Hydrogen Penetration Research Articles

Time-Dependent Measurement of Hydrogen Penetration into Iron Sheets from a Borate Buffer Solution Using FFT Analysis

Hydrogen penetration into iron sheets from a borate buffer solution (pH 8.4) was investigated using a modified Devanathan-Stachurski cell with flow paths. A sinusoidal perturbation method was applied to evaluate the hydrogen-diffusion coefficient D and its dependence on specimen thickness, polarization potential, and electrolyte flow rate. A fast Fourier transform (FFT) technique was employed to achieve automated derivation of the diffusion coefficient with precision and rapid screening of the experimental conditions. The obtained value of D increased with an increase in the specimen thickness or with an increase in the overpotential of the hydrogen evolution reaction, indicating the effect of a surface barrier layer-like oxide film on the hydrogen-entry side. On the other hand, D is not dependent on the electrolyte flow rate in the entry-side cell. From the viewpoint of hydrogen penetration, the properties of the barrier layer are almost immune to the flow rate, though it is affected by the polarization potential. The sinusoidal perturbation method combined with FFT allows the time-dependent evaluation of the hydrogen-penetration behavior in specimens with temporal changes, such as oxide-film formation and corrosion.

The Influence of Air Exposition of the Zr-Mn-Cr-Ni-Al Alloy on Cycle Life

It was found by scanning electron microscopy method that the ZrMn0.5Ni1.2Cr0.18А0.1 alloy has a dendritic structure, and the shooting of a typical section of the surface of the metallographic sample in characteristic radiation determined its chemical heterogeneity. The X-ray diffraction method has found that the C15 and C14 are the main phases of the alloy. In addition, the alloy contains Ni10Zr7 and Ni11Zr9 secondary phases. The method of potentiometric cycling has established that the air exposition of ZrMn0.5Ni1.2Cr0.18А0.1 alloy powder results in an increase in the electrochemical stability of the electrodes pressed from this powder and causes a significant increase of their cycle life. It is important that the cycle life of the AB2 alloy doped simultaneously with chromium and aluminum increased. Such doping is usually carried out in order to increase the cycle life due to the creation of hydrogen penetrating stable oxide films. Alloys with the same content of the Ni10Zr7 phase have the same activation rate of the initial electrodes. According to investigations, corrosion of the material originates on the interphase surface and begins to spread along it, indicating its pitting nature, and the surface of the pitting itself has the form of flake.

Electronic properties of hydrogen terminated n-Si (111)/electrolyte interface: Effect of saccharin addition

In the present study, electrochemical impedance spectroscopy (EIS) has been used to determine how saccharin (SAC) affects the electronic properties of the hydrogen terminated Si(111) (n-Si(111)-H)/electrolyte interface. The presence of surface states energy levels on the n-Si(111)-H surface is well demonstrated by surface states capacitance measurements. Absorption of SAC on the n-Si(111)-H is evidenced by the changes observed in surface states distribution and density. Two monoenergetic state levels situated at nearly −0.3V and 0.11V vs. SCE were found in SAC containing bath. The first surface states level have been related to the penetration of hydrogen into subsurface region, whereas the second surface states level is expected to be associated with oxidation intermediates.

Formation of H a - hydrogen centers upon additive coloration of alkaline-earth fluoride crystals

The mechanism of coloration of alkaline-earth fluoride crystals CaF2, SrF2, and BaF2 in calcium vapors in an autoclave with a cold zone is studied. It was found that the pressure in the autoclave upon constant evacuation by a vacuum pump within the temperature range of 500–800°C increases due to evaporation of metal calcium. In addition to the optical-absorption bands of color centers in the additively colored undoped crystals or to the bands of divalent ions in the crystals doped with rare-earth Sm, Yb, and Tm elements, there appear intense bands in the vacuum ultraviolet region at 7.7, 7.0, and 6.025 eV in CaF2, SrF2, and BaF2, respectively. These bands belong to the Ha - hydrogen centers. The formation of hydrogen centers is also confirmed by the appearance of the EPR signal of interstitial hydrogen atoms after X-ray irradiation of the additively colored crystals. Grinding of the outer edges of the colored crystals leads to a decrease in the hydrogen absorption-band intensity with depth to complete disappearance. The rate of hydrogen penetration inside the crystal is lower than the corresponding rate of color centers (anion vacancies) by a factor of tens. The visible color density of the outer regions of the hydrogen-containing crystals is several times lower than that of the inner region due to the competition between the color centers and hydrogen centers.

