Research On The Impacting Factors Of DC Breakdown Strength Of 95 Alumina Ceramics

In recent years, The demand of ultrahigh vacuum tube shell has increased greatly by the great development of High-speed rail network and west-east electricity transmission strategy.But the gap between domestic and foreign level is large. The gap is mainly from two aspects:firstly the DC breakdown strength of domestic vacuum tube shell is too low, the high level of DC breakdown strength of domestic vacuum tube shell is about 32.9kV/mm, but the high level of DC breakdown strength of foreign vacuum tube shell is above 40kV/mm. Secondly the sintering temperature of domestic vacuum tube shell is on the high side. The sintering of domestic vacuum tube mainly proceeds in air atmosphere, which lead to high sintering temperature(about 1680 ℃). Foreign related enterprises have adopted special sintering methods that can reduce sintering temperature to 1530℃. The above two reasons cause 30 percents of consumption of domestic vacuum tubes are imported from abroad, and ultrahigh vacuum tube shells are all imported from abroad.The ultrahigh vacuum tube shell is a kind of 95 oxide alumina ceramics. According to improve DC breakdown strength of domestic vacuum tube shell as well as reduce the sintering temperature, this article has carried on the two aspect of the research. The first part is the study of the influence of the structure and properties of 95 oxide alumina ceramics affected by the liquid phase sintering additives,sintering temperature and alumina types.Through the orthogonal experiment method, the optimal level of liquid phase sintering additives is CaCO3+SiO2. In order to further improve the DC breakdown strength of 95 oxide alumina ceramics, the second part of this article takes CaCO3+SiO2 as the liquid phase sintering additives of the test samples. According to the orthogonal experiment method, the 95 oxide alumina ceramics with industrial alumina,0.75%wt CeO2,0.77%wt CaCO3,4.90%wt SiO2,0.30%wt ZrO2 and 0.45%wt MgO, sintering at 1630℃ has high DC breakdown strength,which can reach 57.6kV/mm.The experimental results show The grain size determine the DC breakdown way of 95 alumina ceramics, the DC breakdown strength of 95 alumina ceramics is decided by bulk density, dielectric loss and DC breakdown way. The 95 oxide alumina ceramics with thermal breakdown has higher DC breakdown strength. In order to form thermal breakdown, theaverage grain size and big grain size of 95 oxide alumina ceramics should be small. In order to improve the DC breakdown strength of 95 oxide alumina ceramics with thermal breakdown,reducing the dielectric loss is prior after the 95 oxide alumina gets a certain bulk density.