion, burnt lime, natural gypsum and aluminium powder used as a pore generating admixture. From the literature we can see that fly ashes coming from the fluidized brown and hard coal combustion combined with desulphurization can be utilized in AAC production. The main phase components of AAC are C-S-H and tobermorite (Ca5[Si6O18H2]·4H2O), small amount of C3A6, C3A·CaSO4·12H2O and hydrated calcium aluminosilicate (C3ASxH6-2x) which contain SiO2 in their chemical composition. Due to the increased amount of amorphous dehydrated silty minerals of metakaolin type, it is expected for fly ash from the fluidized combustion to result in a bigger amount of tobermorite (C5S6H5) in the fly ash added AAC. Fly ash from fluidized combustion also contains calcite. The presence of calcium carbonate in the mix may result in formation of crystalline calcium carboaluminate (C3A·CaCO3·11H2O) as well as scawtite (Ca7[Si6O18]·(CO3)·2H2O). It is expected that these phases will improve the properties of the fi nal material. The paper presents the influence of fly ashes generated in burning brown coals in fluidized boilers on AAC phase composition. The investigations were supported by X-ray diffraction (XRD), thermal analysis (DTA, DTG, TG) and scanning electron microscopy (SEM).
- Porosity Evolution of Cement Pastes Containing Sewage Sludge
- Strony: 93-97
In the presented paper the influence of addition of galvanic sewage sludge derived from industrial waste water on porosity of cement pastes were investigated. The pastes were made basing on common cements and binders containing Portland cement mixed with fly ash from the fluidized bed coal combustion of fuels. Porosity evolution of cement pastes containing sewage sludge additives and pastes without any additives was determined after 28, 90 and 180 days of hydration.
- Augmentation of Flexural Strength of Concrete Beams Glued with Carbon Laminate
- Strony: 98-103
Improvement of performance of building objects particularly made of concrete and stone (bridges, ceilings, girders) is more and more often obtained via reinforcing with thin, high-strength bands made of carbon polymers. The reinforcement comprises gluing high-module, or high-strength thin carbon laminate (using suitable resin) to the building element at its supporting side. Additional reinforcement is obtained in result of gluing carbon laminate, having suitable orientation of fibres at the beam side planes, within shearing areas. Bending strength tests, measurements of fracturing energy and measurements of static Young’s modulus were executed with the use of 500 x 26 x 26 mm concrete beams cut of the concrete B-30 blocks, made of concrete of C25/30 class, as well as with use of sandstone beams. 13.8-fold increase of bending strength, 124-fold increase of the destruction work and slight increase of Young’s modulus (1.6-fold) was observed for the concrete B-30 – carbon laminate system. Reinforcement with laminate and additional reinforcement of shearing zones resulted in 17.7-fold bending strength increase (load capacity) and 187-fold increase of destruction work. Reinforcement of shearing zones of concrete beams with laminate has no influence on the system Young’s modulus. Reinforcing 530 x 32 x 32 mm sandstone beams with carbon laminate results in 9.2-fold increase of bending strength and 23.2-fold increase of destruction work. Additional reinforcement of the shearing zones improved the bending strength with over 50 % and increased fracturing energy about 3 times. Analogous tests executed with the use of shorter sandstone beams proved considerably smaller values of the bending strength and destruction work. Freezing-corrosion tests with the use of concrete beams having low strength class and reinforced with laminate proved that bending strength is reduced with 60 % after 30 freezing-corrosion cycles, whereas the sandstone beams reinforced with laminate lose their bending strength with 20 % after 30 cycles.
- Influence of Processing on Magnesium Aluminate Precursors Morphology Prepared by Co-Precipitation
- Strony: 104-108
The aim of the presented work was to study the influence of processing conditions on the morphology of magnesium aluminate spinel precursor powders, co-precipitated using ammonium hydrogen carbonate at temperatures ranging from 10 to 70°C. XRD showed the same phase composition of precursor powders independent of precipitation temperature (NH4Al(OH)2CO3·H2O and Mg6Al2(CO3)(OH)16·4H2O). However, a strong difference in powder morphologies was found. The precursor prepared at 10°C consisted of round particles, while increasing the co-precipitation temperature resulted in rod-like grains. Magnesium aluminate precursors were calcined in air and then pressure-free vacuum sintered (1750°C/2h) without any powder pre-treatment or sintering additives. The best relative density of 98.9 % was obtained for ceramics prepared from the powder obtained at the lowest co-precipitation temperature.
- Dense and Porous Zirconia Prepared by Gelatine and Agar Gel-Casting: Microstructural and Mechanical Characterization
- Strony: 109-116
Dense and cellular yttria-tetragonal zirconia polycrystal (Y-TZP) bodies were produced by using a natural gelatine and two different agars as gelling agents, while commercial polyethylene (PE) spheres were added (125 to 300 μm diameter) as a volatile pore forming agent to create 50-65 vol.% spherical macro-pores, uniformly distributed in a micro-porous matrix. The microstructure of all dense and cellular ceramics was characterized by FEG-SEM and Focused Ion Beam (FIB) techniques. The mechanical properties of both dense and porous samples were investigated at the microscale by nanoindentation testing, while the influence of microporosity was obtained by the analysis of hardness and modulus depth profiles, coupled with FIB-SEM section observations of selected indentation marks. Mechanical characterization at the macroscale consisted of uniaxial compression tests and four point bending tests.
- ZrO2 Submicropowder Compaction Using Slip and Dry Methods
- Strony: 117-122
Three compaction methods of ZrO2 submicropowder: traditional uniaxial pressing, the pressure filtration method, and centrifugal compaction of slips using the HCP method (High-Speed Centrifugal Compaction Process), were compared. Pore size distribution of ZrO2 green compacts was measured using the method of mercury porosimetry. The most important influence on the HCP deposition process was expected by the centrifugal sedimentation conditions (velocity, duration of the process, dispersing agent) and the rotor geometry. The deposition process was carried out using an ultra-centrifuge with a rotational speed of 20000 rpm through 15 min for dispersive liquids of various pH. The influence of powder compaction method on properties of pressureless sintered ZrO2 compacts was analyzed. Microstructure observations were performed by SEM, and Vickers hardness measurements, dependent on a distance from the top surface to the bottom surface of samples, were taken. The HCP powder compaction strongly depends on pH of the ZrO2 colloidal suspensions. The highest density and hardness values are obtained for ZrO2 compacts which are prepared by the traditional uniaxial pressing of powders. The samples compacted using the HCP and the pressure filtration method are characterized by the layering of properties and variations in hardness distribution. But in the HCP compaction material, there is a nonporous area which is transparent.
- Sintering Studies of Transparent Yttria Ceramics
- Strony: 123-126
In the present work, transparent yttria ceramics were prepared by hot pressing using lithium fluoride as a sintering aid. The influence of lithium fluoride concentration (0.1 to 1.5 wt%) and sintering parameters (temperature, pressure) on properties of the ceramic were evaluated. The best transmittance was obtained for 1 wt% addition of LiF and sintering temperature of 1450°C. It was found that the appropriate temperature of pressure application, related to the temperature of LiF melting and further reaction between Y2O3 and LiF are the crucial points for good sintering effects.
- Rheological Behaviour of Gold Containing Screen Paints
- Strony: 127-130
A technique of silk-screen printing is the most of all used technology of decoration of ceramic articles. It is still developing in the direction of automation process and manner of bringing, fixing and the other useful properties of decoration. In the article, the results of rheological behaviour of both gold colours belong to the so-called screen paints no-water systems and lustre gold screen paints that due to their special behaviour are practically used in ceramic industry have been presented.
- Diamond–Ceramic Bonding Phase Composites for Application in Cutting Tools
- Strony: 131-137
Commercially available polycrystalline diamond compacts (PCD), consisting of a polycrystalline diamond-cobalt layer on a WC-Co substrate are used in drilling and machining applications. The presence of a cobalt phase in the diamond layer has the effect of significantly reducing thermal resistance. The thermal stability of a PCD material can be defined as its resistance to graphitization in an inert atmosphere at elevated temperatures. One of the possibilities to increase the thermal resistance of PCD materials is to reduce the cobalt content. The second one is the manufacturing of diamond compacts with a non-cobalt bonding phase. Presented in this paper are new trends for this type of material and my own experimental results of high-temperature sintering of diamond with carbides and/or silicides. The WC-Co layer allows for brazing of the PCD material to the tool body. Direct brazing of diamond materials to metal bodies is diffi cult and requires special solders and special conditions. Due to differences in thermal and mechanical properties between diamond and WC-Co, residual stresses develop in the interface region during the cooling from sintering, brazing or cutting temperatures. In an effort to reduce residual stresses, functionally graded material (FGM) diamond compacts with a ceramic bonding phase were designed and obtained. The results of X-ray phase composition analysis, electron microscopy microstructure observations, and selected physical and mechanical properties together with thermal resistance studies are presented.
- Expanded Polystyrene (EPS) Pattern Application in Investment Casting and Chemical Removing
- Strony: 138-142
In this study, expanded polystyrene (EPS) was used as a pattern material in investment casting and removed chemically by acetone. It is shown that EPS is an alternative pattern material to the wax material which is used in the conventional investment moulding. EPS pattern usage and chemical removing change basically the investment moulding process. The ceramic shell moulds with wax and EPS patterns were produced at the same dimensions and with the same techniques. Unmodified A 413 Al-Si alloy was cast into these moulds. XRD and SEM characterizations were performed on the mould internal surfaces, and image, EDS and surface roughness analysis were carried out on the cast parts for comparison. The effects of chemical removing of patterns on the structure of mould internal surfaces were investigated.
- Analysis and Optimization of Using Hemihydrates Plaster (β) for Casting Mould in Sanitary Ware Industry
- Strony: 143-146
Slip casting is a common method for producing sanitary ware, and it is just possible by plaster moulds. Therefore, in order to reach the best quality of sanitary ware, plaster moulds are playing an important role. Lifetime, water absorption and finished surface of Plaster moulds qualify the quality of final product significantly. Although, some characteristics of plaster mould depends on the plaster directly, others are affected by preparation process of moulds such as mixing time, plaster to water ratio, water temperature and drying process. In this investigation, hemihydrates plaster (β) of different suppliers has been studied by XRD; also particle size distribution of plasters has been analyzed by sieve shaker. Afterward, the best one has been selected, and effects of parameters involved in process of mould making have been studied to make an efficient plaster mould.
- Anode Materials for Solid Oxide Fuel Cells
- Strony: 147-150
The ceramic-metal composites (cermets) containing yttria-stabilized zirconia, YSZ, and Ni particles are commonly used as anode materials in solid oxide fuel cells. The long-term performance of fuel cells is strictly related to both the structural and electrical properties of anode materials. The chemical composition and preparation method are key to achieving high mixed electrical conductivity and high activity of electrochemical reactions and hydrocarbon fuel reforming. The materials containing 8 mol.% yttria-stabilized zirconia and Ni were prepared by co-precipitation method. The structure of the materials was characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and porosity studies. The coefficient of thermal expansion (CTE) was determined via a dilatometric method. Electrochemical impedance spectroscopy (EIS) was used to determine electrical conductivity.
- Structural and electrical properties of STF materials for SOFC applications
- Strony: 151-156
In this study, iron doped strontium titanates (STF) are considered as possible SOFC cathode materials in the temperature range of 600-800°C. Their synthesis, electrochemical and structural parameters are evaluated. Electrochemical performance analysis is performed by means of the Electrochemical Impedance Spectroscopy on symmetrical cells sintered at different temperatures. Chemical interaction of STF materials with yttria stabilized zirconia solid electrolyte is considered by the X-ray diffractometry analysis of reacted powders. Comparison with available data is presented and discussed.
- Impedance Spectroscopy Study of Electrode- Electrolyte System in Solid Oxide Fuel Cells
- Strony: 157-163
Planar electrolyte-supported solid oxide fuel cells were studied. Dense membranes of the dimensions: 100 x 100 mm and a thickness of 130 μm, made from yttria-stabilized zirconia (both tetragonal and cubic) were used as solid electrolytes. Ni-zirconia cermet and La0.8Sr0.2MnO3 layers were deposited on the surfaces of the electrolyte as the anode and the cathode, respectively. Electrochemical impedance spectroscopy was used in order to characterize the electrical properties of the solid electrolyte membranes and the electrolyte-anode and electrolyte-cathode systems. It was found that an equivalent circuit is composed of two series of resistor- constant phase element connected in parallel. No additional elements in the equivalent circuit originated from either the anode or the cathode layers have been observed with respect to the single electrolyte sample.
- Effects of size reduction of pigments from the Y2O3-Al2O3-Cr2O3 system on colour of transparent glazes
- Strony: 164-170
Red yttrium-aluminium pigment of perovskite structure doped with chromium has been worked out. After grinding, it was applied for industrial transparent glazes destined for stoneware tiles fi red at 1170°C and for gres porcellanato tiles fired at 1205 and 1230°C. The
pigment was wet-milled and dry-milled with different duration time of the process. Crystallinity of the pigments was determined depending on size reduction of the pigment powders and after the application for above mentioned glazes. Phase compositions of the pigments were also determined. Colour parameters of the pigments and glazes were measured in the CIE L*a*b* system. The stability of the pigments with different grain size distribution was determined depending on the chemical composition of glazes and the fi ring temperature.
- Post-operating studies of low cement refractory cements
- Strony: 171-174
Low cement refractory concretes are used in the lining of heating equipment and exposed to influences of mechanical and chemical factors and high temperatures. The time and conditions of the use contribute to the deterioration of functional properties. Post-operating studies allow estimation of the time of safety work and avoidance of costly repairs of the equipment. Three species of low cement refractory concretes used in various conditions were examined. The changes in their physical and mechanical properties were assessed.
