Correlation of the surface composition of degassed 347 stainless steel with thermally desorbed H2 and CO

Variations in the surface composition of stainless steel after a 24 h, 250 8C bakeout over the temperature range of room temperature to 800 8C have been correlated with desorption of H2 and CO. The surface composition of the 347 stainless steel was monitored by Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) and desorption kinetics were determined from temperature desorption spectroscopy (TDS). Non-linear TDS was used to resolve the surface hydrogen from the bulk hydrogen. H2 and CO were observed to desorb from degassed 347 stainless steel by second-order kinetics, i.e., the gases were generated from atoms at the surface. The oxygen exchange from the surface CrxOy, FexOy to the residing carbon in the surface complex appears to control the CO generation. The onset of H2 desorption occurred slightly ahead of the CO, reached a maximum almost simultaneously ( 420 8C) and then declined in concert with the AES detected surface C and O. Non-linear TDS applied to large, cylindrical samples of 347 stainless steel showed H2 and CO surface desorption completely resolved from H2 bulk desorption. The steady state hydrogen desorption rate following the bakeout is bulk diffusion limited and was found to be 5:6 10 12 Torr l/(s cm2). Some discussion of the surface complex stress on the aforementioned oxide decomposition with temperature is also presented. Similar experiments on 304L stainless steel gave the same results as were observed on 347 stainless steel. # 2004 Elsevier B.V. All rights reserved