Behavior of Solute Elements and Oxygen during Internal Oxidation of Ag-In-Sn Alloys

Abstract

Ag-In-Sn alloys with various compositions containing total solute elements of 8 at% were oxidized at 873 to 1133 K in air. The depth of the internally oxidized layer, ξ, and the amount of solute elements diffused into the oxidized layer from the unoxidized region, J, were measured in order to investigate the behavior of solute elements and oxygen during internal oxidation. The diffusion coefficient of In, D_In, and Sn, D_Sn, in the unoxidized region, and that of oxygen, D_O, in the internally oxidized layer, and the volume fraction of oxide, f_OX, were calculated from J and information about structures of oxides.
The results obtained are as follows:
(1) The relation between the depth of the internal oxidation layer and the oxidation time was expressed by a parabolic law at every temperature in the composition range of 0.14≤C_Sn≤0.53 (C_Sn=at%Sn/at%(In+Sn)). But the parabolic law was established only at 823 to 1023 K in the alloy of C_Sn=0.65, and at 973 and 1023 K in the alloy of C_Sn=0.78.
(2) The parabolic rate constant, k, increased with C_Sn up to 0.4 and was reduced with C_Sn above 0.4.
(3) D_O in the internal oxidation layer was in approximate agreement with the calculated value, D_O(cal), by considering the reduction of the Ag phase by oxide dispersion to the diffusion coefficient of oxgen in Ag determined by Eichenauer and Müller. D_O was larger than D_O(cal) in the alloys containing agglomerated needle-like oxides, while it was reversed in the alloys containing fine oxides.
(4) The relations among J, D_In, D_Sn, f_OX and the enrichment factor of solute elements in the internal oxidation layer were different in the composition range C_Sn≤0.4, 0.4<C_Sn<0.65 and C_Sn≥0.65. Composition dependence of parabolic rate constant, k, and the tendency of oxide film formation were dominated by f_OX determined by the enrichment of solute elements and crystal structures of precipitated oxides.