Monitoring of hydrogen absorption/desorption into pressed cobalt powder using resistometry

The kinetics of hydrogen absorption/desorption into pressed cobalt powder samples was monitored using resistometry. The samples were prepared by pressing Co powder at 100 MPa and t = 25 °C. The equivalent diameter of the species varied from 5 to 200 μm. The study showed that hydrogen absorption leads to an increase in the electrical resistivity of the pressed samples. During diffusion into the crystal lattice, the absorbed hydrogen atoms simultaneously trap an electron from the conduction band of the metal and form H− ions, consequently inducing an increase in the electrical resistivity of the pressed sample. On the basis of the change in resistivity, a mechanism of hydrogen absorption has been proposed. During the initial period of absorption, the hydrogen absorption reaction is limited by the dissociative adsorption of hydrogen over a short period of time, following which the diffusion of H− ions into the bulk of the pressed Co powder is identified as the rate-determining step. The hydrogen desorption rate in an argon atmosphere is limited by H2,ad formation; recombination of adsorbed hydrogen atoms, Had, or by the diffusion of H− ions from the crystal lattice over a prolonged period of time.