The effect of minor elements on the growth and electrical properties of NiO on Ni

In this study, the effects of Cu additions and external doping with CeO2 on the oxidation of nickel were evaluated. The materials studied were pure Ni, Ni–5 wt.% Cu, and Ni with the surface doped with CeO2 by pulsed laser deposition (PLD). The oxidation kinetics were measured using thermogravimetric analysis (TGA). The oxidation microstructures were observed by scanning electron microscopy (SEM) with energy dispersive X-ray analysis (EDS). A 4-point probe was used to measure the area-specific resistance (ASR) of the NiO scales.The Cu additions had a negligible effect on the oxidation kinetics but Cu was found to be present in the outer portions of the scale in significant concentrations. Doping with CeO2 resulted in a significant decrease in the NiO growth rate. The scales on doped Ni grew primarily inward whereas those on the undoped Ni grew primarily outward. Deposition of the CeO2 dopant onto Ni with a thin, preformed NiO layer produced a similar reduction in the subsequent NiO growth rate. This suggests that the poisoned interface model, proposed by Pieraggi and Rapp, does not describe the effect of the CeO2 dopant. The ASR values decreased commensurate with the scale thicknesses indicating that there was insignificant doping of Ce+ 4 ions onto the Ni sublattice in the scales.Mechanisms are presented to attempt to describe the above observations and a theoretical model for calculating ASR is presented.