Evaluation of hydrogen-trap binding enthalpy l

Abstract

In order to evaluate hydrogen-trap binding enthalpy H_s from the elevated temperature hydrogen evolution peaksT _P, theH _B-T _P relation was analytically deduced in low hydrogen concentration approximation. The plot of H _B againstT _P revealed that in aT _P regionT _P ≧T _O + ΔT whereT _O is the initial temperature in heating and ΔT ≈ 80 K, H _B + 0.11 eV is substantially proportional tok _B T _P ,i.e., H _B + 0.11 eV = γ(N, ώ _O )k_B T _P for fixed geometrical and heating conditions, and the proportionality factor γ(N, ώ _O ) is influenced by hydrogen trap densityN and parameter of release ώ _O defined in the text. Thus for exact and precise determination of H _B parameter of release ώ _O as well as hydrogen trap densityN generally play an important part. In the present theory it is assumed that a specimen contais two kinds of deep traps (irreversible in the diffusion process at ambient temperature) and does not contain shallow traps (reversible at ambient temperature). The theory was applied to steels which vary in sulfur contents. The steels produced hydrogen release peaks at slightly different temperatures ranging from 588 K to 613 K, but the hydrogen-trap binding enthalpies H _B for these steels are shown to be substantially the same:H _P = 0.86 ± 0.005 eV.