Si(OC₂H₅)₄-ZrOCl₂・8H₂Oを用いたゾル-ゲル法によるZrSiO₄生成反応の機構

抄録

The mechanism for the formation of ZrSiO₄ from a system of Si(OC₂H₅)₄-ZrOCl₂·8H₂O-C₂H₅OH solution was investigated in relation to the T-→M-transformation of ZrO₂. The heat-treated powders were mixtures of metastable fine T-ZrO₂ and amorphous SiO₂. The T-ZrO₂ aggregates were gradually transformed into M-ZrO₂ with an increase in temperature. This is due to the decrease of surface energy. The solid state reaction between ZrO₂ and SiO₂ is crystallographically assumed to have a large activation energy, and, therefore, the T-→M-transformation is preferentially proceeded below ca. 1300°C without forming ZrSiO₄. Beyond the temperature, the interface reaction between T-ZrO₂ and SiO₂ took place and resulted in the formation of ZrSiO₄. With an increase in temperature, the formation reaction was accelerated due to the Hedvall effect, whence T-ZrO₂ was responsible only for the reaction not for the transformation. With decreasing amount of T-ZrO₂, the formation reaction terminated, but the addition of transition metal ions such as Ni²⁺ promoted the interface reaction between M-ZrO₂ and SiO₂. In order to increase the formation rate of ZrSiO₄, it was important to maintain the T-ZrO₂ powders metastable and fine by adding transition metal ions and by grinding the dried powders.