日本金属学会誌

J. Japan Inst. Metals, Vol. 49, No. 9 (1985),
pp. 701-706

119Sn Mössbauer Study on Internally Oxidized Au-Sn Alloy

Isao Tanaka1, Saburo Nasu2 and F.~Eiichi Fujita2

1Graduate Student, Osaka University, Toyonaka
2Department of Material Physics, Faculty of Engineering Science, Osaka University, Toyonaka

Abstract:

Mössbauer spectra of 119Sn nuclei have been measured for an Au-2.0 at%Sn alloy annealed in air at temperatures between 673 K and 1073 K. An internally oxidized phase was observed and determined to be SnO2. The internal oxidation process was discussed by the changes in Mössbauer spectra and their parameters. The results are summarized as follows:
(1)  The oxide phases formed during the internal oxidation process were found to be only SnO2, in which the 119Sn isomer shift Δ SI=0.02±0.04 mm/s relative to BaSnO3, and the magnitude of quadrupole splitting Δ EQ=0.49±0.02 mm/s.
(2)  By annealing in H2 gas flow for 1.8 ks at 1123 K, the oxide was completely reduced and Sn atoms dissolved into Au matrix.
(3)  The oxide phase was localized near the specimen surface within the depth of 0.8 μ m. No preferential oxidation along grain boundary was observed.
(4)  During a short-period annealing, the formation of oxide proceeded with the internal oxidation, the rate of which was controlled by the diffusion of oxygen in Au matrix. Dependence of the oxidation process on the annealing temperature was of the Arrhenius type, and its activation energy was obtained to be 0.49±0.07 eV. After annealing at 973 K for 0.6 ks, transition from the internal to the external oxidation occurred, and the oxidation rate was sharply diminished.
(5)  Using Wagner's theory for the internal oxidation, the sum of EOS, the heat of solution for oxygen in Au and EOD, the activation energy of diffusion for oxygen in Au, were determined. The obtained value of EOS+EOD, 1.2±0.1 eV, suggests that the mechanism of diffusion of oxygen in Au is the same as in Cu and Ag.


(Received 1985/4/15)

Keywords:

119Sn Mössbauer spectroscopy, gold-tin alloy, internal oxidation, external oxidation, oxidation mechanism, tin-oxide, oxygen diffusion


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