Fabricating a denser SiO2-CaO co-doped 95 wt% alumina ceramic to verify that small pores have no effect on the dielectric breakdown strength of alumina ceramics

To verify an increase in porosity due to small pores dose not reduce the dielectric breakdown strength (DBS) of alumina ceramics, we sinter a SiO2-CaO co-doped 95 wt% alumina ceramic via step-controlled atmosphere sintering (first sintering in oxygen, then sintering in air) and conventional sintering (sintering in air) to fabricate samples of different porosities. The dielectric breakdown (DB) test under an AC high voltage shows that the two samples have almost equal DBS in spite of different porosities. Microscopic analysis reveals that the conventionally sintered sample contains more small pores of size range 5–25 μm than the step-controlled atmosphere sintered sample, so the increase in the small pores does not reduce the DBS of the alumina ceramic. The partial discharge in the small pores does not occur before the DB of the alumina ceramic, and this is the reason why the two samples have equal DBS.