Effect Of Hydrogen Pressure Research Articles

Effects of hydrogen pressure and test frequency on fatigue crack growth properties of Ni–Cr–Mo steel candidate for a storage cylinder of a 70 MPa hydrogen filling station

Experiments to investigate the effect of hydrogen pressure and test frequency on the fatigue crack growth properties of a Ni–Cr–Mo steel for the storage cylinder of a 70 MPa hydrogen storage station were conducted. Compact tension specimens were cut out from the storage cylinder. The crack growth properties obtained in hydrogen gas were compared with those obtained in air. Higher hydrogen pressures and lower loading frequencies lead to faster crack growth. However, there is an upper limit to the acceleration of the fatigue crack growth rate in hydrogen gas, which can be used for the design of the hydrogen cylinder. The effect of long and large inclusions present in the steel was also verified. The observations carried out on specimen fracture surfaces showed that the low population of inclusions did not influence the fatigue crack growth rate.

Synthesis and Application of Polystyrene Nanospheres Supported Platinum Catalysts in Enantioselective Hydrogenations

Nearly monodisperse polystyrene nanospheres coated with platinum have been synthesized and applied successfully in the cinchona alkaloid-modified enantioselective hydrogenation of ethyl pyruvate. During the catalyst preparation broadly varied experimental conditions were used resulting in several catalysts with different properties. The effect of hydrogen pressure, solvent, modifier and polystyrene nanoparticle size on the enantioselectivity was also studied. Based on the results the effect of support on the mechanism of the enantiodifferentiation has been discussed.

Hydrocracking of Di(1-Naphthyl)methane over Acid Solid Catalyst

As a model reaction for coal liquefaction, the hydrocraking of di(1-naphthyl)methane (DNM) was investigated using acid solid catalyst (ASC) under different reaction conditions. The results show that acid solid catalyst selectively catalyzes DNM hydrocraking to give 1-methylnaphthalene and naphthalene, without hydrogenation product. The rate of DNM hydrocraking strongly depended on reaction temperature, reaction time and the catalyst feed, whereas effect of hydrogen pressure was not serious. The effects of acid solid catalyst is to make Car-Calk bond cleavage.

Hydrogen Content and Microvoid Hydrogen Pressure in Steel Wall of Spherical High Pressure Vessel

Hydrogen in the steel wall can cause hydrogen embrittlement of the wall material and thereby change the carrying capacity of the vessel. A theoretical model of hydrogen diffusion in the steel wall of a high pressure vessel was established and the formula of hydrogen content in the steel wall was deduced. Based on the hydrogen content formula, the formula of hydrogen pressure within microvoids which naturally exist in the steel wall of a spherical pressure vessel was deduced. At last, as an example to demonstrate the meaning of solving hydrogen pressure in microvoids, by using a representative volume element (RVE) model to carry out FE numerical simulation, the effects of hydrogen pressure on equivalent mechanical properties of the wall material were studied. It is found that the higher the gas pressures are, the lower the ultimate strength, specific elongation and percentage contraction of area are, which is in good accordance with the phenomena of metal hydrogen embrittlement.

Self-ignition combustion synthesis of LaNi 5 at different hydrogen pressures

In this paper, we describe the self-ignition combustion synthesis (SICS) of LaNi 5 utilizing the hydrogenation heat of metallic calcium at different hydrogen pressures, and focus on the effect of hydrogen pressure on the ignition temperature and the initial activation of hydrogenation. In the experiments, La 2O 3, Ni, and Ca were dry-mixed, and then heated at 0.1, 0.5, and 1.0 MPa of hydrogen pressure until ignition due to the hydrogenation of calcium. The products were recovered after natural cooling for 2 h. The results showed that the ignition temperature lowered with hydrogen pressure. The products changed from bulk to powder with hydrogen pressure. This was probably caused by volume expansion due to hydrogenation at higher pressure. The product obtained at 1.0 MPa showed the highest hydrogen storage capacity under an initial hydrogen pressure of 0.95 MPa. The results of this research can be applied as an innovative production route for LaNi 5 without the conventional melting of La and Ni.

Effect of hydrogen pressure on growth kinetics of Nd2Fe14B phase during hydrogen-induced reverse phase transformation in Nd2Fe14B type hard magnetic alloy

The effect of initial hydrogen pressure on growth kinetics of Nd₂Fe₁₄B phase during hydrogen-induced reverse phase transformation in the industrial Nd₂Fe₁₄B hard magnetic alloy has been studied. It has been determined that, as the temperature and the initial hydrogen pressure increase, a reverse phase transformation significantly accelerates. It has been shown that the kinetics of growth of Nd₂Fe₁₄B phase is controlled by the Fe atoms diffusion and that the rate growth of new Nd₂Fe₁₄B phase increase with increase of initial hydrogen pressure. On the base of the Kolmogorov-Hillert-Smirnov kinetic models the kinetic equation for describing of influence of initial hydrogen pressure on the isothermal kinetic diagram for this transformation has been proposed.

