770 THE BELL SYSTEM TECHNICAL JOURNAL, MAY 1957 



6. Activation in Air 803 



6.1 Burning of Carbon 804 



6.2 Diffusion of Activating Vapor 806 



6.3 Sputtering and Burning in a Glow Discharge 807 



6.4 "Hysteresis" Effects 800 



7. Brown Deposit 810 



7.1 Composition 810 



7.2 Rate of Production 811 



7.3 Brown Deposit and the Carbon of Activation 811 



INTRODUCTION 



Contamination of surfaces by organic vapors is a subtle factor that 

 influences the electrical erosion of relay contacts. Because of this con- 

 tamination, 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^ on activation produced by organic 

 vapors, t 



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 de- 

 tecting incipient activation, since the carbon can easily be seen before 

 any electrical effects are observed. The minimum amount of carbon 

 necessary for activation is of the order of 0.05 microgram. 



Activation has been produced on noble metals only, and only b}' un- 

 saturated 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. After a surface has become active, the amount 

 of carbon formed by each arc is considerably increased and corresponds 

 to the decomposition of several monolayers of molecules. In air, the situ- 



* The term "activation" has sometimes been used heretofore to signify en- 

 hanced erosion resulting from organic vapors. This is a different definition from 

 that used in this paper, due to the fact that in some cases, long sustained arcs 

 produce less erosion than arcs of shorter duration. This is often true for silver 

 surfaces, as described below. In a case of this sort, a surface may have a great 

 deal of carbon on it and be very "active" by our definition, when it would be 

 considered not active at all by the definition that relates activation to rate of 

 erosion. 



t Other causes of activation will not be considered here. See Reference 2, page 

 961. 



