The fabrication of cristobalite membrane filtres

This study indicates the possibility of fabrication a thermally stable microporous silica filter with varied pore sizes (mean pore sizes: 0.7-45 ? m) by preparing the ceramic powder having fully crystallized beta-cristobalite. Sol-gel technique was used for the powder synthesizes through the composition was designed as where . Tetraethylortosilicate (TEOS) was of the silica source and the alumina and calcium ions as doping was obtained from nitrates. The fully beta-phase was investigated from different water/TEOS ratio (2, 4, 6, 8, 16) and sintering temperatures (1000-1450°C) of the gel powder after calcinations at 850°C. The wide range of pore sizes filters were obtained by milling and sieving of the calcinated powder for different size intervals (250-125µm, 125-63 µm, 63-45 µm, finer than 45 µm and finer than 1.4 µm). The powders were shaped uniaxial pressing at different pressures (10, 20, 30 and 50 bar). The water/TEOS ratio prepared up to four and sintering temperature applied between 1150 to 1300°C produced fully beta-crystallization. The finer particles shaped at high pressure and sintering applied at 1300°C produced the filter with high selective during filtration in which narrow size interval could be obtained (0.1-3 ? m). Thermal shock test was conducted on the present filters through varied pore sizes (mean pore sizes: 45, 20, 9 and 0.7 ? m) and observed no any cracking. The thermal shock resistance to heating and cooling was conducted by transferring the specimens from the air at 20°C into the furnace at the temperature about 700°C, following that the specimens were held for 30 min and then were cooled to room temperature with nitrogen atmosphere through the time of cooling was of one minute. The thermal shock processing was repeated for three times. On the other hand, the same test was conducted on the alpha-cristobalite and quartz filters and observed that crack occurrence.