OBSERVATIONS OF CHROMIUM-OXIDE FILMS CONTAINING CERIUM AND YTTRIUM USING TRANSMISSION ELECTRON-MICROSCOPY

Samples of a pure Fe-26%Cr alloy were sputter-coated with a 4-nm layer of CeO2 or Y2O3, then oxidized at 900 degrees C in 5x10(-3) torr of oxygen. The oxide scale was removed from the substrate by dissolution of the alloy substrate in a solution of iodine in anhydrous methanol and examined in a transmission electron microscope to determine the microstructure of the oxide and the phases present in the scab. The phases CeCrO3 (space group 62, Pnma and space group 221, Pm (3) over bar m), YCrO3 (space group 62, Pnma), and Y2O3 (space group 164, P (3) over bar m1) were found in the oxide scale in the initial stages of oxidation. The relevance of these species in the reactive-element effect is discussed.