Reduction Of Hydrogen Concentration Research Articles

Effect of gases on crystallization of heat-resistant chromium steels

It has been shown that the main influence on the crystallization of heat‑resistant chromium steels is hydrogen. It is a demodifying element of the casting structure. The mechanism of the influence of hydrogen on the crystallization of heat‑resistant chromium steels can be explained from the position of nanostructured crystallization of casting alloys. Dissolved hydrogen atoms, adsorbing on elementary nanocrystals of iron and chromium in melts of heat‑resistant chromium steels, prevent the combination of nanocrystals into nuclei of crystallization of α‑phase microcrystals. As a result, castings with an unmodified structure are obtained. Reduction of hydrogen concentration in melts of heat‑resistant chromium steels contributes to formation of modified structure in castings at their hardening.

Hydrogen diffusion model at welding high-strength steels

Physical and mathematical models for hydrogen diffusion taking into account welded joint inhomogeneity in microstructure, temperature distribution, residual stresses, and reversible and irreversible traps of hydrogen are presented. The problem of diffusion is formulated with respect to the conditional potential of mass transfer and chemical potential. By the example of single-pass butt welding of 2.25Cr—1Mo high strength ferritic steel, the effects of welding consumables on diffusion processes are demonstrated. Utilization of austenitic consumables instead of ferritic ones leads to a reduction in hydrogen concentration in the HAZ by 3 times. The residual stresses affect slightly.

Improved Hydrogen Embrittlement Resistance of Steel by Shot Peening and Subsequent Low-temperature Annealing

The effect of shot peening and subsequent low-temperature annealing (SP treatment) on hydrogen embrittlement in tempered martensitic steel was investigated comparing the typical hydrogen charging methods, constant current controlled cathodic charging test and combined cyclic corrosion test (CCT). The hydrogen entry behavior was evaluated by hydrogen permeation technique and hydrogen visualization using secondary ion mass spectrometry. The SP treatment improved hydrogen embrittlement resistance in both hydrogen charging methods. On the other hand, the effect of SP treatment on the hydrogen entry was different depending on hydrogen charging method. The hydrogen entry was suppressed by SP treatment in the cathodic charging test because the compressive residual stress reduced hydrogen concentration in the surface layer and the potential increased by the increase of surface roughness and the formation of a surface film. In CCT, although the surface hydrogen concentration decreased due to compressive residual stress, the total hydrogen content did not decrease by SP treatment since the surface film disappeared by corrosion and an increase of surface roughness led to an increase in hydrogen entry sites. The improved hydrogen embrittlement resistance by the SP treatment in the cathodic charging test is a result of hydrogen entry suppression in addition to the effect of compressive residual stress. In CCT, the hydrogen embrittlement resistance was improved by SP treatment due to effect of compressive residual stress, i.e., the suppression of stress concentration as well as the stress-induced hydrogen diffusion in stress concentration area and the reduction of hydrogen concentration in the surface layer.

Effect of microstructural inhomogeneity on hydrogen diffusion in welded joints

Hydrogen is a main factor in cold cracking or hydrogen-induced cracking. The most crack susceptible region of a steel welded joint is the heat affected zone (HAZ). Formulation and functional-analytical solution of the one-dimensional problem of hydrogen diffusion in an inhomogeneous butt-welded joint taking into account weld and joint dimensions as well as hydrogen diffusion coefficients and solubilities are presented. It is shown that the peak hydrogen concentration in the HAZ of inhomogeneous joints varies in direct proportion to the initial hydrogen concentration in the weld metal. Peak hydrogen concentration is inversely proportional to the ratio of hydrogen solubilities in the weld and HAZ and the square root of diffusion coefficient ratio of the HAZ and weld. The peak hydrogen concentration in the HAZ can exceed 80% of the initial concentration in the weld if martensitic steel is welded using low-carbon low-alloy welding consumables. Utilization of austenitic consumables leads to reduction in hydrogen concentration in the HAZ by 75–85% in comparison with non-austenitic consumables.

