Improved Workability of the Nanocomposited AgSnO₂ Contact Material and Its Microstructure Control During the Arcing Process

There are two major weaknesses for the AgSnO₂ contacts used in the low voltage switch devices. One is poor workability, which causes the AgSnO₂ materials to hardly deform into the required shape. Another is the increased contact resistance after arcing, which, in turn, causes an unfavorable temperature rise in the switches. In this article, the nanocomposited AgSnO₂ materials were developed to overcome the weaknesses. The nanosized SnO₂ powders with or without CuO additive were prepared by the chemical precipitation method. The SnO₂ powders and Ag powders were high energy milled together to obtain AgSnO₂ composite powders, which were then sintered, hot pressed and extruded. It was found that the SnO₂ particles mainly distribute in the interior of Ag grains with Ag film on the grain boundary. The hardness of AgSnO₂ composites and the wetting angle of Ag melt on SnO₂ particles decreased with the addition of a small amount of CuO. By the combining effect of Ag film on grain boundary and the addition of CuO, the elongation and workability of the AgSnO₂ materials improved. The experiments of rapid solidification revealed that more SnO₂ particles with CuO addition were engulfed in the Ag matrix than those without CuO, which inhibited the redistribution of SnO₂ particles on the contact surface during the arcing process. The industrial type test in the 45A contactor suggested that the nanocomposited AgSnO₂ materials are suitable to be used as contacts in low voltage switches.