INFLUENCE OF CEO2-COATING ON THE HIGH-TEMPERATURE OXIDATION OF CHROMIUM

The reactive-element effect on high-temperature oxidation of chromium metal was studied at oxygen pressures of 10(5) Pa (1 atm) and 0.67 Pa and at temperatures of 800 and 1050 degrees C under both isothermal and cyclic conditions. The reactive element, cerium, was applied as a cerium-oxide coating by sol-gel deposition. Growth and adherence of the chromia scale on the metallic substrate were investigated by kinetic weight-gain measurements, and the microstructure was characterized by scanning electron microscopy, transmission electron microscopy, EDX-analysis, X-ray diffraction, and Auger analysis. The study of the oxidation kinetics under isothermal conditions at 800 degrees C clearly showed a reduction in the growth rate of the oxide film when cerium oxide was present. Improvement of the oxide-scale adhesion was also observed when ceria-coated chromium was subjected to thermal cycling. The applicability of a number of models which have been used to explain the reactive-element effect is discussed