Analysis of the Reactive Element Effect on the Oxidation of Ceria Doped Nickel

Abstract

The effects of external doping with CeO₂ on the oxidation of nickel have been evaluated. The materials studied were pure Ni and Ni with the surface doped with CeO₂ by pulsed laser deposition. The oxidation kinetics were measured using thermogravimetric analysis. The oxidation microstructures were observed by scanning electron microscopy and cross-sectional transmission electron microscopy. Compositional analysis was performed with energy dispersive X-ray analysis and sputtering neutrals mass spectrometry. Phase identification was performed using X-ray diffraction. Doping with CeO₂ resulted in a significant decrease in the NiO growth rate at intermediate temperatures, e.g. 800 °C. 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. The CeO₂ dopant did not reduce the growth rate at high temperature (1,300 °C). The results indicate that the CeO₂ dopant influences grain boundary transport in the NiO. Mechanisms are presented to attempt to describe the above observations.