Dielectric breakdown of ceramics and glass ceramics

Discusses the AC dielectric breakdown of alumina, aluminium nitride and cordierite glass ceramics (MgO-Al₂O₃-SiO₂) at room temperature. The importance of specimen shape, thickness, surface finish and test conditions are assessed. For dielectric breakdown tests specimens were prepared in the form of 26 mm discs of various thicknesses (in the range 0.2-10.0 mm). In the case of alumina ceramics, plano-concave specimens were also prepared by diamond grinding one face to provide a curved surface (concave region 22 mm diameter, thickness at the centre 0.5-6.0 mm). The surface finish of the specimens ranged from as-received to 0.25 μm diamond polished