On the Defect Structure and Transport Properties of Co3O4 Spinel Oxide

• Main Authors: Kaczmarska A., Grzesik Z., Mrowec S.
• Format: Article
• Language: English
• Published: De Gruyter 2012-10-01
• Series: High Temperature Materials and Processes
• Subjects: co3o4; defects; oxidation kinetics; mechanism; diffusion
• Online Access: https://doi.org/10.1515/htmp-2012-0069

Defect structure and transport properties of Co3O4 cobalt oxide have been studied as a function of temperature and oxygen pressure, using marker and thermogravimetric techniques. It has been found that the oxidation of CoO to form Co3O4 follows parabolic kinetic, being thus diffusion controlled. Marker experiments have demonstrated that cation sublattice of Co3O4 oxide is predominantly disordered, but the defect structure is rather complex. At very low oxygen pressures, close to the dissociation pressure of the oxide, interstitial cations are the predominant point defects, while at high pressures cation vacancies predominate. This behavior is reflected in complex dependence of the parabolic rate constant of CoO oxidation on oxygen pressure. At low pressures, namely, parabolic rate constant of the reaction increases with oxygen pressure, reaching then virtually constant value in intermediate pressure range and increases again in highest pressure range. Theoretical analysis of kinetic results in terms of point defect thermodynamics confirmed the above conclusion, concerning complex defect structure of Co3±yO4 oxide. Finally, self-diffusion coefficient of cations in the discussed oxide has been calculated as a function of temperature and oxygen pressure from kinetic rate measurements, using Wagner's theory of metals oxidation.