The high thermal conductivity epoxy resin composites filled with inorganic filler can improve the low thermal conductivity of epoxy resin. However, a large number of fillers with high thermal conductivity will reduce other properties of the composites, which limits their use under high voltage, high temperature and strong mechanical force during operation. In this study, the dopamine-modified BN (DBN) and k-DBN (DBN modified by coupling agent KH-560) were prepared by employed the dopamine with catechol groups and coupling agent to modify boron nitride. The thermal conductivity, thermal stability, and dielectric properties of composites with different contents of modified fillers were studied. The results showed that surface modification improved the dispersibility of BN in the resin matrix and compatibility with the resin. Among BN/EP, DBN/EP, k-DBN/EP composites, k-DBN/EP composites had the highest thermal conductivity at the same number of additions. When the k-DBN/EP content was 30 wt%, the thermal conductivity of the composite was 0.892 W/(mÁK), which was an increase of 25.5% compared with the BN/EP composite. The appropriate amount of BN filling (20 wt%) can improve the breakdown strength of the composite material.

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As the surface conditions play a significant role on corona discharge and its related effects of the conductors, the influence of fine particulate matter on positive‐polarity, direct‐current conductors was studied experimentally in this study. The surface morphologies of the conductor could be discovered from the experiments. The typical morphologies are the parallel chains of particles. To evaluate the surface condition quantitively, the surface roughness of the conductors is measured. It is found that the applied voltage and testing time have a great influence on the surface condition. After that, the corona characteristics of conductors are tested. It reveals that the total ground level electric field and ion flow density increases with the surface roughness growing.

Orderly arranged Silicon carbide (SiC)/epoxy (EP) composites were fabricated. SiC was made magnetically responsive by decorating the surface with iron oxide (Fe3O4) nanoparticles. Three treatment methods, including without magnetization, pre-magnetization and curing magnetization, were used to prepare SiC/EP composites with different filler distributions. Compared with unmodified SiC, magnetic SiC with core-shell structure was conducive to improve the breakdown strength of SiC/EP composites and the maximum enhancement rate was 20.86%. Among the three treatment methods, SiC/EP composites prepared in the curing-magnetization case had better comprehensive properties. Under the action of magnetic field, magnetic SiC were orderly oriented along the direction of an external field, thereby forming SiC chains. The magnetic alignment of SiC restricted the movement of EP macromolecules or polar groups to some extent, resulting in the decrease in the dielectric constant and dielectric loss. The SiC chains are equivalent to heat flow channels, which can improve the heat transfer efficiency, and the maximum improvement rate was 23.6%. The results prove that the orderly arrangement of SiC had a favorable effect on dielectric properties and thermal conductivity of SiC/EP composites. For future applications, the orderly arranged SiC/EP composites have potential for fabricating insulation materials in the power electronic device packaging field.