Effect of interaction zone on short-time breakdown of NanoAl₂O₃-epoxy composites

To investigate the interrelation of nano-composite dielectrics between electrical performance and microstructure, nanoAl₂O₃-epoxy composites are prepared by mechanical dispersion method. It is observed by SEM that nanoAl₂O₃ particles are well dispersed in epoxy matrix. The effects of nanoAl₂O₃ on dielectric response and breakdown of epoxy are studied by dielectric property test and breakdown examination. With the increasing filler loading, the dielectric constant decreases first and then increases, and reaches the lowest when the mass fraction of nanoAl₂O₃ gets 1%. The breakdown field strength has the opposite trend: it increases first and then decreases, and reaches the highest value of 43 400 V when the mass fraction of nanoAl₂O₃ gets 1%, increasing by 11.8% compared with pure epoxy. It is indicated that interaction zone between nanoparticle and epoxy matrix plays an important role in short-time breakdown. When the content of the particles is small, the thickness of interaction zone is less than the carriers' free path to block carriers to migrate, so the breakdown field strength increases. When the content increases, the overlapped interaction zone leads a lower breakdown field strength.