Apparent Hydrogen Diffusivity Research Articles

Effect of carbon content on hydrogen occlusivity and embrittlement of ferrite–pearlite steels

Experiments on a series of pure Fe–C alloys consisting of ferrite and pearlite only have shown that the ferrite/pearlite and pearlite/pearlite interfaces are effective hydrogen trapping sites. The ferrite/cementite interfaces within the pearlite colonies, however, have little effect on the hydrogen occlusivity. With an increase in carbon content, more ferrite/pearlite interfaces are created and these increase the hydrogen occlusivity. Although the ferrite/cementite lamella interface has little effect on the hydrogen occlusivity, it does appear that the lamellae interfere with the hydrogen diffusion path across the pearlite colonies. Thus, the higher-carbon alloys in the pearlitic condition have a lower apparent hydrogen diffusivity. Hydrogen has little effect on the tensile strength, but significantly reduces the ductility. After hydrogen charging, high-carbon alloys suffer a lower ductility loss. However, in terms of absolute values, the low-carbon specimens are always more ductile than the high-carbon alloys when saturated with hydrogen.MST/433

The effect of mechanical polishing on hydrogen permeation in iron single crystal

The permeation of hydrogen through a metal such as iron or steel which contains saturable traps has been analyzed in several ways. Using an arrangement of specimen and electrolyte one can measure the time of transit of the hydrogen through the specimen after charging began. This is the ''break-through time.'' It is known that the apparent hydrogen diffusivity is reduced by structural defects such as a dislocation, a microvoid, a grain-boundary, and an interface of nonmetallic inclusions, etc.. Changes of dislocation density in the surface layer were monitored b, positron annihilation. Agreement between hydrogen traps and positron traps was established. Using positron annihilation, they have shown that the effect of mechanically polishing a single crystal of iron is to produce a layer about 25 ..mu..m thick which contains dislocation traps. The purpose of this investigation is to assess the effect of a thin layer of such traps on the diffusion of hydrogen through the specimens which are several hundred ..mu..m thick, and to determine the trap concentration profile in the sub-surface layers of and to determine the trap concentration profile in the sub-surface layers of it.

Development of deuterium-tritium loading vessel for laser fusion target.

Tritium permeation at 350°C through stainless steel wall of a vessel filled with deuterium-tritium gas of 6.1 × 106 Pa pressure was practically suppressed by Au plating of 20μm thick applied to the outside surface. The apparent diffusivity of hydrogen through plated Au layer, derived from the experimental data, was 2 x 10−11 cm2/s for 470°C, which is 10−5–10−6 times smaller than what would be expected from values reported for wrought Au, and the apparent solubility was very significantly higher than similarly expected level. Gas analysis of the Au layer indicated that the effective suppression of tritium permeation is attributable to trapping of hydrogen by C contained in the Au as impurity. Adequate tightness against tritium leakage has been achieved by Au plating on a vessel used for loading glass microspheres with deuterium-tritium gas, intended for laser fusion targets.

Effect of cathodic charging current density on the apparent hydrogen diffusivity through pure iron

The dependence of the apparent hydrogen diffusivity in pure iron on the cathodic charging current density has been measured using an electropermeation cell, establishing the relationship $$D_A (cm^2 \sec ^{ - 1} ) = - 3.18\operatorname{x} 10^{ - 9} + 1.25\operatorname{x} 10^{ - 9/{\raise0.5ex\hbox{$\scriptstyle 1$}\kern-0.1em/\kern-0.15em\lower0.25ex\hbox{$\scriptstyle 2$}}} (\mu \operatorname{A} cm^{ - 2} )$$ This cathodic charging current dependence is explained in terms of trap theory and the basic electrochemical model. This explanation is totally different from the general concept of a concentration dependence of diffusivity. A double plateau in the permeation curve is detected in this experiment at low charging current density.

