Role of fluorinated h-BN in enhancing electrical breakdown voltage and stability of transformer oil

This work is a maiden attempt to investigate the role of fluorinated boron nitride nanosheets (f-BNNs) in monitoring electrical properties of transformer oil (TO). Ultrathin (~5 nm) f-BNNs of 100–500 nm width were obtained by exfoliating pristine h-BN using NH 4 F. The exfoliation resulted in attaching few electronegative fluorine (F) to boron atoms and converted h-BN from insulator to semiconductor. TO nanofluids (NFs) at 0.005 wt. % of f-BNNs showed ~27 % surge in AC breakdown voltage (BDV) (validated by Weibull statistics), high volume resistivity and excellent stability, superior than h-BN nanosheets or BN nanoparticle. The leap in the electrical insulation was explained due to the fluorination assisted reduction in charge relaxation time from 60 ms–30 s in h-BN to 63 μs–0.6 s in f-BNNs, higher degree of streamer charge scavenging in the electrical double layers (EDLs) and interfacial polarization at the large oil-nanofiller interface. A theoretical calculation yielded in a potential depth of 13.8 V and 19.5 V at h-BN and f-BNNs surface, respectively, which implied f-BNNs provided a huge potential barrier and propagation delay to the streamer charges. Finally, the superior stability of f-BNNs in TO with time and temperature was observed from multiple tests and was explained owing to its 2D morphology, lipophilicity, and F induced large natural electrostatic repulsion between the nanosheets. Such excellent responses at low filler fractions recommends f-BNNs as a better alternative among all reported BN brothers for future TO applications. Graphical abstract