Effect of hydrogen pressure and temperature on the reaction kinetics between Fe-doped Mg and hydrogen gas

The effect of hydrogen pressure and of reaction temperature on the phase transformation from Mg to MgH 2 by exposure of Fe doped metallic Mg to hydrogen gas has been studied with the purpose of evaluating the importance of operative parameters on the hydrogen storage characteristics of this system. Two temperatures have been investigated and, for each temperature, two values of the hydrogen gas pressure. The gas pressure has been adjusted in order to induce the same thermodynamic driving force in samples processed at different temperatures, with the aim of separating the effect of temperature from the one of gas pressure. Experimental results show that the reaction mechanism is independent from the value of the operative parameters which, instead, influence strongly the absolute value of the kinetics constant. Sample microstructure during phase transformation is affected in a major way by the reaction temperature, with the gas pressure playing a minor role.

Thermochemical approach to the mechanism and kinetics of NiO reduction with hydrogen

The possibility of using the thermochemical approach to thermal decomposition of solids, previously developed by the author, to interpretation of the mechanism and kinetics of reduction of metal oxides with hydrogen was studied. Many properties of NiO reduction with hydrogen, including formation of metal nuclea, the nature of induction period, autocatalysis effect, equimolar and isobaric periods of reduction, the character of the effect of hydrogen pressure on reduction rate, and the nanocrystalline structure of a reduced metal, were explained in terms of the given approach.

Gel-synthesis, structure, and properties of sulfur-containing chitosan derivatives

The possibility of using the thermochemical approach to thermal decomposition of solids, previously developed by the author, to interpretation of the mechanism and kinetics of reduction of metal oxides with hydrogen was studied. Many properties of NiO reduction with hydrogen, including formation of metal nuclea, the nature of induction period, autocatalysis effect, equimolar and isobaric periods of reduction, the character of the effect of hydrogen pressure on reduction rate, and the nanocrystalline structure of a reduced metal, were explained in terms of the given approach.

Hydrogen Diffusivity and Solubility in Internally Oxidized Pd<sub>0.97</sub>Zr<sub>0.03</sub> and Pd<sub>0.97</sub>Nb<sub>0.03</sub> Alloys

Internally oxidized (I.O.) Pd0.97Zr0.03 and Pd0.97Nb0.03 alloys were submitted to gas permeation tests with temperatures in the range of 473-873 K. The internal oxidation was kept in a conventional furnace at 1073 K for 24 hours in air contact. The formation of nano-oxides, ZrO2 and Nb2O5, dispersed in the Pd matrix was observed. SEM images showed a preferential segregation of these oxides in the grain boundaries. It was observed that the diffusion coefficient in the sample containing Nb oxide was smaller than that in the Pd-Zr oxide. The effect of hydrogen pressure was investigated in the Pd-Nb samples. It was observed that the hydrogen diffusion coefficient increases with increasing the pressure. The hydrogen solubility is bigger for the Pd-Zr internally oxidized. This effect is attributed to the Zr nanoxides, which are smaller than Pd-Nb precipitates and then offer more interface for trapping the hydrogen.

Liquid phase hydrogenation of acethydrazone to N'-methyl acethydrazide over Pd/γ-Al2O3 catalyst

Catalytic hydrogenation of acethydrazide (AH) is the main step in the production of N'-methyl acethydrazide (MAH). In this step, AH reacts with formaldehyde to produce acetylhydrazone (AOH). AOH is hydrogenated in the presence of 5% Pd/γ-Al2O3 catalyst to MAH. In this paper, the effects of hydrogen pressure, catalyst loading and initial concentration of AOH on the initial rate of hydrogenation were studied in a batch slurry reactor within a temperature range of 303-333K. The hydrogenation rate was first order with respect to hydrogen concentration at lower hydrogen pressures. However, at higher pressures, the rate became independent of both hydrogen and initial AOH concentrations. A single site Langmuir-Hinshelwood type formulation was found to describe adequately the kinetic data. A good correlation was observed between the predicted concentration vs. time profiles and those determined experimentally. The apparent activation energy was calculated from the initial rates as 40.6 kJ/mol.

