Activation of Electrical Contacts by Organic Vapors

803 804 806 807 809 810 810 811 811 Contamination of surfaces by organic vapors is a subtle factor that influences the electrical erosion of relay contacts. Because of this contamination, contacts in the telephone plant sometimes erode very much more than one would expect from simple laboratory life tests. This caused considerable confusion until about 1945 when the influence of organic vapors was recognized. The term "activation" is used here to describe changes in the surfaces of electrical contacts which give rise to greater arcing when an electrical circuit is completed or broken than would occur if the metal surfaces were clean.* Although its cause is generally carbon from organic vapors, there are occasionally other causes. This paper is an account of recent research 1 on activation produced by organic vapors, f It has been found that the carbon that causes activation is formed on the electrode surfaces by decomposition of adsorbed organic molecules. Microscopic examination of contacts gives a very sensitive way of detecting incipient activation, since the carbon can easily be seen before any electrical effects are observed. The minimum amount of carbon necessaiy for activation is of the order of 0.05 microgram. Activation has been produced on noble metals only, and only by unsaturated ring compounds. When experiments are carried out on clean noble metal surfaces under controlled conditions which do not permit burning of carbon, it is found that the amount of carbon formed by an arc corresponds to approximately a monolayer of organic molecules on the area heated by the arc.