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M: Metallphysik

M 26: Postersitzung

M 26.8: Poster

Donnerstag, 14. März 2002, 14:30–16:30, Saal C

Segregation of Oxygen at Internal Metal-Oxide Interfaces: Microstructure, Nanochemistry, Thermodynamics, and Kinetics — •Jürgen Gegner — Department of Material Physics, SKF GmbH, Ernst-Sachs-Str. 5, 97424 Schweinfurt

Metal-oxide interfaces are of great technical importance within the fields of dispersion hardening, nanostructured composites, coatings, and micro-miniature electronics (e.g. MOS-FET). Segregation of oxygen at these heterophase boundaries results in a modification of their chemical composition and can thus affect the material properties. A review of recent experimental studies on the systems Pd-MgO and Ag-MgO using quantitative volumetric measurements, electrochemical techniques, (high resolution) transmission electron microscopy, electron energy-loss spectrometry, and image analysis is presented. The varying oxygen coverage at the phase boundary is discussed in the frame of Langmuir-McLean isotherm-equations and a structural vacancy model [1,2]. As interfacial segregation within the matrix metal palladium predominantly occurs during sample cooling after sorption anneal, a diffusion-controlled kinetics model based on an analytical solution of Fick’s second law is proposed. The distribution of the oxide particles formed by internal oxidation is estimated by computer-aided image analysis [3] of TEM micrographs. For the perfect example system Pd-MgO, it is demonstrated that the results obtained agree well with sample cooling curves and concerning electrochemical data.
(1) X.Y. Huang, W. Mader, R. Kirchheim, Acta Met. 39, 893 (1991).
(2) E. Pippel, J. Woltersdorf, J. Gegner, R. Kirchheim, Acta Mater. 48, 2571 (2000).
(3) J. Gegner, A. Öchsner, Prakt. Metallogr. 38, 499 (2001).