X-ray diffraction studies of oxidized high-palladium alloys

Abstract

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, CuGa 2O 4 and β-Ga 2O 3 were detected on the 79Pd-10Cu-9Ga-2Au alloy, whereas SnO 2 and CuGa 2O 4 were detected on the 79Pd-10Cu-5.5Ga-6Sn-2Au alloy. The oxide layers on both Pd Cu Ga alloys contained Cu 2O, and the oxide layer on the 76Pd-10Cu-5.5Ga-6Sn-2Au alloy may contain β-Ga 2O 3. The principal phase in the oxide layers on both Pd Ga alloys that had been polished and etched was In 2O 3, which exhibited extreme preferred orientation. No other phase was detected in the oxide layer on the 85Pd-10Ga-2Au-1Ag-1In alloy, whereas β-Ga 2O 3 was found in the oxide layer on the 75Pd-6Ga-6Au-6Ag-6.5In alloy. For the air-abraded specimens, β-Ga 2O 3 was not present in the oxide layers on the Pd Cu Ga alloys, and β-Ga 2O 3 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.