ABSTRACT
The closed electric contact has to perform its function of passing electric current reliably and with no change in its contact resistance (Re) for the duration of its life. The contacts have to perform this function even though the ambient atmosphere in which they reside contains pollutants which can cause the contacts to tarnish or corrode. While most ambients no longer show the obvious pollution levels of Pittsburgh on 5 November 1945, where at 11 :00 a.m. the city was in complete darkness (1), electric contacts are used in many environments that can create a severe reduction in their useful life. Again the polluted cities such as Los Angeles, New Delhi, Tokyo, etc. where temperature inversions prevent the dispersion of the exhaust gases from the internal combustion engine, and where you can smell and taste the air, present an obvious problem. Contacts are used, however, in ambients where the levels of pollution are not so obvious. Many of these ambients still do give rise to contact corrosion. While power connectors have been used for many years in harsh outdoor environments such as steel mills and paper mills, it is only in the past 25 years that research has intensified on connectors used in indoor environments. This is especially true for electronic connectors that have found increasing use in equipment for controlling the processes of industrial production that create these harsh outdoor environments. This chapter serves as a brief introduction to the subject of contact corrosion. It initiates a discussion on business and industrial environments and how these are reproduced in laboratory testing. It discusses briefly the types of observed corrosion, and how they are measured. The discussion of environmental effects on electronic connectors and the laboratory experiments on analyzing the effects of mixed gas atmospheres are presented in more detail in Chapter 3. The effects of corrosion on power connections are discussed in Chapters 4 and 5. The effects of plating are presented in Chapter 7. Finally Chapters 4-6 give a detailed discussion of Fretting Corrosion. The effects of the ambient
90 Slade
atmosphere on opening contacts will be discussed in Chapter 9 and 16 and the effect on sliding contacts in Chapter 19.