The influence of hydrogen pressure on the heterogeneous hydrogenation of β-myrcene in a CO 2-expanded liquid

This paper presents the second part of work on the effect of hydrogen partial pressure on the hydrogenation of a terpene in a CO 2-expanded liquid. The effect of hydrogen partial pressure on the hydrogenation of β-myrcene possessing three C C bonds catalysed by alumina-supported ruthenium and rhodium was studied. Experiments were performed at various hydrogen pressures in the range from 2.0 up to 4.5 MPa at a fixed total pressure of 12.5 MPa. In all the conditions the reaction proceeded in two phases (liquid + gas), that is, the total pressure was below the critical pressure of the CO 2 + β-myrcene + H 2 system. The liquid phase volume is expanded in relation to the initial volume of β-myrcene in a fashion that is strongly dependent on the hydrogen and carbon dioxide pressures. An increase of H 2 pressure concomitantly diminishes carbon dioxide pressure, which leads to the enhancement of the liquid phase in hydrogen and a terpene. It does not direct to straightforward higher reaction rate, but surprisingly the effect of higher concentrations either hydrogen or β-myrcene is opposite. It is attributed to the fact that the hydrogenation of β-myrcene rate-controlling factor turns out to be the hydrogen to β-myrcene ratio which decreases as the hydrogen pressure increases. These unexpected appealing results present that lower pressures of hydrogen guide to higher hydrogen/β-myrcene ratios in the liquid phase, but on the other hand they also amplify the initial reaction rate constant. The obtained results are opposite to the results achieved for effect of hydrogen pressure on the Pd-catalysed hydrogenation of limonene consisting of two C C double bonds.

水素ガス中におけるフェライト・パーライト鋼の疲労き裂進展特性に及ぼす水素圧力と試験周波数の影響

水素ガス中におけるフェライト・パーライト鋼の疲労き裂進展特性に及ぼす水素圧力と試験周波数の影響

Measurement of steady-state hydrogen electrode reactions on Alloys 600 and 690 tubes

The steady-state polarization measurements for HER and HOR were carried out in order to obtain the effects of hydrogen pressure, solution pH, and temperature on the current densities of Alloys 600 and 690, respectively. Optimization was performed to obtain the electrokinetic parameters of HER and HOR on Alloys 600 and 690 such as forward and reverse transfer coefficients and equilibrium corrosion densities. From the optimization process, the activation energies, E ac, of both hydrogen reactions on the surfaces of the Alloys 600 and 690 tubes were obtained as 30.5 kJ/mole on the surface of Alloy 600 tube and 35.6 kJ/mole on Alloy 690 tube. Furthermore, the equilibrium exchange current densities of hydrogen electrode reaction, i 0(H 2), on the surface of the Alloys 600 and 690, respectively, were proposed as functions of hydrogen pressure, solution pH, and temperatures.

Effect of Hydrogen Pressure on the Size of Nickel Nanoparticles Formed during Dewetting and Reduction of Thin Nickel Films

We report a study of the formation of nickel nanoparticles by the dewetting of nickel metal films under different reduction conditions. The effects of both film thickness and temperature of dewetting on the size distributions of Ni nanoparticles are in agreement with previously reported studies. However, our work evidences that the hydrogen pressure applied during the reduction process has a drastic influence on the size of the formed Ni nanoparticles, the hydrogen pressure effect being all the more important that the film thickness is small. We interpret this effect by the formation of nickel metal hydride displacing the surface free energy balance of the system in favor of the dewetting. Moreover, the replacement of hydrogen by an inert gas allows us to rule out Ostwald’s ripening as the mechanism originating the sintering of the nanoparticles.

Effect of Boron on the Activation Energy of the Decomposition of LiBH4

We studied the decomposition reaction kinetics of lithium borohydride (LiBH4) with and without boron as an additive under various hydrogen pressures. The decomposition of LiBH4+B was studied by means of differential scanning calorimetry and thermogravimetry. Boron addition improves the dehydrogenation process, resulting in a decomposition temperature of 150 °C. A novel model was applied to separate thermodynamic and kinetic effects and to evaluate the activation energy of decomposition. The model takes into account the effect of hydrogen pressure on the reaction and allows us to evaluate the thermodynamic parameters, i.e., the enthalpy and entropy of reaction. Moreover, the effect of boron on the reaction kinetics is also demonstrated by the reduction of the activation energy from Ea* = 59 ± 2 kJ/mol (pure system) to Ea* = 54.8 ± 0.7 kJ/mol.

