Mass material transfer of Ag-SnO2 contact material in DC level

A composite contact materials Ag-SnO₂ have been used in low current switching devices for its good anti-welding properties and resistance to arc erosion. But the mass material transfer occurred at large surge current in DC switching now and then. Mass material transfer have an increased probability of early failures because the effective contact gap reduces or two contacts lock together. In this research, the shape and distribution of crystals at the contact surfaces were observed to analyse the reason of mass transfer. It was found that the shape and distribution of the crystals are like sunflower at the contact surfaces. The equal axes crystals distributed over the surfaces center, and the radial club-shaped crystals distributed around the center. One test showed that the melting phenomena at the interface of crystals had precedence over that in other sections at large surge current for the composite contact materials Ag-SnO₂, it result in individual crystal transfer or several crystals transfer together.