The solubility and diffusivity of hydrogen in well-annealed and deformed iron

We present calculations of free energy barriers and diffusivities as functions of temperature for the diffusion of hydrogen in α-Fe. This is a fully quantum mechanical approach since the total energy landscape is computed using a new self consistent, transferable tight binding model for interstitial impurities in magnetic iron. Also the hydrogen nucleus is treated quantum mechanically and we compare here two approaches in the literature both based in the Feynman path integral formulation of statistical mechanics. We find that the quantum transition state theory which admits greater freedom for the proton to explore phase space gives result in better agreement with experiment than the alternative which is based on fixed centroid calculations of the free energy barrier. We also find results in better agreement compared to recent centroid molecular dynamics (CMD) calculations of the diffusivity which employed a classical interatomic potential rather than our quantum mechanical tight binding theory. In particular we find first that quantum effects persist to higher temperatures than previously thought, and conversely that the low temperature diffusivity is smaller than predicted in CMD calculations and larger than predicted by classical transition state theory. This will have impact on future modeling and simulation of hydrogen trapping and diffusion.

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“…from electrochemical permeation experiments, assessed in ref. [3] and measured in ref. [6] respectively.…”

Section: Calculation Of the Hydrogen Diffusivity In Ironmentioning

confidence: 99%

Fully quantum mechanical calculation of the diffusivity of hydrogen in iron using the tight-binding approximation and path integral theory

2013

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“…Such a data scattering has mainly been attributed to the surface effect (2)- (5) and/ or the trapping (6)-(9) at lattice imperfections or impurities (10), however, their detailed role in hydrogen transport in iron has not been clarified yet. While most of diffusion data(1)(11)- (15) given by the gaseous permeation technique are rather consistent with each other at higher temperatures, those below 700K are still widely scattered(1) (15 ), and values extrapolated to room temperature are mostly much smaller than recent data (16) (17) given by the electrochemical method with high pure iron.…”

mentioning

confidence: 52%

“…Because of lower hydrogen fugacity (less than 0.1 MPa (1atm) in most cases) in the gaseous permeation technique, the measurement at lower temperatures is not only very difficult but also influenced by impurities in the hydrogen gas, and only a few works (8) (11)- (15) have been performed at temperatures below 500K. Moreover, earlier works have scarecely taken account of contamination of hydrogen gas which originates from desorption of gas (mainly H2O) adsorbed on and/or absorbed in the system wall.…”

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confidence: 99%

Hydrogen Transport through Highly Purified Iron

1984

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Precise measurements of hydrogen permeation through highly purified iron have been performed utilizing the gaseous permeation technique with the hydrogen pressure ranging between 0.001 and 0.1 MPa in a wide temperature range from 420 to 1100K. The effect of surface oxide and/or lattice imperfections on hydrogen transport has also been investigated by changing the impurity level of hydrogen gas or by introducing the lattice imperfections due to deformation of the specimen without

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“…This phenomenon is called hydrogen embrittlement [1,2,3,4]. Many studies were conducted on the diffusion and trapping of hydrogen in steel [4,5,6,7,8,9,10] and other metals [10]. Hydrogen can be introduced in the steel through cathodic charging.…”

Section: Introductionmentioning

confidence: 99%

Hydrogen Absorption and Desorption in Steel by Electrolytic Charging

Mertens¹,

Duprez²,

Cooman³

et al. 2006

Advanced Materials Research

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Abstract. The presence of hydrogen in steel decreases its toughness and formability leading to hydrogen embrittlement. To understand the failure mechanisms of steel due to the presence of hydrogen, a profound insight in the hydrogen household of the steel is needed. This includes a study of the solubility, the diffusion and the trapping of hydrogen. Next, the absorption and desorption behavior during and after electrolytic charging must be well determined. This was investigated in this research for steels with various types of traps, e.g. dislocations, microcracks, grain boundaries and precipitates such as TiC and Ti 4 C 2 S 2 . The samples were cathodically charged at three different current densities: 0.8mA/cm 2 ; 8.3mA/cm 2 and 62.5mA/cm 2 . It was noticed that the cathodic current density used for hydrogen loading had a great influence on the results. Observation of the samples by scanning electron microscopy (SEM) showed that at the highest current density major damage of the surface had occurred. Hence it was decided to study more systematically the influence of charging current density on the resulting surface aspect and on hydrogen absorption and desorption. The hydrogen charging kinetics, maximum hydrogen solubility and hydrogen desorption behavior have also been evaluated for the different current densities during charging.

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The solubility and diffusivity of hydrogen in well-annealed and deformed iron

Cited by 407 publications

References 63 publications

Fully quantum mechanical calculation of the diffusivity of hydrogen in iron using the tight-binding approximation and path integral theory

Fully quantum mechanical calculation of the diffusivity of hydrogen in iron using the tight-binding approximation and path integral theory

Hydrogen Transport through Highly Purified Iron

Hydrogen Absorption and Desorption in Steel by Electrolytic Charging

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