INVESTIGATION OF CONTACT SURFACES IN MODEL REED SWITCHES FILLED WITH SELECTED GASES

The physical and chemical processes which take place in miniature reed switches under electrical load have been investigated. The temperatur e of the contact spot just before the break was determined from measur ements of the bridge voltage. Model reed switches were filled with the protective gas mixture N2-H-2 containing small quantities of CH4 or C 2H2. These two gases decompose at the contact spot, since its temperat ure rises to approximately the boiling point of gold. Contamination sp ots consisting mostly of carbon were detected on the contact surfaces after the lifetime test. Auger electron spectroscopy showed that the q uantity of carbon in the spots is the highest if the protective gas is doped with C2H2. IR analysis of the spots showed that they are of pur e amorphous carbon. Because of the carbon deposition a considerable in crease in the contact resistance of the switches was observed. Traces of carbon were also found on the surfaces of the contacts of switches filled with pure N2-H-2, although in this case the contact resistance remained low.