Microscopic observation of shear-mode fatigue crack growth behavior under the condition of continuous hydrogen-charging

Rolling bearings facilitate the smooth motion of moving mechanical transmission devices substantially reducing the energy loss. However, flaking failure caused in bearings by rolling contact fatigue can crucially deteriorate the integrity of an overall mechanical system composed using bearings. It is understood nowadays that this phenomenon is intimately associated with shear-mode (Mode II and III) fatigue crack growth caused by cyclic shear stress in the presence of large compression. Further, a problem has become of importance that the premature flaking in ball bearings could be caused by the assistance of the penetration of hydrogen into material during the operation. In this study, torsional fatigue test of a bearing steel (JIS SUJ2) was performed by using a newly-developed method of continuous hydrogen-charging. Based on the microscopic observation, it was found that continuous hydrogen-charging had an influence on the shear-mode fatigue crack growth behavior in the high-cycle fatigue regime and reduced the threshold level.

Investigation on Jet Characteristics of Hydrogen Injection and Injection Strategy for Backfire Control in a Port Fuel Injection Hydrogen Engine

Abstract Hydrogen injections in the manifold and diffusion processes have an important influence on the formation of mixture and the preventing of backfire of hydrogen internal combustion engine. An experimental study on jet characteristics of injection hydrogen under high pressure was investigated in a constant volume chamber using high speed photograph. Acquiring the development process of hydrogen injection form, at the same time, the law of hydrogen injection penetration distance with time under various injection conditions was obtained. The test results show that: as injection pressure increases, the hydrogen penetration rate increases; as ambient pressure increases, the penetration rate decreases; as the injection pulse width increases, the injection rate has no significant change. When the ratio of injection pressure and ambient pressure is less than or equal to 2.5, the hydrogen injection column will be broken into two sections; when this ratio is larger than 2.5, the hydrogen injection is a consequent column. A 3D calculation model of PFI hydrogen engine was established based on the characteristics of hydrogen injection. Experimental results demonstrated the CFD calculation model under various engine speeds and loads. The complete calculation of these results permitted to obtain the optimum injection control strategy which meets the power demand and avoids backfire.

A new testing method for investigating the shear-mode fatigue crack growth behavior in hydrogen environment

Ball bearing is widely used in a variety of machines including the transportation equipments of the automobiles and airplanes. Flaking failure is a common problem for ball bearing and it is caused by shear-mode fatigue crack growth under cyclic shear stress. Further, it is known that the premature flaking is attributed to the combined effect of hydrogen penetration into the material and cyclic shear stress during the operation. Therefore, in order to ensure the integrity of ball bearing, it is necessary to clarify the effect of hydrogen on shear-mode fatigue crack growth behavior, in particular, the threshold behavior. The evaluation of the shear-mode crack growth behavior is not easy because mode I crack branching occurs easily. Our previous studies revealed that it is required to apply static compression in the direction of specimen axis to attain a stable shear-mode fatigue crack growth. In addition, successive hydrogen supply to the specimen is essential for the evaluation of hydrogen effect on the fatigue threshold because hydrogen emits from the specimen during the fatigue test. In other words, the hydrogen-precharging method, commonly used for the research on hydrogen embrittlement, is not appropriate for the evaluation of fatigue threshold. In this study, to solve these problems, we have developed a novel, easy-to-use experimental method to evaluate the threshold behavior of shear-mode fatigue crack in the presence of hydrogen. The fundamental principle of the method is introduced in this paper.

