Kinetics and Mechanisms of the Hydrothermal Crystallization of Calcium Titanate Species

Abstract

Calcium titanate crystallization has been observed following the hydrothermal reaction of titanium dioxide (TiO2) and calcium in alkaline solution at 250 °C, using time-resolved in situ energy-dispersive diffraction. The nature of the calcium source used was found to influence the type of calcium titanate formed; CaTiO3 was produced when calcium carbonate was used and Ca(TiO2)2(OH)2 was produced when the calcium aluminosilicate, Ca3Al2(SiO4)(OH)8 was used. Temperature had a significant effect on the formation of CaTiO3, as observed in the range 200−250 °C. A less-significant effect was apparent for the formation of Ca(TiO2)2(OH)2 in the same range. Kinetic analysis of the crystallization of both calcium titanates was performed in the region 200−250 °C by applying the Avrami-Erofe’ev equation to the growth data. Activation energies of 89 and 58 kJ mol−1 were returned for the formation of CaTiO3 and Ca(TiO2)2(OH)2, respectively.