FABRICATION OF MICROPOROUS SILICA CERAMICS WITH VARIED POLYMORPHIC FORMS AND INVESTIGATION OF THEIR THERMAL SHOCK BEHAVIOUR

In this study; the SiO micro-porous ceramics in the phase α-quartz, α-cristobalite and β-cristobalite were produced and thermal shock resistance of products were compared. In the production of ceramic materials; α-quartz obtained from natural quartz powder, α-cristobalite from pure silica powder which prepared by St ber technique and β-cristobalite from sol-gel approach. The β-composition was designed as Si Al Ca / O where x=0.05 and obtained gel was calcined at 850 °C. Before shaping, α-quartz powder and calcined β-cristobalite powder were grind in the planetary mill and the powder produced by St ber technique was shaped directly without any milling process. The prepared powders were shaped by uniaxally press at 50 bars. The samples produced from α-quartz and β-cristobalite powders were sintered at 1150 °C and α-cristobalite obtained by St ber technique was sintered at 1400 °C. In the defined polymorphic structure, micro-porous materials with pore size ~0.1-5 μm were produced and thermal shock tests were applied. Irrespective of β-cristobalite material, the samples were cracked and the tests could only repeat on the samples with β-cristobalite material. In the result, the β-cristobalite sample is believed to be great potential to use as a membrane filters for harsh thermal environments.