Comparative Study on Microstructure and Properties of Alumina and Bauxite Insulator for UHV

In this paper, the differences in composition, structure and mechanical properties of alumina and bauxite insulators for ultra high voltage (UHV) from two domestic manufacturers were systematically studied, and the reasons for the higher deterioration rate of bauxite insulator compared to alumina insulator were analyzed and summarized. The results show that for bauxite insulator, due to the use of calcined bauxite with high Fe₂O₃ and TiO₂ contents as high aluminum raw materials, the Fe₂O₃ and TiO₂ contents of the two bauxite insulators are 3.51% and 3.56%, respectively, which are more than three times that of the two alumina ceramics. (2) A certain amount of quartz raw material is added to the formula of alumina insulators, so the quartz phase content of the two alumina ceramics (6.29% and 7.00%, respectively) is significantly higher than that of bauxite insulators. In addition to primary mullite generated from metakaolinite (decomposition product of kaolin), and needle like secondary mullite precipitated from the aluminum rich feldspar melt, the mullite in bauxite insulators also comes from calcined bauxite raw materials, therefore, the mullite content of bauxite insulators (12.59% and 14.91%, respectively) is higher than that of alumina ceramics. (3) The true porosity of the two bauxite insulators is 10.62% and 9.62%, respectively, which is significantly higher than that of alumina insulators. (4) The average value of the three-point bending strength of bauxite insulators is 140 MPa and 148 MPa, respectively, which are more than 20 MP lower than that of alumina insulators, and the strength dispersion are greater. The flat, slender, cracked, aggregated, and interconnected pores, as well as uneven structures such as porous corundum aggregates and coarse prismatic mullite aggregates, exist inside bauxite insulators, which are the fundamental reasons for their low strength, high dispersibility, and high deterioration rate.