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 metal-chelate gel route based on gelation of the aqueous solution of citric acid has been successfully applied to the synthesis of calcium silicates (Ca2SiO4 and Ca3SiO5) 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-Ca2SiO4 (high-temperature phase) and γ-Ca2SiO4 (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, ΔGβ→γ*. The particle size effect governs both the statistic of martensitic nucleation and the propagation of the β→γ transformation. In contrast to Ca2SiO4, triclinic Ca3SiO5 (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, ΔGM-T*, are considered to be small.
ASJC Scopus subject areas
- 化学 (全般)