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 (TiO 2 ) 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; CaTiO 3 was produced when calcium carbonate was used and Ca(TiO 2 ) 2 (OH) 2 was produced when the calcium aluminosilicate, Ca 3 Al 2 (SiO 4 )(OH) 8 was used. Temperature had a significant effect on the formation of CaTiO 3 , as observed in the range 200-250 °C. A less-significant effect was apparent for the formation of Ca(TiO 2 ) 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 CaTiO 3 and Ca(TiO 2 ) 2 (OH) 2 , respectively.

Application of Optical Floating Zone Method to Dissolution Kinetics of Inclusions in a Steelmaking Slag

“…The discrepancy with respect to the value shown in Table may be related to the difference in experimental conditions for the formation of CaTiO 3 in the two cases. In the work of Croker et al, CaCO 3 was reacted with TiO 2 in sodium aluminate solution to produce CaTiO 3 whereas in the current work Ca 2+ and O 2 − from ionic slag reacts with TiO 2 to form CaTiO 3 . Also, anatase was used in their work while rutile is used in the current study.…”

“…Croker et al reported k R values for in situ crystallization of CaTiO 3 at 250 °C. The obtained rate constant value from their study is extrapolated to 1430 °C following Arrhenius relationship. The rate constant value thus obtained is 6.3 × 10 4 s −1 .…”

Synthesis, Spectral and Thermal Studies on Schiff Base Derivatives of Heterobimetallic [Ca(II)-Ti(IV)]-μ-oxoisopropoxide

“…PerkinElmer 1710 FTIR spectrometer over the range 4000-400 cm -1 used to record the Infrared spectra. The 1 H, 13 C NMR spectra were recorded in CDCl 3 on Bruker Avance II 400 NMR spectrometer. TG study has been made on Diamond TG/DTA PerkinElmer instrument.…”

“…The alkaline earth metal titanates like barium titanate, calcium titanate (CaTiO 3 ), strontium titanate (SrTiO 3 and Ba x Sr 1-x TiO 3 ) due to their exceptional properties expose potential applications in multilayer ceramic capacitors, electro-optic, dielectric and piezoelectric devices [9][10][11][12] . The perovskite CaTiO 3 with its unique structure, higher stability and biocompatibility, finds potential application in the fields of communication, electronics and in biotechnology [13][14][15] . The ability of immobilizing the rare earths of CaTiO 3 by forming solid solutions with highly radioactive wastes makes the CaTiO 3 useful for disposal of highly radioactive wastes [16][17] .…”

Reaction behaviors and amorphization effects of titanate species in pure substance systems relating to Bayer digestion

“…It is frequently introduced in bauxite digestion processing and other processes for alumina production (Malts, 1992;Whittington, 1996;Whittington and Cardile, 1996). When added to Bayer liquor, CaO is generally thought to minimize the formation of sodium titanate by reacting with titanate in solution to form insoluble crystalline perovskite (CaTiO 3 ), which can be removed with red mud (Loan et al, 2005;Shultze-Rhonhof and Winkhaus, 1972;Croker et al, 2009). Other views propose that CaO itself has a catalytic (Malts, 1992) or activating (Qiu, 2010) effect on diaspore, but the activation mechanism is unclear.…”