Generated compounds at the V-slag/CaO diffusion surface and diffusion characteristics of V and Ca in calcium vanadate

Vanadium slag/CaO diffusion couples were prepared to study the diffusion characteristics of the vanadium slag/CaO interface at 1083 K in the air. The generated phases at different regions were characterized by EPMA, EDS, XRD, and element maps analysis. At the vanadium slag surface that the diffused Ca dose not reached, the main generated phases were Mn₂O₃ and Fe₂O₃. V³⁺ was oxidized to V⁵⁺ and reacted with the Ca²⁺ to form a small amount of Ca₂V₂O₇. Cr was at a disadvantage compared with V in occupying the original Ca²⁺ of the slag. At the vanadium slag surface that the diffused Ca had reached, the main generated phases were Ca₂V₂O₇. At the CaO surface, the main generated phases were Ca₂V₂O₇ and Ca₃V₂O₈. The interdiffusion coefficients were calculated by a new approach that modified from the Boltzmann-Matano method including the determination of the Matano surface, calculation of the integral and differential using the raw data of the concentration profiles. As the molar fraction of Ca was in the range of 0.15 to 0.86, the average interdiffusion coefficient of Ca²⁺ was 2.54 × 10^-8 cm²·s^-1. The average interdiffusion coefficient of V⁵⁺ at the V molar fraction of 0.001 to 0.43 was 1.96 × 10^-8 cm²·s^-1.