On the electrical characteristics of latent finger mark corrosion of brass

Apparatus constructed to measure the variation (Δ V ) in applied potential ( V ) over the surface of brass discs subject to corrosion by latent finger mark deposits is described. Results show values of Δ V of up to 14 V for V = 1400 V on regions of disc coincident with the location of finger mark corrosion. Measurement of Δ V for 0 V ⩽ V ⩽ 1400 V has revealed a non-linear relationship, which is very similar to that measured for a commercial metal–semiconductor Schottky rectifier. Further experiments have shown the corrosion product on the brass to be a p-type semiconductor with current/voltage characteristics for the brass-corrosion contact consistent with the characteristics expected for a rectifying metal–semiconductor contact. The composition of the semiconductor is discussed in terms of metal oxide corrosion products with p-type copper (I) and copper (II) oxides thought most likely to be responsible for the semiconductor behaviour of the corrosion product. A simple model is described for the galvanic corrosion of brass by finger mark deposits that is consistent with the experimental results.