Abstract
The theoretical relation between the thickness of the oxide-layer and the oxidizing time was discussed in the case of oxidation of cylindrical and sliced copper to Cu2O in air at 990∼1045°C. Comparing the theoretical relation with experimental results, we obtain D=0.060exp[−(1.46±0.18)(eV)⁄kT] (cm2/sec) for the cylindrical specimen, and D=0.29exp[−(1.63±0.12)(eV)⁄kT] (cm2/sec) for the sliced one for the diffusion coefficients of ions in the oxide-layer. The obtained values for the activation energies and pre-exponential factors agree very well with those of cations in Cu2O obtained by the tracer method. The order of magnitude of the pre-exponential factors can be also estimated quantitatively by the diatomic-chain model of an ionic crystal.
It is concluded that the above fomulas represent the diffusion of cations via the vacancy mechanism in Cu2O formed on the metal and this diffusion determines the rate of oxidation of Cu to Cu2O.
