FORMATION OF A NEW ALUMINUM-OXIDE WITH THE COMPOSITION ALO2 BY INTERFACIAL REACTION BETWEEN PT AND ALPHA-AL2O3

A new aluminum oxide, with the nominal composition AlO2, very likely an aluminum peroxide oxide. was formed at the interface between Pt and alpha-Al2O3 diffusion-bonded in a reducing atmosphere at 1200-degrees-C. The structure, chemistry and kinetics of formation of AlO2 were characterized by X-ray fluorescence microanalysis, Rutherford backscattering spectrometry, forward recoil spectroscopy, X-ray diffraction, electron spin resonance, electron energy loss spectroscopy, X-ray photoelectron spectroscopy, optical microscopy, scanning electron microscopy, transmission electron microscopy and electron diffraction. Near bulk quantities of AlO2 were obtained for long bonding times; a 13 mum thick interlayer after 96 h at 1200-degrees-C. The thickness of the interlayer increased linearly with time indicating that the kinetics of the reaction are interface controlled. Based on electron diffraction and powder X-ray diffraction observations the structure of AlO2 was shown to be orthorhombic. It is suggested that a metastable oxide can form in direct contact with alpha-Al2O3 under a special set of conditions where the dissolution of Al into Pt provides a sufficient decrease in free energy to allow the oxidation of alpha-Al2O3, with very slow transport of oxygen away from the reaction front along the Pt-Al2O3 interface.