Preliminary exploration of the electrical insulation performance of APPJ SiO2 coating on 304 stainless steel pipes

Abstract

The atmospheric pressure plasma jet (APPJ) technique is used to prepare SiO2 insulation coatings onto the outer surface of 304 stainless steel pipes (304-SSPs). The diameter and surface roughness of 304-SSPs increase from 18 to 32 mm and 0.1 to 1.0 μm. The results show that APPJ scanning methods have little influence on the chemical composition, chemical bond structure, crystal structure, and surface morphology of SiO2 coatings, which display Si/O = 1/(1.95 ± 0.02), dominant Si-O bond, amorphous structure, and dense layer structure. However, APPJ scanning methods have obvious influence on the uniformity and electrical insulation resistance (REI) of SiO2 coatings. Only when APPJ is parallel to the normal direction of 304-SSPs outer surface, the balance between APPJ impingement, gravity, and coating surface tension could reach the optimal condition, which improves the uniformity and REI of SiO2 coatings. With the optimal scanning method, REI of SiO2 coatings decrease with the increase of surface roughness of 304-SSPs, which are caused by the decrease of effective thickness of SiO2 coatings. Most importantly, with the other parameters as constant, REI of SiO2 coatings reaches to ∼101 MΩ and displays the better uniformity when the diameter of 304-SSPs is about 5 times the diameter of APPJ tube.