High-pressure Hydrogen Atmosphere Research Articles

Chemical Stability of High-Entropy Spinel in a High-Pressure Pure Hydrogen Atmosphere.

This paper focuses on high-entropy spinels, which represent a rapidly growing group of materials with physicochemical properties that make them suitable for hydrogen energy applications. The influence of high-pressure pure hydrogen on the chemical stability of three high-entropy oxide (HEO) sinter samples with a spinel structure was investigated. Multicomponent HEO samples were obtained via mechanochemical synthesis (MS) combined with high-temperature thermal treatment. Performing the free sintering procedure on powders after MS at 1000 °C for 3 h in air enabled achieving single-phase (Cr0.2Fe0.2Mg0.2Mn0.2Ni0.2)3O4 and (Cu0.2Fe0.2Mg0.2Ni0.2Ti0.2)3O4 powders with a spinel structure, and in the case of (Cu0.2Fe0.2Mg0.2Ti0.2Zn0.2)3O4, a spinel phase in the amount of 95 wt.% was achieved. A decrease in spinel phase crystallite size and an increase in lattice strains were established in the synthesized spinel powders. The hydrogenation of the synthesized samples in a high-pressure hydrogen atmosphere was investigated using Sievert's technique. The results of XRD, SEM, and EDS investigations clearly showed that pure hydrogen at temperatures of up to 250 °C and a pressure of up to 40 bar did not significantly impact the structure and microstructure of the (Cr0.2Fe0.2Mg0.2Mn0.2Ni0.2)3O4 ceramic, which demonstrates its potential for application in hydrogen technologies.

Nagynyomású hidrogénatmoszférás kemence gyártása szénacélok elridegedésének vizsgálatához

Összefoglalás. A hidrogén tárolása iránti igény egyre növekszik, melynek oka az, hogy a hidrogén mint alternatív energiahordozó jelentős szerepet játszik a szén-dioxidkibocsátás-csökkentési törekvésekben. Azonban, az elridegedési folyamatok körében a hidrogén által előidézett károsodások jelentik a legkomolyabb problémát az acélokra nézve. Kutatómunkánk során egy nagynyomású hidrogénatmoszférás hőkezelésre alkalmas autoklávot terveztünk, majd gyártottunk. Az autoklávban P355 NH minőségű alapanyagból kimunkált szabványos Charpy-féle ütőpróbatesteket hőkezeltünk 150 °C-on, 40 bar túlnyomáson, 200 órán keresztül, tiszta hidrogén atmoszférában. A vizsgálatok eredményei alapján megállapítottuk, hogy a jelentős mértékű elridegedés a hidrogénezési folyamat után sem történt. Summary. The demand for hydrogen storage is growing. The primary reason for this is that hydrogen as an alternative energy carrier is playing a significant role in carbon reduction efforts as a fuel for road and maritime transport. In addition, hydrogen can be seen as a long-term flexible energy storage option. Hydrogen as an energy carrier is expected to play a significant role in residential and industrial use in the future. A first step in this development is the mixing of hydrogen with natural gas in small quantities. Increasing the share of hydrogen would not only reduce CO2 emissions, but would also facilitate the development of different hydrogen production methods and thus reduce production costs. The upper safety limit for hydrogen blending with natural gas is set by the national specification of the natural gas supply, possible material quality restrictions and the tolerance of the most sensitive equipment in the network. For this reason, the maximum allowable hydrogen content in natural gas is generally limited to 2,5%. However, among the embrittlement processes, hydrogen-induced damage is the most serious problem for both non-alloy and low-alloy steels. Atomic hydrogen diffuses in steel at high rates. The diffusion rate is orders of magnitude higher than that of other elements; this is due to the small atomic diameter of hydrogen. To investigate the degradation of different carbon steels in a high-pressure hydrogen atmosphere, a hydrogenation furnace was designed and fabricated at the Department of Materials Science and Engineering at BME. The hydrogenation furnace is the main part of a complex mechanical engineering system, for the operation of which the mechanical, heating, electrical supply, control and gas handling components are indispensable. The entire design process of the furnace was led by József Blücher, Professor Emeritus at BME, with the help of the engineers and technicians working on the project. Standard Charpy impact test specimens were machined from P355 NH grade material to test the embrittlement of carbon steels. The hydrogenation temperature was 150 °C, the internal overpressure in the chamber was 40 bar, the hydrogenation time was 200 hours and the atmosphere was hydrogen gas of purity 5.0. The impact test was carried out at -20, 0 and +20 °C. Based on the results of the tests, it can be concluded that there was no significant degree of degradation both before hydrogenation and after prolonged exposure to hydrogen. It can be concluded that the tube material used as a sample is suitable for operation in a hydrogen medium. Based on the analysis of the burst areas and impact values of the impact test specimens, it was concluded that hydrogen did not cause any observable damage to the test material.

