Oxidation kinetics of ZrO₂-C-ZrB₂ composites

The oxidation kinetics of ZrO₂-C₂ZrB₂ composites with 10% ZrB₂ were investigated in the temperature range from 800 to 1100℃ in air by differential thermal analysis (DTA) and thermogravimetry (TG) techniques. A mathematical model was proposed based on the reaction principle between gas and solid. The apparent activation energy and experimental expression of oxidation rate vs temperature were obtained. The results show that the oxidation process of the composites at 800℃can be controlled by two stages：chemical reaction-controlled process and then the mixture processes both chemical reaction-controlled and gas diffusion. However，the oxidation rate within 900～1100℃ is controlled by the chemical reaction at the initial stage；then both chemical reaction and diffusion at an intermediate stage and finally controlled only by diffusion. The apparent activation energy for the three stages was calculated and equal to 111.7，71.5 and 166.0kJ·mol^-1 respectively. The rules of the unit area mass change as a function of isothermal processes for specimens indicate that the protective oxidation was performed during 900℃ to 1100℃.