Electrical Characteristics of Contacts Contaminated with Silver Sulfide Film

Frequently the electrical performance of silver contacts is impaired by the unavoidable growth of a sulfide film on the mating contact surfaces. In the case where one or both of the electrodes are silver, or partly silver, and a silver sulfide film is formed on one or both of the electrodes, the electrical performance is greatly deteriorated and is among the most complex found on contaminated contacts. A recent study of the electrical performance of various sulfided contacts is reported that showed that they are characterized by an increased contact resistance that is dependent on the voltage polarity, by a nonohmic relationship between the contact voltage and current, and by a resistance that changes with time. A theory is proposed to account for the observations made with these contacts that is based on the semiconduction properties of silver sulfide, the high mobility of positive silver ions in silver sulfide, the tunnel effect, the widening of established conduction channels through the film by electrical forces (B fritting), and the crystal structure of silver sulfide, which can be found in either one of two forms depending on its temperature.