The effects of citric acid on the synthesis and performance of silver-tin oxide electrical contact materials

A sol-gel auto-combustion method was developed to synthesize the Ag-SnO2 composite powders, which were then used as the starting material to prepare Ag-SnO2 electrical contact materials by hot pressing. It was found that citric acid strongly influences the thermal behaviors, phase evolution, morphology and composition distribution of the Ag-SnO2 composite powders. During the synthesis of Ag-SnO2 composite powders, citric acid can facilitate the formation of sol solution, lower the energy required for the decomposition of dry gel, and reduce the agglomeration of particles. Besides, a comparatively high molar ratio of citric acid to metal ions prevents effectively the occurrence of composition segregation in the Ag-SnO2 electrical contact materials. Therefore, the prepared Ag-SnO2 electrical contact materials have good performances in density, hardness and electric conductivity.