- Characteristics of carbon clay shale from the lublin coal basin (LCB) and technological additives designed for the clinker production. Part I
- Strony: 175-185
A high content of organic matter in carbon clay shale increases porosity and water absorption of ceramic products with a simultaneous decrease of their mechanical strength. As a result, products manufactured from the clay shale in industrial conditions do not reach the appropriate parameters required for clinker bricks (Rc ≥ 25 MPa, N < 6 %). Mixing of the slate with additives to facilitate the sintering process and modify the physical properties of ceramic materials is one way to improve the properties of ceramic products. In the present study, quartz sand, different clays and melaphyre were used as additional raw materials to the shale. The article presents characteristics of raw materials used for the production of clinker bricks, i.e., black shale from the Lublin Coal Basin (LCB), Jaroszów clay, Harasiuki clay, loess of Izbica and melaphyre. The grain size distribution, chemical and mineral composition and thermal properties of the raw materials were studied by using dilatometric, DTA-TG and XRD methods. It was found that the tested raw materials exhibit significant variations in their properties, arising from their different origin and geological age. The influence of technological additives introduced to the carbon clay shale on physic-mechanical properties and microstructure of fired ceramic materials is presented as a separate paper.
- Properties of masses and bulk materials from lcb carbon clay shale and technological additives. Part II
- Strony: 186-194
The paper presents the results of technological research of plastic masses and bulk materials involving carbon clay shale from LCB as the basic material and various mineral additives. It was found that the masses require a small quantity of water to obtain a state of plasticity, and simultaneously exhibit low drying shrinkage. After firing, some of the materials were characterized by a compressive strength around 45 MPa and water absorption less than 6 %, which classifies them as clinker materials. Despite the materials with generally good properties, there are some examples that do not meet frost resistance requirements. This depends on designing the appropriate firing curve.
- The use of vertically perforated bricks filled with expanded perlite In energy-saving technologies
- Strony: 195-200
Perlite is a volcanic glass. It was formed as a result of lava cooling underwater. In this paper, based on worldwide literature review, information is presented concerning basic physical properties of perlite and a process of its expansion. The utilization of perlite in energy efficient building technologies is demonstrated. The special attention is paid to hollow bricks filled with perlite insulation. The thermal properties and results of numerical simulations of heat transfer through Poroton-T9 brick are shown. Information about the possibility of using these types of materials for external wall construction is presented in the current paper. Another alternative example of using the expanded perlite with high insulating properties for filling caves of vertically perforated bricks is also shown. This technology is applied directly at the building site. Some conclusions finish the paper.
- Periclase-spinel refractories for the tandem furnace roof
- Strony: 201-205
The properties of periclase-spinel bricks after the use in the tandem furnace roof were thoroughly tested. A zonal texture of clearly visible working, transition and unchanged zones was observed. The individual zones differed significantly with regard to the chemical composition, phase composition and texture. The closer to the working area, the smaller content of magnesium oxide and aluminium oxide was observed while the content of iron oxides and calcium oxide increased. The working zone contained only periclase (probably magnezjowüstite), magnesioferrite and hercynite without the silicate phase. Refractoriness of this zone was very high, above 1750 °C. The transition and working zones had a clearly higher apparent density and lower porosity compared with the unchanged zone. The frontal corrosion as a result of ‘leakage’ of the liquid phase and ‘spalling’ due to different physical-chemical properties of particular zones were the main causes of wear of magnesia-spinel bricks in the tandem furnace roof. Postulates were formulated to further improve the properties of periclase-spinel refractories for the tandem furnace roofs.
- Sialon bonded corundum refractory
- Strony: 206-209
Sialon bonded corundum refractories were developed by reaction firing. Corundum and Si3N4 were used as raw materials together with calcium aluminate cement as the bonding agent. Materials were fired at 1500°C and characterized with respect to the phase composition, microstructure and basic application properties. A decrease of open porosity and improved strength characteristics were found as a result of the formation of sialon bond.
- Suitability of dolomite from ząbkowice for refractory production
- Strony: 210-214
The sinterability of Triassic dolomite from Ząbkowice Będzińskie was studied in comparison with the dolomite from Brudzowice (near Siewierz) which is currently used at ArcelorMittal Refractories. It was found that the dolomite from Ząbkowice can be a potential raw material providing its selective exploitation due to changeability of the chemical composition and porosity. It was found that the porous Triassic dolomite sinters much easier if the two-stage method is used consisting in the decarbonization, crushing, pressing and sintering the compacts (pellets), compared to the single-stage method of sintering of the raw material lumps. The two-stage method should result in the improvement of the dolomite clinker quality and possibly the reduction of the sintering temperature. This work will be continued at ArcelorMittal Refractories Sp. z o.o.
- The oldest ceramic - evidences of ceramic production in past societies 30-20/16 thousand years ago
- Strony: 215-220
The production of ceramic materials in the Upper Palaeolithic epoch has not known universally especially as pottery was used in the Neolithic epoch on a large scale some thousand years later. The majority of ceramic fragments was found in Czech Republic and the minority in Slovakia, Austria and Russia. There are some aspects of the ceramics production in the Upper Palaeolithic mentioned in the article. The ceramic fragments were found in various places in the sites. The studies revealed that clay was local and the production route encompassed a few stages, including preparation of ceramic mass and heat treatment at different conditions. Many different representations were made such as animals, people and unspecified. Many burn techniques were known. So far, the Upper Palaeolithic ceramic production has been analyzed in detail only in Czech Republic, but it has not been done comprehensively in other sites.
- Strony: 221-222
List of Contents
Volume 63, Issue 2
- Experimental Study of Deformations and State of Tension in Traditional Ceramic Materials
- Strony: 226-232
Generally, the deformations of ceramic materials during and after firing may have a complex origin. If the products are made up of a single material, such deformations are mainly due to pyroplastic phenomena. In the case of glazed materials, two further factors must be considered: the state of tension established between glaze and body, and their differences in behaviour during sintering. A novel optical technique is described to measure the state of tension of ceramic glazed bodies and applied to the study of delayed crazing and pyroplastic deformation of the body. This article outlines how can ceramists avail themselves of new optical equipment in order to design high quality products and avoid ordinary deflects. Combining dilatometric tests and bending analysis, a full study of residual stresses on glazed ceramic can be performed; therefore, this is how planarity problems can be solved. Furthermore the Optical Fleximeter MISURA® is able to get information about viscosity changes during fi ring process in porcelain stoneware tiles: study of pyroplastic behaviour.
- Advances in Test Methods for Designing Optimised Ceramic Blends from a Raw Material Supply Perspective
- Strony: 233-238
Traditionally, clay blend development for ceramic applications has been done empirically from background knowledge of how the individual components are likely to behave in a given ceramic system. At Sibelco, modern advances in testing methodologies allows the rapid design and development of new clay blends tailored to customer needs. Three topics of key importance in the development of optimised ceramic clay blends are presented and discussed; namely, particle size, rheology and mineralogy. The paper concludes with two examples of how these methods can be brought together to develop high performance clay blends that meet the customers’ needs.
- Influence of Preparation Methods on Colourfulness of Ce1-(x+y)TbxTiyO2
- Strony: 239-243
Compounds based on CeO2 were synthesized as high-temperature environment-friendly inorganic pigments with interesting hues. The pigments have been prepared by using the solid state reaction and suspension mixing of raw materials. The goal was to develop conditions for the synthesis of this type of pigments and to determine the influence of preparation methods on the colouring effects of these compounds. The colour properties were investigated depending on the method of preparation, calcination temperature and concentration of Ti4+ ions. All prepared pigments were applied into organic matrix and ceramic glaze. The pigments were evaluated from the standpoint of their structure, colour properties and particle sizes. Our results indicated that these compounds can provide light orange colour hues that are stable in ceramic glazes and dark brown colour shades in the organic matrix.
- The Effect of Lanthanides on Colour Properties of the Ln2Zr1.5V0.5O7 Pigments
- Strony: 244-247
New yellow and orange ceramic pigments based on the pyrochlore solid solution of Ln2Zr1.5V0.5O7 were synthesized as high-temperature environment friendly inorganic materials. This work is focused on mixed oxides based on ZrO2, which are doped by rare earth elements. The optimum conditions for their synthesis were determined. Their colour properties were investigated depending on the content of various lanthanides and temperature of calcination. The richest hues were obtained by using holmium and thulium. All pigments give the yellow colour in ceramic glazes but Ho and Er provide orange hues. The pigments were evaluated from the standpoint of their structure, colour, ability to colour ceramic glaze, and particle size.
- Study of Compounds Based on SrMxSn1-xO3±x/2
- Strony: 248-250
Inorganic pigments of SrMxSn1-xO3±x/2 type (where M = V, Cr), based on a pseudo cubic structure of SrSnO3, have been prepared by the solid state reaction between SrCO3, SnO2 and oxides V2O5 or Cr2O3 in the temperature range 1300-1500°C with nominal compositions: x = 0.05, 0.1, 0.3. The resultant materials were characterised by XRD, TG-DTA, and colourimetric techniques were used. The pigments containing vanadium as chromophore give creamy, sand and yellow colour into an organic matrix. The increase of temperature caused the creation of pigments with deeper and brighter colour hue. The presence of chromium in compounds produces colour hues from reddish brown to brown. The compounds with higher content of chromium have the lower chroma colour hue.
- Comparison of Creep Behaviour in Alumina Based Ceramics Densified by SPS and HP
- Strony: 251-255
For more than a decade, the spark plasma sintering method (SPS) is an interesting alternative to classical densification processes for ceramic materials. Furthermore, SPS has recently been paid attention as an alternative method to obtain dense and fine-grained ceramics at low temperatures. SPS, also known as plasma activated sintering, is a method applicable for rapid sintering of metals and ceramics. Owing to the advantage of rapid heating, the alumina ceramics obtained by SPS have a grain size and density comparable to those of HPed ones. The increase of densification rate may be related to some difference in ion transport characteristics. In fact, if there is alteration in those transport characteristics, there may be some difference in all subsequent diffusion related to the processes such as grain growth, creep and high temperature deformation of SPS densifi ed materials. This study describes creep behaviour and deformation mechanisms of alumina based materials densified by SPS, and compared with hot pressing (HP) to some extent. Pure alumina (SM8, Baikowski) was densified by SPS at 65 MPa (1200°C), and 45 MPa (1400°C) by hot pressing (HP).The grain size of the HP alumina was more twice bigger than the grain size of SPS sample (1000 nm versus 440 nm). The grain growth is more active during creep of SPS alumina (1300°C, σ = 30 MPa and fi nal deformation 30 %) than during creep of HP alumina, about 70 % versus 25 %. Generally, the fi neness of SPS materials microstructure shall speed up all processes related to diffusion.
- SEM and TEM Studies of β-SiC Nano-Whiskers Microstructures Produced at Different Temperatures
- Strony: 256-260
SiC whisker is excellent regarding characteristics such as specific strength, specific modules, heat resistance, chemical stability etc., and it is useful as a composite reinforcing material. ß-SiC whiskers were synthesized by the VLS mechanism and using an iron catalyst at different temperatures. This process was done by the carbothermal reaction of Si and C at 1100, 1400 and 1500ºC. SEM and TEM observations of the samples from the temperatures of 1400ºC and 1500ºC show that the β-SiC nano-whiskers in these samples are created and they are growing. In fact, the driving force is enough at these temperatures for nucleation and growth of the β-SiC whiskers. At the temperature of 1100ºC, the nucleation of the β-SiC nano-whiskers was observed but they did not fully grow. It shows that the driving force is not enough at this temperature. So, to form the β-SiC nano-whiskers in this process, temperature is very important. EDX analysis on nucleation areas of the whiskers (bulges) by SEM and TEM confi rms the presence of Fe (iron), Si and C. In the other word, it proves the in-situ formation of SiC nano-whiskers by the VLS mechanism and using the iron catalyst.
- Synthesis and properties of LiFePO4 – A cathode material for the Li-ion type cells – obtained by low temperature method
- Strony: 261-265
In this work, we describe a procedure of synthesis of the LiFePO4 material based on precipitation from a solution containing LiOH, FeSO4 and H3PO4. Single-phased material composed of lamellar crystallites of 50x50x500 nm in size was obtained after drying the precipitated deposit at 50°C. Annealing pellets at temperatures in the range from 300 to 800°C under inert atmosphere led to improvement of crystallinity, intense grain growth (above 600°C), and sintering (above 700°C). For the pellet annealed at 800°C, a density close to theoretical one was achieved. X-ray diffraction revealed that during annealing above 400°C the volume of unit cell gradually increased. Probably this can be connected with evaporation of lithium, which can be associated with the creation of cation vacancies and electron holes. Electrical conductivity measurements showed that LiFePO4 annealed at 700 and 800°C possesses nearly twice as high conductivity (9.6 S·cm-1) as LiFePO4 annealed at lower temperatures (5.5-6.3 S·cm-1). At the same time, the materials from higher temperatures were characterised by lower activation energy of electrical conductivity (0.61-0.66 eV) in comparison with the samples from lower temperatures (0.76-0.85 eV). The conducted research was complemented with the charge/discharge tests performed on a Li/Li+/LixFePO4 cell. According to the measured data, the discharge cell voltage was between 3.2 and 3.5 V. The first discharge capacity was about 60 mAhg-1. In the several following cycles, the capacity slightly increased and then gradually decreased to 12 mAhg-1 in the 50th cycle.
- Strony: 266-272
Wet milling and production of granulates in spray dryers is the current technological standard of the production of ceramic granulates in the manufacturing of ceramic tiles. These solutions, and particularly the process of producing the granulate from a ceramic slurry, are highly energy-consuming. The article presents a new technological concept characterized by significantly lower consumption of energy. The use of the modern continuous milling of wet materials with grain separation leads to significant reduction of energy consumption. High automation of the milling process control allows for easy control of the milling degree depending on the feed size and moisture. Dry material obtained in the presented installation is granulated in an intensive mixer with the minimum addition of water. During the standardization process, the granulate obtained is of the same graining as the granulate obtained in spray dryers. Density of granulate obtained by means of this method is about 10 % higher as it does not contain hollow granules and the granulated material is more concentrated. The article depicts the results of laboratory analyses and industrial tests; it also analyses the economic effects arising from the reduction of water and energy consumption. Moreover, the article focuses on the possibility to eliminate fluidifying additives and binding agents used in the traditional technology. The suggested technology is characterized with small device dimensions, high level of automation, and it makes it possible to reduce energy consumption by approximately 8 and 4-5 times in case of using the dry and medium moisture materials, respectively.