Effect of hydrogen pressure on disproportionation kinetics of Nd–Fe–B alloy

In the anisotropic HDDR treatment of the Nd–Fe–B alloy, the critical step determining the texture in the final product is the disproportionation. In the present study, the effect of hydrogen pressure on the disproportionation kinetics of the Nd 12.5Fe 80.6B 6.4Ga 0.3Nb 0.2 alloy was examined by isothermal thermopiezic analysis (TPA). It was found that the overall reaction rate of disproportionation of the hydrogenated Nd 12.5Fe 80.6B 6.4Ga 0.3Nb 0.2 alloy was influenced strongly by the hydrogen pressure. With the hydrogen pressure of 0.1 and 0.06 MPa, the overall reaction rate of disproportionation was controlled by simple linear relationship. However, the overall reaction rate of disproportionation with the low hydrogen pressure of 0.02 MPa was expressed by parabolic rate equation. The activation energy for the disproportionation of Nd 12.5Fe 80.6B 6.4Ga 0.3Nb 0.2 alloy with hydrogen pressure of 0.02 MPa was significantly higher than those with hydrogen pressure of 0.1 and 0.06 MPa. The activation energy for the disproportionation with hydrogen pressure of 0.1, 0.06 and 0.02 MPa was calculated to be approximately 272, 262, and 321 kJ/mol H, respectively. It was suggested that the disproportionation of the alloy with initial hydrogen pressure of 0.02 MPa might take place via different mechanisms from that with initial hydrogen pressure of 0.1 and 0.06 MPa.

Direct synthesis of MgH2 nanofibers at different hydrogen pressures

Abstract This paper describes the direct synthesis of magnesium hydride (MgH 2 ) nanofibers by hydriding chemical vapor deposition (HCVD), in which the effect of hydrogen pressure on the production rate, the composition and the shape of products obtained were examined by using X-ray diffraction (XRD), scanning electron microscopy (SEM) and Brunauer–Emmett–Teller (BET). The XRD patterns showed that the main product in each case was MgH 2 ; in particular, the products formed at 2, 3 and 4 MPa were highly pure. In contrast, at a hydrogen pressure of 1 MPa, unhydrided Mg was deposited along with MgH 2 . The SEM images also revealed orientation of the as-deposited products; higher pressures of 3 and 4 MPa caused the formation of straight and curved nanofibers, and lower ones of 1 and 2 MPa, highly curved nanofibers and nanorods with a few straight nanofibers. With pressurizing hydrogen, not only the BET specific surface areas of the products but also the production rate increased. The results also appealed that HCVD could control the shape/size of MgH 2 nanofibers by changing the pressure via only a single operation.

Electrochemical corrosion and mechanical behaviors of the charged magnesium

The electrochemical corrosion and mechanical behaviors of the charged magnesium were investigated using Mott–Schottky (M–S) test and slow strain rate test (SSRT), respectively. The results showed that the hole carrier and vacancy concentrations in the corrosion film increased after cathodic charging due to the formation of magnesium hydroxide. The increasing vacancy concentration caused the increase of the permeation rate of hydrogen to the interior of matrix. When the inner stress caused by synergistic effect of hydrogen pressure and expansion stress of the formation of magnesium hydride was above the fracture strength, crack initiated and propagated. It indicated that hydrogen embrittlement (HE) mechanism for the stress cracking corrosion (SCC) of magnesium and its alloys. After cathodic charging, the corrosion resistance and mechanical properties of matrix deteriorated.

Extensive Re‐Investigations of Pressure Effects in Rhodium‐ Catalyzed Asymmetric Hydrogenations

AbstractThe catalytic hydrogenation of three pro‐chiral substrates methyl Z‐α‐acetamidocinnamate (MAC), methyl 2‐acetamidoacrylate (M‐Acrylate) and ethyl 4‐methyl‐3‐acetamido‐2‐propanoate (E‐EMAP) with rhodium precursors complexed with chiral diphosphines is reported at 1–30 bar hydrogen pressure. A library of 56 chiral diphosphines, including 23 BINAP derivatives, 7 JOSIPHOS, 5 BIPHEP, 3 DUPHOS derivatives, and 18 other ligands, was used. While it was generally accepted that high hydrogen pressure would result in lower ees, it is now demonstrated on a statistical basis that an equivalent distribution between beneficial and detrimental pressure effects on ee prevails and that the hydrogen pressure effect on enantioslectivity is not an isolated phenomenon since more than 33% of the reaction systems studied are strongly affected. In some case, the enantioselectivity can be improved up to 97% just by applying a higher hydrogen pressure. Extension of these conclusions to other non‐chiral reagents is proposed.