Effect of heat surface treatment on photoelectric work function of silver-metal alloys

Abstract

Contact materials used for electrical breakers are often made with silver alloys. Mechanical and thermodynamical properties as well as electron emission of such complicated alloys present a lack of reliable and accurate experimental data. At present, new types of contactors with longer duration are marketed, but manufacturers do not understand well why this improvement. This paper deals mainly with electron work function (EWF) measurements in UHV conditions. Also, the photoelectric emission from silver-metal (Ag-Me) electrical contacts (Ag-Ni (60/40), Ag-Ni (70/30) and Ag-W (50/50)) has been investigated in the spectral range of 196-256 nm. The effects of thermal surface treatment on EWF of the abovementioned contacts were studied at room temperature and residual gas pressure of 1.4 x 10-7 mbar. The EWF of the contact pastille made with silver alloys Ag-Ni and Ag-W varies with surface treatments: cleaning by vacuum outgassing and annealing (long heating time in UHV). By heating alloy contact in ultra high vacuum large variations of EWF have been observed, which result from material component vaporization by sheets. In addition, the influence of arcing on EWF of binary alloys has been investigated. Also, EWF varies with the number of applied arcs. Therefore, after 500 arcs in air, the observed EWF increasing is probably due to progressive inclusion of oxide on alloy surface. Microscopic examination is necessary to get better understandings on EWF of silver alloys, for both virgin and eroded electric contacts. So, surface analysis by SEM and EDS have been performed to produce proofs of these various phenomena