SiO<sub>2</sub>-TiO<sub>2</sub>-ZrO<sub>2</sub>系ゲルの生成とその熱的安定性

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  • Formation and Thermal Stability of Gels in the SiO<sub>2</sub>-TiO<sub>2</sub>-ZrO<sub>2</sub> System
  • Formation and Thermal Stability of Gels

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Gels were prepared in the SiO2-TiO2-ZrO2 system (SiO2, TiO2 and ZrO2=0-100mol%) from Si(OC2H5)4, Ti(O-isoC3H7)4 and Zr(O-nC3H7)4 solutions with or without H2O and CH3COOH. Without H2O and CH3COOH transparent bulk gels were formed in the range 30-100mol% SiO2, 0-70mol% TiO2 and 0-50mol% ZrO2 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°C for 3 days. Crystallization peak temperatures Tc were determined by DTA on the dried gels preliminarily heat-treated at 200°C for 1h. Tc was low in the TiO2-ZrO2 rich compositions (Tc=366°C for TiO2 and 419°C for ZrO2). Tc increased up to 1258°C with increasing SiO2 content. From Tc and liquidus temperature TL, Tc/TL ratio was calculated. Tc/TL ratio means the thermal stability of the amorphous solids. It was discovered that TiO2 and ZrO2 alone are thermally unstable (Tc/TL=0.3 for TiO2 and 0.23 for ZrO2) but mixing TiO2 with ZrO2 enhances the thermal stability (for example, Tc/TL=0.45 for 50TiO2⋅50ZrO2) with increased ability of forming amorphous phase (amorphous-forming ability). This is true in the SiO2-TiO2-ZrO2 system for fixed SiO2 concentrations. Tc/TL increased with SiO2 content and reached the highest value of 0.86 at 90SiO2⋅10TiO2 composition, which is higher than that of SiO2 (0.77). Yet it seems likely that there are more stable compositions centering around the 80SiO2⋅10TiO2⋅10ZrO2 in the SiO2-TiO2-ZrO2 system. It is expected that compositions of high Tc/TL value have a high amorphous-forming ability.

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