Oxidation of Ag-Sn-La alloy powders

The gas atomized Ag-9.26wt%Sn-0.44wt%La alloy powders were oxidized in air between 400 and 900 degrees C. The oxidation thermodynamics, kinetics and microstructure of the alloy were investigated. We suggested that the addition of La may accelerate oxidation of Sn and prevent the formation of the dense SnO2 film. The suitable oxidation temperature of the alloy powders is 800 degrees C in air. After internal oxidation, many cracks were observed on the surface of the alloy powders. In addition, the whole oxidation process of the alloy powders is controlled by the oxygen diffusion. The diffusion coefficient of oxygen in the alloy powders at 800 degrees C is about 1.5 times larger than that at 700 degrees C on the initial stage of internal oxidation, while that is 4.5 times on the subsequent stage.