Volume 65 (2013)
List of Contents
Volume 65, Issue 1
- Synthesis of aluminium nitride nanopowder
- Strony: 4-7
Aluminium nitride (AlN) nanopowder was successfully synthesized from aluminium oxide via a single-step reaction with ammonia as a source of nitrogen. The process was carried out in a horizontal mullite tube reactor located in an electric furnace in the ranges of temperature, time and gas flow rate of 1050-1350 ºC, 1-5 h and 100-150 l/h, respectively. Nanopowders of γ-Al2O3 and α-Al2O3 were used as starting materials. Influence of temperature, time, gas flow rate and type of aluminium oxide on reaction productivity, powder morphology and product phase composition was investigated. Dynamic light scattering (DLS), Ramman spectroscopy, powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and specific surface area measurements by the BET isotherm technique were used to characterized the obtained materials.
Aluminium nitride prepared under optimal reaction conditions, comprising the reaction time of 5 h, the temperature of 1250 ºC, and the gas flow rate of 150 l/h, was found to be nanocrystalline powder with a mean crystallite size of about 60 nm in the synthesis from gamma aluminium oxide and 65 nm in case of alfa aluminium oxide as a starting material. The productivity of nitridation reaction in such conditions was close to 99%, basing on gravimetric measurements. In case of the synthesis from gamma oxide, PXRD analysis indicated the pure hexagonal aluminium nitride structure which was confirmed by TEM analysis. In case of alfa aluminium oxide nitridation, the obtained aluminium nitride contained the unreacted oxide. Additionally, the investigation of average agglomerate sizes in the water suspension conducted by DLS showed that aluminium nitride obtained from γ-Al2O3 had an average particle size of 282 nm, and in the case of α-Al2O3 used as a starting material it was 2219 nm.
- Physicochemical properties of the Fe-25Cr/(La,Ca)CrO3 layer system in air and the mixtures OF Ar-H2-H2O and Ar-CH4-H2O gas
- Strony: 8-19
The oxidation kinetics and electrical properties of the Fe-25Cr stainless steel coated in the (La,Ca)CrO3 thick film were studied during its oxidation at 1073 K in air and Ar/H2/H2O and Ar/CH4/H2O gas mixtures. The material for the experiments was the DIN 50049 steel covered with the (La,Ca)CrO3 paste, using the screen printing method. To prepare the paste, La0.8Ca0.2CrO3 micropowder was obtained via co-precipitation and calcination. The kinetic growth of the scale on pure steel and of the intermediate reactive layer at the steel/coating interface of the Fe-25Cr/(La,Ca)CrO3 layer system in the afore-mentioned conditions approximately follows the parabolic rate law. The morphology, and the chemical and phase compositions of the oxidation products of pure steel and the steel coated with (La,Ca)CrO3 were investigated using SEM-EDS, TEM-SAD and XRD analyses. The effect of the intermediate reactive layer on the electrical properties of the studied system is discussed in terms of its applicability for the construction of metallic interconnects used in SOFCs.
- Protective (Mn,Co)3O4/AL453 composite materials as metallic interconnects for IT-SOFCs
- Strony: 20-27
Ferritic steel AL453 is one of the potential metallic interconnect construction materials for the intermediate temperature solid oxide fuel cells (IT-SOFC). However, the evaporation of chromium from the scale formed on this ferritic steel results in slow degradation of the electrical properties of the interconnect elements. In order to improve cell efficiency the surface of the interconnect material was modified by applying a protective coating on a manganese-cobalt spinel matrix. The Mn1.5Co1.5O4 coating was formed via screen-printing combined with the appropriate thermal treatment. This coating is an effective barrier against outward chromium diffusion from the AL453 steel and, therefore, significantly inhibits the formation of volatile Cr vapours from the scale. This fact was confirmed by measuring the chromium vaporization rate from the surface of the steel/coating layer system in a flowing air/H2O mixture at 1073 K.
- Investigation of glass surface using ion beam
- Strony: 28-30
The surface of sodium aluminosilicate glass was analysed by means of secondary ion mass spectrometry (SIMS). An influence of oxygen and argon ion beams on depth profiles of particular glass constituents was investigated. The results obtained were interpreted on the basis of the mechanical and field interactions of the ion beam with the glass surface.
- Pressureless sintering of niobium carbide and tantalum carbide - Part I. Polythermal sintering
- Strony: 31-39
This work presents the results of studies on the preparation of single-phase polycrystalline tantalum carbide and niobium carbide materials. It has been found that it is possible to obtain polycrystals with high density in the process of presureless sintering at the temperatures up to 2000 °C, that are relatively low as for the compounds with one of the highest melting points reaching ~4000 °C. Carbon was only used as a sintering additive. Its main role is to reduce the oxide contamination. It has been shown that the determination of the amount of carbon required to reduce the oxide contamination is only possible by using the experimental method.
- The moisture content and mechanical properties of ceramic masses
- Strony: 40-43
The material strength of different ceramic masses in dependence on their moisture content is presented in this paper. The experiments were carried out by using a universal strength machine. The compressive strength tests were performed for three different materials widely used in ceramic industry: KOC kaolin clay, illite clay and electrotechnical porcelain mass C130. In addition one dimensional tensile tests were carried out for kaolin clay to compare tensile and compressive strength.
- Determination of fracture toughness of ceramic masses
- Strony: 44-49
Main aim of this study was the characterization of fracture toughness of ceramic masses by measuring critical stress intensity factor KIc. Two different measuring techniques were applied: the three-point bending of rectangular cross-section beams with a notch in the middle and the Vickers test. The materials chosen for the test were KOC kaolin and POZ clay. Mechanical properties of these materials strictly depend on moisture contents. Fracture toughness determination for the analyzed ceramic masses was performed in the moisture content range used in industrial drying.
- Basic Properties of Lead-Zirconate-Titanate Ceramics at Morphotropic Boundary
- Strony: 50-54
Investigations into lead zirconate-titanate (PZT) ceramics with the chemical composition from the morphotropic region are reviewed. It is shown that to improve the properties of the basic PZT ceramic material almost always a dopant, modifier, or other composition in the solid solution is included. In order to achieve the appropriate set of properties more than one type of additive (donor, acceptor or isovalent) is included to the given chemical composition. It is indicated that PZT ceramics exhibits high sensitivity to technological conditions, temperature and electric field applied. Quality of ceramics can be checked by means of structural analysis and thus temperature dependencies of electrophysical parameters of PZT-type ceramics and their changes caused by changes of PbTiO3 content in PZT-type solid solution can be explained.
- Tm3+/Ho3+ co-doped optical fibre
- Strony: 55-60
The infrared emission of Tm3+/Ho3+ – doped antimony-silicate glass was investigated. Strong emission at 2.1 μm corresponding to the transition 5I7 → 5I8 in holium ions was measured under 795 nm diode laser excitation. The energy transfer processes of Tm → Ho was analyzed and the results show that energy transfer between Tm3+ and Ho3+ plays an important role in the luminescence mechanism. According to Förster-Dexter theory the efficiency of energy transfer of 3F4 (Tm3+) → 5I7 (Ho3+) transition was calculated. As a result of optimizations of rare earth concentration the best efficiency of energy transfer in fabricated glasses was obtained for the molar composition of 1%Tm2O3 : 0.75%Tm2O3. Based on the optimal concentration of active ions the optical fibre was fabricated. As a result of optical pumping (795 nm) of the fabricated fibre the narrowing and red-shifting of emission peak at 2.1 μm was observed. Measured values of maximum emission peak and FWHM for the 100 mm length optical fibre are λe = 2108 nm and ΔλFWHM = 63 nm, respectively.
- Numerical modelling of effect of drying rate on kaolin fracturing.
- Strony: 61-64
Non-uniform distributions of moisture inside the porous materials during drying results in compressive stresses inside the material and tensional ones close to the surface. The tensional stresses together with brittleness of dry material are the reasons of fracturing of the material. In the paper the model describing the fracturing is used to examine the influence of the drying rate on fracturing. It is shown that slow drying does not involve any cracks. The quicker drying generates higher risk of fracturing, and the final fracture pattern is more complicated.
- Selected properties of self-compacting concretes added with calcium fly ash
- Strony: 65-70
The research shows the possibility of using the high-calcium fly ash (HCFA) in normal and high-performance self-compacting concrete both as the addition to concrete and as the cement constituent. The presence of fly ash can reduce the self-compacting properties of the mixture, especially if a superplasticizer is used. This effect is lesser, if the ash is grinded or used as the cement constituent. At the same time, the presence of ash improves stability (resistance to segregation) of self-compacting mixture. The compressive strength of concrete made of cements modified with HCFA and with ash addition does not differ significantly from the compressive strength reached by the analogical concrete made of CEM I, if a concrete strength class is similar. In the initial stage of curing, the presence of high HCFA inhibits the development of compressive strength. The research confirms the possibility of using high-ash multi-component cements X (which contain HCFA) for new generation concrete.
