Year 2006, Volume 26

Abstract

Ceramic materials were obtained from mixtures of aluminium sludge and slate powder (with different Al₂O₃:SiO₂ molar proportions), which were dried, shaped by uniaxial pressing and sintered at temperatures in the range of 950 to 1300 oC, in order both to detoxify the sludge by fixing the metals in a leach-resistant ceramic matrix and to yield a new material from the reactions of the above compounds at high temperature. The most promising material was obtained from the 2:1 mixture sintered at 1300 oC, which was also found to be inert after leaching tests. The average Vickers hardness HV3 (683), bend strength (126 MPa),Young’s modulus (161GPa) and fracture toughness (3.35 MPa.m^1/2) are significantly higher than those found for the as sintered slate powders, which is attributed to the increased fraction of a-alumina and reduced content of glassy phase in the microstructure of the material due to the sludge addition.

Abstract

Chemically-bonded refractory ramming mixes from Egyptian quartz and quartzite raw materials were processed for application in lining induction furnaces for ductile iron production.Two Egyptian quartz samples and one quartzite sample as well as an imported quartz mix were used. Chemical and mineralogical composition as well as crystallite size of quartz mineral and grain-size distribution of the latter mix were determined, using wet-chemical, XRD and sieve analysis methods. The obtained data were applied to process similar mixes from the Egyptian quartz and quartzite samples. Densification and thermo-mechanical properties of all mixes were determined along with the rate of transformation of quartz to cristobalite after firing up to 1400°C.The results led to recommend the Egyptian Rod EL-Lekah quartz raw material for processing chemically-bonded ramming silica mixes similar to the imported types in lining induction furnaces for ductile iron production after adding 1.2% boric acid. This is based on its relatively higher purity, larger crystallite size and hence lower rate of quartz-cristobalite transformation as compared with the other Egyptian quartz and quartzite mixes. Hence, the recommended mix shows relatively lower percentage of thermal expansion at 100-300°C and higher rate of subsidence under load up to 1500°C with higher degree of densification after firing up to 1400°C.The increase of boric acid content up to 3.2% leads to excessive development of liquid phase on firing up to 1400°C at the expense of quartz and cristobalite. Accordingly, higher rate of vitrification occurs which deteriorates the thermo-mechanical properties of the fired mixes.

Abstract

Main objective of this study is to recycle shell wastes from the investment casting industry, using powder technology to produce refractory parts. Refractory powders were recovered from bulk wastes using a ball-milling technique and injection-moulded to produce refractory parts. Many thousands of complex-shaped parts were injection-moulded by optimising the process parameters. Recycled powders and the parts were characterized by particle size analysis, scanning electron microscopy, thermogravimetric analysis, density, and size measurements. Performance of the injection-moulded products was tested in sampling operations at molten steel under industrial steelmaking practice.The results allow us to conclude that the shell wastes can be effectively milled and used to produce refractory parts by the injection moulding process.After injection moulding followed by sintering, the final products present a porous microstructure, which has a beneficial effect on their thermal shock resistance.

Abstract

The effect of zircon additions on cordierite stabilization, porosity and thermal shock resistance of mullite-cordierite refractories with different content of mullite and cordierite was examined. The results show that the cordierite peaks are more sharp in composites fired from 1250 ° to 1350 °C in presence of zircon addition,while in zircon-free composites cordierite decomposes at 1300 °C. The thermal shock of specimens increases by the addition of zircon, especially in the composites containing a lower cordierite phase.

Abstract

The most common method of controlling the variable parameters in the process of spray drying ceramic powders is based on heuristic rules which are known to very few people and are difficult to extrapolate to other spray-drying plants. In our research, the orthogonal experimental design was applied to determine the variable parameters that exert the greatest effect on the quality of the powder, which is expressed as being the smallest deviation away from the nominal maximum grain size.A preliminary analysis allowed us to select an initial set of independent parameters that consisted of the intake temperature, the outlet temperature, slip flow rate and the depression inside the spray dryer. Application of the Taguchi Approach made it possible to determine the relative importance of each of these parameters as well as the optimal operating conditions.The optimal operating conditions were confirmed by implementing them in an industrial plant.

Abstract

The effect of progressive replacement of limestone by marble waste on the thermo-mechanical properties of a traditional earthenware wall tile composition has been studied. It was observed that the body mixes containing more than 7.5 wt % of marble waste showed a marginal decrease in dry strength and bulk density while particle size distribution were almost identical.The body mixes containing up to 7.5 wt % of marble waste showed improvement in fired properties in the biscuit firing temperature range of 1000 o to 1100 oC.A reverse trend was observed beyond this temperature range due to an increased proportion of high expansion residual quartz.The body mixes containing up to 7.5 wt % of marble waste showed significant reduction in percent thermal expansion at 600 oC in the sample fired at 1100 oC. As a result, the body mixes become more thermal shock resistant compared to the reference body.The study concluded that marble waste can be added in small amounts (7.5 % or less) in earthenware wall tile improving their thermo-mechanical properties.

