The Influence of Carbonyl Sulphide on the Inhibition of Filamentary Carbon Deposition on Stainless Steel

This paper examines the role that COS plays in the inhibition of carbon deposition onto a Si-free 20Cr-25Ni-Nb-stabilized austenitic stainless steel. We have shown that the addition of just 240 vppb of COS to a standard gas deposit mixture of high carbon activity (1000 VPPM C2H4, 1% CO, balance CO2) yields a dramatic fall in the amount of filamentous carbon deposited. The inhibitive effect persists when treatment is continued after COS has been subsequently removed from the treatment gas. Clearly, in these experiments the phenomenon is a result of substrate surface modification by the COS rather than changes in gas phase kinetics. Deposition onto surfaces where filamentous carbon has already been laid down is similarly inhibited.