A Thin Passivating Tin(Ⅳ) Oxide Layer on Tin(Ⅱ)-Containing Fluoride Particles, or not? The M_(1-x)Sn_xF_2 Solid Solutions

摘要

Tin-119 Mossbauer spectroscopy shows that all powdered tin(Ⅱ) compounds give a small tin(Ⅳ) signal that has been attributed to the presence of a very thin layer of SnO_2 on the surface of the particles, that passivates against further oxidation, and is undetectable by X-ray diffraction. In a new development of this work, efficient passivation against further oxidation of the M_(1-x)Sn_xF_2 (M = Ca and Pb) solid solution poor in tin was found to be as high as for phases rich in tin, even though the amount of tin is way too low to be able to produce full coating of the particles by a thin layer of SnO_2. This observation required developing a new model to explain the sluggish oxidation of phases poor in tin, based on bonding type and strength.