Hydrogenation behavior of Ti-implanted Zr-1Nb alloy with TiN films deposited using filtered vacuum arc and magnetron sputtering

More than 60 years of operation of water-cooled reactors have shown that local or general critical hydrogen concentration is one of the basic limiting criteria of zirconium-based fuel element claddings. During the coolant radiolysis, released hydrogen penetrates and accumulates in zirconium alloys. Hydrogenation of zirconium alloys leads to degradation of their mechanical properties, hydride cracking and stress corrosion cracking. In this research the effect of titanium nitride (TiN) deposition on hydrogenation behavior of Ti-implanted Zr-1Nb alloy was described. Ti-implanted interlayer was fabricated by plasma immersion ion implantation (PIII) at the pulsed bias voltage of 1500V to improve the adhesion of TiN and reduce hydrogen penetration into Zr-1Nb alloy. We conducted the comparative analysis on hydrogenation behavior of the Ti-implanted alloy with sputtered and evaporated TiN films by reactive dc magnetron sputtering (dcMS) and filtered cathodic vacuum arc deposition (FVAD), respectively. The crystalline structure and surface morphology were investigated using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The elemental distribution was analyzed using glow-discharge optical emission spectroscopy (GD-OES). Hydrogenation was performed from gas atmosphere at 350°C and 2atm hydrogen pressure. The results revealed that TiN films as well as Ti implantation significantly reduce hydrogen absorption rate of Zr-1Nb alloy. The best performance to reduce the rate of hydrogen absorption is Ti-implanted layer with evaporated TiN film. Morphology of the films impacted hydrogen permeation through TiN films: the denser film the lower hydrogen permeation. The Ti-implanted interface plays an important role of hydrogen accumulation layer for trapping the penetrated hydrogen. No deterioration of adhesive properties of TiN films on Zr-1Nb alloy with Ti-implanted interface occurs under high-temperature hydrogen exposure. Thus, the fabrication of Ti-implanted layer with dense TiN films can be an effective way to protect Zr-1Nb alloy from hydrogen embrittlement.

Investigation of Hydrogen Sorption-Desorption Processes at Gas-Phase Hydrogenation and Defects Formation in Titanium by Means of Electron-Positron Annihilation Techniques

The results of hydrogen sorption and desorption processes investigation at commercially pure titanium alloy during hydrogenation at gas atmosphere are shown in this article. Titanium alloy hydrogenation at temperatures 350, 450 и 550 °С leads to δ-hydrides formation in samples’ volume. Hydrogen sorption rates were calculated on the linear parts of sorption curves and equal to 0.15·10-4 wt%/s at 350 °C, 0.86·10-4 wt%/s at 450 °C, 1.55·10-4 wt%/s at 550 °C. Phase transition in titanium-hydrogen system during thermally stimulated hydrogen desorption investigation by the means of short-wave diffraction of synchrotron radiation shows hydrides dissociation until 520-530 °C. Then α→β transition takes place until 690-720 °C and at this temperatures the phase transformation ends and additional hydrogen desorption peak appears in thermally stimulated hydrogen desorption curve. Defect structure at different hydrogen concentration investigation by the means of electron-positron annihilation techniques shows that hydrogen penetration into titanium leads to crystal lattice expansion. It initiates vacancy-type defects formation which reacts with hydrogen and forms defect-hydrogen complexes.

Gas-phase hydrogenation influence on defect behavior in titanium-based hydrogen-storage material

Titanium and its alloys are promising materials for hydrogen storage. However, hydrogen penetration accompanies the exploitation of hydrogen storage alloys. In particular, hydrogen penetration and accumulation in titanium alloys changes their mechanical properties. Therefore, the research works of such materials are mainly focused on improving the reversibility of hydrogen absorption-liberation processes, increasing the thermodynamic characteristics of the alloys, and augmenting their hydrogen storage capacity. In the process of hydrogenation-dehydrogenation, the formed defects both significantly reduce hydrogen storage capacity and can also be used to create effective traps for hydrogen. Therefore, the investigation of hydrogen interaction with structural defects in titanium and its alloys is very important. The present work, the hydrogen-induced formation of defects in the alloys of commercially pure titanium under temperature gas-phase hydrogenation (873K) has studied by positron lifetime spectroscopy and Doppler broadening spectroscopy. Based on the evolution of positron annihilation parameters τf, τd, their corresponding intensities If, Id and relative changes of parameters S/S0 and W/W0, the peculiarities of hydrogen interaction with titanium lattice defects were investigated in a wide range of hydrogen concentrations from 0.8at% to 32.0at%.

