Determination of the Parameters that Control Oxidation Using Optical Interference, Applied to the Two Phase Oxide Scale on Copper

The oxidation of a metal forming a transparent oxide allows it to be followed in situ by optical interference. The layer thickness is determined from the interference pattern. The method can be applied to any tarnishing process as long as the resulting layer stays transparent. Oxidation of copper is followed in air, at T = 230 degrees C, making use of the three colors of a video camera. In this case a two phase, Cu2O/CuO scale is formed on Cu. An analysis of the rate of formation of two layers of two phases is presented. The rate constants are related to a surface reaction rate or to bulk diffusion and conductivity. It is shown that while the total amount of oxide increases with time the layer thickness of one of the phases can temporarily decrease. In the long time limit both layers follow the parabolic law i.e. increase as root time. The method can be applied also to the inverse process of reduction and decrease in the scale thickness.