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An overview is provided of the feldspar mines and raw materials produced in Sardinia, including mineral-petrological and technological data as well as deposit geology. The different types of raw feldspar produced in Sardinia can be divided into: 1 - Palaeozoic metarhyolites and "porphyroids"; 2 - Metasomatic albitites; 3 - Tertiary quartz-feldspar sands. A number of mines are currentlly being worked on the island at San Nicolò Gerrei (1), Orani-Ottana (4) and Florinas (5). The raw materials extracted and processed to meet different commercial specifications, are, in order of decreasing importance: Na-feldspar, Na-K-feldspar, low-melting feldspar-bearing rocks, low-melting and filler feldspar-quartz-bearing rocks. Over the last twenty years several mines have gone into operation and exploration work has been conducted on other geological formations. Though not all prospecting has been successful, the experience gained has enabled to refine feldspar prospecting, characterization and beneficiation technologies so as keep pace with the continually changing market requirements and to stave off foreign competition. At the present time the extractive industry is suffering because of the demonization taken up by the mass media, which has resulted in the introduction of administrative and legislative measures that handicap the industry. These problems are compounded by the competition from the developing countries which, unlike European producers, do not have to bear the costs associated with occupational safety and environmental protection.
Ceramic Factory, located Mid-West of Turkey, produces wall and floor tiles. The factory recipe consists mainly of clay, pegmatite, quartz, albite and calcite. Wollastonite and barite were introduced into the factory recipe in order to improve the physical properties of tiles. At the optimum conditions, the addition of barite improved the properties of ceramic body significantly. Water absorption decreased from 6.99 % to 3.78%, dry strength increased from 1.1 kg/cm2 to 2.4 kg/cm2 and firing strength increased from 342 kg/cm2 to 411 kg/cm2. The addition of wollastonite did not improve the properties of the ceramic body: although shrinkage was reduced and dry strength increased, water absorption increased and firing strength decreased.
The effect of grog addition on the technological properties of a kaolinitic plastic clay used for bricks and roofing tiles production, from Campos dos Goytacazes, southeast of Brazil, has been studied. Grog from red bricks, produced at temperatures < 600ºC, was added to the clay up to 20 wt%. Extruded bodies were fired in an industrial furnace at 970ºC, a temperature normally used for roofing tiles. Green body samples were tested for mixing water, linear shrinkage and dry bulk density. Fired samples were tested for linear shrinkage, water absorption and flexural rupture strength. The microstructure of fired samples was evaluated by pore-size distribution, X-ray diffraction and scanning electron microscopy. The results showed that grog addition reduces the total linear shrinkage but does not effectively alter water absorption and flexural strength. These results indicate the possibility of use fired brick waste on roofing tile production.
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.
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