Hydrogen In Voids Research Articles

Hydrogen trapping by irradiation-induced defects in 316 Lstainless steel: A combined experimental and modeling study

The irradiation-induced defects in stainless steel internal components of pressurized water reactors combined with hydrogen uptake during the oxidation process could be a key parameter in the mechanism for Irradiation-Assisted Stress Corrosion Cracking (IASCC). A heat-treated 316 L SS containing a low amount of defects was Fe3+ ions-implanted; irradiation-induced defects types and depth distributions were characterized by Transmission electron microscopy (TEM). Deuterium was then inserted in the specimens either by cathodic charging or by sample exposure to deuterated primary water. Secondary Ions Mass Spectrometry – SIMS – permitted to access the deuterium distribution at the implanted stainless steel surface. A finite difference numerical solver accounting for hydrogen diffusion/trapping coupling was used to simulate the hydrogen transport in the implanted material, taken into consideration the specific heterogeneous character of the irradiation-induced defects distribution in matter. Taking as input data the experimental defects distribution associated with Frank loops or voids, the main trapping sites for hydrogen were assigned to voids, not Frank loops. Such numerical approach was able to deal accurately with the problem of hydrogen transport in a heterogeneous material as well as to differentiate two potential trap sites contributions to the experimental deuterium distribution. In addition, according to results obtained after primary water exposure, trapping at voids was still effective at 320 °C, signature of a high binding energy of hydrogen in voids.

水素昇温脱離特性に及ぼすクリープボイドの影響

For the clarification of the creep damage detection mechanism by hydrogen, the simulation technique for investigating the effect of creep void on hydrogen thermal desorption characteristics of pure iron has been developed. The dissolved hydrogen was calculated by a kinetics calculation in consideration of trapping and dissociation of hydrogen in voids. In the interaction between hydrogen atoms and voids, the effect of dissociation and adsorption, recombination of hydrogen at the void surface was also taken into account. In addition, hydrogen diffusion inside of samples was calculated according to the diffusion equation. The void number density was used as an input parameter of the simulation. The hydrogen evolution curve obtained from the simulation did not accord with the experimental one. The latter might include the hydrogen desorption from the damages which were too small to be observed by a scanning electron microscope.

Hydrogen-induced blistering of Mo/Si multilayers: Uptake and distribution

We report on the uptake of deuterium by thin-film Mo/Si multilayer samples as a result of exposure to fluxes of predominantly thermal atomic and molecular species, but also containing a small fraction of energetic (800–1000eV) ions. These exposures result in blister formation characterized by layer detachment occurring exclusively in the vicinity of the Mo-on-Si interfaces. This localization is attributed to strained centers introduced within the interfacial region during silicide formation and subsequent Mo crystallization. The correlation between D-content and blistering was studied. After an initial uptake period the D-content stabilized at ~1.3×1016 at./cm2. Blister development is not simply a function of the content. Different blistering processes are simultaneously operative, with three distinct distributions being observed. The areal number densities of the initial two blister distributions to appear are established before the content stabilizes, while the multilayer is susceptible to successive stages of blistering associated with the effects of energetic ions. H-atom depth profiling of hydrogen-exposed samples by resonant nuclear reaction analysis shows preferential accumulation in the Mo layers. A distinct local maximum with a remarkably high hydrogen concentration (~19at.%) develops in the outermost Mo layer. This is attributed to enhanced accommodation of hydrogen in voids and vacancies within the layer as a consequence of its polycrystalline structure and its highly-constrained state.

Hydrogen Embrittlement of Zirconium Alloys

The process of hydrogen embrittlement of zirconium alloys caused by the pressure of molecular hydrogen in voids formed near threefold junctions of grain boundaries and by volume changes due to formation of hydride phases is considered. The embrittling mechanisms are physically based on the diffusion processes near structural imperfections, the leading role among which belongs to threefold junctions of grain boundaries. These structural defects possess strong stress fields and directly adjoin grain boundaries.

The mechanism of the evolution of hydrogen on palladium and associated internal damage phenomena

The mechanism of the hydrogen evolution reaction has been examined and the knowledge thus obtained applied to the interpretation of various aspects of internal damage found above a critical overpotential in alkaline solution. Tafel slopes showed a change at η=−0.3 V; the stoichiometric number is 1< ν<1.2, separation factor ( S TH=8±1); FTIR measurements give ∂ln θ/∂ η=(4.7 RT/ F) −1, and permeation measurements show ∂ln P ∞/∂ η=(6.1RT/F) −1. These facts are consistent (up to an overpotential ( η) of −0.3 V) with a rate determining proton discharge, coupled to Tafel recombination; at η more negative than −0.3 V, the mechanism changes to a fast proton discharge with rate determining electrochemical desorption to H 2. Damage within the Pd electrode appears markedly at pinholes along the hexagonal sides of grain boundaries. The number of hexagonal units and pinholes increases with overpotential and time. An increased solubility of hydrogen at points of high stress is seen as the cause of damage discernible at triaxial points and that generated along the sides of grain boundaries. The high fugacities of hydrogen in voids around these regions serves to interpret the further deterioration of the structure observed with increasing overpotential. Calculations of pressures inside the voids suggest that initiation of damage to the Pd corresponds to a change in reaction mechanism at η≃−0.3 V.