Abstract

A wet grinding study of ceramic glazes by varying material to pebble ratio established that the increased material to pebble ratio of 1:4 has not only improved the efficiency of grinding leading to increased reduction in particle size but also resulted in reduction of maturing temperature of commercial opaque and transparent raw glazes and bone china fritted glaze by ~ 150 °C due to prolonged grinding to the fineness of ~ 90.0 to 97.0% particles finer than 2 μm and d₁₀₀ value of 3 to 4 μm. However, the glazed surfaces were found not free from defects like crawling, craters etc. A systematic grinding study of the said opaque glaze followed by evaluation of glaze properties such as gloss, smoothness, opacity, maturity etc. has led to the conclusion that the opaque glaze mix containing particles in the range of 72.7 to 85.5% below 10 μm and d₁₀₀ of 25 to 20 μm not only matured at 1160 °C, which is ~ 40 °C lower in comparison to the standard glaze maturing at 1200 °C but also the fired glazed specimens showed improved gloss (90-91 GU), smoothness, opacity etc. without any surface faults. Further, the glaze maturing range has also been enhanced by ~ 40 °C from 1160° to 1200 °C.

Abstract

A clay mixture, a residue in the gypsum extraction process in the Araripina region – PE / Brazil, was characterised by X-ray diffraction (XRD), X-ray fluorescence (XRF), thermo gravimetric analysis (TGA), infrared spectrometry (IR),Atterberg indices and particle size distribution for use in red ceramic products. Extruded clay specimens were tested for mechanical properties, drying shrinkage, water absorption, specific apparent mass and their changes on drying and firing.The results suggest that the studied clay mixture possess properties, which may encourage deeper technological experiments aimed at assessing their suitability to red wall brick and tile production.

Abstract

Two Egyptian carbonaceous fireclay samples from west central Sinai (Roof and Floor samples) were investigated for their chemical and mineralogical composition as well as microstructure and ceramic properties.These investigation were carried out to assess their suitability for production of insulating shaped products.Wet chemical analysis, XRD, DTA,TG and transmission light microscope methods were applied for revealing composition and microstructure of the raw clays. On the other side, microstructure and densification parameters of four shaped clay batches fired up to 1100-1300 oC were investigated by using reflected light microscope as well as Archimedes water-saturation methods and by determining linear changes and crushing strength of the fired bodies. It is concluded that both of the roof (RCC) and floor (FCC) clay samples can be considered as carbonaceous siliceous kaolinitic clays.The FCC sample contains relatively higher carbonaceous material and Al₂O₃/SiO₂ ratio than the former one. The batch containing 70% (RCC):30 (FCC) can be utilized in processing insulating shaped siliceous fireclay products after firing up to 1300 oC.The fired briquettes are mainly composed of quartz, cristobalite,mullite and glassy phase.They have > 45.0% apparent porosity, 1.50g/cm3 bulk density and 160 kg/cm2 crushing strength. Such lightweight siliceous fireclay bricks can be used as face and / or back refractory lining for insulating industrial furnaces up to 1300 oC.

Abstract

Five batches of low cement zircon- magnesia concretes were prepared using dead burned magnesite aggregate, fine zircon sand and high alumina refractory cement.The concretes were shaped and fired at 1500°C. Densification parameters were determined through bulk density (BD) and apparent porosity (AP). High temperature phases were examined by XRD. A correlation between the densification properties and the phases formed was made through SEM examination of the microstructure.The cold crushing strength, thermal shock resistance (TSR) and refractoriness under load (RUL) of the fired concretes were evaluated.The results showed that increasing zircon is beneficial to densification up to 20% after which a decrease in sintering occurred. Zirconia evolved mainly in tetragonal form beside spinel, periclase and CaO, MgO- silicate glassy phases. The concretes showed high cold crushing strength and good resistance to both thermal shock (Dt=1000°C) and refractoriness under load (0.2Mpa).

Abstract

A carbon free precast block was prepared by using high-alumina fused corundum as aggregate, and fused magnesia and ultra-fine Al₂O₃ and SiO₂ powders as matrix materials. A small linear expansion for the precast block was achieved through spinel formation from the reaction of MgO with Al₂O₃.The precast block showed a lower apparent porosity, higher hot modulus of rupture and better slag corrosion resistance compared to the traditional Al₂O₃-MgO-C brick. Moreover, the practical application of the precast block to the ladle lining proved it to possess a better thermal insulation which could effectively prevent the temperature drop of molten steel during the refining process. It can be assumed that the carbon free precast block could possibly be accepted as a new type of ladle lining material for the production of low-carbon and ultra-low-carbon steel.

Abstract

The sintering behavior of nano sized and submicron sized alumina was investigated.Two methods i.e. uniaxial pressing and slip casting were used to shape the samples.The effect of Nd₂O₃ and MgO addition on sintering was also investigated. Samples were sintered at 1250, 1350 and 1450oC for 2 h.Taguchi statistical method was used to design the experiments.The results revealed that the nano sized powder did not show a proper sintering behavior and therefore the density of these samples was less than the samples made of the submicron powder. It is believed that most probably the presence of agglomerates in the nano sized powder is the main reason for this behavior. Due to this effect, the density of the samples made of nano sized powder increased slightly when they were formed through pressing, since the agglomerates crashed slightly during pressing. Also it was demonstrated that Nd₂O₃ had a negative effect and MgO had a positive effect on densification.Temperature, of course, improved densification.