TiO2/Al2O3-Al2O3-TiO2/Al2O3绝缘结构的真空沿面闪络特性

基于变插入层介电常数的多层绝缘结构能改善电场分布、提高真空沿面闪络特性.通过真空热压烧结制备了TiO2/Al2O3-Al2O3-TiO2/Al2O3(A-B-A)3层绝缘结构,A层w(TiO2)为0.5%到20%.测量了该绝缘结构的真空沿面闪络特性,发现闪络特性随w(TiO2)的增加而提高,当w(TiO2)为20%时,其脉冲初次闪络电压较同等厚度的Al2O3陶瓷提高了63%.研究发现:A层的介电常数可由w(TiO2)调控,介电常数的增大能有效降低真空-绝缘子-阴极三结合点处的电场强度;A层表面存在的TiO2颗粒可以减小二次电子发射系数并改善表面电荷分布;TiO2的电导率虽比Al2O3高,但其仍为绝缘体,即使TiO2含量较高时也不会形成贯穿的导电通道.

Surface Flashover Performance of TiO2/Al2O3-Al2O3-TiO2/Al2O3 Insulation System in Vacuum

For the fact that inserting permittivity-gradient multilayer insulation reduces electric field and improves the characteristics of surface flashover in vacuum,a new insulation system of TiO2/Al2O3-Al2O3-TiO2/Al2O3(A-B-A) is designed by vacuum hot-pressing sintering,where the mass fraction of TiO2 in layer A was managed from 0.5% to 20%.Then the surface flashover voltage of samples in vacuum are experimentally investigated.It is found that the flashover voltage is increased with the additions of TiO2,and when the mass fraction of TiO2 reaches to 20% the flashover voltage is improved by 63% compared with the Al2O3 ceramic.The results reveal that the permittivity of TiO2/Al2O3ceramic is changed by different additions of TiO2,and the increasing permittivity weakens the electric field at triple junction.The TiO2 existing on the surface of layer A reduces the secondary electron emission coefficient and perfects the surface charge distribution.It is also concluded that even if the conductivity of TiO2 is higher than Al2O3 and the mass fraction of TiO2 gets larger,but no throughout conductive path generates due to the insulation essentiality of TiO2.