Improving insulating performance of alumina ceramic in vacuum through surface modification

It is experimentally testified that the voltage hold-off capability of alumina in vacuum is usually less than that of a similar-sized vacuum gap and also is far below its bulk breakdown strength. In this work, both bulk doping and surface coating were taken into consideration to modify the surface of 95%alumina in hope to improve its insulating property in vacuum and satisfying results were achieved. The as-blended 95% alumina powder was selected as initial powder to be doped with oxides combination such as MnCO₃, Cr₂O₃, MgO and TiO₂ separately or assembly. Conventional manufacturing procedures were applied for preparing all ceramic samples. Cr₂O₃ and Cu₂O were selected as main ingredient separately to be coated on 95% alumina samples with different shapes. Samples doped with proper Cr₂O₃ and MgO and those doped with proper MnCO₃ and Cr₂O₃ were found to possess higher surface hold-off voltage than original 95% alumina. It was point out through properties measurements that proper bulk doping and surface coatings were effective to reduce both the secondary electron emission (SEE) coefficient and surface resistivity of 95% alumina and so to enhance its surface insulating ability.