X-ray diffraction studies of oxidized high-palladium alloys

Objective. The purpose of this study was to use x-ray diffraction (XRD) to obtain new information about the oxide layers on four representative oxidized high-palladium alloys. Methods. Cast specimens of two Pd---Cu---Ga alloys and two Pd---Ga alloys, with both polished and etched surfaces and air-abraded surfaces, were subjected to oxidation procedures recommended by the manufacturers. The specimens were analyzed by x-ray diffraction using CuKα radiation, and the peaks were compared to appropriate Joint Committee on Powder Diffraction Standards (JCPDS). Results. The surface preparation procedure had a profound effect on the phases present in the oxide layers. For the specimens that had been polished and etched, CuGa2O4 and β-Ga2O3 were detected on the 79Pd-10Cu-9Ga-2Au alloy, whereas SnO2 and CuGa2O4 were detected on the 79Pd-10Cu-5.5Ga-6Sn-2Au alloy. The oxide layers on both Pd---Cu---Ga alloys contained Cu2O, and the oxide layer on the 76Pd-10Cu-5.5Ga-6Sn-2Au alloy may contain β-Ga2O3. The principal phase in the oxide layers on both Pd---Ga alloys that had been polished and etched was In2O3, which exhibited extreme preferred orientation. No other phase was detected in the oxide layer on the 85Pd-10Ga-2Au-1Ag-1In alloy, whereas β-Ga2O3 was found in the oxide layer on the 75Pd-6Ga-6Au-6Ag-6.5In alloy. For the air-abraded specimens, β-Ga2O3 was not present in the oxide layers on the Pd---Cu---Ga alloys, and β-Ga2O3 was the major phase in the oxide layers on the Pd---Ga alloys. Palladium oxide(s) in varying amounts were detected for both surface preparations of the Pd---Cu---Ga alloys and for the air-abraded Pd---Ga alloys. Except for the 76Pd-10Cu-5.5Ga-6Sn-2Au alloy, the oxide layer caused minimal change in the lattice parameter of the palladium solid solution compared to that for the as-cast alloy. Significance. Knowledge of the phases found in the oxide layers on these high-palladium alloys is of fundamental importance for interpreting differences in the adherence of dental porcelain to the metal substrates under static and dynamic conditions, and may provide guidance in the development of new high-palladium alloys with improved metal-ceramic bonding.