On the coupled growth of oxide phases during internal oxidation of Ag–Sn–Bi alloys

Abstract

AbstractInternal oxidation experiments using two Ag–Sn–Bi alloys with Bi contents of 2.6 wt.% and 5.0 wt.% were carried out. The presence and spatial distribution of Bi2O3, SnO2and Bi2Sn2O7in the oxidized microstructure was characterized using a field emission gun secondary electron microscope, energy dispersive X-ray analysis and X-ray diffraction techniques. It is shown that the addition of Bi prevents both external oxidation and internal oxide bands in Ag–Sn alloys with Sn content above 4 wt.%. Conditions are defined under which these alloys develop instabilities at the internal oxidation front. A result of the unstable growth of the reaction front is a dendritic morphology consisting of different oxide phases. Coupled growth of Bi2Sn2O7 and SnO2 inside the dendrites determines the local arrangement and distribution of the phases.