On the effects of surface coatings on the high-temperature oxidation of nickel

Ni and Ni coated with superficial oxide coatings including SiO2, CeO2 and La2O3 have been oxidized in the temperature range 500-1200 degreesC in 10(-4)-1 atm oxygen. The oxidation kinetics and the surface kinetics have been determined, and the microstructure and the composition of the oxide coatings and the thermally grown NiO scales have been characterized by a range of different microscopy and spectroscopy techniques. At 800-900 degreesC, the coatings decrease the oxidation rate by approximately one order of magnitude. The oxide coatings increase the relative growth inside the scale compared to uncoated Ni. Still, the major growth mechanism is governed by outward Ni diffusion, which indicates that the reason for the improved oxidation resistance is due to a decrease in the overall outward flux of Ni across the scales. (C) 2003 Elsevier Science Ltd. All rights reserved.