Some Physical Aspects of bcc Hydrogen Storage Alloys

摘要

Hydrogen absorption/desorption has been investigated in the three series of solid solution bcc alloys Ti_(35)V_xCr_(65-x)(x = 18.22), Ti_(40)V_xMn_(50-x)Cr_(10) (x = 32.36) and Ti_xCr_(97.5-x)Mo_(2.5) (x = 43.46). It has been found that H absorption at pressures smaller than one bar can only occur after elimination of the oxide films by heating the alloys to temperatures higher than 600 K. Hydrogen desorption from pre-loaded materials (n_H = H/Me ≤ 0.27) takes place on heating at much lower temperatures in the Ti_(40)V_xMn_(50-x)Cr_(10) and Ti_(35)V_xCr_(65-x) than in the Ti_xCr_(97.5-x)Mo_(2.5) alloys. The H diffusion parameters W and D_o deduced from high temperature (>450 K) absorption experiments are: W = 0.318 ± 0.005 eV, D_o= (4 ± 1) × 10~(-7) m~2/s for Ti_(40)V_xMn_(50-x)Cr_(10); W = 0.32 ± 0.02 eV, D_o= (3 ± 2) × 10~(-7) m~2/s for Ti_(35)V_xCr_(65-x); W = 0.79 ± 0.06 eV, D_o = (4 ± 2) x 10~(-8) m~2/s for Ti_xCr_(97.5-x)Mo_(2.5). The higher value of the activation energy for H diffusion in Mo containing alloys is most likely due to H trapping by Mo atoms.