- The use of a vibratory crusher in processes of very fine crushing of raw materials and industrial waste ceramics.
- Strony: 71-75
Preparing materials for grinding processes, final products production and recycling or disposal of industrial ceramic wastes require grinding machines. Machines that ensure the achievement of high degree of fragmentation are vibratory crushers. Possible applications of such crushers are the subject of this paper. Investigation of vibratory crushing was carried out in a laboratory vibratory crusher KW 40/1. The scheme and technical parameters of the crusher were given in the paper. The work also provides the results of the process of very fine crushing, i.e. to a grain size of the product characterized by the participation of a class of 0 mm to 2 mm in the range of (60-90)%, when the feed grain size is 0 mm to 50 mm, of materials such as limestone, dolomite, quartzite, diabase, sanitary and red ceramic waste, alumina and ferrite. In the vibratory jaw crusher it is possible to obtain the crushing product of a size smaller than 0,5 mm in the amount ranging from 20% to 50%. The results show that the vibratory jaw crusher can be a very useful machine to allow reduction of the number of grinding machines for the industrial crushing.
- Procedure of preparation of LiFePO4-C composites of high electrochemical activity for Li-ion batteries
- Strony: 76-80
This work presents procedures of the nano-sized LiFePO4 synthesis and preparation of LiFePO4-based composite cathode material with carbon addition for Li-ion batteries. Three methods of preparing the LiFePO4-C composite materials were investigated: grinding in an agate mortar, mechanical milling and pyrolysis of novolac resin. The obtained powders were applied as cathode materials in Li|Li+|LixFePO4-type cells. Cyclic voltammetry, specific capacity of the cathode material, reversibility and stability during charge-discharge cycles measurements were carried out to characterize electrochemical properties of the cells. The LiFePO4-C cathode material prepared by grinding in the mortar showed stable voltage of 3.46–3.50 V during charge and discharge cycling. The discharge capacity was about 166 mAh·g-1 with reversibility around 98% and high stability of capacity within the first ten cycles.
- The preliminary investigation of very fine milling of dolomite
- Strony: 81-86
The study was conducted in a laboratory vibratory mill of periodic work and low-frequency vibrations – below 16 Hz. The aim of the study was to gain ground dolomite containing the largest content of the grain size class 0-10 µm and the highest level of WI. Dolomite was initially ground in an industrial gravitational mill before milling. The milling media made of steel and ceramics – corundum were used in the experiments. The obtained results indicate that even at a very short milling time one can get very favorable results of milling in the vibratory mill: the average (1,5-3,5)% content of the grain class +63 µm, the grain size dav below 7,1 µm with the average (60-70)% increase of the grain class 0-10 µm to. The whiteness index of milled dolomite was (83,5-92,5)%. These results indicate that in the vibratory mill of low frequency of vibrations 10-12 Hz the significantly finer grain size of ground dolomite can be obtained than in a ball mill. This indicates much greater technological capabilities of the vibratory mill compared to the gravitational ball mill.
- The texture and microstructure of ceramic brick contaminated by chloride and sulfate ions
- Strony: 87-91
This paper presents the results of research on the changes of texture and microstructure parameters of ordinary bricks, exposed to corrosion in environments containing sulfate and/or chloride ions. The tests were performed after 5 and 10 cycles of action in corrosive environment. The results indicate a significant change in the texture of the samples after 10 cycles of the corrosive exposure. The presence of corrosion products in the form of fine crystals of sodium chloride and gypsum in the pores of the samples and the sulfate ions in the structure of the aluminosilicate phase was observed. The corrosion products were located in pores of 0.1-5µm in size, causing the population express smaller pore size of 0.1 to 1 um. Texture and microstructure of the corrosion exposed samples was a result of the chemical composition of the corrosive environment and the time of exposure.
- Ceramic materials based on BaYMn2O5+δ double perovskites for oxygen storage technology
- Strony: 92-96
Characterization of structural properties and results of measurements of oxygen storage capacity of ceramic materials from the BaY1-xSmxMn2O5+δ (x = 0, 0.25, 0.5, 0.75 and 1) group of double perovskites are presented in this work. Similarly to initial BaYMn2O5+δ, Sm-substituted compounds exhibit the structure with layered arrangement of the Ba-Y1-xSmx sublattice. Reduced materials (δ ≈ 0) crystallize in tetragonal symmetry with P4/nmm space group. In the case of oxidized materials (δ ≈ 1), the triclinic P-1 structure was observed for compositions with samarium content x ≤ 0.5. For compounds with x > 0.5 the oxidation process does not cause a change of the symmetry, and these materials differ from the reduced one only by occupation of crystal positions by oxygen and by unit cell volume. In case of whole series of the materials, the measured reversible oxygen storage capacity exceeded 99% of theoretical one, which was from 3.35 wt.% for BaSmMn2O5+δ up to 3.82 wt.% for BaYMn2O5+δ. Lower capacity of Sm-containing materials was due to their higher molar mass. The substitution of yttrium by samarium significantly influenced the temperature and kinetics of reduction and oxidation, which allows for designing of material exhibiting required properties for technological applications.
- Influence of addition of biologically active silver microparticles on properties of mineral mortars
- Strony: 97-104
The activity of microorganisms, especially bacteria and fungi, affects considerably the individual features and utility of building materials. It is a type of biological corrosion (a special case of chemical corrosion) which causes the loss or decrease in the material’s utility. Apart from biological corrosion, fungi may also generate a threat to the users of infected buildings. Their toxic influence on human and animal health is considered to have much more fatal consequences than the biocorrosion of materials. Biocidal agents in the form of biocides and silver nanoparticles, that are in common use these days, are also likely to pose a serious threat. This paper presents the results of comparative research on limestone-cement mortars implanted of silver particles of micrometres in size on the surface and in the mass. It has been concluded that the applied addition of silver microparticles has no significant effect on the physical features of the tested mortar. However, it clearly hinders the development of mycelium, which confirms the biocidal activity of the element in the mortar solutions in question.
- The study on fly-ash granulation in a new type vibratory pipe device
- Strony: 105-109
The paper presents the study on granulation of fly-ashes originating from a fluidized bed of the Czechowice-Dziedzice power plant. Dusts of this kind is very difficult for granulation in conventional granulating devices without the use of additional binder. The study was conducted on a new type of granulator i.e. a vibrating chute granulator constructed at AGH-UST in the Department of Mining, Dressing and Transport. The study determined the best operating parameters of the machine that produced granules of the highest compressive strength and discharges. Grain size distributions and mean granule sizes were measured. Then, for the most favorable mechanical parameters, effects of moisture content on granule size, compressive strength and discharge of the granules were determined.
- Influence of the powder morphology on properties of the OE-PICA hierarchic granules
- Strony: 110-115
The influence of the powder morphology on properties of OE-PICA (Oil Emulsion – Polymer Induced Colloid Aggregation) hierarchic granules has been examined. For preparation of the PICA granules, several hydrothermal unstabilized zirconia nanopowders of various crystallite shapes were used, including needle-shaped, plate-shaped and spherical particles. The PICA powders were granulated by using the OE method, forming hierarchic granules. In the paper, the pressing characteristics, bulk density and sinterability of the resultant powders have been examined. The sinterability of the powders was studied for the powders pressed using various pressures, ensuring destruction of the OE-PICA granules, or OE granules only. Some similarities in sinterability of the granules prepared from plate-shaped and spherical powders have been noticed; the granules prepared from needle-shaped powders showed the highest sintering temperature. The powders prepared using the OE-PICA method had noticeably different dilatometric curves comparing to the starting powders at the temperatures from 600 °C to 1180 °C. The sintering ratio wass also faster, then sintering ratio of the reference powders.
- The effect of calcium on the phase composition change of Al2SiO5-ZrSiO4 refractory materials
- Strony: 116-120
The study of corrosion of the Al2SiO5-ZrSiO4 refractories in corroding environment of an external heat exchanger of the cement kiln was carried out at the temperature of 1000 ± 100 °C. Main corrosive agents in the external heat exchanger were in the solid (CaO) and gaseous (K+/K2O, SO2, Cl-) form. The XRD and SEM/EDS analyses showed a reaction of calcium and potassium with the refractory matrix. As a consequence of these reactions, gehlenite Ca2Al2SiO7, leucite KAlSi2O6 and kalsilite KAlSiO4 were formed in the corroded refractory brick. Kalsilite was the main compound formed in the corroded sample. Moreover, zircon was decomposed, and high refractory calcium zirconate CaZrO3 (Tmp = 2345 °C) was formed. In the early stages of reactions, the CSZ (C = CaO, S = SiO2, Z = ZrO2) disordered structures were formed.
- The usage of spectrophotometric measurements in technological laboratory works
- Strony: 121-125
List of Contents
Volume 65, Issue 2
- Self-Cleaning Layers of TiO2 on the Brick Surfaces
- Strony: 130-134
A deposition method of TiO2 layers on the surface of commercial bricks has been proposed. X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy ( EDS) were used to determine chemical and phase compositions as well as microstructure of the fabricated layers. In spite of high temperature heating, comparable to that needed to firing raw bricks (above 1000 °C) the deposited TiO2, as the rutile phase, remains on the brick surface, and then it is enable to photocatalytic degradation of typical contaminants of the building surface playing role of a self-cleaning agent.