Effect of cold working on the hydrogen trapping phenomena in pure iron

Hydrogen trapping in iron with various types and amounts of trapping sites was investigated through permeation experiments. The apparent hydrogen diffusivity decreases as the degree of cold working increases. This decrease is attributed to an increase in dislocation density and microvoid concentration. Analysis of the permeation data suggests that hydrogen binding energies of dislocation and microvoid are 25.6 kJ/mole and 29.1 kJ/mole, respectively. The data further show that the apparent hydrogen diffusivity increases as applied hydrogen pressure increases. Energy level diagrams around various trapping sites are proposed.

Deuterium trapping by impurities in copper

The addition of Er, Zr, or Ti to copper provides trapping sites for hydrogen isotopes, which causes the apparent diffusivity of hydrogen to take on values that are smaller than its normal diffusivity in pure copper. This apparent diffusivity can be described in terms of the dopant concentration and the binding energy of the hydrogen isotope to the traps. Criteria are met that enable the results of permeation breakthrough measurements, which were made between 300° and 700 °C, to be extrapolated to room temperature. The resultant lag‐time for deuterium breakthrough for a 0.25‐mm‐thick membrane of Cu containing 0.88 at.% Er, for example, exceeds 1000 years at 25 °C. Therefore, this alloy is suitable for use in vacuum enclosures where it is necessary to restrict hydrogen permeation for long periods of time. Thermodesorption measurements for samples that were exposed to deuterium reveal that there are two types of traps in these alloys, and demonstrate that deuterium‐to‐dopant atomic ratios approaching two can be obtained.

The effect of plastic deformation on the transport of hydrogen in nickel

Abstract : The permeation of hydrogen into crystalline metals may occur in part by lattice diffusion, by grain boundary (or other short circuit) diffusion, or, in the case of specimens undergoing plastic deformation, by dislocation transport. In this work, electrochemical permeation measurements indicate that the apparent diffusivity of hydrogen is increased by several orders of magnitude when permeation specimens are plastically deformed and simultaneously charged with hydrogen. (Author)

The Effect of Oxygen on Hydrogen Transport in Copper

Abstract Hydrogen interaction with oxygen in copper exerts a significant influence on the apparent hydrogen diffusivity and the quantity of hydrogen absorbed. This interaction associated with steam embrittlement has been well established in alloys with high oxygen contents, such as electrolytic tough pitch (ETP) copper. However, the importance of this interaction on hydrogen transport in 99.999%, oxygen-free high conductivity (OFHC) copper and boron-deoxidized (BD) copper, apparently has not been recognized. Correlation of the amount of absorbed tritium with oxygen content and dependence of permeation transients on both oxygen content and prior treatment indicate that both reversible and irreversible interactions occur between hydrogen and dissolved oxygen.

Techniques for Investigating Hydrogen-Induced Cracking of Steels With High Yield Strength

Abstract As part of a Song range study to develop grades of steel with improved resistance to hydrogen-induced cracking, techniques for measuring hydrogen uptake and hydrogen permeability were investigated and these parameters were correlated with resistance to hydrogen-induced cracking at different strength levels. The steel used for these studies was a Ni-Cr-Mo steel heat treated to four yield strength values ranging from 95 ksi to 150 ksi. The environment studied was a hydrogen sulfide saturated aqueous solution of 3% sodium chloride and 0.5% acetic acid. The technique used to measure hydrogen permeability consisted of exposing one side of a steel specimen to the sulfide environment and electrochemically measuring the hydrogen permeating to the opposite side. Hydrogen uptake was measured by the vacuum extraction method with specimens exposed to the environment for various time periods. The results of this comparison Stowed that both the resistance to cracking and the apparent diffusivity of hydrogen decreased as the yield strength was increased. Hydrogen uptake increased with increasing yield strength but the steady state permeation rate was not affected by strength level. A concept of hydrogen trapping is proposed to explain the observed relationships among the parameters studied and the mechanical strength of the steel.