Electrospun zeolite-templated carbon composite fibres for hydrogen storage applications

The current study explored the application of the electrospinning technique to produce multi-hierarchical composites for hydrogen storage applications. Predetermined control of fibre porosity is expected to enable production of well-defined hierarchical pore structure. The study involved encapsulation of highly porous zeolite-templated carbon (ZTC) into electrospun fibres and testing of the resulting composites for hydrogen storage. The hydrogen storage capacity of the composite fibres was 1.83%, compared with 2.39 wt% for powder ZTC material. The potential of the electrospinning technique as a shaping option for preparing composites from loose powder is demonstrated. The ZTC–polyacrylonitrile (ZTC-PAN) composite retained about 76% of the hydrogen storage capacity of the ZTC. Vacuum degassing of the ZTC–PAN electrospun composite was also found to enhance the development of porosity, aiding hydrogen penetration into zeolite pores.

How the hydrogen sorption properties of palladium are modified through interaction with iridium.

Hydrogen sorption (adsorption/absorption) in metals, in the form of thin films or nanoparticles, is a key process in the fields of energy storage and heterogeneous catalysis. Atomic hydrogen dissolved in the subsurface of a metal affects its surface atomic and electronic structures, and thereby its surface reactivity and catalytic properties. In addition, alloy effects modify both catalytic and hydrogen sorption phenomena. In order to rationalize recent experimental results showing the negative impact of hydrogen absorption on catalysis, the present article proposes an insight into structure-reactivity relationships through computational simulations, using density functional theory, of hydrogen sorption in the near-surface region of palladium atomic layers interacting with an iridium substrate. A detailed analysis of the electronic structure using local projected densities of states (PDOS) and crystal orbital overlap population (COOP) curves was carried out. It is found that the Pd/Ir system, with respect to pure Pd surfaces, keeps acceptable adsorption properties for surface reactions while preventing hydrogen penetration. The results of electronic structure calculations show that the most important difference between Pd and Ir is related to the strong anti-bonding character of the 1s-H/5p-Ir interaction, leading to the non-bonding character of the sp-Ir interaction with hydrogen. Thus, increasing the Ir concentration in a Pd-based system increases the anti-bonding contribution, which strongly weakens the overall metal-hydrogen interaction.

Investigations for the substantiation of high-temperature nuclear power generation technology using fast sodium-cooled reactor for hydrogen production and other innovative applications (Part 1)

Neutronics and thermal physics studies of BN-VT reactor installation with 600-MW thermal power demonstrated the possibility in principle to achieve the required parameters of high-temperature fast reactor for production of large quantities of hydrogen on the basis, for instance, of one of thermal chemical cycles or high-temperature hydrolysis with high thermal efficiency of use of electric power. Relatively small dimensions, the type of coolant, selection of fissile material and structural materials allow developing nuclear reactor with particular inherent properties (exclusion of prompt-neutron reactor power excursions, removal of decay heat in passive mode) while ensuring enhanced nuclear and radiation safety.Composition of BN-VT reactor facility includes sodium-cooled fast reactor, three cooling loops for emergency heat removal and three sets of equipment of the secondary cooling loop for heat transfer from the reactor to chemical installations generating hydrogen or to gas-turbine plant for supplying chemical equipment with electric power. Composition of each of the cooling loops includes intermediate heat exchanger arranged inside the reactor vessel, centrifugal pump and pipeline for removal and re-introduction of sodium in the reactor core. Contemporary requirements on the safety and financial performance of future generations of nuclear reactors were taken into consideration in the development of the reactor under study. Implemented calculation studies demonstrated that penetration of hydrogen within the limits of permissible allowances produce practically no effect on the neutronics and safety parameters of the reactor. Solution of the problem of fuel pin stability was mitigated due to the selection of low thermal load on fuel pins. Application of EP-912-VD steel as a possible optional structural material was examined.Continued studies of heat-resistant materials and their behavior under irradiation are required.

