The effect of an electric field on the high temperature oxidation of copper in air

Two copper disks were connected as d.c. capacitor electrodes while heated in an air atmosphere. The capacitor was positioned in a furnace with controlled temperatures of 500°C and 600°C for 1 h in air with an imposed electrical field of 2.5 x 10³ V/cm. The surface structure of the electrodes was examined by X-ray diffraction (XRD), scanning electron microscopy and energy dispersive X-ray analysis. After annealing, XRD showed the presence of Cu, Cu₂O and a small quantity of CuO. The O/Cu atomic concentration ratio after annealing at 500°C was 2/3 on the anode and 1/2 on the cathode. The CuO phase was not observed at 500°C, whereas at 600°C the intensity of the CuO XRD lines on the anode was greater than those on the cathode. Areas with approximately equal concentrations of Cu and O were observed at 600°C only on the anode. After annealing at 600°C the grain size on the anode was approximately 2.2 μm, whereas on the cathode the observed grain size was approximately 4 μm.