SiO_2-TiO_2-ZrO_2系ゲルの生成とその熱的安定性

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Gels were prepared in the SiO_2-TiO_2-ZrO_2 system (SiO_2, TiO_2 and ZrO_2=0-100 mol%) from Si (OC_2H_5)_4, Ti (O-isoC_3H_7)_4 and Zr (O-nC_3H_7)_4 solutions with or without H_2O and CH_3COOH. Without H_2O and CH_3COOH transparent bulk gels were formed in the range 30-100 mol%. SiO_2, 0-70 mol% TiO_2 and 0-50 mol% ZrO_2 and opaque bulk gels in the rest compositions. X-ray diffraction measurement indicated that all the gels were non-crystalline even after drying at 50℃ for 3 days. Crystallization peak temperatures T_c were determined by DTA on the dried gels preliminarily heat-treated at 200℃ for 1h. T_c was low in the TiO_2-ZrO_2 rich compositions (T_c=366℃ for TiO_2 and 419℃ for ZrO_2). T_c increased up to 1258℃ with increasing SiO_2 content. From T_c and liquidus temperature T_L, T_c/T_L ratio was calculated. T_c/T_L ratio means the thermal stability of the amorphous solids. It was discovered that TiO_2 and ZrO_2 alone are thermally unstable (T_c/T_L=0.3 for TiO_2 and 0.23 for ZrO_2) but mixing TiO_2 with ZrO_2 enhances the thermal stability (for example, T_c/T_L= 0.45 for 50 TiO_2・50ZrO_2) with increased ability of forming amorphous phase (amorphous-forming ability). This is true in the SiO_2-TiO_2-ZrO_2 system for fixed SiO_2 concentrations. T_c/T_L increased with SiO_2 content and reached the highest value of 0.86 at 90SiO_2・10TiO_2 composition, which is higher than that of SiO_2 (0.77) . Yet it seems likely that there are more stable compositions centering around the 80SiO_2・10TiO_2・10ZrO_2 in the SiO_2-TiO_2-ZrO_2 system. It is expected that compositions of high T_c/T_L value have a high amorphous-forming ability.
社団法人日本セラミックス協会の論文
1997-11-01

SiO_2-TiO_2-ZrO_2系ゲルの生成とその熱的安定性

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