Oxidation mechanism of Cu₂O to CuO at 600-1050 °C

To clarify the oxidation mechanism □□₂□ to CuO, □□₂□ oxidation was studied at 600-1050°C under1 atm □₂. The □□₂□ specimens were prepared through completely oxidizing 99.99999 and 99.5% pure copper at 1000°C in an Ar +1% □₂ atmosphere. The oxidation kinetics □□ ₂□ specimens prepared from both purity levels followed the logarithmic law, not the parabolic law or the cubic law as reported in the literature. The activation energy for □□₂□ oxidation is relatively high in the lower-temperature range, but becomes very small or even negative at higher temperatures. The logarithmic oxidation rate law can be explained by Davies et al.'s model related to grain-boundary diffusion in the oxide layers. The very small or negative activation energies in the higher-temperature range can be attributed to the very small thermodynamic driving force and the fast lateral growth of CuO grains related to a sintering effect. The influence of small amount of impurities is also discussed.