Testing future hydrogen penetration at local scale through an optimisation tool

The diffusion of smart energy systems at the local scale will lead to the implementation of innovative design, plans and applications mainly involving integrated energy infrastructures and distribution systems. In this framework, hydrogen will have the chance to play a major role but its penetration rate still represents a considerable uncertainty and needs to be investigated with special attention to show the real feasibility of a hydrogen economy advent.The paper presents the results obtained analysing a set of scenarios applied to a comprehensive TIMES-based bottom-up energy model developed to describe and assess the energy systems of the single European countries and of macroareas of the rest of the world in an integrated approach. The modelling tool considers the hydrogen supply chain since its production stage (together with its storage and distribution) and evaluates – minimising the total system cost and over a mid-long time horizon – the penetration of the hydrogen-based end-use technologies.The analysis shows that the residential and, above all, the transport sector may see a considerable diffusion of technologies supplied with hydrogen and especially for urban application, pushed by the upcoming stricter environmental constraints to the energy sector.

Hydrogen dissociation and incorporation on Mg17Al12(100) surface: A density functional theory study

Hydrogen adsorption, dissociation, and penetration on (in) Mg17Al12 (100) surface are studied extensively by DFT total-energy calculations. The adsorption geometries, dissociation barriers, various diffusion pathways, penetrative processes, and electronic structures were investigated. Results show that the atomic and molecular hydrogen forms prefer to be adsorbed on the Mg3-Mg3 bridge sites (C sites). Hydrogen molecules are dissociated on the surface with the minimum barrier energy of 0.63eV. There are two stages in the process of hydrogen incorporation, which are hydrogen diffusion on the surface and the penetration from the surface into the subsurface. Two possible pathways of atomic hydrogen penetration from surface into subsurface are found. The calculations of electronic structures show that the hybridization between the s orbital of H and the s orbitals of Mg is major. The Mg-Mg bond on the outmost surface is shortened from 4.48Å to 3.30Å after the hydrogen adsorption on C sites, showing the strong interaction between Mg and H atoms.

Penetration and diffusion of hydrogen in Mg2Ni: A first-principles investigation

First-principles calculations have been used to study the hydrogen adsorption and diffusion in both hexagonal Mg2Ni surface and bulk Mg2Ni, and the hydrogen diffusion rate in bulk Mg2Ni is evaluated. The calculation shows that the adsorption energies on Mg2Ni (100) surface are much higher than in bulk Mg2Ni. For hydrogen diffusing from Mg2Ni (100) surface to subsurface, three diffusion pathways have been studied, and the lowest energy barrier is found to be 0.64 eV. To study the hydrogen atom diffusion in bulk Mg2Ni, nine possible diffusion paths have been considered. The results show hydrogen diffusion from NiNi bridge sites to the most nearby MgNi bridges site is energetically more favorable than the other paths. The energy barrier of this process is 0.34eV, which is close to experimental data of 0.28 ± 0.04 eV. The temperature dependence of the jump rates has been investigated in some details using harmonic transition state theory and semi-classically corrected harmonic transition state theory. The calculated diffusion constant is in good agreement with the experimental data.