- Application of fracture mechanics parameters for assessment of changes in concrete properties caused by cyclic freezing and thawing
- Strony: 135-139
Concrete is heterogeneous material with the complex microstructure determining its applicable physical and mechanical properties. Changes in the microstructure, caused by internal and external factors, have significant effects on material’s mechanical properties evaluated using the methods of fracture mechanics. The description of the damage process in cement based composites by means of the methods of fracture mechanics gives the results similar to those for the real processes occurring in the microstructure of concrete in structures subjected to service life conditions. The applicability of fracture mechanics parameters to the investigations of changes in concrete properties caused by accumulation of damages due to cyclic freezing and thawing is presented in the paper. The values of the critical stress intensity factor, critical tip opening displacement as well as fracture energy were analysed.
- Preliminary experimental studies of the grinding process intensification in a vibratory mill by means of an additional working part installed in the chamber
- Strony: 140-144
The work contains the results of studies on the influence of additional structural parts having the shape of a cylinder and placed in the chamber of a vibratory mill on intensity of the grinding process. The investigations were performed by using a laboratory vibratory mill for periodic operation. Quartz sand was used in the experiments. The milling process was carried out in the air environment in the chamber equipped in its geometrical axis with the replaceable cylindrical part. For comparison, the investigations were also performed in the chamber without the additional part. The research program enclosed also the study on effects of grinding media on the control grain size and the specific surface of the milled material. The research results indicate that the use of the additional structural part in the chamber of the vibratory mill causes a significant increase of the grinding process intensity and a decrease of the control grains size.
- Corrosion of refractory lining in fluidized bed combustors with co-combustion
- Strony: 145-150
After introduction of co-combustion in many combustors accelerated wear of refractory lining was found. High temperature corrosion of metallic parts of combustors is known and described in literature. However there is a little informations on corrosion of refractories in combustors conditions. Results of investigations of refractories after service in third fluidized bed combustors were presented. Tested materials characterized different composition: that were alumosilica materials consisting 50 and 70% Al2O3 and SiC mix. On the base of chemical and phase composition and microstructure analysis the corrosion processes were characterized. It was find that in all cases the gas corrosion was the main wear factor. Application of low emission combustion processes accelerate the wear of refractory linings.
- Young’s modulus of magnesia-chrome refractories
- Strony: 151-155
Young’s modulus is the material constant necessary for engineering calculations related to design of refractory linings and operation of thermal units. Calculation of thermal stresses, determination of allowable heating rates of furnace linings or criterion-referenced assessment of ceramics’ resistance to thermal shocks are the examples of technical problems to be solved, requiring the knowledge of E modulus, which is usually determined by static or dynamic methods. In calculations the values of E modulus obtained at ambient temperature are frequently applied . This is where the problem arises: is it right to adopt one value of the modulus in calculations concerning a wide range of temperatures, do materials with a similar chemical and phase composition differ considerably in their E modulus values and do all the varieties of the currently applied methods for determining the modulus give equally reliable results? This article is an attempt to answer the above questions. Comprehensive investigations into 5 varieties of magnesia-chrome products having a similar content of Cr2O3 have been conducted, the dependence between Young’s modulus and temperature ranging from 20-1000 °C has been established, E values at 450 °C, 700 °C, 950 °C and 1200 °C have been determined by the static method. The results have been compared to the values determined by the resonance method at 20 °C. The results obtained at the current stage of research have been summarized.
- Tool life of ZrO2/TiB2 cutting inserts during dry machining of steel and cast iron
- Strony: 156-162
This paper presents the results of tool life tests of Y-ZrO2/TiB2 composite cutting inserts during dry machining of C45 steel (165HB ±6 HB) and EN-GJL-XNiCuCr15-6-2 cast iron (121HB ±2 HB). The composite contained 12-37 vol.% of sub-micrometric TiB2 inclusions and it was fabricated with in situ process, based on solid state reaction. Cutting inserts type SNGN 120408 T 02020 were used, which is compatible with ISO 1832.1991 standard. Commercial cutting plates, TA-Z (Al2O3/ZrO2 composite) and TW (Al2O3/TiC composite) made by The Institute of Advanced Manufacturing Technology in Cracow, were used as the reference samples. The tool life tests were conducted with numerical turning centre type TZC-32 N Uniwersal. A dry machine cutting velocity was 150 m/min. A depth of the cut was set to 1.0 mm, while its rate of feed was 0.15 mm/rev. and 0.10 mm/rev. for the steel and the cast iron respectively. Time required to blunt the cutting tool by 0.3 mm was used as criterion of the cutting edge lifespan. The cutting plates durability was correlated with their phase composition and also with their mechanical properties, particularly with “Dry Sand” wear resistance of the materials (test according to ASTM G 6585 standard). As result of research there was no monotonic correlation found between the wear resistance, influenced by TiB2 content, and a lifespan of composite cutting plate during turning of the C45 steel. However, the composite containing 37 vol.% of TiB2 performed very well during turning. It was especially visible in case of dry machining of the steel, in which that ceramics showed 16 % longer life than the commercial Al2O3/ZrO2 material (TA-Z grade). Similar performance was observed for cutting tool made of Y-ZrO2/TiB2 composite containing 20 vol.% of TiB2. Nevertheless above mentioned TiB2 containing composites played worse than TA-Z materials during turning EN-GJL-XNiCuCr15-6-2 cast iron.
- Reaction sintering of ZrSiO4 and Al2O3 powders
- Strony: 168-173
The investigation of the microstructure evolution during firing of a mixture of zircon (ZrSiO4) and corundum (Al2O3) powders is presented in the paper. Solid state reactions between ZrSiO4 and a-Al2O3 in the mixture of stoichiometric composition (3Al2O3·2SiO2) were studied by XRD method (Rietveld analysis) and electron scanning microscopy with energy-dispersive X-ray spectroscopy (SEM+EDS). The data were obtained at temperatures ranging from 1400 °C to 1600 °C for a period of time ranging from 30 min. to 60 h. High-temperature reactions within the ZrSiO4-Al2O3 mixture led to the formation of mullite and zirconia. The rate of reactions depended, as expected, on the process temperature. The effects of the reactions were meaningful only at the temperatures around 1600 °C. There is no doubt that at this temperature, the first-order reaction of ZrSiO4 decomposition into the oxide components proceeded. The dissolution of Al2O3 particles with diffusion of Al+3 into the non-crystalline aluminosilicate phase seems to be the slowest step of the reaction.
- The microstructure of refractory corundum materials after service in chemical reactors
- Strony: 174-179
The characteristics of changes in the microstructure of refractory corundum materials under conditions existed inside reactors for synthesis gas production, i.e. the temperature range of 1400‒1700 °C, the pressure of 3‒4 MPa and the H2-rich atmosphere have been analysed. Castable refractory and two fired materials that differed in the type of aggregate were studied. The microstuctural changes have been related to the changes in the phase and chemical compositions as well as to the basic properties of these materials. On the basis of the obtained results it was found that in the case of the castable these changes in the microstructure are related to SiO2 reduction and its removal from the product’s matrix in the form of SiO. In the case of the fired materials the changes are caused by recrystallization of corundum grains and evaporation of alkalis.
- Microwave drying of ceramic masses
- Strony: 180-185
The selection of optimal drying conditions in microwave driers is being carried out through the adjustment of the electromagnetic field strength. The aim of this work is to analyze the influence of the microwave power on the material being dried. At the work a kinetics of the microwave drying by different levels of microwave power was determined. The temperature distribution inside the samples was also determined with applying a thermal imaging camera. The analysis of destruction of the samples caused by the microwave drying was performed by using the acoustic emission method, and shown in photographs. The strength of the samples dried at different levels of the microwave power was examined by single axis compression tests. The experiments were carried out on kaolin KOC.
- Preparation of pigments from the Y2O3-Al2O3-Cr2O3 system by soft chemistry methods
- Strony: 186-191
The use of wet methods of co-precipitation-calcination and thermal decomposition of an organo-metallic precursor enabled to obtain the powders being solid solutions of chromium ions in yttrium-aluminium perovskite (Y(Cr0.1Al0.9)O3). The results of this study show that the formation of such a phase, its structural properties and colour parameters depend on the type of precursor applied as well as on temperature, time and atmosphere of calcination process.
