Absorption and desorption of H by NbMo alloys at high temperature

摘要

Absorption and desorption of hydrogen have been investigated in Nb_(-95)Mo_5 and Nb_8oMo_20 alloys over wide temperature ranges. On continuous heating H desorption from Nb_95Mo_5 was found to take place between 800 and 1000 K and from Nb_80Mo_20 between 900 and 1100 K. The observed increase in the desorption temperature with increasing Mo content has been attributed to a higher stability of the Mo and NbMo oxides with respect to those of Nb. The solid-gas reaction during absorption was first order and the rate limiting process consisted in the penetration of H atoms through surface oxides. At high temperatures and in the presence of H the oxides are expected to become permeable to H due to the reduction of higher valence to lower valence oxides. The values of the activation energy for H diffusion within the oxide films were 0.82 ± 0.04 eV for Nb_(95)Mo_5 and 1.1 ± 0.1 eV for Nb_(80)Mo_(20) The thicknesses of the oxide films estimated from the absorption data were of the order of 1 μm.