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,
DIn, and Sn,
DSn, in the unoxidized region, and that of oxygen,
DO, in the internally oxidized layer, and the volume fraction of oxide,
fOX, 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≤
CSn≤0.53 (
CSn=at%Sn/at%(In+Sn)). But the parabolic law was established only at 823 to 1023 K in the alloy of
CSn=0.65, and at 973 and 1023 K in the alloy of
CSn=0.78.
(2) The parabolic rate constant,
k, increased with
CSn up to 0.4 and was reduced with
CSn above 0.4.
(3)
DO in the internal oxidation layer was in approximate agreement with the calculated value,
DO(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.
DO was larger than
DO(cal) in the alloys containing agglomerated needle-like oxides, while it was reversed in the alloys containing fine oxides.
(4) The relations among
J,
DIn,
DSn,
fOX and the enrichment factor of solute elements in the internal oxidation layer were different in the composition range
CSn≤0.4, 0.4<
CSn<0.65 and
CSn≥0.65. Composition dependence of parabolic rate constant,
k, and the tendency of oxide film formation were dominated by
fOX determined by the enrichment of solute elements and crystal structures of precipitated oxides.
View full abstract