- Design of Al2O3–Ni composites using electrokinetic property measurements
- Strony: 273-277
The main advantage of ceramic-metal composites is an increase of fracture toughness of a brittle ceramic matrix. In the paper, the results concerning characterization of electrokinetic behaviour of ceramic and metallic particles used for fabrication of the ceramic matrix ceramic-metal composite via slip casting method are presented. The following materials were used: alumina powder (TM-DAR, Tamei Japan) of average particle size D50 = 0.21 μm, specific surface area of SBET = 14.5 m2/g and density of d = 3,8 g/cm3, and nickel powder (Sigma-Aldrich) of average particle size D50 = 2.17 μm, specific surface area of SBET = 2.1 m2/g and density d = 8.9 g/cm3. Zeta potential as a function of pH was measured for suspensions of pure powders and powder mixtures in both water and water solutions containing deflocculants used for the slurry preparation. Together with zeta potential, particle size distributions were determined for the investigated suspensions of the powders and their mixtures. The studied ceramic and metallic powders show great differences in the electrokinetic behaviour, which can cause the heteroflocculation effect occurring in the suspension. Furthermore, from the rheological examination of the slurries with the different nickel powder content (0-5 vol.%), an influence of the nickel particles presence on slurry properties can be observed. With increase of the nickel powder concentration, the viscosity of slurry increased, and the rheopexy behaviour appeared.
- Pseudothixotropic properties of clay-cement sluries
- Strony: 278-282
A new concept of rheological qualification of clay-cement suspensions containing structure agents has been shown. Special attention has been paid on reversible and irreversible thixotropic properties. This paper display, that some complicated phenomena connected with syneresis and channel flow occur inside clay-cement suspensions during shearing. The reversible week thixotropic structure connected with clay minerals is interlaced with the irreversible strong internal structure, creating as a result of the cement hydratation process. During developing this quasi-thixotropic structure, the clay-cement suspension at a rest state gains a gel structure, which successively becomes stronger as a result of the hydratation process, and finally arises a high-quality hydro-isolation binder.
- Evaluation of freeze–thaw resistance of clay masonry units
- Strony: 283-287
The last polish standard regulating the procedure of evaluation of clay masonry units frost resistance (PN–B–12012:2007) specifies conditions of the test and criteria of frost resistance evaluation. If certain type of damage appears on units subjected to the proper number of cyclic freezing–thawing, the compressive strength of the examined units must be determined. The 20 % decrease of compressive strength of the units caused by cyclic freezing–thawing is allowed. This criterion rises doubts, since it is not clear if such a decrease is actually critical. In author’s opinion, the standard criterion should be defi ne more precisely by taking into consideration properties of kinetics of the ceramic units compressive strength decrease caused by cyclic freezing–thawing. Based on statistical analysis of the numerous experimental data, it was indicated that the evaluation of frost resistance of ceramic masonry units using standard criteria can lead to false conclusions. The procedure of specification of frost resistance evaluation criteria is proposed in this paper, basing on the decrease of compressive strength of the ceramic masonry units.
- Decrease in compressive strength of clay bricks due to cyclic freezing–thawing
- Strony: 288-293
The aim of this work is to explain various aspects of the compressive strength decrease caused by cyclic freezing–thawing of two series of ceramic specimens. The specimens were prepared using unburned bricks formed out of plastic clay in industrial conditions, and then burned at 850 and 1050°C in laboratory conditions. The experimental data were obtained according to the rules of randomization, and analyzed by using statistical methods. It was shown that the most complete picture of kinetics of the frost destruction process of ceramic material can be obtained by monitoring a decrease of compressive strength of specimens under cyclic freezing and thawing. Furthermore, the water sorption coefficient was experimentally determined for the ceramic specimens parallel and perpendicular to the forming direction. On this basis, it was explained that the main reason of low frost resistance in case of the ceramic bricks formed from plastic clay by using an extruding press is the defective layered texture, which exposes even after burning at high temperature.
- Possibilities of using asbestos-cement in the ceramic industry
- Strony: 294-300
The work reports the results of study on using the raw cement-asbestos slates as an additive to ceramic masses. The masses containing stoneware clay, feldspar and quartz sand were used in which the latter was later replaced by the raw ground cement-asbestos slates. The green compacts were sintered at temperatures of 1150-1250°C. The ceramic product properties such as linear shrinkage, water absorbability, open porosity, apparent density and compressive strength were determined. The microstructure was examined by scanning electron microscopy and the mineral composition by X-ray diffraction. The preliminary results of this investigations show that the asbestos-containing materials can be used as one of the raw materials for the traditional ceramic industry.
- Selected application properties of gres porcellanato tiles
- Strony: 301-309
The impact of the properties found for the selected gres porcellanato tiles on their functional qualities is presented. The studies included chemical, microscopic, SEM/EDS, X-ray and thermal analyses as well as determinations of porosity, density, stain resistance, bending strength, fracture toughness, hardness, grindability and crack propagation in the gres porcellanato tiles. The tiles studied were composed of the amorphous aluminosilicate phase, mullite and quartz. In the Polish tiles, contrary to the Italian ones, the content of primary mullite is higher than the content of secondary one, and hardness tests have revealed better quality of domestic products in comparison with the Italian ones. Those findings result from differences in the composition of feldspar commodities used by Polish and Italian manufacturers. It has been shown that open porosity significantly affects the stain resistance. The investigations of fracture toughness indicate a substantial role of large quartz grains in which cracks are usually of the transgranular character.
- Syenite detritus from lower silesia as a valuable raw material for the ceramic industry
- Strony: 310-315
At present in Poland, during execution of a large number of structural investments, the demand grows up on different kind mineral crushed aggregates. As a result, a number of exploited deposits of that type also increases. During the aggregate production, some wastes are generated many a time, which are not suitable for the aggregate application, but can be applied as a raw material to produce different kinds of ceramic wares. The presented paper shows the results of investigations concerning feldspar-quartz material called “Sjenit zwietrzelina” (a kind of weathered syenite) from Multi-Krusz Company from Wałbrzych (Poland). This material makes up a layer over the exploited deposit and now is treated as a waste and dumped. The results of investigations carried out at the Department of Ceramic Technology and Refractory Materials AGH-UST show that there is a possibility to apply this material in different ceramic technologies, for example for the production of sewerage ceramic ware, stoneware, faience ceramics and building ceramics. Depending on the applied temperature, this raw material can be used as a leaning material, fluxing agent or colour agent. Its addition as a component of body recipes can vary between a few to over 90 wt.% within the range of firing temperatures from 1000 to almost 1200°C. The large content of iron oxide and bloating properties at elevated temperatures limit the possible applications.
- Influence of glazing techniques upon the wear resistance of glass-ceramic glaze for tiles
- Strony: 316-320
Wear resistance is one of the most important functional parameter of glazes for floor tiles. Devitrification resulting in the formation of glass-ceramic glazes is the most common way for increasing the wear resistance of tile glazes. Glaze layers of different texture are obtained due to a variety of techniques in the production lines used to apply glazes on the floor tiles. Recognition of possible effects of the glaze application method on wear resistance of the glaze layer after fi ring is an interesting issue. In the work, the effect of selected techniques of glazing on the wear resistance of glass-ceramic glaze in the MgO-CaO-Al2O3-SiO2 system is shown.
- Ceramic pigments of fluorite structure
- Strony: 321-326
In this study, the results of investigation of pigments based on cerium(IV) dioxide doped with praseodymium(IV) are presented. The optimal chemical composition and synthesis conditions of the pigment were developed. The obtained pigment was ground by different methods for 10 to 60 minutes. The pigment morphology was determined by analyzing the grain size distribution, and SEM observations. The ground pigments were applied for colouring transparent glazes used for stoneware tiles. Both glazes and tiles were of industrial origin. Colour parameters of the pigment powders and selected stoneware tile glazes were measured.
- Influence of economic crisis, eu rules and chinese competition on the european ceramic industry and main directions of research and development
- Strony: 327-331
Production of ceramic sectors in Europe in a period of 2004-2008 and 2009 together with a prognosis of crisis conquer were presented. The factors influencing the situation of the sectors were characterized. The attainability of raw materials, particularly in case of the refractory industry was described. Influence of rules introduced by KE on ceramic producers was characterized. On the basis of presented factors determining development of the ceramic industry in Europe, the main directions of investigations were proposed.
- A ZrO2–Al2O3–SiO2–Mo ceramic-metal composite
- Strony: 332-336
Ceramic–metal composites enjoy a growing interest because of their unattainable properties as compared with single-phase ceramic materials. The introduction of a metallic component to the ceramic matrix influences improvement of mechanical properties. It is known that molybdenum doped composites, i.e., mullite/Mo, Al2O3/Mo, 3Y-TZP/Mo or AlN/Mo show the fracture toughness reaching 11 MPa·m1/2 and the bending strength of 2100 MPa. The molybdenum is the interesting component for high-temperature composites. It is characterized by a high melting point, a high hot flexure strength and a low thermal expansion coefficient. Moreover the molybdenum demonstrated low corrosive properties to some kinds of glasses and ceramic materials. All these characteristics cause that the molybdenum is useful material in the glass industry. The aim of the work was to verify the possibility to produce sintered ceramic-metal composites in the ZrO2-Al2O3-SiO2–Mo system, showing large compactness of the texture, and being the alternative material designed for the work in contact with liquid soda-calcium glass. As a result of the optimization of grain size distribution curves, and selection of the phase composition of the mixtures, the composite material with a content of ~84 % wt. ZrO2 and ~10% wt. Mo, an open porosity below 8 % and a compressive strength of approx. 470 MPa was obtained.
- Development of material composition for low pressure injection moulding of blade cores of gas turbines and turbocompressors
- Strony: 337-341
Application of ceramic cores in the manufacture process of blades caused an increase in efficiency of gas turbines and turbo compressors because internal channels obtained in such a way allowed the blades to be cooled, and as a result to work at a higher temperature of combustion gases. In this paper, a manufacture technology of the cores for the gas turbine and turbo compressor blades by low pressure injection moulding is presented. Material for the cores should be characterised by the following properties: possibility to form the complicated shapes, small shrinkage during the forming and sintering processes, high resistance to the alloy impact and low coefficient of thermal expansion. Moreover, it often must satisfy very opposing requirements as for example high mechanical strength which enables to assemble the cores in casting moulds and simultaneously core porosity up to 30 % needed for easy leaching the cores with a base in water solution. In order to satisfy these requirements, a recipe for the material was worked out which based on activated silica glass and modifying additives, and thermoplasticizers of low both melting temperature and solidification shrinkage were selected. In order to optimize the recipe, research and development works were carried out, including the determination of influence of the particle size distribution of silica powders on their formability, binder removal and final properties of the cores. The influence of low shrinkage thermoplasticizers on mass viscosity, state of filling small sections and shrinkage during forming was also studied. Moreover, the application of compositions of different thermoplasticizers enabling their gradual removal during the debinding process was investigated, and the influence of a mould powder used for the debinding process on deformation and fracture of the cores was determined. Additionally, effects of heating rate and final temperature on deformation and fracture of the cores were studied during the debinding process, and characterised during the sintering process with respect to final properties of the cores. Finally, the possibility of leaching the samples with a basic aqueous solution was checked. For an assessment of the ceramic material properties and the usability of core masses for the injection, the following parameters were determined: particle size distribution of the powder used for the feedstock preparation, material viscosity at the injection temperature, density, porosity and water absorbability after sintering, coefficient of thermal expansion, bending strength, surface roughness and core microstructure. The obtained results point out getting the low pressure injection moulding material of the appropriate properties applicable for the blade cores.
- Potential phase compositions for refractory materials in the MgO-CaO-Al2O3-ZrO2 system
- Strony: 342-349
Phase equilibriums in the binary and ternary subsystems of the quaternary MgO-CaO-Al2O3-ZrO2 system are presented. The potential phase compositions of refractory materials in this system refer to the refractories originating from the MgO-CaZrO3-MgAl2O4, MgO-CaZrO3- CaAl2O4 or MgO-CaZrO3-CaAl2O4-MgAl2O4 systems. The MgO-CaZrO3 refractories with the aluminium bonding can be an alternative to the MgO-CaZrO3 refractories with the silicate bonding.
- New refractories of low thermal expansion based on CaAl4O7 in different combinations
- Strony: 350-354
New non-silicate refractories based on CaAl4O7 and containing various oxides were studied. These materials have very low thermal expansion coefficients. Their specific properties were discussed on the basis of thermodynamical data (including phase diagrams). A possibility of application of these new materials in various industry branches was indicated.
- Graphite containing castables part II – effect of graphite content on strength and resistance properties
- Strony: 355-360
This study is a continuation of investigations on the graphite incorporation to castable refractory concretes used for linings of blast furnace troughs and the effects of graphite on properties of the castables. In the Part I, delivered at the Polska Ceramika 2008 Conference, the results of investigations were presented on graphite processing, allowing the graphite to be inserted to a castable refractory concrete. In this study, the effect of processed graphite amount on strength and resistance properties of the castable was investigated. The results revealed that the castable refractory concrete with 10 % processed graphite granules possessed excellent properties. Increasing the content of graphite granules up to 15-20 % led to a decrease of mechanical and resistance properties of the samples. The microstructure of the castable samples with excellent properties was observed using the optical microscopy method and the phase composition was determined using the X-ray diffraction method. Microstructural study on the samples containing 10 % graphite granules was carried out after the blast furnace slag corrosion tests. The corrosion mechanism was characterized.
- Influence of dolomite composites on application properties of the basic refractoriesies
- Strony: 361-366
The present work contains the examination results of the influence of dolomite composites on properties of the basic refractories, which are used in the cement industry and some thermal devices in the steel industry. It was found out that the addition of the dolomite composites leads to a considerable increase of mechanical properties and resistance to thermal shocks of the basic refractories.