- Synthesis of Al2O3-C layers by the MOCVD method
- Strony: 192-197
Aluminium oxide layers were synthesized by using aluminium acetyloacetonate as the precursor and the MOCVD (Metal Organic Chemical Vapour Deposition) method. The layers were deposited on quartz glass tubes in the temperature range of 700‒1000 °C at their high growth rate. Argon was used as a carrier gas. Initially, the obtained samples were visually assessed. Considering high transparency of quartz glass, it was possible to verify whether the homogeneous nucleation process was present during the layer growth (the presence of this process significantly decreases of quartz glass transparency). The presence of interference colours enabled to establish approximately the thickness and thickness distribution of the obtained layers. Selected samples were examined by SEM and XRD. The performed tests have indicated that the layers synthesized at temperatures below 800 °C were amorphous or contained low temperature forms of Al2O3. The synthesis of layers at higher temperatures has caused their crystallization: the higher temperature of the synthesis process, the more advanced crystallization of the layers.
- Synthesis of Al2O3 - C/Al2O3 layers by the MOCVD method
- Strony: 198-203
Al2O3-C/Al2O3 layers were synthesized on quartz glass substrates by the MOCVD method at temperatures of 700‒1050 oC, using aluminium acetyloacetonate as a precursor. The layers were deposited at two stages. First stage comprised the synthesis of a thin Al2O3-C layer of 0.07 µm in thickness. Argon was used as a carrier gas. Next stage covered deposition of Al2O3 without carbon. The process was running in air and argon. The Al2O3 layer with no carbon was significantly thicker (about 4 µm) than the layer with carbon. The part of the obtained layers was additionally annealed in the temperature range of 900‒1050 °C. Selected samples were tested by SEM and XRD.
- Influence of hot isostatic pressing on selected microstructural and mechanical properties of alumina and silicon carbide
- Strony: 204-208
In this paper selected results of materials investigations obtained during the realization of a R&D project are described. The aim of the project was to examine protective properties of ballistic armour which consisted of ceramic-polymer composite and bulk ceramics. The hot isostatic pressing technique (HIP) was used to improve mechanical properties of bulk ceramics assigned to produce ceramic-polymer composites by infiltration of porous cellular ceramics with elastomer. The studies of wetting angle were carried out to determine suitability of cellular ceramics for infiltration by polymer. Moreover, the influence of hipping on mechanical properties and microstructure of alumina and silicon carbide was examined. In this paper, the results of tree point bending test, compression test and apparent density measurements are presented. In case of silicon carbide a quantitative phase analysis (XRD) was carried out. Average values of the crystallite size were also determined for each detected phase. The investigations showed that hot isostatic pressing increased materials density. It led As a consequence of this, an improvement in mechanical properties of hipped materials when compared to the pressureless sintered samples has been detected. The sintering under the isostatic pressure did not cause the growth of crystallites. There was observed that applying of the HIP process resulted in improving the wetting and increased the surface energy in case of alumina samples. Such an effect was not observed in case of silicon carbide sample.
- The influence of annealing time on thermal properties of polycrystalline aluminium nitride
- Strony: 209-213
The presented work concerns the study on the influence of manufacturing process conditions on thermal conductivity of polycrystalline aluminum nitride. Commercial powder was applied to prepare AlN polycrystals, differing in the amount of yttria added, by using a rotary mill to homogenize batches of component powders. The resultant powder mixtures were preliminary uniaxially pressed, and then cold isostatic pressing was applied. The green compacts were pressureless sintered, and powders hot-pressed in nitrogen flow. In both cases the sinters were also additionally annealed at the sintering temperature. Densification of the obtained polycrystals was measured. Scanning electron microscopy observations of the microstructure were made using the polished and mechanically etched surfaces of the sintered bodies. The elemental distribution analysis was carried out by EDS. Thermal conductivity of the AlN sinters was measured by the LFA method. The results of thermal and microstructural examinations were compared in the context of sintering conditions applied to manufacture the AlN polycrystals.
- Elastic properties of Al2O3 - hBN anisotropic composite materials
- Strony: 214-219
The paper presents the results of a study on composite materials with aluminium oxide matrix containing from 0% to 30% hexagonal boron nitride. Composite materials were obtained by hot pressing. To assess the effect of hBN phase on the elastic properties of composites a new method of determining the elastic constants and material constants e.g.: Young\'s module, shear module and Poisson\'s coefficients was developed. The method consisted of measurements of ultrasonic wave propagation velocity in composite materials, that were treated as anisotropic materials. The material constants obtained by using this method were compared with values achieved from the ultrasonic measurement of the composites treated as isotropic materials.
Studies have shown a significant effect of the presence of hBN phase on anisotropy of the composite materials’ elastic properties. The highest anisotropy of Young’s modulus, up to 50% was observed in the case of composite materials containing of 30% hBN.
- Effect of silica nanoparticles with vinyl groups on mechanical properties of ceramics–polymer composites
- Strony: 220-226
The paper presents effects of application of silica nanoparticles containing vinyl groups on some mechanical properties of ceramics–polymer composites. Silica nanoparticles with vinyl groups were obtained during silanization of surfaces with vinyltriethoxysilane. The degree of modification of the silica powders with vinylsilane was investigated by IR spectroscopy. Ceramic composites containing silicon carbide were obtained by gel-casting methods. In these composites ceramic powder is the dispersed phase, and polymer is the continuous phase. It was shown that samples containing silica powders with vinyl groups had higher bulk densities than the samples with and without native silica powders. The threefold increase in compressive strength of the sintered samples has been found.
- Effects of the nickel oxalate precursor and SPS consolidation process on properties of Ni/Al2O3composites
- Strony: 227-234
A precipitation-calcination method based on nickel oxalate reduction was used to obtain nickel nanoparticles dispersed within alumina powder. The powder was SPS consolidated to manufacture Ni/Al2O3 composites, containing a nickel additive of 1.7 vol.% and 10 vol.%. Two ways of incorporation of the nickel oxalate particles into the alumina powder were applied: (i) attrition milling assisted dispersion of a mixture of the dried powder of precipitation derived nickel oxalate and the alumina one in ethanol, (ii) direct precipitation of nickel oxalate on alumina particles. The SPS sintering of the studied powders was carried out for 7 min at 1400 °C under a pressure of 20 MPa in an argon atmosphere with purity 5.0 (99.999%). XRD and TEM measurements were performed to characterize the phase composition and morphology of the powders, respectively. XRD, microstructural (SEM/EDS) and mechanical tests were carried out for sintered bodies. It has been stated that agglomerated nanoparticles of nickel oxalate were the precursor of nano-nickel in the studied Ni-alumina powders. The way of incorporation of the nickel oxalate precursor and SPS sintering influenced the microstructure and properties of the Ni/Al2O3 composites. The segregation of nickel enhanced with the SPS sintering has been detected in the composite microstructure. The Ni/Al2O3 composites showed increased hardness, fracture toughness and abrasive resistance when compared to alumina with no nickelic particles.
- Acoustic emission monitoring of fracture in dryed kaolin-clay processed with surfactant water solution
- Strony: 235-238
The method of fracture reduction in kaolin-clay products during intensive drying, which comprises application of surfactant water solutions for their forming, is the objective of this paper. Two oxyethylates surfactants, Rokacet R26 and Rokanol IT6, were used for the tests. Before forming the samples, the kaolin-clay in the form of dry powder was wetted with a prescribed amount of distilled water mixed with a different amount of surfactants to get a plastic mass. The samples in the form of cylinders were extruded and, after leveling the moisture distribution, subjected to convective drying in hot air. The acoustic emission (AE) method was used to monitor on line the development of crack formation in dried samples. It was stated that application of water solutions with the specific concentration of surfactants during material processing may significantly reduce material fractures due to intensive drying.
- Application of stirred ball mills in very fine milling processes
- Strony: 239-244
Stirred ball mills, also called attritors, are the mills, in that the free energy of milling medium is replaced by a rotating impeller mounted in a stationary chamber. Their harmfulness on the environment has lower impact in comparison to other mills. These mills are of different construction, and have extensive technological capabilities. The milling process takes place in air or liquid, with or with no granular classification. The industrial mills are composed of the chamber having the volume ranging from 5 dm3 to 10 m3. Laboratory mills are equipped with the chambers of 0,5-5 dm3 volume. They are used in fine, very fine and colloidal milling processes, and for the production of nanopowders. The stirred ball mills have capacity from 0,1 Mg/h to 150 Mg/h when milling product particles below 7-10 µm are produced. The paper describes the construction, operation and classification of the stirred ball mills. It provides also an overview of new construction solutions of the mills, rotors and grinding systems in that these mills are used. It also gives examples of applications of the stirred ball mills in the ceramic industry.
- The influence of marble dust on sintering of ceramic masses and properties of brick - a review
- Strony: 245-250
Calcite is traditionally present in clays used for production of ceramic building materials, but dolomite is more rarely found . The analysis of the literature data shows that these minerals are harmful if the grain size is of over 0.5 mm. It is known that, limestone dust in a fraction < 0.063 mm is used in technology of ceramics (for example, in the manufacture of ceramic tiles). These materials lead to reduction of sintering temperatures and formation of new phases such as wollastonite or diopside, that improve the mechanical strength of the final product. This paper is the literature review concerning an impact of calcareous materials on the sintering process and the properties of building ceramics. The reported data can be useful to develop research on utilisation of marble dust produced as the waste in the limestone industry.
