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Kinetic Theory of the Hydrogen Diffusion in Metals
Author(s) -
Fujita S.
Publication year - 1987
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.2221430206
Subject(s) - hydrogen , arrhenius equation , diffusion , activation energy , crystal (programming language) , mean free path , phonon , kinetic energy , thermodynamics , metal , condensed matter physics , lattice (music) , melting point , chemistry , physics , atomic physics , materials science , quantum mechanics , electron , organic chemistry , acoustics , computer science , programming language
The diffusion coefficient D for hydrogen in a metal normally obeys the Arrhenius law: D = D 0 exp (– E a / k B T ), where E a is the activation energy, which represents the barrier potential for the most favorable interstitial channel. The pre‐exponential factor D 0 can be related to the mean straight path l in the crystal by D o = (1/3) gvl , where v is the average migration speed and g a statistical weight of order one. The mean straight path l for a pure crystal can be very long, since the migrating atoms cannot readily be scattered or stopped by the (phonon) motion of the regular lattice. This physical picture, reasonable but not widely recognized, is supported by experimental evidence and theoretical considerations. In particular, the distinct isotope effects for hydrogen diffusion in f.c.c. and b.c.c. metals are explained in terms of quantum mechanical zero‐point energies associated with the crystal channel potentials. A few experimental tests for the theory are suggested.