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 oxi de 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 segreg ation of impurities were also studied by X-ray photoelectron spectrosc opy and Auger electron spectroscopy. Textural properties and structura l orientation of both the primary oxide layer and the platelets were a nalyzed by X-ray diffraction and transmission electron microscopy. Pla telets grew along {111} planes, leading to elliptical or semicircular bicrystals. The driving force for the present type of growth originate s from the stresses accumulated in the thin, primary oxide layer. Impu rities do not directly interact with this growth, but enable a specifi c grain structure to be developed thereby favoring platelet growth.