Solid-State Reaction and Diffusion Behaviors of CaFe2O4 and TiO2 at 1373 K to 1473 K

The solid-state reaction and diffusion behaviors of CaFe2O4 and TiO2 were investigated using a diffusion couple method at 1373 K to 1473 K under air atmosphere, and an in situ XRD method was used to analyze the solid-state reaction process. The reactions between calcium ferrite and TiO2 in the solid state are displacement reactions that produce perovskite and Fe2O3. The diffusion interface was divided into three layers based on phase analysis: layer I was composed of CaTiO3; layer II was composed of Fe2O3, CaTiO3, CaFe2O4, and Ca2Fe2O5; and layer III was composed of CaTiO3, Fe2O3, CaFe2O3, and CaFe4O7. The interface was formed in three stages. In stage I, CaTiO3 formed at the interface. In stage II, the gradual thickening of layers I and II was accompanied by the growth of the amount of CaTiO3 phase. In stage III, CF decomposed into CF2, and layer III formed. Micropores were formed in layer II due to the Kirkendall effect, and the diffusion rate of Ca-2(+) in CaFe2O4 was greater than that in CaTiO3. The squared thickness of layer I was found to depend linearly on time, and the expression for predicting the thickness of layer I was proposed: Delta x = (1.1731 x 10(-18) T-2 - 3.0206 x 10(-15) T + 1.9652 x 10(-12))(1/2) . t(1/2)