High-Temperature Corrosion of AISI 316L in Chlorosilane Environments at 550°C

Abstract

High temperature chlorosilane gas streams are used throughout the photovoltaic, polycrystalline silicon, and fumed silica industries as a means to purify, refine, and produce silicon species. These gas streams create a unique corrosion environment due the ability of many metals to form metal-silicides or metal-chlorides depending on the atmosphere. In this study, a method was developed to test AISI 316L stainless steel in a high temperature (550°C) chlorosilane environment by exposing the samples to variable amounts of hydrogen, hydrogen chloride (HCl), and silicon tetrachloride (STC). In this method, the mole fraction of HCl was adjusted to investigate when the transition from silicide formation to chloride formation occurs. Gravimetric and surface analysis was performed before and after exposure, revealing that without any HCl in the system, there was predominately metal silicide formation. As the HCl mole fraction was increased up to about 0.027, there was increasing metal chloride formation and decreasing silicide formation. Above an HCl mole fraction of 0.027, there was predominately chloride formation. The silicide formation was accompanied with a net mass gain due to the relatively low vapor pressure of iron silicide and nickel silicide species. Chloride formation was accompanied with a net mass loss due to the reactive evaporation of iron, nickel, and some chromium with chlorine. Lastly, the implications of this study as they relate to industrial processes are discussed.