Hydrogen permeation through magnesium

Hydrogen permeation characteristics have been investigated for pure magnesi um membranes with a palladium overlayer using a gas permeation technique in the temperature range 473-493 K and in the hydrogen pressure range 0.1-10 kPa. For thicker specimens (thickness >2 mm), the permeation process was ra te-controlled by the diffusion of hydrogen in bulk magnesium. The diffusion coefficient was determined to be D = 1.54 x 10(-6) exp(-24,100/RT) m(2) s( -1). The steady-state hydrogen permeability was determined to be Phi(ss) = 2.77 X 10(-7) exp(-35,700/RT) mol H-2 m(-1) s(-1) Pa-1/2. D and Phi(ss) wer e independent of the applied hydrogen pressure, suggesting that D is indepe ndent of hydrogen content and the solubility of hydrogen obeys Sieverts' la w. The hydrogen solution constant K was determined to be K = 1.8 x 10(-1) e xp(-11,600/RT) mol H-2 m(-3) Pa-1/2. (C) 1999 Elsevier Science S.A. All rig hts reserved.