- Strony: 251-254
List of Contents
Volume 65, Issue 3
- Mechanical properties and low temperature degradation resistance of 2.5Y-TZP – alumina composites
- Strony: 258-266
Yttria stabilized zirconia polycrystals (Y-TZP) become increasingly important in the field of biomedical and engineering components. The commercially available standard material 3Y-TZP made from coprecipitated powders has very high strength but limited fracture toughness, resistance to subcritical crack growth and low temperature degradation resistance.
In this study a 2.5Y-TZP powder was produced by coating of monoclinic zirconia with yttria via the nitrate route. Y-TZP-alumina composites with compositions ranging from 0-27.5 vol.% were produced by mixing and milling and subsequent hot-pressing at 1400 °C for 2 h.
The mechanical properties and ageing resistance of the materials was tested. All materials showed attractive mechanical properties with bending strength of 1000-1250 MPa, fracture resistance declined with increasing alumina content while resistance to subcritical crack growth KI0 was maintained at a high level of 5–5.7 MPa∙√m. Alumina addition had a non-linear grain growth inhibition effect.
Ageing test showed that while the pure 2.5-TZP was inherently instable a small addition of alumina increased the low temperature ageing resistance considerably. Evaluation of ageing kinetics according to the Mehl-Avrami-Johnson model showed that the TZP-alumina composites did not follow a nucleation and growth mechanism but that the transformation front rather proceeds into the bulk by a zero-order kinetics.
- The effect of curing temperature on the properties of different types of refractory concrete
- Strony: 267-271
At different curing temperatures, in alumina cement-based concrete, various crystalline hydrates are formed such as CAH10, C2AH8, C3AH6, AH3.While developing or modifying compositions of refractory concrete, it is necessary to take into consideration the impact of curing temperature on the process of formation of the structure and operating characteristics of concrete. This study investigates the properties of the following refractory concretes: the conventional concrete, the concrete modified by microsilica additive and the medium-cement concrete based on chamotte filler with alumina cement, of the grade Gorkal 70, at the curing temperatures of 10 ºC, 20 ºC and 30 ºC. Using the ultrasonic method of investigation, the differences were revealed in formation of the structure of concrete at its hardening in the course of 48 hours. It was established that the differences formed in the structure at hardening of concrete exert influence on properties of concrete after its firing at temperatures of 1100 ºC and 1200 ºC.
- Consolidation of SHS-Derived Aluminium Oxynitride Powder
- Strony: 272-276
Aluminium oxynitride with the spinel-type structure, γ-alon, is the material with high potential for refractory applications. Single-phase alon materials or composites show good mechanical properties, i.e. high thermal shock, high corrosion and erosion resistances. Another advantage concerning γ-alon is the possibility of the usage of the SHS method for producing relatively good powders for sintering, but of rather poor compressibility. This paper describes a method of compaction of SHS-derived γ-alon powder using the hydrolysis reaction of aluminium nitride, which belongs to the products of SHS synthesis. The green bodies made from the powder with an addition of 10 wt.% of water after two weeks of storage reached a strength level up to 30 MPa and an open porosity less than 30%. Pressureless sintering of those compacts for less than one minute at 1700 °C allowed achieving materials of 95% of theoretical density.
- Shaping of aqueous suspensions of silicon carbide and aluminium oxide
- Strony: 277-282
The work presents the results of investigations on the shaping of aqueous suspensions of silicon carbide (SiC) and aluminium oxide (Al2O3) by the centrifugal casting technique. The centrifuge was designed in the Department of Special Ceramics, the Faculty of Materials Science and Ceramics, AGH-University of Science and Technology. The effect of the composition of suspensions and process parameters, including a rotational speed, corresponding acceleration and centrifugation duration time on macroscopic properties of shaped bodies such as the presence of flaws and deformations were investigated. The best parameters of the centrifugation depended on characteristics of the powders, i.e. the particle size and density. The shaping of the suspension of SiC powder, which had both smaller density and particle size, required higher rotational speeds and longer centrifugation times than the suspension of Al2O3 powder, which contained larger particles. The conducted tests permitted to chose the best conditions of centrifugal casting leading to production of cylindrical shapes that gained almost full density after sintering.
- Effect of alumina grain size distribution on mechanical properties and microstructure of the alumina porcelain type 130
- Strony: 283-289
Large-size and high voltage ceramic insulators traditionally are produced from high alumina porcelain type 130. This material is based on the typical hard porcelain composition: 50% kaolin, 25% feldspar and 25% quartz, but all content of quartz is replaced by alumina. Addition of Al2O3 powders allows increasing the content of mullite significantly and therefore improvement of physicochemical parameters of the material after firing. In this investigation, three kinds of alumina powders were applied that differed in grain size. The powders showed BET specific surfaces of 6.6 m2/g, 1.1 m2/g i 0.3 m2/g. The presented results show the significant influence of the grain size of alumina powders on physicochemical properties and the microstructure of the fired materials.
- Qualitative criteria of ceramic pigments
- Strony: 290-294
Division of ceramic pigments can be done in various ways. There are three groups of pigments distinguished with reference to their application characteristics: (i) pigments for colouring of ceramic glazes, (ii) masses ( particularly of gres ones) and (iii) enamels. For each group, there are specified application characteristics, and application in accordance with manufacturer’s recommendations ensures obtaining assumed aesthetical effects of coloured products. Colouring characteristics of the pigment of a given type depend on manufacturing conditions such as quantity and quality of mineralizers and grain size distribution of the pigment, and on application conditions that mean a proper concentration, type of coloured medium and firing temperature. The basic technological procedure is production of a crystaline lattice which is characteristic for the given pigment, being resistant to chemical agents at firing temperatures of glazes, enamels and ceramic masses. Effects of technological parameters, including the type of mineralizer, amount of chromophore and granulation, on colouring characteristics of zirconium and spinel pigments with the sphene and corundum structure were presented. The quantitative effect of these parameters depended on the crystal structure and appropriation of the pigment.
- Mechanical properties and microstructure of sinters in the B4C-CrxSiy-C system
- Strony: 295-301
In the work, composites with a boron carbide matrix added with chromium silicides and carbon were obtained by the hot-pressing process in the flow of argon. The sintering temperature was 2000 °C, what was lower by 120 °C than in the case of boron carbide sintered with a carbon additive only. The obtained and polished sintered bodies were subjected to phase analysis, SEM microstructural observations and EDS element distribution analysis. The materials were mechanically tested for bending strength, fracture toughness, abrasion wear and friction coefficient.
- Consolidation of aqueous suspensions of silicon carbide by a spray forming method
- Strony: 302-307
The paper presents the results of research on preparation of aqueous suspensions of silicon carbide for manufacturing dense SiC materials by means of sintering. Acrylic binder was added to the suspensions in order to ensure adequate mechanical properties of the consolidated green bodies. Rheological characteristics of the suspensions was studied and optimized in order to match the parameters to a novel spray forming technique. The spray forming of the suspensions was carried out using a prototype equipment designed at the Department of Special Ceramics of the Faculty of Materials Science and Ceramics, AGH-UST. The equipment allows flat or cylindrical products to be produced. A key step of the shaping process appeared to be proper de-airing of the suspensions. The consolidated bodies were sintered at 2050 ºC and 2150 ºC, and the resultant relative densities of SiC bodies exceeded 97%. It was observed that the sintering temperature affects the density of material and the morphology of grains.
- Pressure-less sintering of niobium carbide and tantalum carbide - Part II. Isothermal sintering
- Strony: 308-316
NbC and TaC single-phase polycrystals with high density could be obtained in a pressure-less sintering process at temperatures as low as 2000 °C. Two sintering models were used to verify this statement. To study the sintering of carbides, a modification of the sintering model proposed by Frenkel, which is valid for non-crystalline viscous solids has been proposed, presuming the viscosity term to be linearly related to time. Parameters describing the sintering process of investigated carbides such as the initial shrinkage rate α-1, the limit of shrinkage at infinite time β-1 and initial apparent viscosity η0 of system were in turn determined using the Frenkel model. According to the Kuczynski model, to describe the sintering of carbides, it was attempted to determine mechanisms of mass transport dominating at each sintering stage. Such data allowed achieving full description of tantalum and niobium carbides sintering.
- New type refractories of low thermal expansion
- Strony: 317-322
Phase composition of refractory materials under consideration is based on calcium dialuminate CaAl4O7 of a melting point of about 1760 °C. The materials show deeply depressed reversible thermal expansion. The low thermal expansion of the refractories is a precondition for securing a good thermal shock resistance of any lining. From the chemical point of view, the common merit of the studied refractories is their non-silicate chemical composition, very important if the molten slag or flux attack is taken into account. Some microstructural and thermal features of refractory composites based on calcium dialuminate and contained granular fractions of high refractory MgAl2O4 (MA) were studied. The effect of addition of metallic Al on the after-contraction was verified additionally. Identification of phases appearing in these systems was performed by XRD. Porosity and thermal expansion coefficients as a function of temperature were determined. The relations between the microstructure of the materials received and their thermal expansion were analyzed.
