Effects of firings in hydrogen on the insulation performances of a 95 wt% alumina ceramic.

To investigate the effects of point defects on the insulation performances of alumina ceramics, we fire a 95 wt% alumina ceramic in wet hydrogen, dry hydrogen, and supplementary air, to change the concentrations of aluminum vacancy (V Al ‴) and oxygen vacancy (V O • • ). The dielectric breakdown strength (DBS) and flashover voltage (FV) are tested, and the point defects are characterized by XPS and optical reflectance. Firing in wet hydrogen decreases the concentration of V O • • , improving DBS but deteriorating FV. Nevertheless, firing in dry hydrogen increases the concentration of V Al ‴ , improving FV but deteriorating DBS. Supplementary firing in air weakens the effects of firing in dry hydrogen on the point defects and insulation performances. The effects of firings on insulation performances are attributed to the concentrations of electrical carriers that are determined by the point defects, and this is confirmed by the results of electrical resistivity. [ABSTRACT FROM AUTHOR]