Mechanism of Surface Charge Regulation with Nonlinear Conductivity Coating in C4F7N/CO2 Mixture

The study of charge regulation mechanism in C4F7N/CO2 is of significant importance for advancing the applications of C4F7N/CO2. In this study, coating samples with varying SiC content were fabricated using conventional brush coating method, and the surface charge distribution of these samples under negative voltage was measured using a surface potential measurement system. The results revealed that in the absence of coating, the surface charge in C4F7N/CO2 exhibited bipolar distribution, with a large number of negative charges concentrated near the high voltage electrode and a small number of positive charges concentrated near the ground electrode. When coatings existed, the pattern of surface charge distribution changed. Under the same voltage, with the increase of SiC content, the maximum potential along the electrode centerline first increased and then decreased, reaching a decrease of 70.7% at 30% wt of SiC content, and charges on both sides of the electrode continuously increased. Through the measurement of coating material's conductivity and trap distribution characteristics, it was found that the coating material reduced the surface trap energy level, increased the trap density, and exhibited nonlinear conductivity characteristics. It is suggested that nonlinear conductivity played a role in equalizing the electric field, reducing the gas ionization in C4F7N/CO2. Lower trap energy level and higher conductivity will promote charge gas neutralization and accelerate surface conduction. The combined effect of both factors effectively suppresses the charge accumulation at the electrode front origin. However, the increased conductivity and trap density also promotes charge injection and charge-captured possibility, as a result of the lack of dissipation channels, the charges at both sides of the electrode increase with the increase of SiC content.