- Effect of annealing on the microstructure and structure of mesoporous silica obtained on the basis of octahydro-octasilsesquioxane
- Strony: 323-326
Many applications require materials with porosity greater than the porosity of zeolites, and much smaller than of microporous materials. Mesoporous materials belong to this group of materials. In the paper, it is proposed to obtain mesoporous silica by hydrolytic polycondensation of spherical octahydro-octasilsesquioxane (T8H). It has been shown that this method permits to receive mesoporous silica completely devoid of organic substituents. The resulting mesoporous silica underwent a series of tests, that helped to determine both its microstructure and structure. The structure of the mesoporous material was specifically identified by using spectroscopic (MIR, FIR), and X-ray study (XRD). Based on these studies, it was found that the resulting material was completely amorphous. It was also found that after annealing at 500 °C a stable material devoid of Si-H bonds was obtained. Using adsorption methods (BET and BJH), A specific surface area of the material received and the shape and size of current mesopores.
- The influence of the type of magnesia raw materials on physical and thermo-mechanical properties of magnesia castables
- Strony: 327-331
In this work a correlation between hydration susceptibility and chemical composition of magnesia raw materials and physico-chemical, thermo-mechanical properties of castables made of these magnesia raw materials was discussed. The four types of magnesia raw materials of different chemical compositions were selected to examine. First, susceptibility to hydration of magnesia raw materials was determined under hydrothermal conditions. Then castables were prepared with the use of the selected magnesia raw materials. Finally, the castables were tested to determine moduli of rupture at room and elevated temperatures, cold crushing strength, permeability, open porosity and apparent density.
- Synthesis of the Grossular-Hydrogrossular Hydrogarnets Series in the System C3A-SiO2-H2O Under Hydrothermal Conditions
- Strony: 332-342
The paper summarises the results of testing in the model systems, that are associated with synthesis of the C3AS3-C6AH6 series of hydrogarnets, forming solid solutions. On account of the presence of either incomplete or complete hydrogarnet substitution following the pattern 4(OH)- ↔(SiO4)4-, the composition of particular elements in the series changes in the continuous manner, in accordance with the general formula Ca3Al2(SiO4)3-x(OH)4x in which x may assume any value from the range (0-3). With the change in chemical composition of hydrogarnets in the series, their properties will change in the continuous manner, too. For the given value of x, therefore, we get a given element in this series whose chemical composition is determined accordingly. The value of x determines the molar ratios C/(A+S) and A/(A+S), their values falling in the respective ranges of (0.75-3.0) and (0.25-1.0). Hydrogarnets considered in this study were synthesised for selected values of the parameter x and the chemical composition was established accordingly. The main component of reactant mixture was synthetic C3A and the deficiency of SiO2 was compensated by admixing a specified amount of a silica material. The mixtures of these components were then turned into suspensions, subjected to further treatment under hydrothermal conditions at a variable temperature (150°C and 180°C) and for a variable period of time (24 h, 168 h and 336 h). Thus obtained materials were analysed to determine the phase composition by the XRD, DTA, TG and IR methods. Microstructure analyses were performed by the SEM method supported by the EDS analysis. Tests revealed that no matter what the initial composition of the reactant mixtures, the synthesised product in most cases would be hydrogarnet containing tiny amounts of quartz. Therefore, the chemical compositions of hydrogarnets formed under these conditions do not correspond to the initial compositions of reactant mixtures. It appears that the extent of hydrogarnet substitution is less than that implied by stechiometric calculation.
- Application properties of materials from the B4C–CrSi2–hBN system
- Strony: 343-351
In the paper, the results on the manufacturing boron carbide matrix materials were presented. The synthesized chromium silicide phase was added to the matrix to lower the sintering temperature and to increase the fracture toughness. Hexagonal boron nitride was introduced in a quantity of (2-8) vol.% to the composite as a solid lubricate. The materials were hot-pressed at the temperature of 150 ºC lower than used for the naturally sintered B4C/h-BN composites. The studied bodies were subjected to the phase and microstructural analysis, microstructural observations, and elastic and mechanical property measurements. The materials with a bending strength of 540 MPa and a fracture toughness of 4.7 MPam1/2 were manufactured. The lowered friction coefficient and lowered abrasion wear were recorded in comparison to the pure boron carbide material.
- Modification of yttria-stabilized tetragonal zirconia for IT-SOFC electrolyte applications
- Strony: 352-360
The paper presents issues related to the modification of the microstructure of tetragonal zirconia stabilized with yttrium oxide via the formation of a dispersed composite 3Y-TZP/Al2O3 electrolyte. These studies point to the potential application of this composite as a solid electrolyte with stable functional parameters for the Intermediate-Temperature Solid Oxide Fuel Cells (IT-SOFC) designed for operation in the temperature range of 600-800 °C.
- Silica functional coatings on glass
- Strony: 361-365
Multifunctional coatings on glass have been used widespread in electronics and telecommunication in the last decades. It is hard to imagine a touch panels of smartphones, touch screens, or even photovoltaic cells in household appliances without them. Thanks to the multifunctional coatings that consist of many different layers arranged hierarchically, it is possible to obtain the functional compiled application properties, including the connection between hydrophobic and/or oleophobic surfaces with conductive and reflection ones. Based on studies to date in the field of multifunctional coatings, it is worth noting the fact that silica layers are most commonly used, that are anti-reflective and water-repellent, when a sufficient degree of roughness of the surface is achieved. The silica layer is also a barrier for diffusion of sodium ions from the interior to the surface. This work presents different ways of the preparing silica functional coatings including as a sol-gel synthesis, chemical etching, and electrostatic deposition of silica nanoparticles. The selection of suitable chemical precursors in each technique is essential for the obtaining functional coatings with appropriate properties. Each of the layers showed increased values of transmittance both in the visible and infrared regions. SEM/EDS observations of the microstructure confirmed the presence of a hierarchical structure in all the analyzed coatings.
- Sintering of boron carbide materials added with hexagonal boron nitride
- Strony: 366-373
The influence of hexagonal boron nitride, chromium carbide and chromium silicide on densification of boron carbide polycrystals is studied. The first additive was used as a solid lubricant, the latter two were sintering additives, that enhance densification. A high-temperature dilatometer was used to run the measurements of linear dimension changes of the boron carbide based materials during sintering. The sintering additives were added in the quantity of 5 vol. % and the h-BN content was 2-8 vol.%. The densification of the obtained materials was determined. The phase composition changes were studied as a function of sintering temperature. Simultaneously, the trials of hot-pressing of the studied materials were made. The influence of the applied pressure on material’s densification during the sintering was determined. The densification measurements, phase and structural analysis, microstructural observations were made and compared with dilatometric data.
- Study of the structure and physicochemical properties of spinels obtained from the Cu-Mn-Co-O system using EDTA gel processes
- Strony: 374-381
Materials that may potentially be used to manufacture metallic interconnects for intermediate-temperature solid oxide fuel cells (IT-SOFCs) include heat-resistant ferritic steels. However, volatile chromium compounds that evaporate from the chromia scale formed on the surface of steel during oxidation cause slow degradation of the electrical properties of the cell’s elements. At the same time the product of the steel’s oxidation exhibits high electrical resistance and inhibits conductivity. In order to counter these unfavorable phenomena, the metallic interconnect is modified by depositing an appropriate protective layer over its surface. Materials that may be used to do this include spinels from the Mn1+xCo2-xO4 (0 £ x £ 0.5) group; these substances provide an effective barrier against outward chromium diffusion from the interconnect’s core, thereby significantly inhibiting the evolution of Cr vapour. Nevertheless, the electrical conductivity of these spinels over the temperature range of 600-800 °C needs to be improved. This can be done by doping them with the appropriate metals. The present paper describes the results of physicochemical investigations of a manganese-cobaltite doped with various quantities of copper.
- Application of clay-cement binders for improvement of geotechnical conditions of soil for hydrotechnical construction and civil engineering
- Strony: 382-385
For several years in Poland fixes and reconstruction of hydro-technical objects, including flood protection are intensively carried on. An important element of the works is an improvement of hydroinsulation barriers. Depending on local conditions, the barriers are made using different technologies and to various depths. The basic expectations for waterproofing barriers can be determined as follows: high insulating properties, long-term functionality, resistance to hydrostatic pressure, resistance to deformation, high resistance to water corrosion, no negative impact on the environment. These requirements are met by a waterproofing barrier made using binders based on modified clays. Application of clay–cement systems to geotechnical works requires suitable rheological parameters of liquid binders. The article shows the results of a comparison of selected geotechnical parameters, before and after construction of waterproofing barriers.
