Transport Properties of Metal Oxides in the Presence of Sulfur.
Final scientific rept. 1 Jan 75-31 Dec 77,
GENERAL ELECTRIC CORPORATE RESEARCH AND DEVELOPMENT SCHENECTADY N Y
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The electrical conductivities of polycrystalline NiO, single crystal NiO, and single crystal CoO were measured to determine 1 the effect of SO2 in O2 - SO2 mixtures on conductivity, and 2 the effect of exposure to SO2 on defect diffusivity. Only the single crystal oxides proved to be satisfactory for measurement. Small conductivity increases of the order of 1 were found on exposure to SO2. Diffusivity measurements agreed well with literature values for sulfur-free specimens, and indicated the presence of a sulfur-induced defect having a diffusivity no more than an order of magnitude less than that of cation vacancies in specimens that had been exposed to SO2. Mechanisms that might cause an increase in sulfur activity or chemical potential during oxidation of metals are considered. A sulfur-induced defect consisting of S ions on cation sites is postulated as being consistent with the observations, and it is shown that such a defect can lead to an increase in sulfur activity at the metaloxide interface of a growing oxide. Supplementary thermogravimetric measurements indicated a sulfur solubility in CoO of about 0.05 mole percent. Author
- Physical Chemistry
- Solid State Physics