Effect of Controlling Factors on Reduction of Hydrogen Concentration in Fuel Debris Storage Containers for 1F

Effect of Controlling Factors on Reduction of Hydrogen Concentration in Fuel Debris Storage Containers for 1F

Thermal and electrochemical performance assessment of a high temperature PEM electrolyzer

In this paper, detailed effects of operating conditions and design parameters including temperature, pressure, gas diffusion layer (GDL) thickness, membrane thickness and GDL porosity on the performance of a high temperature proton exchange membrane electrolyzer cell (PEMEC) are studied. A CFD analysis is carried out using a finite volume method based on a fully three-dimensional model. The model is verified against experimental data and the realistic effects of varying operating conditions are considered. The results indicate that decrease of operating temperature from 403 K to 373 K results in reduction of hydrogen concentration at the membrane-catalyst interface from 2.2 × 10−4 to 1.9 × 10−4 mol/m3. The temperature and hydrogen concentration under rib area of channel are relatively higher due to the accumulation of water under this area that leads to higher electrochemical rate. An increase of GDL thickness from 0.2 mm to 0.5 mm at a voltage of 1.65 V leads to reduction of current density from 0.426 A/cm2 to 0.409 A/cm2. The porosity of the GDL has no significant effect on the polarization curve. The current density of the PEMEC for a membrane thickness of 50μm at voltage of 1.6 V is 48% higher than a membrane thickness of 200μm.

Stress corrosion cracking susceptibility of 310S stainless steel in hydrogenated hot water

The stress corrosion cracking (SCC) susceptibility of solution-annealed 310S stainless steel (SS) was examined by means of slow-strain rate test (SSRT) method in hot water (288 °C) with dissolved-hydrogen (DH), and the results were compared with those of 316L SS. Almost no SCC was observed in 310S SS, while a remarkable SCC was found in 316L SS showing brittle fracture surfaces and cracks on specimen side surfaces. The SCC observed in 316L SS started as IGSCC while necking, and transferred to TGSCC. It was also shown that sensitization resulted in the suppression of IGSCC of 316L SS. On the assumption that the SCC in hydrogenated hot water can be interpreted in terms of hydrogen assisted SCC, the mechanism of the suppression of SCC in 310S SS is related with a higher nickel content which increases stacking fault energy and facilitates cross slip of dislocations, resulting in the reduction of hydrogen concentration on a unit area of slip plane.

Basic Study on Reduction of Hydrogen Concentration by a Passive Autocatalytic Recombiner Installed in a Seated Container

Basic Study on Reduction of Hydrogen Concentration by a Passive Autocatalytic Recombiner Installed in a Seated Container

Fundamental Experiments on Reduction of Hydrogen Concentration in a Long-Term Waste Storage Container with PAR

Fundamental Experiments on Reduction of Hydrogen Concentration in a Long-Term Waste Storage Container with PAR

CFD modelling of hydrogen starvation conditions in a planar Solid Oxide Fuel Cell

Abstract The aim of this study was to highlight the interest of using CFD technique as a diagnostic tool of a malfunctioning Solid Oxide Fuel Cells. Hydrogen starvation of a SOFC due to nitrogen dilution is one of the cell dysfunctions and can lead to its degradation. Identification of the starvation point allows to improve cell performance and establish the best conditions for degradation tests. To illustrate a potential of the CFD tool, several simulations of a single planar SOFC and its behaviour under hydrogen starvation were performed and analysed. The results showed that at lower cell voltage values of 0.3 and 0.5 V significant gradients in the electric current were noticed due to a local reduction in hydrogen concentration. The CFD analysis allowed defining desirable mass flow rate of hydrogen to SOFCs to avoid fuel starvation. The model constitutes a helpful tool for optimizing cell design and operational conditions.

Effects of Surface Temperature on High-Rate Etching of Silicon by Narrow-Gap Microwave Hydrogen Plasma

Effects of surface temperature on high-rate etching of Si by narrow-gap microwave hydrogen plasma have been investigated. The etch rate strongly depended on the surface temperature. The optimum temperature for the etching at high rate was about 70 °C. With increasing the temperature higher than 70 °C, decrease in etch rate was observed, and activation energy for the reaction process was estimated to be about -1.8 kcal/mol. This value agreed well with the result of the previous studies using low-pressure plasma conditions. In addition, hydrogen concentration was also affected by the surface temperature. The reduction in hydrogen concentration near the surface was observed in the etched sample at higher temperature. From these results, reaction mechanism causing the decrease in etch rate with the temperature increase has been discussed in terms of both desorption and in-diffusion of hydrogen from the surface.

