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Reducing Cr<sup>6+</sup> emissions from gas tungsten arc welding using a silica precursor
Topham, Nate,Kalivoda, Mark,Hsu, Yu-Mei,Wu, Chang-Yu,Oh, Sewon,Cho, Kuk Elsevier 2010 Journal of aerosol science Vol.41 No.3
<P><B>Abstract</B></P><P>Hexavalent chromium (Cr<SUP>6+</SUP>) 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<SUP>6+</SUP> exposure reduction. Fume aerosol samples were analyzed for Cr<SUP>6+</SUP> concentration using ion chromatography (IC) and for total Cr by inductively coupled plasma with atomic emission spectroscopy (ICP-AES).</P><P>At high temperature, silica precursors are pyrolyzed to form amorphous silica (SiO<SUB>2</SUB>) 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<SUP>6+</SUP> 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<SUB>2</SUB> coating on metal particles, verifying the proposed mechanism.</P>
Decreasing biotoxicity of fume particles produced in welding process
Yu, Kuei-Min,Topham, Nathan,Wang, Jun,Kalivoda, Mark,Tseng, Yiider,Wu, Chang-Yu,Lee, Wen-Jhy,Cho, Kuk Elsevier 2011 Journal of hazardous materials Vol.185 No.2
<P><B>Abstract</B></P><P>Welding fumes contain heavy metals, such as chromium, manganese, and nickel, which cause respiratory diseases and cancer. In this study, a SiO<SUB>2</SUB> precursor was evaluated as an additive to the shielding gas in an arc welding process to reduce the biotoxicity caused by welding fume particles. Transmission electron micrographic images show that SiO<SUB>2</SUB> coats on the surface of welding fume particles and promotes particle agglomeration. Energy dispersive X-ray spectroscopy further shows that the relative amount of silicon in these SiO<SUB>2</SUB>-coated agglomerates is higher than in baseline agglomerates. In addition, <I>Escherichia coli</I> (<I>E. coli</I>) exposed to different concentrations of pure SiO<SUB>2</SUB> particles generated from the arc welding process exhibits similar responses, suggesting that SiO<SUB>2</SUB> does not contribute to welding fume particle toxicity. The trend of <I>E. coli</I> growth in different concentrations of baseline welding fume particle shows the most significant inhibition occurs in higher exposure concentrations. The 50% lethal logarithmic concentrations for <I>E. coli</I> in arc welding particles of baseline, 2%, and 4.2% SiO<SUB>2</SUB> precursor additives were 823, 1605, and 1800mg/L, respectively. Taken together, these results suggest that using SiO<SUB>2</SUB> precursors as an additive to arc welding shielding gas can effectively reduce the biotoxicity of welding fume.</P>