Papers by Keyword: Volatilisation

Abstract: To investigate the behaviour of oxidation and chromium volatilisation, AISI 430 stainless steel was oxidised in O₂-H₂O and Ar-CO₂-H₂O atmospheres for 96 h at 800°C with varying water vapour content. In the O₂-H₂O environment, the volatilisation rate of Cr and Mn increased as the water vapour content increased from 5% to 20%. In the case of Ar-CO₂-H₂O conditions, the presence of water vapour in the Ar-20%CO₂ environment reduced the oxidation rates of the steel. However, increasing the H₂O content in Ar-20%CO₂ had an insignificant effect on the oxidation rate. Water vapour was found to accelerate the volatilisation rate of Cr and Mn. Breakaway oxidation occurred in Ar-20%CO₂-40%H₂O, resulting in the highest volatilisation rates of Cr and Mn.

Abstract: Water vapour interacts with growing chromia scales in several different ways. Formation and volatilisation of Cr2O2(OH)2 is shown to account quantitatively for chromium loss from thin alloy foils reacted with air-steam mixtures over periods of 103 h. In the shorter term, water vapour is shown to refine the grain structure of Cr2O3 scales grown on Ni-25Cr. Scaling kinetics are at the same time accelerated by an additional, larger contribution to diffusion by a grain boundary species, either OH- or H2O. A slight increase in scaling rate observed at low water vapour partial pressures in H2/H2O gases is thought to be due to hydrogen doping.