Studies of the interaction of copper with atomic and molecular oxygen

Oxidation of copper by atomic oxygen was found to differ significantly from oxidation by ordinary molecular oxygen. Firstly, a strong enhancement of oxidation was observed, particularly at the initial stages of oxidation (up to 10(6) times compared to molecular oxygen). The reaction probability of atomic oxygen is between 0.01 and 0.5 for the temperature range 400 to 1100 K. Secondly, while only parabolic oxidation was observed in molecular oxygen under all experimental conditions studies, oxidation in atomic oxygen shows an initial linear stage (20 to 80 min in duration) for oxidation temperatures above 873 K, followed by parabolic stage. At about 1000 K, the parabolic rate constant depends only slightly on temperature and then decreases at above 1073 K. Thirdly, the oxide films formed in atomic oxygen were found to consist of Cu2O only for all the temperature range studied, whereas in the case of molecular oxygen they contain 5 to 25% of CuO depending on oxidation temperature. The last two observations may be qualitatively explained by the "counter oxidation'' reactions (thermodynamically allowed for the Cu/O system) which reduce oxides to the metal or a lower oxide.