A New Method for Analyzing Transient Response of Hydrogen Permeation in Carbon Steel Sheet

In acidic media, corrosion of steel is accompanied by hydrogen evolution reaction and a part of adsorbed hydrogen atoms penetrates into the steel, causing hydrogen embrittlement. There are strong needs to elucidate mechanism and kinetics of hydrogen penetration for inhibiting hydrogen embrittlement. Conventionally, a diffusion coefficient of hydrogen atoms in steel sheet samples was estimated using so-called Devanathan-Stachurski (DS) cell.1 The authors have modified the DS cell with an electrolyte-flow channel in the entry side cell and discovered that the disturbance in a flow-rate causes a similar perturbation in hydrogen exit current i exit as well as hydrogen entry current i entry.2 When a sinusoidal wave perturbation was applied to flow-rate, i entry and i exit showed sinusoidal waveforms with phase shifts θ depending on the perturbation frequency. The phase shift was arisen from a diffusional delay in i exit and could be utilized as a new parameter to discuss the diffusivity of hydrogen atoms in the sample sheets. In previous researches, however, we only focused on the steady value of phase shifts and did not discuss about time-dependent information of the shifts in detail. In this study, we newly developed a method to realize a real-time evaluation of phase shift by fast-Fourier-transform (FFT). We also conducted transient analyses on phase shifts to elucidate more about hydrogen penetration mechanism in carbon sheet. During a series of hydrogen permeation measurement of polycrystalline steel sheet samples, a phase shift obtained by the FFT calculation was gradually increased with measurement time. From an algebraic calculation on diffusion phenomena with sinusoidal perturbation and the previous report,3, 4 the value of θ depends on perturbation frequency f, sheet thickness L, diffusion coefficient D, showing a relationship of θ = tan-1(tan α tanh α) where α = (πfL2 /D)1/2. In the case where the values of f and L are fixed throughout the measurement, therefore, the experimental result indicates that the value of D is gradually decreased. This result suggests the existence and its effect of hydrogen trapping sites in the sample sheet.

The Contribution of Hydrogen to the Loss of Mechanical Properties of a 7046 Aluminium Alloy Pre-Exposed in a Chloride Media

Automotive industry is increasingly affected by standards requiring a major cut of polluting emissions. Rolled sheets of Cu-free 7000-series alloys offer a very attractive compromise between mechanical properties, corrosion resistance, forming and weight. With the continuing need for further down-gauging and light-weighting in transportation sector, as well as other applications, these alloys are being considered for large volume use. Nevertheless, their susceptibility to hydrogen embrittlement (HE) and to stress corrosion cracking (SCC) is a limiting factor. The present work concerns HE susceptibility of a 7046-T4 aluminium alloy exposed to a 0.6M NaCl solution. First results showed a strong decrease of the ultimate elongation for tensile samples after exposure to the chloride solution Surface observations revealed that the alloy was mildly affected by corrosion in this environment: pits initiated rapidly around intermetallic particles but only few pits propagated after several days of exposure. Cross-section of pre-corroded samples showed no intergranular corrosion and the maximal depth for the corrosion defects was about 100 nm which was not enough to lead to a noticeable loss of mechanical properties. Therefore, it was assumed that the decrease of the mechanical properties was related to the penetration of hydrogen inside the materials and the results gave proofs that hydrogen could enter and embrittle the 7046 aluminium alloy even without an applied stress during its exposure to the corrosive solution. Global hydrogen content measurements by melting method confirmed this assertion. Furthermore, comparison of the fracture surface of a healthy specimen and that of a sample pre-exposed to the NaCl solution showed that the ductile fracture mode observed for a healthy specimen was partially replaced by cleavage and brittle intergranular rupture when the sample was pre-corroded. Both fracture modes could be attributed to different hydrogen contents and different trapping sites in the microstructure. The hydrogen localized in the grain boundaries was believed to lead to intergranular decohesion, while the reticular and trapped hydrogen presumably induced cleavage rupture by exacerbating the localization of the plasticity. In addition, tensile tests were performed on samples pre-hydrogenated in a pH 2 sulfuric acid solution with a cathodic potential applied. The aim was to precisely control the hydrogen amount introduced in the samples. The depth and the nature of the fracture mode were then analyzed and related to the hydrogen amount. In parallel, pre-hydrogenated coupons were analyzed by SIMS in order to measure the maximal depth affected by hydrogen and to localize the trapping sites in the microstructure. The coupling of these two methods allowed to conclude about the role of the hydrogen generated by corrosion and to propose a mechanism to explain the embrittlement.

