Improving the voltage holdoff performance of alumina insulators in vacuum through quasimetallizing

Treatment of the surface of an alumina insulator with coatings incorporating varying amounts of Cr, Mn, and Ti was examined for increasing the vacuum voltage holdoff capability of the insulator. During processing (quasimetallizing) the coating penetrates into the alumina, so it is insensitive to mechanical damage. The quasimetallizing treatment and the effectiveness of each metal and the metal mixes toward improving the voltage holdoff capability of alumina are reported. Quasimetallizing with appropriate formulations were shown to change the surface characteristics of alumina in two ways: it decreases the surface resistivity of the alumina, and it decreases the secondary electron emission yield of the alumina.