Reducing Cr 6+ emissions from gas tungsten arc welding using a silica precursor

Abstract

Hexavalent chromium (Cr 6+) emission from stainless steel welding operations poses a serious threat to worker safety and ambient air quality. In this study, tetraethyloxysilane (TEOS) was used as a silica precursor additive to welding shield gas during gas tungsten arc welding (GTAW) operations to determine the feasibility of using these chemicals for Cr 6+ exposure reduction. Fume aerosol samples were analyzed for Cr 6+ concentration using ion chromatography (IC) and for total Cr by inductively coupled plasma with atomic emission spectroscopy (ICP-AES). At high temperature, silica precursors are pyrolyzed to form amorphous silica (SiO 2) which can condense on the existing metal aerosols. The inert silica layer surrounding the aerosols can prevent further chromium oxidation by insulating chromium aerosols. Experimental results showed approximately 45% Cr 6+ reductions when 3.0% TEOS was added to the shield gas. Nitrate concentration also decreased by 53%, indicating that reactive oxygen species were also reduced. Transmission electron microscopy (TEM) images of collected fume aerosols showed SiO 2 coating on metal particles, verifying the proposed mechanism.