Polarization behaviour of copper whisker crystal in acidic cupric sulphate solution

The polarization behaviour of copper whisker crystal was investigated in acidic cupric sulphate solution by a potential sweep method limited to 120 mV of overpotential. When the overpotential limit was above 130 mV, sweep experiments gave scattered results due to random nucleation. The apparent exchange current density on a whisker was around 10^?5 A/cm², three orders of magnitude less than that on a polycrystalline copper.The exchange current density is increased by the twisting of a whisker: it is proportional to the twist angle. The defect dependency of the exchange current is discussed in relation to a surface-diffusion model.Polarization curves at low overpotentials show asymmetry of the cathodic and anodic branch. The surface defects introduced by twisting appear to be four times as effective for anodic dissolution as for cathodic deposition.