Electrical contact phenomena of nickel electrodeposits with sharp micro-asperities

The electrical contact phenomena of gray nickel deposits with unique surface asperities are studied. An insulating oxide layer is assumed to exist because there is no evidence to support its absence. Since the oxide film is known to be as strong as the metal and it scarcely ruptures at contact, the emphasis is to determine which particular surface features contribute to low values of contact resistance, especially after the coating is exposed to humidity testing. Reflection electron micrographs showed that the nickel coatings with low R_c after humidity exposure have sharp asperities on the surface. The oxide layer of these surfaces is shown not to be tenacious since the film resistivity depends strongly on the contact force. These sharp micro-asperities appear to account for the low R _c behavior of gray coatings, as they disrupt the insulating film upon mechanical contact to create many small breaks in the oxide layer. Electrical contact then occurs through these breaks. At a load of 39 g or higher, the oxide is ruptured and the R_c is reduced to a low, stable value with or without exposure to an accelerated oxidizing environment