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Synthesis of mullitic, spinelic and cordieritic materials using greek raw materials

Thomaidis Efstratios

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Summary

There is a variety of Greek minerals rich in Al2O3, SiO2 and MgO which potentially can be used for the production of ceramics materials suitable for high temperature applications. The aim of this thesis was to identify the most suitable mixtures which after all the appropriate processing steps may be used for the production of ceramic products.To accomplish this, ceramics containing a) mullite b) spinel / mullite and c) cordierite have been developed using raw materials obtained from different regions of Greece. Kaolin collected from Lefkogeia region (Drama) and serpentinite / olivinite from Vourino region (Kozani). Bauxite was supplied from “Aluminium of Greece” and kaolin form “S&B Industrial Minerals.” Magnesite was obtained from the Laboratory of Ore Processing (Technical University of Crete) and finally fly ash form Achlada - Melitis thermal power plant in Western Macedonia. After appropriate processing, different compositions have been investigated to produce ceramics containing mullite, spinel/mullite or cordierite phases. All samples were sintered in temperatures ranging between 1225 and 1525°C. The obtained ceramics were analyzed by XRD to identify the crystalline phases. XRF analysis was used to determine the chemical composition of the raw materials and produced ceramics. For ceramics shrinkage, porosity, density, refractoriness, thermal expansion coefficient and compressive strength were also identified. Microstructure analysis of ceramics was performed using SEM.In ceramics produced from bauxite, kaolin and fly ash, mullite phases have been detected. All samples exhibited high refractoriness (1500°C) while porosity varied from 0,2 to 34,1%, density from 1,77 to 3,08 g/cm3 and shrinkage from -0,2 to 17,4%. Mechanical strength was also high, in the range of 40 to 91MPa. Ceramics produced from specific compositions can be considered as candidate materials for the production of refractory blocks and feeders.In ceramics prepared from bauxite, serpentinite or olivinite, spinels and mullite phases have been detected. All samples exhibited high refractoriness (1350°C) while porosity varied from 1,00 to 25,2%, density from 2,46 to 2,95g/cm3 and shrinkage from 4,5 to 7,5%. Mechanical strength was also high, in the range of 43,2 to 49,4MPa. In ceramics prepared from bauxite kaolin and serpentinite / olivinite or magnesite cordierite phases have been detected. All samples exhibited high refractoriness (1300 to 1350°C) while porosity varied from 0,6 to 38,5%, density from 1,43 to 2,59g/cm3 and shrinkage from 0,11 to 9,87%. Mechanical strength was also high, in the range of 13,1 to 31,0MPa. Thermal expansion coefficient varied from 2,19 to 4,11*10-6/oC. These results indicate that ceramics with attractive properties for producing ceramic and honeycomb filters can be obtained.

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