Formation characteristics of CaTiO3 in the vicinity of the calcium ferrite/TiO2 interface

Abstract

Calcium ferrite-TiO 2 (C x F-TiO 2 ) diffusion couples were prepared to investigate the reaction between TiO 2 and CaO of calcium ferrite during sintering vanadium‑titanium magnetite. The distribution, species, and number of phases in the vicinity of the C x F/TiO 2 interface were characterized by electron probe microanalysis (EPMA), Fourier transform-infrared (FT-IR) spectroscopy, and X-ray diffraction (XRD) that could select the scanning location. The phases generated from the C x F side to the TiO 2 side are 66.66% CaFe 2 O 4 + 33.33% Fe 2 O 3 , 100% CaTiO 3 , 66.66% CaTiO 3 + 33.33% Fe 2 O 3 , and 75% CaTiO 3 + 25% Fe 2 O 3 , respectively. The isothermal section was plotted using the experimental data. The diffusion thickness decreased from 90.2 to 8.1 μm as the temperature decreased from 1323 to 1173 K, and increaesed from 47.4 to 121.4 μm as the annealing time increased from 1 to 4 h. The linear relationship between the diffusion thickness and the square root of the annealing time indicates that the formation of CaTiO 3 was controlled by the diffusion process. Vacancy-mediated diffusion mechanism, which was widely used to describe the diffusion-controlled process, was introduced to describe the formation of CaTiO 3 in the vicinity of the C x F/TiO 2 interface. The Ti 4+ in the TiO 2 layer jumped and diffused through the Ti 4+ vacancies in the CaTiO 3 + Fe 2 O 3 layer to the CaFe 2 O 4 + Fe 2 O 3 /CaTiO 3 interface, and reacted with CaFe 2 O 4 and O 2− to generate CaTiO 3 . The concentration data across the C x F/TiO 2 interface were applied in the modified Boltzmann-Matano method to calculate the interdiffusion coefficient. The average interdiffusion coefficients of various Ti concentrations increased with temperature: 2.51 × 10 −10 , 7.49 × 10 −10 , 2.56 × 10 −9 , and 8.06 × 10 −9 cm 2 ·s −1 at 1173, 1223, 1273, and 1323 K, respectively. The relationship between the logarithm of the interdiffusion coefficient and the reciprocal of the temperature was empirically described by the Arrhenius expression. Linear regression analysis showed that the diffusion activation energy of CaTiO 3 formation is 300.14 kJ/mol. • CaFe 2 O 4 , CaTiO 3, and Fe 2 O 3 generate at the calcium ferrite/TiO 2 interface. • CaTiO 3 forms thorough vacancy-mediated diffusion mechanism. • Diffusion of Ti 4+ governs the CaTiO 3 formation in the calcium ferrite-TiO 2 system. • Diffusion thickness and interdiffusion coefficient increase with temperature. • CaTiO 3 formation requires approximately activation energy of 314 kJ/mol.