HYDROGEN DESORPTION BEHAVIOR OF ALUMINUM MATERIALS USED FOR EXTREMELY HIGH-VACUUM CHAMBER

Hydrogen desorption properties of pure Al metal (1050H24 and 1001 Al) and Al alloy (6063T6) were investigated by using a technique of thermal desorption spectroscopy (TDS). In the TDS spectrum of hydrogen, two peaks in the temperature, which may correspond to the desorptions due to second-order surface reaction and diffusion process, were observed. The activation energy of the desorption, due to the surface reaction for the 1050H24 Al, was obtained as 38 kJ/mol. For the 1001 Al, by using a simple diffusion model, the activation energy and diffusion constant of hydrogen due to the diffusion process were calculated as 50 kJ/mol and (0.5-3.5) X 10(-3) cm2/s, respectively. The hydrogen desorption amount of the Al alloy was estimated as 3 X 10(15) mol/cm2 (0. 15 9 cc/100g Al), which was twice compared with that of the 1050H24 Al. Secondary-ion mass spectroscopy (SIMS) analysis was applied to examine the change of the surface atomic composition after baking. It was found that magnesium was considerably segregated by heating. However, the correlation between the concentrations of hydrogen and magnesium was not clearly observed.