The solubility and diffusivity of hydrogen in pure nickel were studied by thermal analysis technique using Gas Chromatograph. The solubility(C) was determined from the evolution rate peak areas of thermal analysis over the temperature range 300 to 550℃.
The activation energy for lattice diffusion of hydrogen was determined from the changes of evolution rate peak temperatures with heating rates. Also, the diffusivity of hydrogen was measured from the changes of the amount of hydrogen diffused into Ni sheet with charging time at a high temperature, i.e. 425℃. At this high temperature, the hydrogen trapping effect by each defect in pure nickel is negligible. Thus, the equation for lattice diffusion of hydrogen in pure nickel was derived by combining the diffusion activation energy and the value of diffusivity at 425℃. The equations of solubility (C) and diffusivity (D) derived were as follows.
$C (atoms/atom) = 1.348\times10^{-3} exp(-2.99Kcal/RT)$
$D (cm^2/sec) = 9.16\times10^{-3} exp(-9.55 Kcal/RT)$
As the results of thermal analysis, it seems that grain boundaries are ineffective trapping site in pure nickel. On thermal analysis, however, the cold working increased the evolution rate peak area relative to the annealed case. This indicates that dislocations in pure nickel behavior as the trapping sites. Also, by comparing the shape of those evolution rate peaks, we could know that the hydrogen trapped at dislocations was evolved by volume diffusion rather than pipe diffusion through dislocations.
