Enhancing Surface Insulation Performance of Ceramic for Spark Plug by APPJ Treatment

Carbon fouling readily occurs on insulating ceramic surfaces of spark plugs due to high polarity, leading to decreased resistance, increased leakage current, and smaller ignition power. In this study, a silicon-oxide film is deposited on ceramic with an Ar/polydimethylsiloxane (PDMS) atmospheric pressure plasma jet (APPJ) to reduce surface polarity and increase surface resistance. The relationships between PDMS flow rate and surface performance, including surface polarity, surface resistance, leakage current, and flashover voltage, are obtained by varying the PDMS flow rate from 0 to 30 mL/min. Surface physiochemical characteristic variations of treated ceramics are analyzed to investigate the mechanism for surface performance enhancement. The results indicate that the optimal surface performance is obtained at a PDMS flow rate of 18 mL/min, with increased surface resistivity by 12.6 times, decreased polarity by 91.8%, and increased flashover voltage by 19.7%. Under optimal PDMS flow, a micro-/nano-double-scale structured film with low-polar Si-containing groups is deposited on the surface, introducing deep traps that enhance the surface charge binding and increase the surface resistance.