Year 2004, Volume 24

Abstract

The suitability of materials formed by weathering of the granodioritic stocks from Linares and Santa Elena in the Central Iberian Zone of the Southern Iberian Massif has been evaluated to make stoneware bodies. Samples from Linares have lower phyllosilicate content and higher feldspar and quartz contents than those from Santa Elena. The highest kaolinite contents are found in the Santa Elena samples. Illite/smectite mixed layer is only present in the weathered materials from Linares. The studied samples have high silica (58-71%) and alumina (14-21%) contents. Fe2O3 contents (6.50-4.55%) from Santa Elena are remarkably higher than those of Linares samples (3.67-2.75%). Clay fraction is the grain size dominant in milled materials, followed by the 2-20 μm fraction. Most of the Santa Elena materials are potentially suitable for shaping by extrusion, while the samples from Linares are only appropriated for shaping by pressing. Low water absorption (<4%) and linear shrinkage values (<13%) at the firing temperature range between 1000 ºC and 1200 ºC are related to the extent of the vitrification process. Mineralogical and chemical composition as well as firing properties of the quartz-feldspathic materials studied suggest that they could be used to make red stoneware.

Abstract

Potential use of waste stone mud from the stone-processing industry has been studied. Waste stone mud can be used as a filler (opening agent), a flux or a glazing material, depending on the composition. It is mostly used in clay-based production, e.g. in the production of clay bricks, blocks, panels, roofing tiles, facing bricks, and ceramic pipes. Due to the partial replacement of basic raw materials by waste mud, quite a significant decrease in costs could be achieved and even the quality of final products improved in the case of high-plasticity basic clay. Mud containing 70 m.% on average of finely-grained silica sand is the residue after the screening of higher fractions of silica sand. Clays and feldspars are also present in certain amounts. Mixtures of clay and mud were prepared in different proportions (up to 50 m.% of mud). Besides water absorption, bulk density, and bending and compressive strengths of fired samples, the influence of the stone mud addition on drying and firing shrinkage was determined.

Abstract

Clay deposits from Turgutlu provide raw materials for the brick-tile production. This clay has been mined since 1980. Before 1980, clays from the agricultural area were used as construction materials. It is well possible that they have also been used for producing pottery during ancient times at Sardes. This study investigates the chemical and mineralogical characteristics of the Turgutlu brick-tile raw materials and their properties after firing between 600 and 1050 ºC. The mineralogical and physical changes of mixtures with addition of 5 and 12% Turgutlu raw material to the receipt of floor-tiles body was studied. The use of this raw material results in smaller consumption of clays for the production of ceramic body receipts, and hence provides significant economics for the producer.

Abstract

the rock-type and lime (CaO) derived from limestone have been studied by X-ray diffraction. The compositions studied covered the range 10 - 90% mixture of porcellanite and limestone batched in powdered form. After firing for 2h at 1150°C and 1200°C, three reaction products were detected: 3CaO.₂SiO₂, 3CaO.Al₂O₃.2SiO₂ and 2CaO.Al₂O₃.SiO₂ in compositions within the ranges 50 - 90%, 30 - 70% and 10 - 70% porcellanite respectively. Further, within the range of composition where each reaction product formed, yield tended to increase through a maximum then to decrease with increasing porcellanite content. However, compared with firing at 1200°C, the yield in reaction products was low after firing at 1150°C. In addition, on firing at 1150°C unreacted free lime (derived from decomposition of the limestone) was retained in all the compositions studied. Nevertheless, on firing at 1200°C free lime was detected only in compositions containing 50% and less porcellanite. These observations suggest that: (i) the thermal energy associated with firing at 1150°C is too low to sustain the reactions, once initiated, and (ii) on firing at 1200°C the retention of unreacted free lime in compositions containing 50% and less porcellanite is a consequence of body composition rather than firing temperature. Finally, scanning electron microscopy suggests that at 1200°C the reaction product 3CaO.2SiO2 is in molten physical state.

Abstract

Boron oxide was synthesized from boric acid in a fluidized bed in two stages. At the first stage, boric acid was converted to metaboric acid at a bed temperature of 130°C and then boron oxide was obtained by the dehydration of metaboric acid in the second stage between 225-235°C. Synthesized boron oxide was amorphous, had bulk density of around 0.61 g/cm3, >98.67% purity and about 650 μm mean particle size. Boron oxide particles had a shape of platelets within large aggregates of between 300-600 μm.

Abstract

Synthetic commercial MgAl₂O₄ spinel and chemically prepared coprecipitated spinels were characterized by XRD, IR, particle size distribution, chemical analysis and utilized as additives in a refractory castable composition. The qualities of those two types of spinel bonded castables were examined in terms of bulk density, apparent porosity, cold crushing strength, spalling resistance and flexural strength. XRD, SEM and slag corrosion tests were also carried out to evaluate the performance of these spinel additives at aggressive atmosphere.

Abstract

Characterisation of off grade sillimanite ore and its reaction sintering with calcined alumina to develop mullite aggregate were studied. Off grade sillimanite ore was vibro milled in water for 8 hrs. The dilatometric study of powdered sillimanite ore indicates that densification starts from 973°C and mullite formation starts at 1425°C. TiO2 (addition favours the densification process upto 1550°C. The mullite formed is mostly acicular in nature. Microstructure shows intergranular vitreous phase. The main crystalline phase is mullite with very small amount of corundum. Mullite sample developed at 1600°C without any TiO2 shows the highest strength of 144.2 MPa at 1200°C

Abstract

Calcined alumina, silica powder and micro-fine aluminum powder were mixed by two different routes, ca., dry and wet route, to prepare the precursor powder for the formation of mullite ceramic. The compacted powders were subjected to sintering at different elevated temperatures with fixed soaking period. Measurement of different physico-mechanical properties, e.g, bulk density, volume change after firing, apparent porosity, specific gravity and compressive strength revealed that wet mixed batch (by the aqueous route) result in better densification and microstructure development after firing. The sintered batches prepared by both the routes were observed to contain large amount of mullite and corundum phases and very small amount of glassy phases in the microstructure.

Abstract

Saudi kaolinitic clay from Az-Zabirah area was experimented for the preparation of cheap technical glass-ceramic materials. The kaolinitic clay was about 59 wt% of the batch constituents, depending on the composition. The batches were melted and then casted into glass, which was subjected to heat treatment to induce crystallization. The resulting glass-ceramic materials were mainly composed of ß-eucryptite ss, ß-spodumene ss, hexacelsian and monoclinic celsian, exhibiting ultra-fine grains and uniform texture. It has been found that an increasing content of the celsian phase in the glasses, results in increased bulk crystallization.

Abstract

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.

Abstract

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.

Abstract

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.