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Porcelain bodies containing kaolin, quartz, different kinds of K and Na feldspar and zircon opacifier were investigated to study their whiteness and other physico-mechanical properties when heated at 1160 to 1200°C. The standard colour measurement and three dimensional plot of L, a and b values has shown higher L value (more lightness in colour) and lower ranges of 'a' and 'b' values for Na-feldspar containing porcelain body. Interestingly it was observed that 'L' value increases with the increase in heating temperature in both the cases. Na-feldspar containing body achieves vitrification 20°C earlier than potash feldspar containing body and its flexural strength was higher than K-feldspar containing body due to its Young's modulus, higher bulk density and lower percent water absorption in the temperature range 1160-1200°C.
Hydrated magnesium aluminate gel additive, prepared by the sol gel route from cheaper precursors, was characterized by X ray diffraction, Infrared spectroscopy, Thermogravimetric analysis, Particle size distribution and utilized in a high alumina based refractory castable to obtain in situ spinel bonds. A commercially available more expensive presintered spinel powder was also characterized and incorporated to the same castable composition. The properties related to the performance of these two kinds of spinel-alumina castables, e.g. Bulk density, Apparent porosity, Cold crushing strength, Thermal shock, Flexural strength, Volume change and Slag corrosion resistance were studied. XRD, Scanning electron microscopy and
Glass/ceramic composites prepared from basalt raw material after its modification, as a glass source, with spinel ceramic were studied. Three batches of these composites, with different amounts of glass and ceramic, were sintered between 900 and 1300°C. Qualitative phase composition by X-ray, microstructure and dielectric constant were examined. The results show that sintering of pyroxenic-basalt based glass with spinel leads to crystallization of augite solid solution (augite ss) and spinel. The effect of glass addition on lowering the porosity has been recognized. By increasing the glass amount, the pores begin to vanish, which consequently lowers the dielectric constant of the composite.
Advances in ceramic processing technology have resulted in a new generation of high performance ceramic cutting tools exhibiting improved properties. In the present work, an alumina-yttria composite ceramic cutting tool insert is developed and machining studies are conducted to evaluate its machining performance on grey cast iron work pieces. For comparison the machining studies are also conducted using a pure alumina insert and a commercially available Ti[C,N] mixed alumina insert. The hardness and fracture toughness of the alumina-yttria insert is higher than for pure alumina insert. The alumina-yttria insert shows better performance than pure alumina insert and its performance is comparable to that of the Ti[C,N] mixed alumina insert.
Several glasses were prepared by melting different compositions containing Sarcheshmeh copper slag, calcium carbonate, and silica. Glassceramics were obtained by heat treatment of these glasses at their DTA peak temperatures. Mechanical properties, microstructure, thermal expansion coefficient and acid resistance of glasses and glass-ceramics were determined. Substitution of Fe2O3 by CaO was found to decrease the acid resistance of glasses while their mechanical strength increases. The acid resistance of the optimum glass was higher than its glassceramic.
The thermal expansion of ceramic samples prepared from the mixture of 50% kaolin, 25% feldspar and 25% quartz was studied in the temperature range of 20 - 1000 °C. The samples were cut from the surface layer of an extruded ceramic cylindrical body. The X-ray structural analysis showed that the basal planes of kaolinite crystals in the samples are predominantly perpendicular to the radius of the blank. The observed shrinkage of the samples is caused by evaporation of the capillary water, dehydroxylation, and high-temperature changes in metakolinite. The shrinkage is larger in samples with kaolinite crystals oriented predominantly perpendicular to the radius of the blank. High temperature firing does not eliminate the texture.
Refractory materials must be disposed of or recycled when removed from service. Off-specification or reject material has been reused by the refractory industry for a number of years, with small percentages of these materials added as a part of refractory formulations. Historically, limited reuse of spent refractory materials in other applications has occurred. Environmental legislation, stewardship programs, and other forces have encouraged some businesses to recycle spent refractories. Reuse of spent refractory material varies considerably among different industries and with the location of the industrial user. Efforts to recycle, the driving forces for recycling, and issues and steps to be taken into account when initiating a recycling program will be discussed.
Municipal seawage sludge (MSS) from municipal wastewater treatments plants (WWTP) of different size were thermally transformed into powders which were pressed into specimens submitted to thermodilatometric tests in order to evaluate their shrinkage and then their softening temperatures on heating up to 1100°C. In addition the shrinkage behaviour of a traditional clay normally used for the production of bricks was studied. Powders from calcined MSS were also attrition milled for 1 or 3 h and the behaviour of the relative samples was compared to that of the as calcined products. Specimens obtained by the various treatments were also sintered in an oven at different temperatures for 1h, their density and their composition were determined and finally they were aged in an acidic (HCl) water solution to evaluate the eventual elution of some components.
The fine ground waste from the manufacture of clay bricks fired at 800 - 1000 °C, was used as an additive (from 10 % to 70 wt%) to the basic body of ceramic wall tiles from Egyptian raw materials. The waste which is produced in small factories in most Egyptian governorates as defective bricks, constitutes a major environmental problem. The Samples were fired at 1100 °C, 1125 °C, and 1150 °C for 5, 10, and 15 min soaking time. Firing shrinkage and vitrification parameters were determined and compared to both Egyptian and ISO standards. Analysis of variance (ANOVA) carried on crushing strength data, showed that the percent replacement was the most influential factor rather than temperature or soaking time. The recommended sample consisting of 20 % ground waste was shaped in tile form. The tiles were tested in accordance to both ISO and Egyptian standards. Results of water absorption, crushing strength, MOR, thermal chock resistance, chemicals and staining resistance, and hardness conformed to standards. The 20 % fired clay waste addition is recommended for both its economical and environmental benefits.
The present study deals with energy savings in brick manufacture. Laboratory driven experiments with additions of Greek lignite (low rank coal) and Spanish claystone have been performed. In particular, co-firing of clay raw material with organic additives is performed in order to minimise the fuel consumption while maintaining the good quality of the brick. Using XRD, ESEM and DTA techniques, mineralogical compositions and mineral transformations were observed both in raw material and in clay-lignite mixtures. For the analyses of hydrated phases, a low-cost and useful modification of a traditional diffractometer has been demonstrated. Fuel saving in brick firing was also revealed with the addition of lignite to claystone samples. Due to the natural variability of both clays and lignites, the results of this study do not necessarily imply that coal-clay mixtures may always have similar performance.
Different methods are described for preparing borides and boron carbide by powder technology. The boron carbide was prepared from amorphous boron, graphite, and petroleum coke, and the borides from amorphous boron and atomized aluminium. The compounds are characterized and compared with their commercial counterparts. In the second part of the work, cheaper materials are used: boric acid and boric oxide instead of boron, petroleum coke and mesophse instead of graphite. Another alternative studied in this work is the use of thermal shock in the sintering, a method that is not usually adopted in powder technology.
Porous tubular ceramic membranes from tunisian clay have been prepared. After a pre-calcination in air at 750°C for two hours, a grinding, and a sieving to 300 µm, natural clays noted SI1 and SI2 were mixed with organic additives in view to elaborate a ceramic paste which can be extruded to form porous tubular configuration with uniform porous structures. The mean pore diameter and the porous volume, measured by mercury porosimetry, are equal to 9.2 µm and 39 % for SI1 and 5.9 µm and 48 % for SI2 when they were repectively fired at 1040 °C and 1090°C. These supports could be used for the coatings of microfiltration and ultrafiltration membranes.
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