Nano dielectrics have brought hope for solving the problem of cable insulation at high voltage levels. In this paper, nano Al2O3 and MgO are doped to silicone rubber and the nanocomposites are aged at 200 °C for 0-80 days. The electrical conductivity and DC breakdown characteristics of aged materials are investigated. The microscopic and elemental properties are also analysis. It is found that with the increase of thermal aging time, electrical conductivity of all sets decreases first and then increases, while the DC breakdown voltage experiences a process of first increasing and then decreasing. During the initial aging process, secondary vulcanization of silicone rubber occurs, however, the cross-linked network degrades with further aging, which could explain the changes in electrical properties. The introduction of metal oxides could react with exfoliated radicals to form s table compounds, thus, the performance of Al2O3 and MgO doped materials have better electrical properties under thermal aging.
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