クエン酸水溶液を用いたキレートゲル法によるカルシウムシリケートの合成

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Recently, novel gel techniques such as the metal-chelate gel method, in situ polymerized complex method and polymer precursor method have been utilized to prepare many kinds of ceramics. These techniques offer the potential advantage of achieving compositionally homogeneous and fine powders with a narrow size distribution. Since the hydration activity of calcium silicates is affected by phase changes and the surface area, it is of vital importance to take into account both polymorphic forms and particle size. In this study, a metalchelate gel route based on gelation of the aqueous solution of citric acid has been successfully applied to the synthesis of calcium silicates (Ca_2SiO_4 and Ca_3SiO_5) for the first time. In addition, their phase transformations and particle size are discussed in comparison to the conventional solid-state reaction route. The novel citrate gel route and the conventional solid-state reaction route were found to produce β-Ca_2SiO_4 (high-tem perature phase) and γ-Ca_2SiO_4 (low-temperature phase), respectively. This result can be explained in terms of the particle size effect and the energy barrier. The nucleation and propagation of microcracks were responsible for overcoming a comparatively high-energy barrier, ΔG^*_<β→γ>. The particle size effect governs both the statistic of martensitic nucleation and the propagation of the β→γ transformation. In contrast to Ca_2SiO_4, triclinic Ca_3SiO_5 (low-temperature phase) was obtained by both the citrate gel route and the conventional solid-state reaction route. The nucleation and propagation are not responsible for the transformation, thus the energy barrier of the monoclinic (M) to the triclinic (T) transformation, ΔG^*_<M-T>, are considered to be small.
2001-05-01

クエン酸水溶液を用いたキレートゲル法によるカルシウムシリケートの合成

スポンサーリンク

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