Optimization study of metal-organic chemical vapor deposition of ZnO on sapphire substrate

Metal-organic chemical vapor deposition (MOCVD) of ZnO with dimethylzinc (DMZn) and tert-butanol (t-BuOH) as Zn and oxygen precursors has been investigated and optimized in this work. Growth experiments show hydrogen addition, usually used to suppress carbon incorporation, should be kept at a low concentration due to its strong etching effect on ZnO. We found that reduction of hydrogen concentration also results in smoother films. Growth at a reactor pressure of 4–8kPa resulted in smoother films as compared to growth at 2kPa, and growth temperature of 470°C is also observed to result in smoother films, while fully suppressing gas phase pre-reactions. A low growth rate also helps to obtain smooth surface morphology, which is helpful to achieve improved crystal quality of the subsequent high temperature epilayer. The optimized growth parameters provided by this work are helpful for achieving high quality ZnO epilayer growth on sapphire substrates.

Thermodynamic study of hydrogen production from crude glycerol autothermal reforming for fuel cell applications

This study presents a thermodynamic analysis of hydrogen production from an autothermal reforming of crude glycerol derived from a biodiesel production process. As a composition of crude glycerol depends on feedstock and processes used in biodiesel production, a mixture of glycerol and methanol, major components in crude glycerol, at different ratios was used to investigate its effect on the autothermal reforming process. Equilibrium compositions of reforming gas obtained were determined as a function of temperature, steam to crude glycerol ratio, and oxygen to crude glycerol ratio. The results showed that at isothermal condition, raising operating temperature increases hydrogen yield, whereas increasing steam to crude glycerol and oxygen to crude glycerol ratios causes a reduction of hydrogen concentration. However, high temperature operation also promotes CO formation which would hinder the performance of low-temperature fuel cells. The steam to crude glycerol ratio is a key factor to reduce the extent of CO but a dilution effect of steam should be considered if reforming gas is fed to fuel cells. An increase in the ratio of glycerol to methanol in crude glycerol can increase the amount of hydrogen produced. In addition, an optimal operating condition of glycerol autothermal reforming at a thermoneutral condition that no external heat to sustain the reformer operation is required, was investigated.

Stress development kinetics in plasma-enhanced chemical-vapor-deposited silicon nitride films

The kinetics of post-deposition irreversible tensile stress development on annealing in plasma-enhanced chemical-vapor-deposited silicon nitride films are described. Films were deposited at 150, 250, and 300 °C, and in situ stress measurements were performed during thermal cycling and annealing at various temperatures up to 500 °C and for annealing times up to 36 h. A constitutive relationship between stress development and hydrogen concentration change based on a modified first-order rate law that assumes a spread in activation energies for hydrogen reaction and exsolution is proposed and found to adequately describe stress development kinetics. The long-standing belief that stress development is generated by the evolution of bonded hydrogen is validated on comparison of film stress and hydrogen concentration, as measured by forward recoil spectrometry and infrared spectroscopy. Stress development is found to be proportional to the reduction in hydrogen concentration throughout annealing with a proportionality constant that depends on deposition temperature.

Low-temperature metalorganic chemical vapor deposition of Al2O3 for advanced complementary metal-oxide semiconductor gate dielectric applications

A low-temperature metalorganic chemical vapor deposition process was developed and optimized, using a design of experiments approach, for the growth of ultrathin aluminum oxide (Al2O3) as a potential gate dielectric in emerging semiconductor device applications. The process used the aluminum β-diketonate metalorganic precursor [aluminum(III) 2,4-pentanedionate] and water as, respectively, the metal and oxygen source reactants to grow Al2O3 films over a temperature range from 250 to 450 °C. The resulting films were analyzed by x-ray photoelectron spectroscopy, x-ray diffraction measurements, Rutherford backscattering spectrometry, nuclear-reaction analysis for hydrogen profiling, scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. The as-deposited Al2O3 phase was amorphous and dense and exhibited carbon and hydrogen incorporation of, respectively, 1 and 10 at.%. Postannealing at 600 °C led to a reduction in hydrogen concentration to 1 at.%, while maintaining an amorphous Al2O3 matrix.