- Properties of silicon carbide refractories infiltrated by the chemical vapour infiltration method (CVI)
- Strony: 367-371
The microstructure of refractories was modified by silicon carbide by means of a CVI method. Chemical vapour infiltration (CVI) is an effective method for microstructure modification of porous materials. This method allows open pores to be infiltrated with metals and high refractory compounds such as carbides, nitrides, borides and oxides. A variation in the microstructure during a number of infiltration cycles was investigated by SEM, ultrasonic wave propagation velocity measurements and mercury porosimetry. The corrosion of material was examined in an oxidizing atmosphere at elevated temperatures. Mechanical strength measurements of infiltrated materials were carried out.
- The influence of baghdadite on the microstructure of dolomite-zirconia composites
- Strony: 372-378
Depending on a CaO/SiO2 molar ratio, the four types of MgO-CaO-ZrO2-SiO2 materials can be distinguished when the reactions in the batches are completed. The presented studies focused on the materials with the CaO/SiO2 molar ratio in a range of 3.0–4.0. The effects of baghdadite on the microstructure forming within the dolomite-zirconia composites during sintering are reported.
- Preparation of glass-ceramics containing ZnAl2O4 due to the elimination of pyroxene structures
- Strony: 379-385
The paper presents an attempt of application of glass-crystalline material, coming from the CaO-MgO-ZnO-Al2O3-B2O3-SiO2 system and being a modification of the CaO-MgO-Al2O3-SiO2 system, as a binder for abrasive grains of microcrystalline alumina of the SG type. The results indicate that a change of the chemical composition can eliminate crystal phases from a silicate group (diopside, augite) in the spinel phase (ZnAl2O4) favour. The glass-ceramic material containing crystal phases of gahnite (ZnAl2O4) and willemite (Zn2SiO4) has better mechanical properties (KIc = 2.04 MPa·m1/2) in comparison to the materials with the pyroxene phases (KIc = 1.28 MPa·m1/2).
- The influence of B3+ ions on the structure and texture of silico-phosphate glasses
- Strony: 386-390
Boron cations addition into the structure of silico-phosphate glasses influences changes of a series of different properties. Boron oxide as the component of glass reduces melting temperature, increases thermal shock resistance, improves chemical resistance and mechanical properties of glass. The influence of boron cations on properties of glass depends particularly on the coordination number. Spectroscopic studies (MIR,NMR) have shown that the boron cations occur in the structure of glasses showing the coordination number three and four. Scanning microscopy have revealed that the incorporation of boron into silico-phosphate glasses leads to homogenization of the glass structure.
- Microstructure of silico-phosphate glasses in the NaMgPO4-SiO2 system
- Strony: 391-395
The studies concern silico-phosphate glasses with the [SiO4]4-/[PO4]3- ratio systematically changed, belonging to the NaMgPO4-SiO2 system. Glasses from this system are considered as bioactive and capable of connecting bonds with tissue. Brittleness is a serious problem limiting exploitation of glasses as biomaterials. The addition of a proper amount of cations (mostly Al+3) or partial devitrification of glass can lead to improvement of the mechanical properties. Detailed structural and textural investigations are necessary to conduct direct crystallization of glass. Microscopic and EDX investigations made it possible to find out that liquation took place in all glasses studied. The presence of aluminium in the glass matrix has the significant influence on the chemical composition of inclusions.
- The influence of manganese on thermal stability of silicate-phosphate glasses
- Strony: 396-401
Silicate-phosphate glass of the SiO2-P2O5-K2O-CaO-MgO system containing manganese cations have been investigated in order to obtain information about the thermal characteristics of manganese in such glasses. The amorphous state of glasses, the course of the phase transformations and crystallizations during their heating were followed by DSC and XRD methods. It was shown that an increasing content of manganese, replacing calcium and magnesium in the structure of the analysed glasses, causes an increase in the structural stresses resulting in lower values of Tg. During the crystallization process of the glasses, manganese incorporated into the structure of silicates crystallizes in the form of braunite. Data interpretation was based on the theory of chemical bonds and interaction strength between the individual components which build the glass structure. On this basis, it was shown that the type of crystalline phase formed during the heating depends on the amount of manganese introduced into the glass structure. The crystallization sequence of the individual phases results from the standard values of thermodynamic potentials, DG.
- The influence of copper on thermal and biochemical activity of silicate-phosphate glasses
- Strony: 402-406
Thermal and biochemical activities of glasses from the SiO2-P2O5-K2O-MgO-CaO system modified with the addition of CuO were studied. The glasses can act as slowly dissolving fertilizers, supplying macroelements P, K, Mg, Ca and microelements in a form of copper for plants. Thermal characteristics of the glasses was carried out using the DSC method to determine the effect of copper on the glassy state transformation and crystallization process of glasses. In order to identify the crystalline phases appearing as a result of crystallization, the glass samples were heated isothermally at the temperatures indicated by the DSC measurements, and then subjected to analysis by X-ray diffractometry (XRD). The chemical activity of the glasses modified with the CuO addition was determined by measuring the solubility of glass samples in the 2 % citric acid solution at the weight ratio of glass to solution of 1:100. The amount of elements released from the glass sample was measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES). Incorporation to the glass structure the growing amount of CuO resulted in a decrease in the glass transition temperature. Reduction of the glass transition temperature is explained by the replacement of calcium ions and magnesium ions by copper having more covalent bonds. In the process of crystallization of the analyzed glasses, copper builds in the structure of phosphates crystallizing in a form of Ca19Cu2(PO4)14 phosphate, while only a small proportion of copper crystallizes as silicates of a type of diopside. The studies have shown that the increase in CuO content in the structure of the analyzed glasses causes a decrease of solubility as a result of increased number of durable phosphate elements in the glass microstructure.
- Phosphate ceramic materials for immobilisation of cadmium in the soil environment
- Strony: 407-412
One of techniques for preventing the recirculation of toxic elements contained in contaminated soils in the environment is a method of restraining them in the form of insoluble phosphates used in in-situ conditions. The aim of this work was to study application of phosphate glasses and relevant glass-crystalline materials acting as carriers of plant nutrients for the simultaneous binding of cadmium in the form of insoluble phosphates. The reaction between glass from the P2O5-K2O-CaO-MgO system and a solution of cadmium nitrate in the presence of citric acid simulating conditions of the natural soil environment was analyzed by using atomic emission spectroscopy (ICP-AES) and electron microscopy (SEM) combined with the analysis of chemical composition in microareas (EDS). It was shown that both the phosphate glass and materials recrystallizing to the form of potassium phosphate dissolved in medium containing cadmium ions, binding them in insoluble cadmium phosphate. The presence of citric acid, simulating the conditions of the soil environment and demonstrating the ability of complexing Cd2+ ions, slightly inhibits the process of cadmium immobilization.
- Ceramization of natural sorbents containing CrO42- ions
- Strony: 413-418
This work presents the results of natural sorbents application for immobilization of chromates from aqueous solutions and the usage of them to prepare building materials. For the study, the natural sorbents originated from a Polish deposit were used. Sorption of the CrO42- ions was carried out on suitably prepared smectite and clinoptilolite. Pretreatment consisted in transformation of the sorbents into sodium forms, and obtaining organic forms by using HDTMA. The process changed a surface charge of the sorbents and transformed them into anion exchangers. These preparations were used to adsorb the CrO42- ions from an aqueous solution of sodium chromate(VI). The quantity of sorption was determined on the basis of UV-VIS spectrophotometric analysis. The sorbents after sorption were applied to obtain building materials. The samples ware obtained by firing the cubic samples at 900°C or 1100°C. The samples were prepared from smectite and zeolite in a weight ratio of 4:1. Immobilization effectiveness of CrO4 2- ions in the mineral matrix is shown. In the work, the results of IR spectroscopy, X-ray diffraction analysis, SEM observations, spectrophotometeric analysis and technological investigations are presented.
- Producing and properties of rare earth doped Al2O3 nanopowder
- Strony: 419-423
An innovatory method for producing nanoalumina with rare earth metal addition is discussed. Organic precursor has been obtained by the mild reaction of aluminum metalorganic compounds with oxygen provided by air. In the next stage, the precursor was doped with a lanthanide compound and calcined to obtain Al2O3/Ln nanopowder. Using this method, the Al2O3 nanopowders doped with ytterbium, praseodymium, holmium and thulium have been obtained, that showed average particle and agglomerate sizes of 40-96 nm and 1.9 to 42.94 μm, respectively. The obtained results indicate that conditions of the organic precursor synthesis and the addition of rare earth metal have a signifi cant effect on the morphology and physical properties of the Al2O3/Ln nanopowders. The nanopowders had signifi cantly developed surface areas (over 370 m2/g-1) and also a high open porosity value, evidencing the only slight tendency to agglomeration and a loose structure of the possible agglomerates. The nanopowders showed also satisfactory optical parameters.
- Mechanical and application properties of alumina materials modified with hexagonal boron nitride
- Strony: 424-427
The work focuses on self-lubricating materials based on nanometric alumina. Hexagonal boron nitride was used in the study as a phase aiming to decrease a friction coefficient of the materials for cutting tools. The modificator was incorporated to the system in the amount of 0.5, 1, 2, 5, 10, 20 and 30 vol.%. A preparation method of materials in the Al2O3–hBN system is described. The studies on effects of boron nitride additive and preparation conditions on such mechanical properties as hardness, fracture toughness, Young’s modulus and Poisson’s ratio were shown. The presented studies were carried out within the confines of the project „Spiekane materiały narzędziowe przeznaczone
na ostrza narzędzi do obróbki z wysokimi prędkościami skrawania” nr POIG.01.03.01-12-024/08.
- Phase, structural and microstructural changes in the Al2O3–hBN materials
- Strony: 428-433
The presented studies concern materials based on alumina micropowder assigned for high speed cutting tools. Hexagonal boron nitride was used as a modificator, aiming to improve thermal properties and to decrease the friction coefficient. The boron nitride additive was 0.5, 1, 2, 5, 10, 20 and 30 vol.%. The methodology of obtaining the hot pressed Al2O3–hBN materials was shown. The structural and phase analyses based on Rietveld refinement of X-ray diffraction patterns were carried out. The changes in microstructure of the studied materials as a function of the modificator content are described. The presented studies were carried out within the confines of the project „Spiekane materiały narzędziowe przeznaczone na ostrza narzędzi do obróbki z wysokimi prędkościami skrawania” nr POIG.01.03.01-12-024/08.
- The alumina matrix composites for cutting tool points
- Strony: 434-438
The article describes a way of production and basic mechanical properties of the Al2O3 – x wt.%TiB2 (x = 1, 2.5, 5, 7.5, 10 and 15) composites. Final densification was carried out by using one of two methods: natural sintering or hot pressing. A series of atmospheric pressure sintered composites showed a low relative density. Thereby only the hot pressed composites were further examined. In case of the hot pressed composites the relative density results were not lower than 98.4 %. In current work, the results of porosity and absorbability measurements are also present. The hot pressed composites have high hardness reaching 1968 HV20 for the Al2O3 – 10 wt.% TiB2 sample. The measured values of Young’s modulus are very close to theoretical values calculated from the rule of mixture, and they range from 399 GPa to 420 GPa.
- Preparation and properties of the Al2O3-10 vol.% YAG (Y3Al5O12) composite
- Strony: 439-443
A preparation technique of particulate composite materials in the alumina/YAG system was elaborated. Within the alumina particles suspension, yttria precursor was precipitated with ammonium carbonate. Drying and calcination at 600°C resulted in a mixture of alumina and yttria particles, the latter being much finer than the alumina particles. This mixture was additionally homogenized by short attrition milling in an aqueous suspension. Sintering of such powders results in the materials composed of YAG inclusions of sizes smaller than shown by the alumina grains and evenly distributed within the matrix. The YAG particles result from the reaction of Y2O3 with Al2O3 during heat treatment. Hardness, fracture toughness, strength and Young modulus of the composites and pure alumina polycrystal were measured. The composites show fracture toughness and hardness essentially higher than the one observed in pure alumina polycrystals.
- Reconstruction of 3d structure of pottery vessels from archaeological excavations
- Strony: 444-449
The main objective of the work presented in the article was the reconstruction of 3D structure of pottery vessels found during archaeological excavations. Stereoscopic microscopy, scanning electron microscopy and X-ray tomography was used in this research. The study material consisted of fragments of clay vessels from the Early Medieval sites at Starosiedle in the Lebus Land in Poland and Rosenhof on the Elbe in Saxony-Anhalt in Germany, dated at the 9-11th centuries. Admixtures and a clay mineral matrix were analyzed. These studies enabled the observation of shape, color and composition of admixtures in the volume of samples, and identifies and describes the cracks and discontinuities of the matrix inside the sample. In particular, the X-ray tomography allowed the reconstruction of the 3D spatial structure of the ceramic mass.
- Modeling of thermal stresses in the TiC-Cr3C2 composites
- Strony: 450-453
Carbides of transition elements are mainly characterised by high hardness and high melting temperatures. However, their broader application as structural materials is limited due to their mediocre fracture toughness. The TiC-Cr3C2 system investigated in the work is characterised by a limited mutual solubility of the components which enables synthesis of composite materials. Moreover, the presence of chromium carbide favourably influences microstructure and properties of particulate composites of titanium carbide. During the investigations, four series of composites with different amounts of chromium and titanium carbide were prepared. Their mechanical properties as well as microstructure were characterised which enabled modelling of thermal stresses state created due to differences in thermal expansion coefficients of the constituent phases. The results of calculations in the form of maps of the thermal stresses made possible to analyse mechanisms of increasing fracture energy which resulted in toughening of the investigated systems.
- Influence of microstructure on the thermal stress distribution and fracture toughness of SiC-TiB2 composites
- Strony: 454-458
The presented experimental work has been based on SiC-TiB2 particulate composites in which the matrix had lower coefficient of thermal expansion (CTE) than particulate filler. Such difference in the thermal expansion coefficients between composite constituents induces thermal stresses in the material, that may lead to increased fracture energy. Several materials having similar filler content but different microstructure were produced. Their basic mechanical properties were measured, and photographic documentation was collected. The data were used for a quantitative analysis of the microstructure parameters and modeling the thermal stress state. The results of calculations were compared with the results of the microstructure analysis. It allowed determination of the influence of size and shape of the filler particles on the distribution of thermal stresses in the composites. It also enabled to find a relation between the observed increase of fracture toughness and the microstructure parameters.
