Hydrogen pumping by austenitic stainless steel

In the present study, hydrogen sorption and desorption kinetics close to equilibrium were investigated in a pinched-off AISI 316 steel cell by a sensitive pressure-rise method. The pressure was monitored with a spinning rotor gauge (SRG) just before the pinch-off and after it for 6 months at two stabilized temperatures: 25 degrees C and 55 degrees C. The preprocessing of the cell (of uniform wall thickness 0.15 mm volume 125 cm(3), and inner surface 460 cm(2)) consisted of baking at 200 degrees C for 109 h with several evacuation cycles to ultrahigh vacuum (UHV). The quantity of released hydrogen during the bake-out procedure equaled the average concentration change Delta C=2.8 c 10(17) at. H cm(-3). After the pinch-off intentionally done in the high vacuum range where hydrogen represented the residual atmosphere, surprisingly the hydrogen pressure slowly declined from the initial p (328 K) = 3.7 x 10(-4) mbar, with an initial rate dp/dt = -5.5 x 10(-11) mbar/s and later attained a stable value, which could be termed the equilibrium. In similar reported experiments, where valving-off began in the UHV, the dp/dt was always positive and constant over several orders of magnitude in pressure. During 6 months of measurements,. a sudden temperature jump from 25 degrees C to 55 degrees C or back was applied a few times to investigate the stability of the equilibrium or the impact on the pressure course. The most plausible explanation of the results is given along with discussion whether hydrogen permeated through the cell wall or if it was absorbed in the cell wall. (c) 2005 American Vacuum Society.