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

Abstract

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 Ca²⁺ 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:

$$ \Delta x = ( 1. 1 7 3 1\times 10^{ - 18} T^{2} - 3.0206 \times 10^{ - 15} T + 1.9652 \times 10^{ - 12} )^{{\frac{1}{2}}} \cdot t^{{\frac{1}{2}}} $$