Copper's oxidation mechanism and purity effects were elucidated by oxidizing 99.99 pct (4N), 99.9999 pct (6N), and floating zone refined (>99.9999 pct) specimens in 0.1 MPa oxygen at 350 °C to 1050 °C. Throughout the temperature range, the oxidation kinetics for all specimens obeys the parabolic oxidation rate law. The Cu2O scale grows predominantly, and the rate-determining step is concluded to be outward diffusion of copper atoms in Cu2O. The activation energy at high temperatures, where the lattice diffusion predominates, is 173 kJ/mol, but it becomes lower at intermediate temperatures and even lower at low temperatures because of the contribution of the grain boundary diffusion. At high temperatures, oxidation kinetics is almost uninfluenced by purity, but the lattice-diffusion temperature range is wider for higher-purity copper. At intermediate temperatures, copper oxidation is enhanced because trace impurities can impede growth of Cu2O grains to facilitate grain boundary diffusion. At low temperatures, grain boundary diffusion is possibly hindered by impurities segregated at grain boundaries.
|Number of pages||7|
|Journal||Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science|
|Publication status||Published - 2006 Apr|
ASJC Scopus subject areas
- Condensed Matter Physics
- Mechanics of Materials
- Metals and Alloys