Formation of a Highly Resistive Deposit in the Reed Contact Unit

The formation of a highly resistive deposit in reed contact units working with low level loads is investigated. The buildup of the deposit is studied. It is analyzed in an Auger electron spectrometer (AES) and is found to consist of mainly carbon. The amount formed is estimated. The load range in which the deposit is formed is studied. It is shown that, under no-load conditions, a deposit is formed on rhodium but not on hard gold. If the load voltage is increased so much that a molten bridge can be developed between the opening contacts, a carbon deposit is formed on the hard gold contact also. In this case the initial phase of the carbon formation is heat controlled. A series of experiments was carried out where the normal hydrogen in the filling gas was replaced by oxygen. By doing so, the carbon formation could be prevented.