Detection of Hydrogen Permeated Under Atmospheric Corrosive Environment By Surface Potential Measurement

Higher strength steels have been used as some of car parts to make vehicle weight lighter and improve fuel efficiency. However, the higher strength of steels than 1200 MPa shows remarkable susceptibility to hydrogen embrittlement. Hydrogen embrittlement is one of serious problems for a fracture of steel materials. Therefore, it is important to understand the behavior of the hydrogen penetration and permeation caused by corrosion reaction. It is reported that the hydrogen embrittlement occurs even by a little amount of penetrated hydrogen under atmospheric corrosive environment. Some methods such as thermal desorption methods and electrochemical methods are suggested in order to evaluate the behavior of the hydrogen penetration and permeation. These methods can give the amount of permeated hydrogen. However, it is difficult to get the information for distribution of permeated hydrogen. The purpose of this paper is to investigate the possibility of visualization by surface potential measurement. The surface potential was measured by the surface reaction measurement device having an X-Y-Z stage. The polished pure iron plates degreased with ethanol were used as samples. The thickness of the sample is approximately 0.5mm. One side of sample is for hydrogen entry and the other side is for detecting hydrogen permeation. The detective probe and X-Y-Z stage are installed to an acrylic case to control the environment around them. Relative humidity is thought to affect the value of surface potential, so the relationship between relative humidity and surface potential was examined using a relative humidity control system. The relative humidity can be controlled by the system from nearly 0% to 40%. The surface potential was measured at the center of the sample while varying the relative humidity from nearly 0% to 40%. The effect of exposure time to the acrylic case was also examined. 100μl droplet of 0.5 M NaCl solution was added on the sample surface to promote hydrogen entry by corrosion reaction. The surface potential distribution was measured during wetting and after drying. The measurement range was 20mm x 20mm, and the relative humidity in the acrylic case was controlled at nearly 0%. The sample at 10% gave a lower surface potential than that at nearly 0%, and the surface potential hardly changed between 10% and 40%. It was reported that the surface potential shifted negatively by adsorption of molecular water on the sample surface. Except for the result at nearly 0%, the surface potential changed to a negative value with an increase of exposure time to the acrylic case. This is also attributed to the adsorption of water. These results suggest that the surface potential measurement should be conducted at nearly RH 0% to obtain an accurate value. In the measurement of the surface potential distribution change by corrosion reaction, the surface potential of the backside of sample decreased, and the negative potential area was spread with time. It is reported that when molecular hydrogen adsorbed on the surface of iron, the surface potential changed negatively. The surface potential distribution finally looked like the shape of the formed rust. These results imply that permeation of hydrogen produced by corrosion reaction at the entry side effects the surface potential and the distribution.

Preparation of tritium permeation barrier consisting of titanium by the pack cementation method

Abstract In this work, tritium permeation barriers were prepared on the surface of super-clean reduced activation martensitic (SCRAM) steel by the pack cementation method. The pack cementation process was conducted by packing samples in a powder mixture consisting of titanium, ammonium chloride and alumina powder at 1000 °C for 30 min to form a titanized coating. Subsequently, the samples were nitrided in an ammonium atmosphere and then oxidized in air at 760 °C for 1 h to obtain a multilayered structure. The results showed that the as-prepared titanized coatings consisted of two layers. The exterior layer was made of TiN and the interior layer was a diffusion layer resulting from titanium atoms diffusing into the substrate. After being nitrided and then oxidized, the coatings were discovered to have transformed into a three-layered structure. The outer layer was rutile TiO2, the middle layer was Ti-N and the inner layer was Ti-C. Hydrogen permeation tests were performed on the coatings and pure matrix steels at room temperature. The results revealed that the three-layered structure coatings exhibited good barrier properties against hydrogen penetration. This three-layered structure coating may be a good material to increase the hydrogen permeation resistance of SCRAM steel.