- ProToLab system in the use for ceramic tiles designing
- Strony: 459-462
The ProtoLab system is used for projection of ceramic tiles coloured overprints. It is an entire set with spectrophotometric devices and special projected printer, enabling to achieve needful colour. The most important advantage is receiving final results without fi ring. It is an innovatory way in designing the ceramic products, definitely reducing time to make the prototype, fully allowing to express the designer’s creativity. In practical use the ProtoLab system gives the complete compositions of ceramic pastes for the projects.
- Strony: 463-469
List of Contents
Volume 63, Issue 3
- Influence of technological parameters on colour of glaze and ceramic masses containing pigment from the Y2O3-Al2O3-Cr2O3 system
- Strony: 472-478
The phase composition of pigments of the Y2O3-Al2O3-Cr2O3system depends on properties of raw materials used for manufacturing the yttrium-aluminium pigment of perovskite structure. Our investigations revealed that aluminium hydroxide has the significant influence on phase composition of the pigment. Properties of the other starting materials, such as yttrium oxide or chromium oxide, are insignificant. Depending on the morphology of aluminium hydroxide grains, the final product, i.e. pigment of the perovskite structure, can contain over 95 % or only about 70 % of the YAP phase. YAM and small amounts of YAG are the other crystalline phases, which are the components of the pigment. Variable phase composition of the yttrium-aluminium pigment of perovskite structure causes differences in colour properties. Usefulness of the pigments obtained by using aluminium hydroxides of different morphology was verified by applying them to industrial transparent and opaque glazes fired at temperatures between 1170°C and 1230°C, and to gres porcellanato bodies fired at temperatures between 1205°C and 1230°C.
- The Influence of SiC on the Properties of Aluminium Powder Obtained from Recycled Materials
- Strony: 479-483
The paper presents the experiments concerning the influence of SiC on the process of mechanical alloying of recycled materials in the form of aluminium chips. Oxidized aluminium chips used for the experiment were derived from waste products. Chemical, physical and engineering properties were characterized in the first step. Study shows repeatable chemical composition of the chips. Technological properties preclude the use of them as material for automatic charge (flow rate about 30 s). Therefore attempts were made to produce a composite powder by using the powder metallurgy method. Mechanical alloying process of aluminium chips with different amounts of SiC (0, 20, 40 wt%) and addition of Zr (2 wt%) was performed in a high energetic mill. Milling time was 20 hours using a milling speed of 200 rpm. Then, the characterization of obtained aluminium matrix composite powder was made by using a light microscope and scanning electron microscopy SEM/EDX. On the basis of the results of the microstructure we can observe that after the MA process, SiC reinforcement is located inside the aluminium particles which confirms the correct course of the process. The experiments showed that 40 wt% amount of SiC and 5 hours of the mechanical alloying allowed us to obtain the particles with an average area less than 2 square micrometers. The composite powders were tested via hot pressing processes (380°C/600 MPa/10 min). In order to determine the effect of addition of SiC reinforcement on the properties for the obtained sinters samples, hardness was studied at small loads by Vickers method. Addition of reinforcement had brought the desired effect of hardness increase in the samples with the SiC content. The influence of SiC on the processing and the properties of aluminium matrix powder was analyzed in details.
- Analysis of the effectiveness of surface hydrophobisation for roof tiles and ceramic bricks
- Strony: 484-489
The research has assessed the possibility of using organosilicon-compound hydrophobic preparations to impregnate ceramic building materials such as bricks and corroded ceramic roof tiles. The process of surface hydrophobisation has been analysed. The effectiveness of five different preparations that differ in the degree of hydrolytic polycondensation, viscosity and concentration has been examined. These factors can influence a hydrophobisation final result. The laboratory tests performed include an analysis of the physical characteristics of materials tested, a water absorption test, weight water absorbability of hydrophobized samples, water vapor diffusion, frost resistance, and an analysis of the characteristics of silica gel in the image of electron microscopy. Organic-solvent hydrophobic preparations such as methylsilicone resins dissolvable in white spirit significantly improve hydrophobisation; water-soluble preparations poorly protect ceramic bricks and roof tiles against water absorption although they effectively protect ceramics against frost. Based on the research it can be noted that preliminary laboratory and in situ tests should be done before any hydrophobic preparations are applied to building ceramics as this could become the basis for predicting the effectiveness of hydrophobisation done under real conditions. This applies particularly to corroded roof tiles which are often engobed when manufactured to determine whether the expected effects will commensurate with the costs incurred.
- Studies on preparation of silicate-organic composite materials
- Strony: 490-494
The paper presents the results of a study on how to obtain transparent silicate-organic composite materials based on acrylic monomers and water glass. Guided by the preliminary studies, we accepted three different methods: (i) introduction of acrylic monomers to water glass, and then polymerization of the resultant mixture; (ii) obtaining the structure of silica-polymer gels through the use of sorption of aqueous solutions by hydrogels; (iii) using mixed techniques based on introduction of the water glass solution to hydrogel and then curing the resultant mixture. The obtained composite materials were tested in terms of transparency grade and colour. The ability to create apertures in EI class during the fire tests was also analyzed. Analysis of the results led to the conclusion that further proceedings concerning the preparation of transparent silicate-organic composites should develop last two schemes of the procedure, because they gave the best results. The composites obtained in this way have a fi re protection property and can be used in building engineering.
- Magnetic-dielectric properties of polycrystalline GdxBi1-XFeO3 ceramics
- Strony: 495-498
GdxBi1-xFeO3 (x = 0.0; 0.05; 0.1; 0.15) solid solutions have been prepared by a conventional ceramic processing technique. The magnetic loops of GdxBi1-xFeO3 were measured over the temperature range from 5 K to 300 K in magnetic field up to 8 T. Substitution of the gadolinium ions for the bismuth ions leads to the appearing of a weak ferromagnetic state. Dielectric properties of the GdxBi1-xFeO3 system over a frequency range of 400–2500 cm-1 have been systematically investigated.
- An analysis of phenomena occurring during the process of laser decoration of porcelain
- Strony: 499-505
The paper presents an analysis of the influence of laser decoration process parameters, namely the laser beam and its scanning parameters, as well as a kind and composition of colour materials on final utility parameters of resulting marks. Particular attention has been paid to the adhesion durability and surface microstructure of applied layers. Attempts were undertaken to describe and explain shortly phenomena on the basis of physical processes accompanying a short interaction of strong, continuous laser radiation with matter. Analyses of experimental results have been supplemented with diagrams of means directed to the process optimization, connected with selection of the laser and scanning parameters, and illustrated by photographs of the resulting marks and decorations.
- Colloidal processing of fine spinel powders
- Strony: 506-511
Magnesium-aluminium spinel (MgAl2O4) in the form of transparent ceramics is applied in shields of infrared detectors or emitters, high temperature widows and elements of military aircrafts and vehicles. Apart from high transparency for specific wave lengths, the materials for indicated applications should have good mechanical properties, especially hardness. This is the reason for production of fi ne-grained materials. It seems that such materials can be produced from submicron powders consolidated by one of colloidal techniques. The work presents the results of investigations on consolidation of fi ne magnesium-aluminium spinel powders by filter pressing and casting. The main aim of the studies was optimisation of conditions of the consolidation, leading to the production of dense green samples with narrow pore size distribution. The samples were sintered in dynamic and isothermal conditions. Vickers hardness and microstructure of dense materials were examined.
- Thermal reactions between Dy0,73Tb0,27Fe2 and pzt characterized by high temperature mössbauer spectroscopy
- Strony: 512-518
High temperature Mössbauer spectroscopy was used to study reactions between phases in Dy0.73Tb0.27Fe2 and PZT mixtures in high vacuum. Dy0.73Tb0.27Fe2 was synthesized using an electric arc melting technique. Crystal structure and atom positions of the compound were determined by XRD measurements. The ab inito computations of electronic bands structure of the investigated material were done and covalent – metallic character of the bonds was confi rmed and elastic constants together with Young’s, shear and bulk moduli were determined. The Dy0.73Tb0.27Fe2 and PZT mixtures were prepared. High temperature Mössbauer effect measurement of the Dy0.73Tb0.27Fe2 /PZT mixtures demonstrate the effect of decomposition the intermetalic compound into rare earth and iron. This decomposition starts already at 400 K. The iron liberated during this decomposition is incorporated in the PZT structure as Fe3+ in tetra and octahedral coordination. Small quantity of iron exists as Fe2O3. The Fe2+ iron was not observed.
- In situ synthesis and sintering of the MgAl2O4 spinel using hot isostatic pressing
- Strony: 519-523
The preliminary results are reported on the in situ synthesis and sintering of aluminium-magnesium spinel with unique optical properties by using encapsulation enhanced hot isostatic pressing (HIP). The process has been provided at a temperature of 1750°C and under a pressure of 200 MPa, using alumina nanopowder and magnesia mikropowder. A method of capsule preparation, preventing undesirable contact of the precursors with silica capsule, is presented in detail.
- Photocatalytic degradation of methyl blue using nanocrystalline TiO2
- Strony: 524-527
A flow measurement equipment was constructed, and a method of determination of the photocatalytic degradation reaction rate of water organic contaminants was elaborated. Commercial P-25 TiO2 nanopowder was used as a photocatalyst. Photocatalytic activity was studied using a model reaction of the decomposition of methyl blue. Considerable effect of the temperature on both mechanism and reaction rate was observed. Estimated activation energy was equal to 8.21 ± 0.90 kJ/mol.
- Comparison of porosity characteristics of self-compacting fresh and hardened concrete modified with SP, AEA, AFA AND VMA additions
- Strony: 528-535
The influence of SP, AEA, AFA and VMA on air content, workability and porosity characteristics of self-compacting concrete (SCC) is presented in the paper. The research results proved that the admixtures influence workability and porosity characteristics of both fresh concrete mix according to the results of AVA research and hardened SCC according to PN-EN 480-11:2008. It has been stated that the relationship between porosity characteristics of the fresh and hardened SCC was not satisfactory.
- Methods of testing pozzolanic activity of mineral additives
- Strony: 536-541
A wide range of methods for determining the pozzolanic activity of mineral additives to cement and concrete are described in this paper. Generally, the methods encompasses studies of pozzolana or analysis of changes in the pozzolana–lime–water or pozzolana– cement–water systems. On this basis, usefulness of pozzolana in given conditions or applications is assessed.
- A flux agents system designed for modification of sanitary ware masses
- Strony: 542-546
In this paper, ways of decrease of sanitary masses costs have been shown. The first one is the use of a set of flux containing feldspar and spodumene, second one is an additive of Turoszów clay which is the accessory material in brown coal mines. The interesting results have been obtained as regards decreasing the temperature of fi ring and increasing technical parameters of sanitary masses. Investigations show that the use of adequate compositions of the ingredients mentioned above can decrease the sintering temperature of about 50°C. Simultaneously, an increase of ceramic materials durability of 50 % has been noticed.
- Rheological properties of ceramic suspensions modified by sodium, potassium and lithium silicates
- Strony: 547-551
Deflocculation of a water suspension containing 40 vol.% of the KOC kaolin with different water soluble silicates was studied and the results are shown. Sodium, potassium and lithium silicates were applied. Flow curves have demonstrated different activity of these deflocculants.
- Energy-efficient technology of preparing ceramic granulates. Part 2 – granulate properties
- Strony: 552-557
The new installation of milling, mixing and granulation machines, preserving high quality of mass preparing, causes appreciable economy of energy. In this paper, characteristics of ceramic gres porcellanato mass granulated by both Eirich typ R mixer and spray dryer have been shown. Special attention has been paid to methods of property determination of granulated ceramic masses.
- The influence of radon exhalation from ceramic products on the concentration level of radon in buildings
- Strony: 558-561
In order to evaluate the ceramic construction products in terms of natural radioactivity, the standard tests of basic concentration levels of three radioactive isotopes, i.e. potassium 40K, radium 226Ra and thorium 228Th are carried out. Using these measurements and the possibility of testing radon emissions directly from the standard samples (containers), there is the possibility of indirect assessment of the radon exhalation from construction products as a function of the emission of radon from previously collected samples of ceramic products and the concentrations of radium. Determination of the concentration of radium 226Ra in relation to the emission of radon 222Rn will create new opportunities for more accurate predictions of activity concentrations of radon in buildings.
- Bisque 3Y-TZP materials for all-ceramic dental restorations
- Strony: 562-569
The manufacturing all-ceramic dental restorations from zirconia ceramics is one of the newest and the most advanced technology in prosthodontics. The zirconia ceramics being a biomaterial gives new perspectives in a fi eld of mechanical strength, esthetics and functionality of dental restorations. Consolidation of zirconia micropowders to a form of biscuit-sintered and dense materials was performed during the present study. A commercially available zironia micropowder stabilised with 3 mol.% yttria was used with no addition and added with 0.2 wt% Al2O3. Selected properties of the bisque materials were measured and compared with the commercial 3Y-TZP materials used in dental technology. Finally, mechanical processing and application of the biscuit-sintered zirconia materials for fabrication of the all-ceramic dental restorations were examined.
- Refractory materials with reduced pore sizes
- Strony: 570-573
The work presents a concept and possibilities resulting from the application of two non-standard technological operations, i.e. fired products impregnation and coarse-grained mix granulation. Impregnation of basic materials with water solutions containing selected salts causes favourable microstructural changes, namely the reduction of open porosity by 2-3 %, the reduction of average pore diameter and pore diameter distribution median by 25-40 % and 30-50 % respectively as well as an increase in the share of pores having diameters below 10 μm at the cost of larger pores. These changes result in enhanced corrosive resistance of products. Additional effects of impregnation have been presented, including increased resistance to hydration in hydrothermal conditions. A possibility to use this procedure for changing the reactivity of a product in a way, which results from the corrosion mechanism has been presented on the basis of a literature example of a high-alumina product. The results of technological investigations into the use of coarse-grained mix granulation technologies to obtain formed micro-porous basic and alumina-silicate materials have been presented. The microporous magnesia material additionally displayed thermal shock resistance reaching the level of 11 cycles (1000°C-water). A novelty in the field of materials is a material from the MgO-Al2O3-SnO2 system, which is microporous and resistant to thermal shocks. A magnesia-chromite material containing ca. 20 % of
Cr2O3 has been obtained. It is characterised by reduced pore sizes and thermal shock resistance by 50 % higher than the standard material. It has been proved that the application of the new technology enables obtaining high-alumina materials with a 70 % share of pores having diameters less than 3 μm. Basic areas of application for the new or improved materials have been identified.
