Occurrence of SiO2 on the contact surface and its dependence on electrodes in silicone vapor

As products made from silicone such as rubbers or oils have excellent characteristics, they are applied to various fields. Silicone vapor evaporates from silicone compounds. However, adsorbed silicone molecules on surfaces decompose to SiO₂ under high temperature. Since SiO₂ is a typical insulator, if SiO₂ is interposed between electrical contacts, contact failure easily occurs. In this paper, to clarify occurrence of SiO₂on the contact electrodes, both statically heating of the electrode applied by high voltage and dynamic condition of contacts for make-break switching operation in actual relays were studied. In the decomposition process, SiO₂₊ ions occur. As the ions attract to cathode, it is expected that SiO₂ formed only on the cathode. Occurrence of SiO₂ was clearly found only on the surface of cathode in the statically heating the electrode under high DC voltage. On the contrary, for the dynamic operation of switching electrical load, SiO₂ was detected both electrode; however, amount of the products on the cathode rather lesser than anode. This difference in occurrence of SiO₂ between static and dynamic condition of contacts was explained by discharge phenomena. Namely, in the arc discharge, metallic and gaseous ions attack to the cathode surface and clean it. Also transfer of SiO₂ to the anode under the switching operation occurs.