Structural Origin of Bulk Molecular Hydrogen in Hydrogenated Amorphous Silicon

AbstractThe elastic anomaly observed previously at the triple point of bulk molecular hydrogen in hydrogenated amorphous silicon films prepared by hot-wire chemical-vapor deposition has also been observed in deuterated films at the triple point of D2. The origin of this anomaly has now been traced to bubbles formed at the crystalline-amorphous interface. An upper limit of the pressure in these bubbles at their formation temperature, 440°C, has been estimated to be 11 MPa, and is suggested to be a measure of the bonding strength between film and substrate at that temperature. Bubble formation after heat treatment at 400°C has also been observed in films prepared by plasma-enhanced chemical-vapor deposition. The internal friction anomalies resemble those observed previously in cold-worked hydrogenated iron where they have been interpreted through plastic deformation of solid hydrogen in voids.

Effect of voids on Arrhenius relationship between H-solubility and temperature in nickel

Many investigations about the states of hydrogen in voids within metals have been carried out over the past years. These probable states of hydrogen in the voids are directly relevant to hydrogen embrittlement mechanisms. Therefore, a knowledge of the states of hydrogen in the voids is important to an understanding of hydrogen-related degradation of material properties. Some results show that hydrogen exists as a molecule in the voids, while others suggest it is in the chemisorbed state on the internal surface of the voids. The results of Sung-Man lee et al. suggested that hydrogen in the voids in nickel exists both in the gaseous and chemisorbed stats, and most of the hydrogen trapped in the voids seems to be present as a chemisorbed state in 1 atm. hydrogen pressure in the temperature range of 350--582 C. But there is no quantitative description concerning the effects of the voids on the solubility of hydrogen in materials. The purpose of this work is to describe quantitatively the effects of the voids on hydrogen solubility in nickel, considering hydrogen exists as gaseous and chemisorbed states in the voids, and the very weak physical adsorption above room temperature is neglected.

The hydrogen effect in copper

The effect of hydrogen on the physical properties of copper is considered with emphasis on determining which form of hydrogen is responsible for the property change. Three situations in which the properties of copper are known to be affected by hydrogen are (1) thermal charging, (2) cathodic charging and (3) electroless copper plating. It is concluded that the hydrogen effect results from two different causes: (1) the development of high pressure of molecular (gaseous) hydrogen in voids, and (2) the formation of defects such as dislocations due to the precipitation of absorbed atomic hydrogen in the form of hydrogen molecules.

The hydrogen effect in copper

The effect of hydrogen on the physical properties of copper is considered with emphasis on determining which form of hydrogen is responsible for the property change. Three situations in which the properties of copper are known to be affected by hydrogen are (1) thermal charging, (2) cathodic charging and (3) electroless copper plating. It is concluded that the hydrogen effect results from two different causes: (1) the development of high pressure of molecular (gaseous) hydrogen in voids, and (2) the formation of defects such as dislocations due to the precipitation of absorbed atomic hydrogen in the form of hydrogen molecules.

Hydrogen interactions with defects in Fe

Abstract Hydrogen interactions with voids and dislocations in neutron-irradiated Fe have been studied by positron-annihilation spectroscopy. The presence of hydrogen in voids reduces the positron-trapping rate by a factor of up to 4, leaving the positron lifetime unchanged. Two hydrogen states are revealed with binding energies, with respect to the solution, of 0·82 ± 0·04eV and 0·96 ± 0·04eV, respectively. The results are in good agreement with surface-desorption and ion-beam analysis results. A surface permeation barrier is assumed to delay the hydrogen release from the samples at temperatures up to 460K. Hydrogen at dislocations does not affect the positron lifetime but decreases the positron-trapping rate by about 25%.

The electro-permeation of hydrogen into metals

It is sought to relate the diffusion coefficient and solubility for hydrogen in metals to the interaction of hydrogen with the metal phase. Determinations of permeation and diffusion coefficient have been made by a very sensitive electrochemical method at room temperature, and in some cases with temperatures up to 80°C, for platinum, nickel, tantalum, titanium, zirconium, manganese, and iron-chromium alloys.The dependence of permeation at high cds on time varies qualitatively with the metal involved. The diffusion coefficient for iron-chromium alloys decreases with increasing chromium; the solubility increases with increasing chromium. In general, the solubility decreases with increasing heat of absorption, and decreases with decreasing d-vacancies. The diffusion coefficient decreases with increasing latent heat of sublimation of the metal.The critical concentration of hydrogen that causes embrittlement in the metal is interpreted in terms of a model involving the pressure of hydrogen in voids. Qualitative support is cited. Gas-phase heats of solution of hydrogen in metals are those obtained for the solution case. Solubility of hydrogen depends upon d-vacancies according to a simple model. A solution of equations relating to the diffusion of hydrogen out of pre-charged metal foils is given.