- Utilization of the finite elements method for solving problems connected with heat conductivity
- Strony: 574-580
This article shows the usability of the finite elements method for problems related to heat transfer and thermal stress. An example of solution applied for a specific industrial problem was presented. This problem rely on verification of heating curves of linings in a steel ladle and selection of adequate materials, adjusted to particular thermo-mechanical conditions in which it are going to be used. Also an example of applying the mentioned computer method to design a laboratory experiment was presented. The authors carried out calculations to design an insulating box, which will allow magnesite shape placed in it to be cooled at the estimated rate. This example was used to intuitive display of the idea of finite element method. The presented calculations were based on the custom software, developed at refractory
Materials Division of ICiMB in Gliwice and the commercially available Comsol Multiphysics software.
- Aluminates in the shaped refractory products
- Strony: 581-589
The aluminate phases in the shaped refractories were discussed. On the one hand, the presence of these phases is the result of conscious action by the process engineer in a design and manufacturing process of shaped refractories. On the other hand may be the result of the corrosion processes that accompany refractory linings work in the cement and steel industries. Aluminates in shaped refractories are introduced to refractory as a final product or may form in situ during fi ring of bricks. Phase composition and microstructure modifications of shaped refractories using aluminate phases improve their properties. The influence of the high alkaline environment on shaped refractory results in the phase synthesis of secondary aluminates. Process of formation of new phases is accompanied with the increasing volume, which lead to the corrosion deepening and ultimately, the complete destruction of the refractory product. The same processes are observed in the unshaped refractories.
- Studies of inelastic properties of basic refractories
- Strony: 590-594
The study presents the results of investigations into inelastic properties of basic refractories versus time. The investigations revealed considerable changes of shear modulus (G) and Young’s modulus (E) over a period of several hours, which in extreme cases reached 4 GPa. This phenomenon was accompanied by changes in internal friction (Q-1), being a measure of mechanical energy dissipation during oscillation of the examined material, which occurred due to structural changes in the material. Investigations were also conducted into the changes of E and G modulus of basic refractories after thermal shocks versus time. On the basis of the results obtained, approximate stress relaxation times after thermal shocks were determined for the magnesia-chrome material,. The discussion of the results has been based on the theory of inelastic material behaviour and the theory of internal friction.
- Stainless steel welding in a protective gas atmosphere with application of special ceramic washers
- Strony: 595-602
Problems related to the welding of stainless steel sheets and the currently used methods of their elimination have been discussed. There has been presented a new concept of ceramic washers’ application, enabling a neutral gas to be supplied to the weld root in the case of flat and arc surface welding. Preliminary trials of the application of cordielite-mullite washers have shown that the quality of weld is significantly influenced by the rate of heat supply from the welded areas. The results of investigations into cordierite-mullite materials containing SiC with a sialon matrix and SiC with a Si3N4 matrix have been discussed. They were characterized by an increasing thermal conductivity, reaching ca. 2.5, 8.2 and 18 W/mK at ambient temperature. Industrial trials of special steel grades welding in a gas shroud while using the washers, which supply gas to the welded surfaces made of the developed materials have been conducted. The influence of the type of washers on the quality of welds depending on the kind and thickness of the welded sheets has been determined. The welding process parameters have been established. The attempts to use the developed system of ceramic washers for stainless sheet welding have been discussed.
- The influence of sintering parameters of mechanochemically activated precursors on properties of the nitride ceramics
- Strony: 603-607
The temperature of nitride ceramics sintering may be lowered in the process of mechanochemical treatment of the initial set of powders, but such a procedure will cause microstructural changes in relation to standard products, and consequently will result in the change of properties. For the needs of this article, the authors conducted investigations into the infl uence of parameters of sintering (time, temperature and heating curve arrangement) of Si3N4 powder with an addition of AlN and Y2O4 after mechanochemical activation on the final product properties. Changes of density, porosity, absorbability and hardness (HV) of sinters have been determined. Fracture toughness (KIc) has also been estimated. Dilatometric tests allowed the best sintering curve to be determined, while LM/SEM structural observations enabled tracking the structural changes which result from the process of sintering.
- Directions in development of refractories for the cement and lime industry
- Strony: 608-613
The article discuses the directions in development of basic refractory materials for the cement and lime industry. The influence of chemical and phase composition as well as the effect of production process parameters on the usable properties of these materials have been presented. On the basis of SEM/EDS investigations, the microstructure of magnesia-spinel products has been discussed. The influence of microstructure on selected corrosive processes in rotary kiln has been presented using selected examples. Basing on the presented investigation results, the phenomenon of liquid phase appearance in products has been discussed and a pattern of corrosive changes depending on their phase composition and CaO/SiO2 mole ratio has been presented.
- Dolomites of polish deposits in aspects of the domestic refractory industry – Possibilities and limitations
- Strony: 614-618
Dolomites are used in different industrial branches, also for the production of refractories. For this purpose they are currently obtained only from “Brudzowice” deposit in the Cracow-Silesian region. In connection with progressive exhausting of dolomites especially advantageous for the refractories, their reserves should be again recognized. For this purpose not only higher and higher quality requirements but also economic aspects must be taken into consideration. The latter are connected with a profit of selective exploitation of dolomites as well as with demands of refractory industry. Such kind of exploitation is often expensive and collides with intensive output. The general review of this problem with respect to earlier elaborations and evaluation is the subject of this paper. The analysis of domestic dolomite resources has shown the greatest possibilities of using these raw materials for refractory production with regard to the “Brudzowice” deposit and also other deposits of the Cracow-Silesian region both under exploitation (e.g., “Ząbkowice Będzińskie” and “Libiąż”) and being a reserve (“Chruszczobród”). The “Winna” deposit in the Świętokrzyskie region and some Lower Silesian deposits (especially “Ołdrzychowice- Romanowo”) can be taken into consideration as the potentially interesting sources. However, the dolomite raw materials of this origin require further investigations both mineralogical-petrographic and chemical, as well as the accurate deposit recognizing to indicate their parts with the most suitable parameters for the production of refractories.
- Some aspects of the thermal analysis of polish dolostones
- Strony: 619-625
Thermal analyses (DTA, TG, EGA) of the dolostones from some Polish deposits (Winna, Libiąż, Żelatowa, Brudzowice) have been carried out by means of traditional method using powdered or solid samples. Preparation of the samples did not affect the temperature of the first endothermic peaks. There is no influence either on the second endothermic peak in the case of fi ne-crystalline dolostones of Brudzowice deposit. On the other hand considerable influence occurs in the case of coarse dolostone from the same deposit. Apparent activation energy determined from the fi rst endothermic peak of dolomite decomposition was more diversified than apparent activation energy calculated from the second one. Probably this is a result of the influence of structural and textural features such as a size and porosity of dolomite grains.
- Refractory castables high thermal shock resistance
- Strony: 626-630
New low-cement refractory castables characterised by high thermal shock resistance have been developed. Samples of refractory castables based on various aggregates (cordierite grog, quartz glass, chamotte grog) with alumina cement were prepared. Their basic properties were determined such as apparent density, open porosity, cold crushing strength and shrinkage. Castables’ resistance to thermal shock was also determined in traditional heating and cooling tests. The investigations have revealed that the obtained refractory castables display better properties after firing than conventional chamotte ones (BOS 135), which until now have been used in linings for coking chamber doors. Compared to BOS 135, the new low-cement castables are characterized by higher cold crushing strength, lower open porosity, lower shrinkage and considerably higher thermal shock resistance. The RSt parameter for the obtained materials has also been calculated on the basis of the measured values of the work of fracture, dynamic Young’s modulus and thermal expansion coefficient. Results of calculations revealed that quartz glass-based castable had highest value of parameter Rst. The value of RSt was compared to the results obtained in heating and cooling tests. Industrial tests were conducted for the developed castables, which were used in the lining of the pusher furnace in Euroblacha S.A. in Ruda Śląska and in the lining of the coking chamber door in ZK Radlin. The trials demonstrated that the performance of the new refractory castables was satisfactory and fulfilled the operational conditions. As a result of application of new castables, the following lifetime was obtained: in the lining of the coking chamber door – 29 months and still, and in the lining of manoeuvring windows in the pusher furnace – 25 months and still.
- Materials and structural requirements for a vacuum degasser of molten steel by the rh method
- Strony: 631-641
Refractory materials intended for use in a steel vacuum degassing unit by the RH method have to be adjusted to the operating conditions in particular areas of the unit. Proper identification of major destructive effects in particular zones of the unit and the most affected areas allows optimal selection of a refractory lining. Magnesia-chromite products (MC) have been widely applied in RH units as they are characterised by high corrosive resistance to iron oxides and liquid calcium-silicate melts. They also display high mechanical strength in working temperatures and good resistance to temperature fluctuations. Further improvement of physical and chemical parameters of magnesia-chromite products may be achieved by subjecting them to an additional saturation procedure with properly selected impregnants, which allows enhancing a number of properties that influence both corrosive resistance and mechanical strength within a certain range of temperatures. The article among others presents the effect of impregnation on such material properties as: pore size distribution, gas permeability and bending strength depending on the temperature. The service life of an RH unit may be enhanced by applying adequate constructional solutions.
- Fired corundum materials bonded with colloidal silica
- Strony: 642-646
Tests of corundum refractory materials with the colloidal silica bond were conducted on a lab scale and on a semi-technical scale. The colloidal silica with diverse content of SiO2 and in various quantities was introduced into the corundum mixtures. It was stated that the addition significantly increased the mechanical strength of material after drying. Also the increases of mechanical strength after firing as well as the improvement of thermo-mechanical properties and thermal shock resistance were achieved. The improvement of corundum materials quality was the result of the increased mullite content in the matrix close to the content potentially available. Prospects of the industrial application of the developed corundum materials were discussed.
- Corrosion of MgO-C products in the steel ladle slag zone
- Strony: 647-652
The authors developed a laboratory model of corrosion processes taking into account the quickly progressing saturation of a slag portion and a controlled temperature gradient in the contact layer of the examined samples. Suitable selection of a resonance frequency and metal-coil distance made it possible to determine the metal and slag velocity which resembled operating conditions in a ladle. Also the phenomenon of decarburized layer formation due to iron oxides and atmospheric oxygen may be reconstructed in laboratory conditions. Comparative investigations into MgO-C and AMC with temperature gradient measurements were conducted in an induction furnace while controlling the changes of slag chemical composition. In order to compare the degree of wear, the cross-sectional area of pits was compared. Such investigations allow a new type of carbon binders and additives to be evaluated which increase the corrosive resistance of MgO-C materials, influencing the sedimentation of new phases in pores in the process of liquid slag penetration. In industrial practice, the corrosion of materials in the slag zone is also influenced by such factors as material surface oxidation in the process of ladle heating, stresses due to thermal expansion in the working layer and intense corrosion in the shapes’ contact area.
- Investigations into the causes of silica products discoloration
- Strony: 653-659
The study deals with the problem of discolorations visible on the surface of fired silica products and the effect of their presence on selected usable properties. In order to explain the reasons for the occurrence of discolorations, investigations into the chemical composition, microstructure (LM, SEM/EDS) and phase composition (XRD) as well as selected properties of silica products (compressive strength, refractoriness under load, thermal expansion) have been conducted. As a result of investigations into the microstructure and phase composition, it was found that the main cause of discolorations on the surface of products were differences in phase composition, related to the heterogeneity of chemical composition in microareas, which resulted in the formation of local eutectics. In the conditions of the examined products firing, discolorations were caused by the crystallization of iron oxides, i.e. magnetite (FeO·Fe2O3), hematite (Fe2O3) and ilmenite (FeO·TiO2) beside wollastonite (CaO·SiO2), the infl uence of temperature and fi ring atmosphere. Investigations into selected parameters of silica products showed that discolorations did not influence their usable properties. The probable reason for the occurrence of discolorations on the surface of fi red silica products was indicated.
- Analysis of silicon carbide chemical composition – the consistence of the obtained results depending on the applied measurement methodology
- Strony: 660-662
The work presents the results of silicon carbide chemical analyses depending on the applied standard. Advantages and drawbacks of particular analytical methods and their occurrence depending on the degree of purity of the analysed SiC have been presented. The work also presents investigations into SiC-containing materials, including castables, and characterises analytical problems, which result from the presence of other refractory components. The presented results refer to certified reference materials and, in the case of castables, to mixes of certified reference materials. The investigations were based on procedures specified in the following standards: PN-86/H-04157 „Refractory materials. Chemical analysis of silicon carbide and silicon carbide products”, ISO 9286:1997 „Abrasive grains and crude – Chemical analysis of silicon carbide” and PN-EN ISO 21068 parts 1-3:2008 „Chemical analysis of silicon-carbide-containing refractory raw materials and refractory products”. In each of these documents, the samples of SiC and SiC-containing products are prepared in a different way, which has been proved to significantly influence the results. The authors presented the results obtained for certified reference materials and for real samples using the measurement methods proposed in the standards. The effect of the applied methodology on the obtained results has also been discussed. Particular attention has been paid to the content of elemental silicon, frequently present in SiC-containing raw materials and products, whose results of determination differ significantly depending on the standard applied. The procedures contained in PN-86/H-04157 and PN-EN ISO 21068 part 1-3:2008 standards take into account the presence of metallic elements when determining the content of elemental silicon, whereas ISO 9286:1997 standard does not take into consideration metallic additives, and the results of elemental silicon contents are overstated due to a possible presence of metals. Nowadays the use of standards is voluntary; in the case of sale of SiC-containing raw materials and products the standards are reference documents accepted by both parties. It is important to be aware of the influence of methodology presented in the standard on the obtained results.
