THE GROWTH OF OXIDE PLATELETS ON NICKEL IN PURE OXYGEN .2. SURFACE-ANALYSES AND GROWTH-MECHANISM

The structural properties of Nio platelets emerging from a primary oxide layer by oxidation of pretreated nickels in pure oxygen between 650 and 800-degrees-C have been investigated in relation with the initial metallic layers and the primary oxide. Surface composition and segregation of impurities were also studied by X-ray photoelectron spectroscopy and Auger electron spectroscopy. Textural properties and structural orientation of both the primary oxide layer and the platelets were analyzed by X-ray diffraction and transmission electron microscopy. Platelets grew along {111} planes, leading to elliptical or semicircular bicrystals. The driving force for the present type of growth originates from the stresses accumulated in the thin, primary oxide layer. Impurities do not directly interact with this growth, but enable a specific grain structure to be developed thereby favoring platelet growth.