- Preparing bulk transparent magnesium aluminium spinel – a few tricks of the trade
- Strony: 386-390
The most successful attempts for preparing transparent magnesium aluminium spinel ceramics have been conducted with using hot isostatic pressing (HIP). In this paper a list of tips and tricks useful for manufacturing bulk transparent HIPed spinel ceramics is presented. The step by step subroutine from starting material to the final product, for manufacturing transparent ceramic armours tiles and three dimensional elements is described. The green body preparation, pre-sintering parameters, HIP temperature/pressure history and discoloration parameters are released and explained in details. Master these four fundamentals, and one stands a good chance of getting MgAl2O4 ceramics with the real-inline transmission over 82% in the spectrum from visible to the mid infrared.
- Strony: 391-392
List of Contents
Volume 65, Issue 4
- New aspects on the corrosion resistance of dense refractory castables containing a novel calcium-magnesia-alumina binder
- Strony: 396-400
This paper presents a detailed analysis and evaluation of corroded samples of Al2O3-pre-formed spinel and Al2O3-MgO castables, thus representing pre-formed spinel castables as well as in-situ castables. Comparisons were made between systems based upon a calcium aluminate binder and a recently developed novel calcium magnesium aluminate cement CMA 72®. A model is presented which gives an explanation for the higher corrosion resistance of the castables based upon the CMA 72® cement. The respective model is based on optical and SEM image analysis. A correlation between the thermo-mechanical properties from phase and particle distributions, microstructural features, amorphous phase of the castables and the corrosion mechanism is established. Moreover, new routes for the optimization of castable corrosion resistance via formulation control are highlighted.
- BSA96 - new european sinter aggregate
- Strony: 401-405
The market situation for high alumina aggregates from China has changed considerably over the past years. Not only the availability and pricing but also the quality has become an issue for European refractory producers. A new aggregate with 96% Al2O3 has been developed and made in Europe, and which is independent from Chinese raw materials. It is produced by a sinter process and provides the same homogeneous product properties which are well known for other established sintered aggregates such as tabular alumina and sintered spinel. This paper presents the properties of the new refractory aggregate and laboratory results of refractories based on it. The new aggregate provides an alternative to other high alumina aggregates, fused, natural, and sintered.
- Determination of criteria for the selection of a carbon carrier in ceramic-carbon suspensions for liquid metal filters
- Strony: 406-411
The aim of the adding carbon to a ceramic filter for liquid metal filtration is to improve filter’s functional properties, including mechanical properties and conditions of the flowing metal through the filter. In the investigations two kinds of precursors were used: (i) liquid (pseudo-liquid) materials playing the role of binders: pitches, tars, resins, asphalts, which as a result of pyrolysis provide a carbonating agent with a high content of elemental carbon, (ii) solid materials applied on the surface of filters in a pulverised form: graphite (natural and electro graphite), anthracites, cokes, coals. The aim of research was to develop a procedure for evaluating basic properties of ceramic-carbon suspension, being a transition stage in production of filters, and to determine the influence of some factors (composition, additives) on their rheological parameters. The results of investigations into the selection of a solid carbon carrier, especially with regard to rheological properties of suspensions, have been presented. In the work thixotropy of ceramic-carbon suspensions was characterised by determination of flow curve hysteresis loops. In order to fulfil the assumed goal, a rotary rheometer type CR, model Haake VT550 with regulated shear rate was applied. The experiment was planned, its course was controlled and mathematical processing of the obtained results was carried out by means of the RheoWin 4.30 programme. Viscosities of carbon suspensions were determined using a measurement system composed of SW-DIN coaxial cylinders. The measurements were taken at 25 °C. Shear rates ranged from 10 s-1 to 500 s-1. Flow curves were determined for the increasing and decreasing values of shear rate. The examined suspensions’ viscosity was determined at a constant shear rate reaching 500 s-1. A comparison of the applied methods, with a special focus on the characteristics of carbon raw materials presented in the work, made it possible to better understand reasons of the thixotropic structure formation. For ceramic-carbon suspensions, thixotropy is a measure of internal energy, dependent on the examined suspensions’ compositions. The area of flow curves hysteresis loops determines the internal energy of a system used for destruction or reconstruction of the suspension structure. On the basis of the measurement of viscosity and thixotropy, the most favourable rheological properties of the obtained suspensions and the applied carbon material were determined.
- Ceramic-carbon filters for metal alloy filtration
- Strony: 412-417
An attempt was undertaken to develop a new, innovative type of ceramic-coal filters which, similarly to the currently applied ceramic filters, should be characterised by high thermal shock resistance, resistance to the corrosive attack of metal alloys (especially cast steel), mechanical strength at high temperatures as well as high effectiveness of filtration. Moreover, new filters must be characterised by a lower mass resulting from the material’s lower density, which will additionally influence filters’ thermal properties and high thermal conductivity. The paper presents the results of previously conducted investigations, which include: selection of raw materials to obtain a new type of filters; determining the composition of suspensions for covering the organic foam matrix and its effect on these suspensions’ rheological properties; determining the effect of suspension composition and thermal treatment conditions on the basic properties of filters (apparent density, open porosity, compressive strength) as well as the behaviour of filters during metal filtration tests.
- The structure and properties of corundum-chrome materials
- Strony: 418-423
Refractory materials of the Al2O3-Cr2O3 system have a number of favourable properties, the major of which are resistance to the attack of acid and alkaline slags as well as abrasion resistance. For this reason they are applied in waste incinerating furnaces, coal gasification plants and thermal equipment used by the metallurgical industry, mainly in lead and copper alloy smelting processes. The article presents the results of research on corundum-chrome materials, including their abrasion resistance and thermal shock resistance. The results of investigations into the basic properties and phase compositions of materials have been presented. Moreover, an attempt has been undertaken to explain the explosive destruction of materials containing brown fused alumina. Materials characterised by enhanced thermal shock resistance were obtained and the cause of explosive destruction of materials containing brown fused alumina was explained. The obtained research results do not explicitly indicate the existence of a correlation between materials’ phase composition and their abrasion resistance.
- Characteristics of fibrous material by using XRF, XPS, SEM and ToF-SIMS methods
- Strony: 424-428
This paper presents the results of industrial investigations of thermal insulation materials by using spectroscopic and microscopic techniques. The goal of this study was to characterize a structure and chemical composition of fibrous material used in production of mineral wool. Analysis of the chemical composition showed the presence of nitrogen, silicon, aluminium, iron, sodium, magnesium and calcium at the level of a few atomic percent, and several atomic percent of carbon and oxygen. The results obtained by XRF and XPS methods showed an inverted value of atomic concentration for oxygen and carbon. The mean diameter of a single fibre was determined. The homogeneous distribution of chemical elements within an individual fibre was determined from a chemical map obtained by SIMS. The obtained results form the basis for planning experiments aimed at finding a relationship between chemical composition of the materials used for production of mineral wool and the thermal properties of final products.
- Application of Mössbauer spectroscopy for determining the Fe2+/Fe3+ content in magnesia aggregates
- Strony: 429-432
The 57Fe Mössbauer effect measurements of sintered and fused magnesia aggregates at room temperature were conducted. The investigated spectra were composed of a different number of subspectra which corresponds to different sites of iron in the material. In all cases there was observed one Fe2+ component and two Fe3+. The Fe2+ content changed from 16% to 60%. The hyperfine interaction parameters for Fe2+ show an almost perfect charge distribution at the iron site which is possible only when Fe2+ substitutes Mg2+ in the MgO lattice. The Fe3+ ion is in octahedral coordination which is highly distorted what was evidenced by hyperfine interaction parameters.
- Mercury porosimetry for evaluation of microstructural parameters of refractory ceramics
- Strony: 433-442
The aim of the article is to present specific examples of solutions to research problems connected with using mercury porosimetry in the research area related to designing, manufacture and the use of refractory ceramics. One of them is selection of high-alumina materials for the elements of a tapping system for forging ingots bottom casting, which includes initial selection of materials and investigations into materials after service. Another example of porosimetry application is selection and investigation into the influence exerted by additives on microstructural parameters of refractory corundum and andalusite castables. Another research problem which was solved among others owing to the results of porosimetric tests was determination of microstructural changes in magnesia-chrome materials subjected to thermal shock.
