Abstract
Influence of hydrogen diffusion parameters, heating conditions, and geometry of specimen on the HB−Tp relation is theoretically estimated, where Hb is the hydrogen-trap binding enthalpy and Tp is the temperature of hydrogen release peak in elevated temperature hydrogen evolution experiments. If we write activation enthalpy for lattice diffusion of hydrogen as HL, then theoretical analysis predicts that HB+HL+ΔH is substantially linearly related to thermal energy kBT at hydrogen release peak temperature, Tp, as HB+HL+ΔH=γkBTp in a temperature region Tp>T0+ΔT, below which deviation from linearity of the relationship takes place; ΔT mainly depends on the value of HL. In the preceding expression, T0 is the initial temperature of heating; excess energy ΔH is found to be a constant, 0.09 eV, for a fixed value of HL, 0.082 eV, for lattice diffusion of hydrogen in body-centered-cubic iron. The influence of diffusion and trap parameters, i.e., pre-exponential factor of hydrogen diffusivity, trap site density, parameter of trapping, heating rate, and specimen size, enters into the single parameter γ in the preceding expression.
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