アルコキシドからのフォルステライト(2MgO・SiO2)とエンスタタイト(MgO・SiO2)の生成

概要

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A mixture with the mole ratio of Mg2+/Si4+=3 : 2 was prepared by the simultaneous hydrolysis of magnesium and silicon alkoxides. The phases and thermal properties of the mixture were studied by means of differential thermal analysis, thermogravimetric analysis and X-ray diffraction. The results obtained are summarized as follows: 1) 2 MgO-SiO2 and MgO·SiO2 were formed at 770°C and 865°C, respectively. 2) For the three modifications of MgO·SiO2, it is presumed that orthoenstatite and clinoenstatite are the low temperature phases, on the other hand, protoenstatite is the high temperature phase. 3) It was considered that the formation of 2 MgO·SiO2 and MgO-SiO2 was followed by the mechanism described by Ball and Taylor for surpentine (3 MgO·2 SiO2·2 H2O). 4) The rate of formation of 2 MgO-SiO2 was determined. Reaction isotherms were best described by the first-order plots. The nucleation process maybe the rate-determing step. The values of the activation energies are about 82 kcal/mol and 27 kcal/mol for initial and final stages, respectively.