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Kinetics of Oxidation Processes in the System Co/Ga studied by in situ X‐Ray Diffraction
Author(s) -
Koops Ulrich,
Martin Manfred
Publication year - 2003
Publication title -
zeitschrift für anorganische und allgemeine chemie
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.354
H-Index - 66
eISSN - 1521-3749
pISSN - 0044-2313
DOI - 10.1002/zaac.200300141
Subject(s) - intermetallic , gallium , oxide , materials science , cobalt , kinetics , diffusion , partial pressure , metal , activation energy , diffraction , analytical chemistry (journal) , crystallography , chemistry , oxygen , metallurgy , thermodynamics , physics , quantum mechanics , optics , organic chemistry , alloy , chromatography
Oxidation processes in the system Co/Ga were studied by in situ X‐ray diffraction at temperatures between 800 and 1000 °C. Experiments were performed with metal powders and planar substrates. Oxidation of cobalt‐rich alloys, Co 1‐x Ga x , results in the formation of mixtures of cobalt‐ and gallium‐containing oxides. During oxidation of the intermetallic compounds CoGa and CoGa 3 only gallium is oxidized, and dense tarnishing layers of β‐Ga 2 O 3 are formed. In all cases the oxide products are only intermediate products on the way to thermodynamic equilibrium, i.e. total oxidation of both metals. The kinetics during oxidation of the intermetallic compound CoGa was studied in detail by time resolved in situ X‐ray diffraction. After an induction time the kinetics can be described by a parabolic rate law with an activation energy of 312 kJ mol —1 . From the decrease of the parabolic rate constant with decreasing oxygen partial pressure and the observation of pore formation at the metal‐oxide interface it can be concluded that (i) outward diffusion of Ga‐ions through β‐Ga 2 O 3 is the rate determining step during this solid state reaction, and (ii) Ga‐ions are mobile by means of gallium vacancies.