Max Deibert

An Auger spectroscopic investigation of the high temperature reduction of zirconium dioxide surfaces in vacuum

Abstract The vacuum reduction of the ZrO 2 surface layer formed on oxygen-saturated zirconium has been investigated by Auger spectroscopy. Sputter-depth-profiles of the ZrO 2 layer show that its outer surface is reduced after exposure to UHV at 900 and 1100 K. The AES spectrum of Zr also evidences an increasing extent of partially reduced Zr on ZrO 2 surfaces as the UHV annealing temperature is increased from 800 to 1200 K. Quantitative Auger analyses of ZrO 2 surfaces show that the O/Zr surface atomic ratio remains near its stoichiometric value of 2 after UHV anneals at temperatures up to about 700 K. The surface O/Zr atomic ratio is about 1.1 after UHV annealing at 1000 K, with intermediate extents of surface reduction after UHV annealing between 700 and 900 K. This surface reduction occurs very rapidly and is essentially unaffected by extending the high temperature UHV anneal time from fractions of a min to 1 h. These observations provide support for a previously proposed mechanism for the catalytic reduction of CO by H 2 on ZrO 2 .

Investigation by Auger spectroscopy of the composition and surface oxidation characteristics of oxygen saturated zirconium

Abstract The surface oxidation characteristics of oxygen saturated zirconium (Zr:O ss ) have been investigated between room temperature and 1190 K using Auger spectroscopy and sputter-depth-profiling techniques. Zr:O ss substrates were prepared by absorbing oxygen from surface oxide layers into Zr foils at high temperature. Quantitative Auger analysis confirms that the composition of Zr:O ss is approximately ZrO 0.44 .Zr:O ss oxidizes slightly faster at room temperature than pure Zr during initial O 2 exposure. The high temperature surface oxidation of Zr:O ss was studied in the absence of interference from the simultaneous bulk absorption of oxygen, which occurs with pure Zr substrates. The thickness of the ZrO 2 surface layer formed on Zr:O ss increases with the extent of O 2 exposure, exposure time and oxidation temperature up to 900 K. Above 900 K the surface oxidation is not complete to ZrO 2 .

High-temperature mechanical behaviour of multidirectional Nicalon/CAS-II composite

High-temperature mechanical behaviour of Nicalon/CAS-II composite has been investigated. Oxidation of the exposed interfaces along matrix cracks at 1000 °C lowered the longitudinal unidirectional strength to the stress level at which matrix cracking began to occur. The strength of cross-plied composites was also severely reduced in 800 °C air. Transverse plies cracked prior to 0° ply matrix cracking. However, embrittlement did not occur until the matrix in the 0° plies cracked. It was established that oxidation does not take part in crack growth parallel to the fibres, except adjacent to exposed edges. Neither does oxygen enter 90° ply cracks in cross-plied composites in sufficient quantity to produce oxidation embrittlement, at least up to the 0° matrix cracking strain.

The surface composition and initial oxidation of zirconium-nickel intermetallic compounds at room temperature

Abstract The surface compositions of five sputter-cleaned zirconium-nickel intermetallic compounds (ZrNi 5 , Zr 2 Ni 7 , ZrNi 3 , ZrNi, and Zr 2 Ni) have been estimated by quantitative Auger analysis. The quantitative analysis was calibrated using Auger intensities measured on UHV fracture exposed alloy surfaces. The five sputter-cleaned alloys are slightly enriched in surface Zr relative to their bulk compositions. Their initial oxidation at room temperature is accompanied by the preferential surface accumulation of oxidized Zr. We have previously shown that the oxidation of Zr 2 Ni 7 , ZrNi 3 , and ZrNi at 673 K results in the preferential surface accumulation of oxidized Ni. This variation with temperature of the surface compositional stratification and preferential oxidation characteristics of Zr-Ni alloys can have a significant influence on their stability in oxidizing environments.