- Minimisation of energy consumption by selecting proper insulation materials
- Strony: 663-669
Insulating firebricks (IFBs) are well established products for solving many problems of high temperature heat containment in industries ranging from ceramic production kilns to anode furnaces for primary aluminium. The volatile energy prices of recent years have increased the importance of maximising energy savings in these industries. In order to optimise energy savings, the kiln designer needs to know which IFB products provide the minimum energy losses. The purpose of this work is to quantify the differences in performance that can be achieved by studying a wide range of IFBs currently available on the market. This is achieved through laboratory based measurements of energy losses from standard kiln arrangements constructed with a variety of test bricks. Since different suppliers manufacture IFBs by different techniques (casting, slinger, extrusion, foaming, pressing), the brick microstructures produced can be very different, leading to a wide variety of thermal conductivities in the market within the same class of product. This in turn leads to a wide variation in the ability of the different types of IFBs to control energy loss from the kiln. This work demonstrates that IFBs can display up to 37 % difference in the energy savings achievable depending on their method of manufacture. The work also presents further consequences of the manufacturing method on performance in terms of heating and cooling rates, and reduction in CO2 emissions.
- Adjusting a tunnel kiln to changeable production, different grades and assortments of refractory materials
- Strony: 670-674
A tunnel kiln for firing refractory materials is a high efficiency unit provided, however, that it is used in line with the design assumptions, i.e. nominal efficiency, firing the intended grades and assortments of products. Market requirements force plants to produce refractories that are sometimes very different from the ones for which the kiln has been designed. As a result, the tunnel kiln works in unstable conditions, which sometimes leads to unsatisfactory quality of products on the one hand, and lower energy efficiency on the other hand. The gas (energy) consumption indexes per a production unit are rising so much that they frequently resemble indexes for periodic rather than tunnel kilns. Modernisation of the existing as well as construction of new tunnel kilns should take consideration the changeability of kiln operation conditions. Such “universal” constructions of tunnel kilns do exist. They have been tested in everyday work and will be discussed in this paper.
- Selection of refractory materials for the lining of furnance doors in coke oven batteries
- Strony: 675-682
In the present work, monophase βTCP or αTCP as well as biphasic BTCP ceramics (βTCP + αTCP) were biologically evaluated using thThe service life and work efficiency of furnace doors in a coke oven battery depends chiefly on the maintenance of its good technical condition. There is a lot of evidence showing that a furnace door lining may be used for many years without much visible damage. There have also been cases where the furnace door ceramic lining had to be repaired after a period of just a few months of operation due to its bad technical condition. Attributing the difference in the time of linings work merely to the level of maintenance service would not be justified. In the process of operation, the furnace door lining is exposed to mechanical, physical-chemical and thermal forces, which cause natural wear of refractory materials over time. The paper presents experiences of ZK Zdzieszowice obtained as a result of operating tests conducted for several grades of refractory castables produced by different manufacturers of ceramic materials. This provided a basis for choosing the material, which fulfi ls our expectations with regard to improved working and operating conditions.
- Czech and slovakian refractory industry in a period of economic crisis
- Strony: 683-686
The global crisis, lasting from 2008, resulted in the hindering economic development of many countries. A decreased production, a drop in demand and unemployment growth were observed. Obviously, the problems did not omit the refractory branch. In the paper, the state of the refractory industry in the Czech and Slovak Republics during the crisis is analysed. Changes in GDP (Gross Domestic Product) and inflation in these countries and EU in the years 2008–2010 are shown. The sale structure of refractory materials in particular industry branches is described in the context of changes in the production of steel, casts, cement and glass in this period of time. Progress of the production of refractory materials in the Czech and Slovak Republics since the year 2000 is discussed. The structure of the production and sale of refractory materials in the years 2008-2010 is compared in these countries. Economic revival after 2009 has been stated. The reasons of difficulties with achieving the state of the refractory industry just from 2007 are indicated.
- Improved additives for high purity low cement castable systems
- Strony: 687-691
Many types of organic molecules that are used as deflocculants in refractory castables are derivates from developments for the building industry with either Portland cement or mixed binder systems consisting, e.g., of Portland cement, Calcium Aluminate cement and Calcium Sulphate. Only few products have been developed which fit specifically to pure Calcium Aluminate cements. Two new Polycarboxylate Ethers, Peramin® AL200 and Peramin® AL300 will be presented in this paper which are molecules tailor-made to deflocculate high purity alumina / alumina spinel castables. Peramin® AL defl occulants provide the desired placing properties of these castable systems. Mixing water can be reduced to a minimum to provide castables with an excellent self-fl owing and vibratable consistency. The rapid wet-out during mixing, predictable and sustained fl ow during placing, and effective de-airing during consolidation will be demonstrated. In addition, by using these additives either singly or in combination, depending on the ambient conditions, it is possible to achieve the required hardening profi le without the addition of classical accelerators. Peramin® AL additives tailor-made for refractory castables that contain high quality 70 %. Calcium Aluminate cements like Secar® 71 and Secar® 712 bring improved quality to the installed castable, and ultimately, improve the in-situ performance of the final lining.
- Refractory Linings of Pig Iron Transfer Ladles
- Strony: 692-695
The paper gives a review of refractory lining designs and materials to be used in pig iron transfer ladles according to experience from different shops. Particular attention is given to the effects of incorporation of the ladle desulphurisation process on a service life of the ladles. The article presents specific physical properties (resistance to corrosion, penetration) of iron ladle lining. The obtained results are compared with the field service durability of ladle linings.
- How PRE and Cerame-Unie make the difference in Europe
- Strony: 696-698
The European Refractories Producers Federation, PRE, represents the refractory industry in Europe. PRE’s mission is to act as a forum for technical exchanges, raise the visibility of the industry and highlight its strategic importance towards the policy makers in the European institutions. As a member of Cerame-Unie, the European Ceramic Industry Association, it tackles the key challenges such as access to raw materials, resource effi ciency and the European climate change policy.
List of Contents
Volume 63, Issue 4
- The texture of plasma sprayed Cr2O3 oxide coatings and remelted with the CO2 laser
- Strony: 702-706
The main objective of this study was the identification of the texture of plasma-sprayed Cr2O3 oxide coatings, remelted with the use of a CO2 laser. The texture of the coatings has been determined with the X-ray method on the basis of XRD patterns and pole figures. The conducted research showed the presence of fibre texture in the plasma-sprayed coatings. This fibre texture is featured with the characteristic, symmetrical location of the diffractive reflections on the pole figure and clearly accentuated figure centre. The presence of the texture in the sprayed material proves that despite the specific structure of the coating resulting from the way of shaping it, the initial orientation which has formed in the material during plasma-spraying had no incidental nature. However, the examination has shown that the level of texturizing of the sprayed material was low. The examination of the coatings remelted by means of the CO2 laser has shown strong concentration of reflections on the pole figure from the analysed crystallographic planes which evidence the existence of preferential orientation in the examined material. Considering that during the remelting treatment, the crystallization process of the coating material proceeds from deeper layers of the coating towards its surface which directly results from the directionality of the heat outflow during the treatment, the presence of the fibre texture seems to be explainable. The analysis of the pole figures and the XRD patterns have shown that this is a fibre texture, the main components of which were <104> and <116> directions. Besides, it has been found that the processes which have caused formation of the texture in the spread layers during the remelting treatment have been intensified and deepened. Additionally, the impact of a cooling rate (being the resultant of the assumed remelting parameters) on the nature of the texture has been stated. The examination of the phase composition has shown the permanence of the phase composition of the coatings which proves high durability of the Cr2O3 oxide in the conditions accompanying the spraying and remelting treatment.
- Influence of powder nature on microstructure and properties of dense magnesia stabilized zirconia materials
- Strony: 707-714
Investigations concern magnesia stabilized zirconia prepared by using physical mixing of component powders in attrition and ball mills. Four commercial powders were used: three of them were of precipitation origin, the fourth was obtained by the fused method. Chemical purity and grain size distribution, determined by the laser method, differed powders one from another. All precipitated powders were of the same grain size determined by electron microscopy. Bulk density and pore size distribution of compacts depended on the nature of the powder and milling manner. Densification rate under sintering depended on the pore size distribution of the compacts. Grain sizes of the sintered materials depended on the grain size of the powder determined by electron microscopy and in case of the fused powder on the crystallite size. The sintered material prepared from the fused powder showed the best mechanical properties.
- Modified polymeric composite materials for power applications
- Strony: 715-719
Two different composite materials: (i) 40 wt% epoxy resin and 60 wt% silica powder, (ii) 40 wt% epoxy resin, 57 wt% silica powder and 3 wt% bentonite were investigated as insulating materials for the electric power industry. The materials were obtained by vacuum casting. Based on c it can be stated that the materials are characterized by homogenous microstructure and they do not posses any defects (voids or pores). The measurements of apparent density and Young’s modulus indicated that partial substitution of silica filers by bentonite powder in the composite material does not lead to the significant changes of densification and elastic properties in reference to the composite filled only with 60 wt% of silica. However, a small addition of bentonite increases mechanical strength and also stabilizes its thermal performance through the decrease of thermal linear expansion coefficient. Improvement of insulating properties of the composite modified with 3 wt% addition of bentonite was also observed. It can be concluded, based on the preliminary study, that the tested composites may be promising materials in the case of production of insulating components for power applications.
- An isothermal chamber for milling in inert gas
- Strony: 720-724
Grinding many materials, especially organic materials, chemicals, ceramics and pharmaceuticals, is carried out in grinding chambers of vibratory, planetary, and other mills with free grinding aids in the air environment, inert gas or liquid (alcohol or other liquids, including flammable). Physical properties of some milling materials require to maintain the correct temperature of a grinding charge, i.e. ground material with grinding aids, and the most often cooling systems with the temperature stabilization during grinding. In addition, some materials can be ground only in an inert gas. It requires the use of the manual chamber equipped with locks, in which air located in the grinding chamber can be removed and replaced with the inert gases. An isothermal milling chamber with a capacity of 500 cm3 was developed in the presented research. The chamber was made of polyamide and equipped with a water jacket, tight lid and system of two valves. One valve was designed to exhaust air, the other one to fill the chamber with inert gas without using a manipulative chamber. One of the valves enabled the sampling of milling material. The isothermal chamber was adapted for milling materials in a periodic manner in a laboratory vibratory mill. A water jacket of the chamber was equipped with two control valves connected to a flexible tube with a system for measurement and stabilization of the temperature. This system comes with temperature sensors, water tank, pump and enables measurement and stabilization of the temperature of grinding chamber coolant at 20-70°C, ±2 %. The study of a process of very fi ne and colloidal milling of the materials, including nanopowders and nanostructures, that show high requirements concerning the grain size distribution and purity can be carried out in the isothermal chamber at total elimination of metallic impurities and oxygen from the grinding environment. The chamber can also be used for mixing single and multi-phase media with high technological requirements, including chemicals, ceramics, organic and pharmaceutical materials at the stable temperatures in the atmospheres without oxygen.
- Investigations on very fine milling of calcite
- Strony: 725-730
Studies of very fine milling of calcite were carried out in a laboratory vibratory mill of periodic operation and low vibration frequency below 16 Hz. The objective was to gain ground calcite of a grain size characterized by the largest possible content of grains in a class below 10 μm, and the largest purity determined by the whiteness index (WI). Two types of calcite pre-ground in an industrial gravity mill were used for milling. The materials differed in graining; the grain sizes, d90, were 43 μm and 37 μm. The research was carried out by using steel and corundum milling media. The milling process was carried out in two manners: with no addtives and with the addition of three types of grinding activators. The collected results indicate that, even at very short grinding times, the very favorable results of grinding can be obtained, i.e. a decrease of the content of grain class +63 μm from 15,6 % in the charge to 0,5-3 % in the product, and growth of the content of grain class below 10 μm from 36 % in the charge to 60-70 % in the milling product were measured. At the same time, whiteness index WI increased from 81-82 % to 90-95 %. It was found that ground calcite of much fi ner grain size than in case of traditional ball mills can be prepared by using the vibratory mill with low vibration frequency (10 to 12 Hz). This suggests the use of the vibratory mill for comminution of calcite in industrial environments, particularly that it is characterized by the mass several times smaller and the power demand per unit several times less than the ball gravitational mills, and additionally much lower investment costs and lower harmful effects on the environment.
- Praseodymium-zircon pigment for the colouring of ceramic glazes
- Strony: 731-735
Praseodymium-zircon pigment is a synthetic inorganic product, characterized by its ability to give a specific yellow–green (lemon) colour to ceramic glazes. The zirconium silicate crystallographic structure of the pigment guarantees, due to its stability, some resistance to any aggressive action of glaze ingredients up to the temperature of 1250°C. The tests revealed a signifycant effect of sodium fluoride as
a mineralizer on the quantitative phase composition of the synthesized pigment. However, no proportional dependence of colour on the amount of zirconium silicate in the pigment structure was found. On the other hand, there is a correlation between the colour of the pigment and the size of the elementary ZrSiO4 cell, which is a consequence of embodiment of praseodymium ions (chromophore) into its structure. The test results concerning dependence of pigment colour parameters on the quality of the crystalline structure, which has been formed in defined thermal conditions and from the strictly defined raw material composition, were presented in the article. Quantitative X-ray analysis was used for the structural tests. Lattice parameters were determined by the Rietveld method. Colour of pigments was determined by means of the parameters L*, a*, b* of glazes that contained 5 % pigment and have been made on the basis of transparent frit with a firing temperature of 1100°C in a fast cycle. Interpretation of the colour measurement results was carried out in the CIELab system, having an advantage that enables the numerical expression of colour (or difference of colour) by means of three numbers.
- Influence of local disorder on electronic structure and topological properties of electron density in AgXSe2 (X = Sb, Sn) solid solutions
- Strony: 736-742
The results of theoretical studies of electronic structure, obtained by means of the full-potential linearized augmented plane wave method within DFT formalism as implemented in Wien2k package, and electron density topology and bonding, obtained by means of the Bader’s quantum theory of atoms in molecules topological analysis of total electron density derived from FP-LAPW calculations, were carried out f orchosen solid solutions of Ag(SbxSn1-x)Se2 and described in the paper. Detailed analysis of the obtained results from the point of view of the dependence of electronic structure and topological properties of bond critical points on local ordering and level of tin doping is presented.
