On the electrical characteristics of latent finger mark corrosion of brass

Apparatus constructed to measure the variation (Delta 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 Delta V of up to 14V for V = 1400V on regions of disc coincident with the location of finger mark corrosion. Measurement of Delta V for 0V <= V <= 1400V 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.