Oxidation of copper by atomic oxygen was found to differ significantly from
oxidation by ordinary molecular oxygen. Firstly, a strong enhancement of o
xidation was observed, particularly at the initial stages of oxidation (up
to 10(6) times compared to molecular oxygen). The reaction probability of a
tomic 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 oxyge
n under all experimental conditions studies, oxidation in atomic oxygen sho
ws an initial linear stage (20 to 80 min in duration) for oxidation tempera
tures above 873 K, followed by parabolic stage. At about 1000 K, the parabo
lic rate constant depends only slightly on temperature and then decreases a
t 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 oxid
ation temperature. The last two observations may be qualitatively explained
by the "counter oxidation'' reactions (thermodynamically allowed for the C
u/O system) which reduce oxides to the metal or a lower oxide.