- Monolithic materials for zinc and lead metallurgy
- Strony: 443-450
Studies were conducted on the development of refractory castable for use in the metallurgy of zinc and lead. Thermodynamic calculation was made in order to identify the type of refractory material resistant to corrosion of these metals. Thermodynamic calculations have shown that under working conditions of a zinc condenser in a shaft furnace used for production of lead and zinc (700 °C, the atmosphere of N2+CO+CO2) only zinc reacts with a castable matrix. Zinc aluminate (ZnAl2O4 – zinc spinel) is mainly the product of this reaction. Furthermore, depending on the chemical composition of the matrix, there is also willemite Zn2SiO4, zinc chromate (ZnCr2O4) and ZnMg2O4. Additionally, in the spinel castable, formation of the liquid phase in reaction with both zinc and lead, was observed. The formed compounds (ZnAl2O4, Zn2SiO4 and ZnCr2O4) have high melting temperatures, so it can be assumed that their presence in castables do not deteriorate the refractory lining in the zinc condenser. The results of thermodynamic calculations indicated the aluminosilicate refractory concretes as the optimum material for the use in contact with zinc and lead. Corundum- and andalusite-based castable samples were prepared according to the Andreassen equation, where the exponent q was 0.34 and 0.36. Samples with an increased content of microsilica (3% and 5%) were also prepared. Properties of the samples were determined together with their resistance to corrosion of zinc and lead. After corrosion tests, the chemical composition of samples was determined, and their microstructure was observed by using an optical microscope. The results have shown that the increasing of the microsilica content in the castables to 3% and 5% led to a significant increase in the compressive strength, up to three times in some samples. The open porosity of the materials decreased with the increase of the microsilica content. An increase of hot modulus of rupture at 700 °C was also observed, although it was not to the extent like in the case of compressive strength. Shrinkage also increased after firing, but its value remained at the acceptable level. Corrosion tests have shown that zinc reacted with castables to a greater extent than lead. The corundum-based castable was more resistant to metal vapours than the andalusite-based one. This study confirmed the results of thermodynamic calculations. Observations coming from optical microscopy showed that the zinc and lead vapours reacted with the castables, particularly with their matrix. There was no penetration of the metals in pores of the tested materials.
- Determination of the influence of test sample preparation on the measured strength on the basis of Weibull modulus
- Strony: 451-455
The significance of requirements of the PN-EN 993-5: 2001 standard to be satisfied by test samples of formed refractory materials has been checked specially with respect to surface quality and selection of cutting tools. A schamotte straight connection pipe of the BS grade was used to prepare cylindrical in shape, both polished and non-polished samples, and cubes cut out with segment or smooth disks. The influence of the sample preparation route for compressive strength tests on the parameters of Weibull distribution was determined. The largest values of Weibull modulus were measured in the case of the cubes cut of with the smooth disk. The necessity of following the requirements of the PN-EN 993-5: 2001 standard according to the test sample preparation has been confirmed.
- Chemical composition and structural-textural features of selected domestic dolostones vs. their usability for manufacturing refractories
- Strony: 456-462
Triassic dolostone from Brudzowice is currentl
- Reactions of the SiC-containing andalusite refractory material with components of the external heat exchanger environment
- Strony: 463-467
Reactions of the SiC-containing andalusite refractories with components of a corroding environment in an external heat exchanger of a cement kiln at 1000 °C ± 100 °C were discussed. The main corrosive agents in the external heat exchanger were agents in the gaseous form (K+/K2O, SO2, CO2 and Pb vapour). The calcium-rich hot kiln meal moving in the counter-current relative to furnace gas the exchanger also reacted with a component of the refractory materials. According to the XRD and SEM/EDS examinations, it has been found that the initial phase of refractory brick disappeared and the new ones appeared. Potassium aluminosilicates, calcium aluminosilicates, CaSiO3, Ca2SiO4, K2Si4O9, Ca2PbSi3O9, spurrites (2Ca2SiO4·CaCO3 and 2Ca2SiO4·CaSO4) and also KCl were identified in the corroded Al2SiO5-SiC refractory brick.
- Changes in the composition of pastes in the MgO-SiO2-H2O phase system
- Strony: 468-471
The aim of this work was to investigate changes that occur in pastes from the MgO-SiO2-H2O phase system during ageing at 20 °C. The study consisted on preparation of pastes showing a MgO:SiO2 ratio of 2 and a water to solid ratio of 0.5. The obtained mixtures were aged up to 460 days at 20 °C. All the samples were placed in sealed polyethylene bags. After the specific time, free water was removed from the pastes. Examination of the aged pastes included thermal, XRD and FTIR analyses. Additionally, after 180 days, the samples of pastes were heated at 500 °C, 700 °C or 900 °C for 24 hours, and after that examined by XRD. The research revealed changes in the internal arrangement of pastes with the aging time, and the formation of new hydrated phases associated with layered magnesium silicates.
- Sialon-bonded corundum ceramics obtained by reaction sintering in air
- Strony: 472-475
In the paper, sialon bonded corundum refractories were developed by air sintering of silicon nitride and aluminium oxide. The influence of sialon on properties of the studied high alumina products and low cement alumina castables was presented. Materials were fired at 1500oC and characterized with respect to the phase composition (XRD), microstructure and composition (SEM/EDS).
- Refractory materials from the CaO-MgO-Al2O3-ZrO2 quaternary system
- Strony: 476-480
The paper describes a method of preparing refractories from the CaO-MgO-Al2O3-ZrO2 quaternary system as the result of one-step sintering at 1580 °C. Properties of two series of the materials with the following reference composition were obtained and compared: the first series: 85 vol.%. MgO and 15 vol.% CaZrO3 and the second series: 70 vol.% MgO and 30 vol.% CaZrO3. The reference compositions were modified by aluminum compounds such as calcium monoaluminate (CaAl2O4), spinel (MgAl2O4) and calcium aluminate cement. The phase composition of the materials was characterized by XRD. Young\'s modulus and linear firing shrinkage were also determined. It has been found that the proposed method permits to obtain materials consisted mainly in MgO, CaZrO3 and CaAl2O4, MgAl2O4.
- The technique for making ceramic foam filters - directions of research and modernization of processes
- Strony: 481-487
Manufacturers of ceramic foam filters in Europe carry out a research program focused on improvement of operational parameters of products while striving to reduce their production costs. Analysis of the results of studies carried out at the Ferro-Term Company Ltd. has indicated the need for changes in the current technological process, leading to an improvement in the quality of filters, and optimisation of the filter performance in the area of economy, ergonomics and ecology. To accomplish the aforementioned tasks, in the years 2011–2012, a team of workers from the Fraunhofer IKTS, Dresden, Foundry Research Institute, Kraków and Ferro-Term, Łódź, was appointed. This paper presents the results of the team activities that were carried out in the following thematic areas: a) detailed study of the properties of ceramic foam filters produced by Ferro-Term Company Ltd. and comparative analysis of the obtained parameters with the parameters of products made by manufacturers in Western Europe. Consequently, the properties of filters made by the leading global manufacturer of filters and Ferro-Term, Łódź were evaluated, comparing the geometry of polyurethane material, its chemical composition, geometrical and mass parameters of filters, mechanical strength, mechanical shock resistance and microstructure of products; b) development of production technology allowing Ferro-Term Ltd to maintain its position of the producer of filters meeting the requirements of the EU standards, while implementing some measures to make the manufacturing process more cost-effective and environment-friendly. The scope of the studies included: (i) selection of ceramic materials, binders and additives, (ii) development of new chemical composition of the liquid ceramic slurries, (iii) making a pilot batch of ceramic filters and their inspection according to the adopted methodology of assessment, (iv) technological tests of the filters – impingement tests.
- Refractory linings of pig iron transfer ladles containing ASC materials
- Strony: 488-490
The problem of durability of linings of pig iron ladles, in which the desulphurization process proceeded, is raised. A survey is given of the refractory lining constructions and the materials used in different zones of the lining. The special attention has been paid to the usage of ASC materials in the slag zone. Achievements in industrial tests on durability of the ladle lining are presented.
- Directions of research and development of the refractory industry in view of current challenges and strategies until the year 2050
- Strony: 491-495
The situation of the refractory industry in Europe and Poland is characterised. The leadership of European producers in the field of innovative products is emphasised. An analysis of basic challenges facing the industry, which results from the European Union policy and limited access to raw materials is presented. The European Committee’s plans regarding a reduction of greenhouse gases emissions and the results of analysis of potential goals to be achieved by the ceramic industry until 2050 are characterised The current situation of raw materials as well as steps taken in order to solve the problems related to a limited access to raw materials are presented. The necessity is highlighted to reduce import dependence, increase the effectiveness of the raw materials use and develop the recycling technology. The effects of some EU regulations, including REACH, on the activity of the refractory industry are discussed. On the basis of the conducted analysis, an attempt to define major directions of research and development in the field of refractory materials has been undertaken.
- Rationalization of energy consumption in tunnel kilns
- Strony: 496-499
Tunnel kilns are adjusted to the uniform production in large series, and they work optimally at a nominal capacity. At present, the changeable market extorts frequent changes in an assortment of refractory materials at different capacity, decreasing efficiency of the kilns. The assumed decrease in fuel consumption causes the necessity of investments to provide a cost-effective project; it is necessary
to make allowance for the economic calculation of modernization of a tunnel kiln with respect to the assumed effects. A statement of heat balances for different working conditions of the tunnel kiln permits to develop constructional changes, keeping the high efficiency of the kiln at the changeable production. Thus it is necessary to use an appropriate set of measurements and a control system, which reacts in time on changes in the working conditions, such as adjustments of temperature in particular sections of a burning zone of the kiln, depending on production demands, or adjustments of air parameters of a cooling zone. In this work, control systems of tunnel kilns applied in some working industrial kilns are described, and effects of the systems on energy consumption are shown.
- Strony: 500-500
- List of Content for Volume 65
- Strony: 501-510
- Spis treści tomu 65