Platinum-a non-inert material reacting with oxides

Platinum is a non-inert material which reacts with oxides when in contact at high temperatures. The degree of such reactions depends strongly on the oxygen partial pressures established in the environment of the Pt-oxide reaction couple. If the oxygen partial pressure is decreased, oxygen is released due to (i) the dissolution of metallic components of oxides into Pt and (ii) changes in the oxide stoichiometry. This oxygen release leads to a decrease in the mass of the Pt-oxide system. Often, this mass change is primarily caused by reaction (i), whereas the contribution from reaction (ii) is insignificant, especially at low oxygen partial pressures and if the Pt/oxide mass ratio and the occurring oxide stoichiometry changes are small. The degree of dissolution of metallic components of oxides into Pt increases with decreasing oxygen activity. The Pt-oxide systems discussed in this article are Pt-ZrO2, Pt-NiO, and Pt-FeOx. For the first two systems experimental data are presented and analyzed thermodynamically. For the Pt-FeOx system results of thermodynamic calculations are discussed and compared with experimental data from the literature. Several consequences arising from the dissolution of metallic components of oxides into Pt are also discussed.