Nonlinear Electrical Conductivity and Thermal Conductivity of g-C3N4/Liquid Silicone Rubber Field Grading Composites

The uneven electric field in cable accessory insulation can be optimized by field grading composite (FGC). We explored graphitic carbon nitride (g-C3N4) as a filler in liquid silicone rubber (LSR) matrices. Oxygen-doped g-C3N4 (O-g-C3N4) was prepared via calcination of g-C3N4 with ascorbic acid. Composites of g-C3N4/LSR and O-g-C3N4/LSR with different filler contents were fabricated. Microstructural and optical characterizations demonstrate that O-g-C3N4 retains the crystal structure of pristine g-C3N4 but exhibits thinner layers, modified elemental composition, and a 27.8% reduction in band gap; fillers are uniformly dispersed in the LSR matrix. Experimental measurements reveal that both composites exhibit nonlinear conductivity, while O-g-C3N4/LSR shows more pronounced nonlinearity at lower filler contents, accompanied by a faster decline in dielectric breakdown strength. There is little difference in thermal conductivity between g-C3N4/LSR and O-g-C3N4/LSR composites with the same filler content, which indicates that the change in band gap width has no significant influence on thermal conductivity. The low-cost synthesis and simple bandgap tuning method of g-C3N4 provide certain advantages for its use as a nonlinear filler in the preparation of FGC, broadening the application fields of g-C3N4, and verifying the possibility of reducing FGC filler usage through bandgap tuning.