Catalytic effect of Ni for activation of Mg-doped GaN in N 2 and N 2O

Catalytic effect of Ni for activation of metalorganic chemical vapor deposition-grown Mg-doped GaN in N 2 and N 2O has been investigated. P-type GaN has been obtained at an annealing temperature as low as 200°C using the Ni catalytic film in N 2O as well as in N 2. Moreover, the hole concentrations for the samples obtained by annealing in N 2O were in good agreement with those obtained in N 2 in the whole annealing temperature range. These results indicate that the Ni film effectively acts as a catalyst to enhance hydrogen desorption at the surface of GaN, which results in the reduction of hydrogen concentration in GaN at low annealing temperatures. It has also been suggested that the catalytic activity of Ni to enhance hydrogen desorption is much stronger than that of N 2O. Therefore, an introduction of oxygen in the annealing atmosphere is not necessary for effective removal of hydrogen under the existence of the Ni film.

Improved performance of laterally oxidized GaInP/AlGaInP lasers by thermal annealing

The improvement of efficiency and threshold of visible AlGaInP/GaInP laser diodes, which use buried AlAs native oxides for carrier and optical confinement, is described. Annealing of completed laser bars in an inert atmosphere lowers the threshold current and dramatically increases the external differential quantum efficiency. The characteristic temperature of the devices also increases from 74.8 to 125 K, indicating that the electron confinement is greatly enhanced in the annealed lasers, resulting in the observed improved performance. Secondary-ion mass spectrometry measurements reveal a reduction in hydrogen concentration in the laser cladding regions. This suggests that the improved electron confinement can be attributed to increased acceptor activation due to reduced hydrogen passivation.

Radiation-induced interface state generation in MOS devices with reoxidised nitrided SiO2 gate dielectrics

In this letter, the radiation-induced interface state generation ADh in MOS devices with reoxidised nitrided gate oxides has been studied. The reoxidised nitrided oxides were fabricated by rapid thermal reoxidation (RTO) of rapidly thermal nitrided (RTN) SiO2. The devices were irradiated by exposure to X-rays at doses of 0.5–5.0 Mrad (Si). It is found that the RTO process improves the radiation hardness of RTN oxides in terms of interface state generation. The enhanced interface ‘hardness’ of reoxidised nitrided oxides is attributed to the strainless interfacial oxide regrowth or reduction of hydrogen concentration during RTO of RTN oxides.

Optical properties of ion-beam-deposited ion-modified diamondlike (a-C:H) carbon

Diamondlike carbon (DLC) is a hard, semitransparent material usually containing varying amounts of hydrogen. These materials have numerous potential applications, including use as coatings for infrared optics, and as such, the effects of damaging irradiation is of practical interest. In this paper we present results of variable angle spectroscopic ellipsometric (VASE) studies of ion-beam-deposited DLC films. These films have been further modified by directing 1-MeV gold ions, as well as 6.4-MeV fluorine ions, through the DLC and into the underlying silicon substrates, and the percentage of hydrogen in the film was measured versus fluence using proton recoil analysis. Optical analysis was performed assuming the Lorentz oscillator model. Three versions were used: one oscillator, two oscillator (with one fixed in energy), and two oscillator with all parameter variable. The latter model fits the VASE data extremely well, and the two oscillators can be interpreted as involving π to π* and σ to σ* band transitions. With ion modification the oscillators shift to lower photon energy, consistent with reduction in hydrogen concentration and possible increased graphitization.

Excellent charge-trapping properties of ultrathin reoxidized nitrided oxides prepared by rapid thermal processing

7.7-nm-thick oxide nitrided at 950 degrees C and 1150 degrees C for 60 s were reoxidized by rapid thermal processing in dry oxygen at 900-1150 degrees C for 15-200 s. The nitridation-condition and reoxidation-condition dependences of charge to breakdown (Q/sub BD/), flat-band voltage shift ( Delta V/sub FB/), and increase of midgap interface state density Delta D/sub itm/ under high-field stress were studied. Rapid reoxidation achieves striking improvement of dielectric integrity: the Q/sub BD/ is improved by about 16 times and both the Delta V/sub FB/ and Delta D/sub itm/ are reduced by more than two orders of magnitude compared with those of thermal oxides. A correlation between the improvement and a reduction of hydrogen concentration by reoxidation is found.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>