Mossbauer spectroscopy investigations of the oxidation of alpha2-Sn and beta -Sn types of structure at room temperature

The initial oxidation of two groups of tin structures with different chemical bindings, designated as alpha 2 -Sn type and beta -Sn type, simultaneously grown by different electrochemical reductions is investigated by Mossbauer spectroscopy, and partly by X-ray photoelectron spectroscopy. It is shown that during the growth process the tin types become oxidized either to a mixture of tin(II) and tin(IV) oxides, or to tin(IV) oxides, but that the later oxidation in air at room temperature, monitored by periodic Mossbauer studies, is always to tin(IV) oxides. The kinetic results show that the mechanisms of oxidation of the two tin types are almost identical and that, if there is some difference, as suggested by parallel electron diffraction studies, it is beyond the sensitivity of the method. The oxidation of the tin types is a two-stage process, with a very large initial rate of oxidation, which decreases after aging for 1 or 2 months. Numerical equations describing parts of the oxidation curves are derived. The influence of impurities on the oxidation process is discussed.