Thermodynamic analysis of erosion effects of silver-based metal oxide contact materials

A simple thermodynamic model is used to analyse the temperature increase of Ag-based contact materials with CdO or SnO/sub 2/ admixtures and the corresponding chemical reactions during make operation. Below an arc energy of about 20 kJ/mole the melting point of silver is not reached in the model and the arc erosion will not depend on the type of oxide particles added to the silver base material. Above 40 kJ/mole an increasing amount of arc energy is put into the oxide sublimation processes which reduces the temperature increase. Part of the different behavior of CdO and SnO/sub 2/ containing contacts could be related to the higher evaporation rate of CdO at lower temperatures. The model allows one to evaluate and helps to optimize heterogeneous contact materials and to analyse chemical reactions and phase changes during arc erosion.