- Sintering kinetics of diamond-like carbides
- Strony: 743-751
In this work, sintering kinetics of SiC and B4C was studied. Sintering of these diamond-like carbides requires activation of the densification process. Small amounts of carbon and boron were used as additives for the activation of silicon carbide sintering. Only carbon was used for the sintering activation of B4C. Measurements of sintering kinetics were made by means of a high temperature dilatometer. Sintering shrinkage as a function of time was recorded under isothermal conditions. An analysis of the sintering kinetics was based on sintering models worked out by Kuczynski and Frenkel. The results of investigations allowed full sintering characteristics of the studied diamond-like carbides to be obtained.
- Gypsum mineral wool and influence of polymer impregnation on its properties
- Strony: 752-757
Beside traditional mineral basalt and glass wools, there is a possibility to manufacture another fiber stuff for the use as thermo isolation. In the paper, a material prepared from needle-shaped crystals of gypsum or anhydrite and polymer siloxane matrix is presented. Needle crystals can be formed in course of gypsum recrystalization performed in sulfuric acid solutions, and then shaped in stable blocks with polymers. The composite materials with a resin content of 50 % do not show typical disadvantages of gypsum materials, and do not undergo destruction after the exposure on wet storage or even after immersion in water; an anhydrite part does not become hydrated. Exhibition on high temperatures does not destroy the physical form of the composite material; on the contrary, mechanical parameters become better in case of the using thermosetting resin. In a context of the application as thermo isolation, main properties of the fiber gypsum/ silicone composite are comparable to the traditional hard insulating materials (density of 250–400 kg/m3 and thermal conductivity, λ, of 0,045-0,06 W/m·K.
- Influence of heat treatment of titanium-doped hydroxyapatite (TiHA) on properties and in vitro behaviour of calcium sulfate – TiHA composites
- Strony: 758-764
Biomaterials with the self-setting in situ properties for the use in human bone tissue augmentation have attracted increasing attention in recent years. Currently many commercial products exist on the market, however the efforts still proceed to achieve a novel bone substitute with improved mechanical and biological properties. Calcium phosphate based materials, including hydroxyapatite (HA), have been of special interest due to their excellent biocompatibility and bioactivity. Calcium sulfate has also a long history of clinical use and it is known to be well-tolerated by organism when used as a bone filler. In this study, a biphasic, self-setting bone substitute was developed, basing on calcium sulfate and titanium doped hydroxyapatite. Calcium sulfate hemihydrate (CSH) and three different Ti doped hydroxyapatite powders (TiHA): raw and calcined at 800°C and 1250°C were used to form the new biomaterial. The aim of this study was to investigate how heat treatment of titanium doped hydroxyapatite influenced the setting time, mechanical properties and in vitro behaviour in simulated body fluid (SBF) of the calcium sulfate - TiHA composites. The results of our studies suggest that TiHA-CS self-setting materials are biocompatible, easily shapeable and have a potential to be applied for bone substitution.
- Influence of hydroxyapatite granules on osteoblast culture in vitro
- Strony: 765-768
Hydroxyapatite (HAp) is the inorganic component of the bone tissue. Synthetic HAp bioceramics with various degree of porosity and pore size distribution is widely used in orthopaedics and dentistry. In this study, the biocompatibility of 3 types of HAp granules with different microstructure and crystallinity was evaluated. In vitro tests were carried out using the hFOB 1.19 human fetal osteoblastic cell line. Biocompatibility was estimated indirectly by means of fl uid extracts obtained by immersing the granules in fresh growth medium for 24 hours at 37°C. Viability of hFOB cells was assessed by 2 methods – MTT and NRU. Biocompatibility of the studied materials was also confirmed by observation under the confocal microscope. Additionally, elemental Mg2+ and Ca2+ concentrations of tested extracts were evaluated by atomic absorption spectrometry (ASA). Our studies clearly indicate that HAp granules depending on their microstructure, mainly porosity, can cause different uptake of Ca2+ and Mg2+ ions from the growth medium what affects the metabolism of cultured cells.
- Proteomic analysis of osteoblasts stimulated with NEW HAp-glucan composte by using the protein microarrays method
- Strony: 769-772
Hydroxyapatite (HAp) is well known as a bone-replacement material, but its widespread use in orthopedic and surgery is limited by its poor surgical handiness. To overcome this problem, Hap is frequently combined with organic polymers. The clinical use of new designed hydroxyapatite-glucan composite should be preceded by its complex tests on transcriptome and proteome level to find and identify changes that may trigger the pathways of apoptosis, necrosis or carcinogenesis. The effective tool, such the protein microarray technology enables simultaneous assessment of changes in concentrations of many proteins involved in the important metabolic pathways. The aim of our study was to compare the changes in the concentration of different osteoblast proteins caused by granular HAp or HAp-glucan composite stimulation. The proteins were assessed as functionally significant, when the ratio between the level of protein in cells stimulated with Hap compared to the cells stimulated with the Hap-glukan composite was changed ≥ 2-fold. Our study showed that the levels of over 90 % of proteins were not statistically changed. The significant changes were observed in the group of proteins that were responsible for regulation of apoptosis pathways. The increase of level of AKT (Anti-Protein Kinase Bα) and the decrease of level of PTEN (Phosphatase and Tensin Homolog) in osteoblasts stimulated with the Hap-glukan composite may lead to enhancement of cell survival and migration.
- Microstructure, phase composition and mechanical strength of novel bone substitutes based on hydroxyapatite, magnesium phosphate and calcium sulphate
- Strony: 773-778
Because of excellent biocompatibility and bioactivity, calcium phosphates such as hydroxyapatite (Ca10(PO4)6(OH)2) and β-TCP (Ca3(PO4)2) are successfully used as bone substitutes in orthopaedics, maxillofacial surgery and dentistry. However, due to low mechanical strength and brittleness, the application of these biomaterials in medicine is limited to places not loaded significantly. Limited surgical handiness is also a disadvantage of calcium phosphates, what makes diffi cult to place the material into bone voids. This study is focused on development of composites containing hydroxyapatite (HA), magnesium–phosphate cement (MPC) and calcium sulphate hemihydrate (CSH), and showing the optimum parameters for medical applications.
- Effect of selected ecological coal-tar pitches on the properties of dolomite refractories
- Strony: 779-785
Formed carbon bonded dolomite bricks are basic refractory materials which use organic binders in order to create carbon bond. The carbon bond is a fundamental element integrating the product, and giving it functional features. Until now, coal tar pitch was one of the most popular binder used in production of the dolomite bricks with the carbon bond. Despite of many advantages of coal tar pitch, but due to its toxicity, it is increasingly frequent search for new binders more safe for health and the environment that could replace it. This work presents effects of ecological binders available on the European market on properties of the dolomite refractory bricks. Industrially produced samples of carbon bonded dolomite refractories were evaluated. Examinations of dolomite clinker included the following properties: crushing strength, bending strength, Young’s modulus, modulus elasticity in shear, and also the thermal TGA-DTA test combined with EGA. The measurements were performed on the samples after different operations of thermal treatment that is after hardening and coking (T = 1000°C, t = 3 h or T = 1400°C, t = 0,5 h), or hardening and oxidation (T = 1000°C, t = 3 h or T = 1400°C, t = 0,5 h). Research has shown a significant difference between the behaviour of various binders, and also significant influence of graphite and sulphur additives on the properties of dolomite refractory bricks. Besides, it was found that binder with the lowest softening temperature had the most beneficial effect on mechanical properties of the bricks after hardening.
- Effect of Fe3+ ion on synthesis of calcium zirconate
- Strony: 786-792
Still, there is a great interest in the binary CaO-ZrO2 phase diagram, and especially in calcium zirconate, CaZrO3, as one of the main topics of materials engineering. Valuable properties of this material allow it to be used in various forms, and offer great opportunities for its application both in a pure form or in modified one, e.g. refractory material, fuel cells, oxygen probes, sensors, solid electrodes, filters, membranes and capacitors. The most important properties of CaZrO3 include high melting point (2345°C), thermal shock resistance, high dielectric constant, resistance to alkalis, electrical conductivity, mechanical, chemical and thermal stability. Influence of Fe3+ ions on microstructure and synthesis of CaZrO3 is reported in this paper. Two series of samples were prepared. The first one, which was a reference material was composed of pure CaZrO3. The second one was CaZrO3 doped with Fe3+ ions. Pure reagents of CaCO3, ZrO2 and Fe2O3 were used to prepared the materials by fi ring at 1200°C, and then, after grinding and compaction, at 1700°C. The material doped with Fe3+ ions when compared to the pure CaZrO3 was characterized by higher density, lower porosity and better sinterability. XRD analysis was used to determine the phase composition of the fi red materials; they were also tested by using mercury porosimetry. The SEM/EDS method was used for microstructure analysis.
- Studies on the apatite-silicate-phosphate layers on metal substrates soaked in SBF
- Strony: 793-797
The modifycation of metal material properties by depositing silicate-phosphate layers makes it possible to improve biocompatibility and bioactivity of the resultant material. The in vitro tests in simulated body fluid (SBF) are useful for the preliminary estimation of material bioactivity. The series of Ti6Al4V alloy materials coated with a silicate-titanate prelayer and a final silicate layer with the addition of calcium or hydroxyapatite (Ca10(PO4)6(OH)2) were prepared, and soaked in SBF. The samples before and after soaking were compared. The specification and comparison of the data results derived from XRD powder diffraction, infrared spectroscopy and electron scanning microscopy how growth of phases containing calcium in all prepared layers. The chemical composition of the layer has influence on amount, crystallinity and type of the formed apatite. The growth of calcium apatite and wollastonite was observed in the case of calcium added layers while only calcium apatite was present in the case of hydroxyapatite additions.
- Hydrolytic resistance of borosilicate glasses assigned for toxic waste immobilization
- Strony: 798-801
Encapsulation is one of the most effective method for toxic waste immobilization. Toxic elements are incorporated into the structure of a glass–ceramic sinter. Glasses from the SiO2-B2O3-Al2O3-Na2O and SiO2 B2O3-Al2O3-Na2O-CaO systems were studied. Additionally the glasses were enriched with 5 % of Cs, which was an indicator of infl uence of radioactive elements on properties of the glasses. Incineration hospital waste ash was used. Effects of chemical composition on hydrolytic resistance of the glasses were determined. It was proved that the applied method of sintering of borosilicate glass and hospital waste incineration ash permanently immobilized the toxic elements.
- Manufacturing and properties of materials from the corundum/γ-alon system
- Strony: 802-808
Alumina and alumina based materials are widely used as machine parts, cutting tools, abrasive and refractory materials, ceramic armours and even biomaterials. Polycrystalline g -alon, the solid solution of alumina and aluminium nitride with spinel structure, and related materials have also great potential for application as high-performance structural ceramics due to good mechanical and thermal properties. The aim of the present work was to manufacture materials in the alumina/ g -alon system, showing a wide range of compositions, and study their microstructure and mechanical properties. Mixtures of commercial alumina and SHS derived g -alon powders were hot-pressed at 1750°C for 1 h. It was found that the chemical reaction between corundum and aluminium oxynitride occurred during the hot-pressing, resulting in the formation of g -alon phase of different chemical composition. The highest value of fracture toughness was reached by the composite material containing about 40 wt% g -alon while the single-phase oxynitride materials had the highest bending strength. The observed changes in mechanical properties can be correlated to the chemical and phase composition, microstructure and specific residual stress distribution.
- Effect of Cr(VI) reducers on leaching of chromium and colouring of cement materials
- Strony: 809-813
The hexavalent chromium is of special importance among many trace elements present in Portland cements, and immobilized in cement pastes more or less effectively. Because of extreme toxicity of Cr(VI) which cannot be fully stabilized in cement matrix, its leachability was limited by the UE directives to the level of 2 ppm. Therefore, the use of chromium reducers as cement admixtures appeared; these admixtures are not without influence on some properties of material. The effect of Cr(VI) reducers, such as iron(II) sulphate, tin(II) sulphate and antimony(III) oxide was studied. The iron sulphate is the most popular, available and economical Cr(VI) reducer, but it reveals lower effectiveness as compared to the latter ones. Moreover, in the presence of oxidized FeSO4 residue the brown stains can appear on the surface of concrete elements, while in the SnSO4 or Sb2O3 containing material there is no colouring effects. However, the intensity of grey colour can be changed in such a way that the samples are brightened. The concentration of Cr(VI) in the leachates was analyzed by colorimetric method. The colour of cement pastes was determined by the use of different spectrophotometers. Because of the significant costs of
SnSO4 or Sb2O3 their use in case of coloured concrete or architectural concrete should be considered.
- Two-step sintering and related properties of 10 vol.% ZrO2-Al2O3 composites derived from filter and cold isostatic pressing
- Strony: 814-819
This work presents a preparation of 10 vol.% zirconia-alumina composites with micrometer alumina and submicrometer zirconia grains via filter pressing and cold isostatic pressing for low temperature consolidation, and constant heating rate sintering (CHR), two-step sintering (TSS) and reverse two-step sintering (RTSS) for high temperature consolidation. The powders of nano-zirconia (10 nm) and alumina (175 nm) were used. Temperatures T1 and T2 of 1600°C and 1350°C were set for TSS, respectively. A reversed sequence of these temperatures was used for RTSS. The resultant composites were characterized in terms of density, microstructural features, hardness and fracture toughness. Both the forming method and the heating schedule showed negligible effects on density of the composites that were sintered using the heating schedules involving a temperature of 1600°C. The microstructure of composites was affected mainly by the heating schedule applied. The composite containing alumina grains of ~2.2 μm and uniformly dispersed zirconia grains of ~0,25 μm was obtained in case of the TSS schedule. The reversed two-step sintering (RTSS) delivered the most coarse-grained microstructures. The temperature T1 of 1600°C generated large grain growth ratios (10.8-18.5), resulting in the composites showing densities close to 95 , but reasonably good hardness (20.8 ± 0.2 GPa) and fracture toughness (7.0 ± 0.2 MPa∙m0.5).
- List of Content for Volume 63
- Strony: 820-833
- Spis treści tomu 63