Oxidation of two high-palladium PFM alloys

Formation of an oxide layer at the alloy surface is important as to porcelain/alloy bonding. In this study the influence of oxygen pressure as well as oxidation temmperature and time on the oxide formation of 2 high-palladium PFM alloys was investigated. Tested were OL (Pd, Cu, Ga, In, Sn and Au) and OS (Pd, In, Sn, Cu, Ga and Co). After oxidation (1–10 min, vacuum/air, 940–1020°C) the oxides were removed selectively by means of leaching in 37% HCl. Concentrations of the metallic parts of the oxide layers were determined by means of an emission spectrometer. Oxygen in the oxide layer and the alloy were computed from weight changes during oxidation and leaching. PdO content decreased with increasing oxidation time. Higher oxidation temperatures gave less PdO in case of OL. These phenomena may be explained on the basis of the relatively low decomposition temperature of PdO. The components In and Ga oxidize preferentially. In both cases approximately twice as much as oxide is found in the oxide layer compared to a non-preferential oxidation model. Copper and tin oxide formation is 30–40% less in comparison with the non-preferential situation. In case of OS Co is oxidized preferentially 2.5 times the amount computed for the non-preferentially oxidizing alloy. The Influence of Co on the oxide formation is such that it suppresses the oxide formation of Cu relative to Ga, as well as the formation of SnO₂.