The determination of self-diffusion coefficient in solid parahydrogen from it’s creep experiences
B. Verkin Institute for Low Temperature Physics and Engineering of the National Academy of Sciences of Ukraine 47 Nauky Ave., Kharkiv 61103, Ukraine
Surface and Corrosion Science, KTN Royal Institute of Technology, Stockholm SE-100 44, Sweden
Received December 18, 2017, revised February 5, 2018, published online July 26, 2018
The dependences of the relative elongation ε on the endurance time t of polycrystalline parahydrogen (p-H2, ~ 0,2% o-H2) of high purity (99.9999 mol.%) on extraneous impurities with different deuterium content under the applied stress at T = 1.8 K were measured. The region of linear dependence between the measured creep rates of samples and the applied load σ was re-vealed. On the basis of the fulfillment of the linear law ε̇ ~ σ, the diffusion character of the low-temperature creep of the vacancy-type p-H2 investigated was concluded. The low-temperature values of the intrinsic diffusion coefficient of vacancies D in solid p-H2, characterizing the rates of low-temperature mass transfer, are calculated. The cases of migration of vacancies in the crystal volume, along the boundaries, separating individual crystallites, are considered, as well as between dislocations existing in crystals. A noticeable decrease in the values of ε̇ and D was observed with an increase of the isotope concentration in the samples, while maintaining a linear relationship between ε̇ and σ for the p-H2 studied.
Key words: parahydrogen, creep, diffusion mass transfer, vacancies, isotopes of hydrogen.