Investigation of the oxidation of plasma sprayed silicon coating

The quality of plasma sprayed silicon coating determined by density and spreading condition of lamella greatly influences its performance. The oxidation of silicon coating deteriorates its performance. However, the investigators mostly focus on the oxidation and mechanism of amorphous silicon, porous silicon and specific crystal planes on single crystal. The factors which influence the quality and oxidation of silicon coating has never be studied. The helium secondary gas flow has more influence on the quality of silicon coating than other spraying parameters. So, we prepare the silicon coating by plasma spraying technology with different secondary gas flow. The relationship between silicon coating's quality and secondary gas flow is investigated. Furthermore, the oxidation of plasma sprayed silicon coating is discussed. We find that the secondary gas has an adverse effect on quality and oxidation degree of silicon coating. With the decrease of secondary gas flow, both quality and oxygen content of coatings increase. Besides, the oxygen atoms heterogeneously concentrate at the outermost layer of silicon lamellas. Components of oxygen enrichment area (OEA) from outside to inside are Si + SiO_x + SiO₂→Si + Si₂O + SiO₂→Si + SiO_x→Si (1<x < 1.5). The width of OEA in lamellas at top layer of silicon coating is about 180 nm, obviously thicker than that in inner lamellas. The results obtained from research can provide support to better understand the behavior of silicon coating in the service process.