Study of dielectric properties of Si-B-Zr/SiO2/FPI composites

Due to the fact that the inter-turn insulation of frequency conversion motors is constantly subjected to harsh environments characterized by strong electric fields and high temperatures, higher requirements are imposed on the corona aging resistance and dielectric properties of inter-turn insulation materials. This study employed a hydrolysis–condensation method to prepare Si-B-Zr nano-oxide dispersion, which was then modified by doping with gas-phase SiO₂ to obtain Si-B-Zr/SiO₂ dispersion. Subsequently, 6FDA-type Si-B-Zr/SiO₂/FPI three-layer composite films were fabricated at different concentration gradients using in situ polymerization and dip-coating methods. The influence of Si-B-Zr/SiO₂ content on the corona resistance of the materials was systematically investigated, aiming to achieve excellent corona resistance while reducing the dielectric constant and dielectric loss. Experimental results demonstrated that compared with pure PI, the Si-B-Zr/SiO₂/FPI three-layer composite films with different doping amounts all exhibited significant improvement in corona resistance. In particular, the composite film with 10 wt% doping showed optimal performance under the test conditions of 155 °C and 80 kV mm⁻¹, with a corona resistance life reaching 8 h, which is 5.3 times that of pure PI and 3.6 times that of FPI. Meanwhile, this composite film displayed excellent dielectric properties, with a dielectric constant as low as 3.4 and a dielectric loss of only 0.0085 at operating frequency. © 2025 Society of Chemical Industry.