Corrosion of ruthenium dioxide hydrate by CeIV ions and other oxidants

Abstract

A ‘test system’ has been developed in order to investigate the corrosion stabilities and O₂-catalytic activities exhibited by samples of RuO₂·xH₂O when exposed to a strong oxidant such as Ce^IV ions. The RuO₂·xH₂O samples included commercial powders as well as one prepared in the laboratory. The majority of these samples, including the prepared samples, were unstable towards anodic corrosion (≈ 86% corrosion) and showed little O₂ catalytic activity (O₂ yields 8%). The small amount of O₂ evolved was believed to originate from water bound in the oxide powder. These RuO₂·xH₂O samples appeared, from thermogravimetric analysis (t.g.a.) and differential gravimetric analysis (d.t.g.a.) measurements, to be highly hydrated (H₂O content = 24–26%). A minority of commercial RuO₂·xH₂O powders, when analysed by t.g.a. and d.t.g.a., were found to be in a partially dehydrated form (H₂O content = 18%). These samples showed a much greater resistance towards corrosion (9–13% corrosion) and were able to mediate the oxidation of water (O₂ yield = 92%) by Ce^IV ions. The corrosion of RuO₂·xH₂O by other oxidants, e.g. BrO^– ₃, MnO^– ₄ or PbO₂, was also studied and the results are discussed. The implications of these findings are considered.