Investigation of Arc Erosion Mechanism for Tin Dioxide-Reinforced Silver-Based Electrical Contact Material Under Direct Current

To get an in-depth insight into the arc erosion mechanism for tin dioxide-reinforced silver-based (Ag-SnO2) contact material, the contact pairs made of Ag-4wt%SnO2 contact material were, respectively, performed for 20,000 switching operations under the direct currents of 19 A and 29 A and the voltage of 12 V, together with the electrode gap of 4 mm. The eroded surfaces and cross-sectional morphologies and the chemical compositions were characterized by scanning electron microscopy equipped with an energy dispersive spectrometer (EDS). The results show that there is a deep erosion pit at the cathode and an apparent protrusion at the anode, suggesting that a serious material transfer generates from cathode to anode. The EDS results show that the Sn contents at the protrusion and at the region around the crater are below 0.75 wt.% and 4 wt.%, respectively. This reveals that SnO2 undergoes severe evaporation during electrical contact testing. Moreover, arc stability decreases with increasing the load current, and the Ag-SnO2 contact material has larger arc power (make arc: 68.2 J/s; break arc: 58.53 J/s at 29 A) as compared to Ag-TiB2 contact material (make arc: 62.85 J/s; break arc: 50.01 J/s at 29 A). As a result, it is thought that SnO2 evaporation reduces Ag dissipation, thus shortening the lasting time of the make arc. However, the emission current is increased owing to the low work function of SnO2, which further promotes the improvement in the density of the charged particles, thereby enhancing the arc power. Additionally, the large density of charged particles can sustain arc burning for a longer time, resulting in an extended break arc duration.