Effect of δ-ferrite on susceptibility to hydrogen embrittlement of 304 austenitic stainless steel in high-pressure hydrogen atmosphere

Purpose The purpose of this paper is to demonstrate the effect of δ-ferrite on the susceptibility to hydrogen embrittlement of type 304 stainless steel in hydrogen gas environment. Design/methodology/approach The mechanical properties of as-received and solution-treated specimens were investigated by the test of tensile and fatigue crack growth (FCG) in 5 MPa argon and hydrogen. Findings The presence of δ-ferrite reduced the relative elongation and the relative reduction area (H2/Ar) of 304 stainless steel, indicating that δ-ferrite increased the susceptibility of hydrogen embrittlement in 304 stainless steel. Moreover, δ-ferrite promoted the fatigue crack initiation and propagation at the interface between δ-ferrite and austenite. The FCG tests were used to investigate the effect of δ-ferrite on the FCG rate in hydrogen gas environment, and it was found that δ-ferrite accelerated the FCG rate, which was attributed to rapid diffusion and accumulation of hydrogen around the fatigue crack tip through δ-ferrite in high-pressure hydrogen gas environment. Originality/value The dependence of the susceptibility to hydrogen embrittlement on δ-ferrite was first investigated in type 304 steel in hydrogen environment with high pressures, which provided the basis for the design and development of a high strength, hydrogen embrittle-resistant austenitic stainless steel.

Tuning structural and magnetic properties of Fe oxide nanoparticles by specific hydrogenation treatments

Structural and magnetic properties of Fe oxide nanoparticles prepared by laser pyrolysis and annealed in high pressure hydrogen atmosphere were investigated. The annealing treatments were performed at 200 °C (sample A200C) and 300 °C (sample A300C). The as prepared sample, A, consists of nanoparticles with ~ 4 nm mean particle size and contains C (~ 11 at.%), Fe and O. The Fe/O ratio is between γ-Fe2O3 and Fe3O4 stoichiometric ratios. A change in the oxidation state, crystallinity and particle size is evidenced for the nanoparticles in sample A200C. The Fe oxide nanoparticles are completely reduced in sample A300C to α-Fe single phase. The blocking temperature increases from 106 K in A to 110 K in A200C and above room temperature in A300C, where strong inter-particle interactions are evidenced. Magnetic parameters, of interest for applications, have been considerably varied by the specific hydrogenation treatments, in direct connection to the induced specific changes of particle size, crystallinity and phase composition. For the A and A200C samples, a field cooling dependent unidirectional anisotropy was observed especially at low temperatures, supporting the presence of nanoparticles with core–shell-like structures. Surprisingly high MS values, almost 50% higher than for bulk metallic Fe, were evidenced in sample A300C.

Improving the performance of crystalline Si solar cell by high-pressure hydrogenation* *Project supported by the National Natural Science Foundation of China (Grant No. 62075044), the Shanghai Science and Technology Committee, China (Grant No. 18JC1411500), and the CIOMP–Fudan University Joint Foundation (Grant No. FC2017-001).

We report an approach of high-pressure hydrogenation to improve the performance of crystalline Si (c-Si) solar cells. As-received p-type c-Si wafer-based PN junctions were subjected to high-pressure (2.5 MPa) hydrogen atmosphere at 200 °C, followed by evaporating antireflection layers, passivation layers, and front and rear electrodes. The efficiency of the so prepared c-Si solar cell was found to increase evidently after high-pressure hydrogenation, with a maximal enhancement of 10%. The incorporation of hydrogen by Si solar cells was identified, and hydrogen passivation of dangling bonds in Si was confirmed. Compared to the regular approach of hydrogen plasma passivation, the approach of high-pressure hydrogenation reported here needs no post-hydrogenation treatment, and can be more convenient and efficient to use in improving the performances of the c-Si and other solar cells.

Effects of Annealing Parameters on Epitaxial Graphene on SiC Substrates

The effects of annealing on epitaxial graphene on SiC substrates with various conditions are investigated. Results show that high pressure hydrogen atmosphere is more effective to decouple the epitaxial graphene from SiC substrate than that of a relative lower pressure process. Besides, the characteristic 2D-peak of graphene in Raman spectra disappeared with an annealing temperature 1000 °C, which means that the epitaxial graphene layer was decomposed in this condition. The study also shows that the decomposition of graphene can be effectively suppressed by increasing carbon vapor partial pressure through introducing ethylene during high pressure hydrogen annealing at 1000 °C. And the epitaxial graphene is successfully transferred to quasi free standing graphene by the annealing with an appropriate flow of ethylene.

Study on fretting behavior of rubber O-ring seal in high-pressure gaseous hydrogen

Fretting is a low-amplitude reciprocating movement which may lead to seal failure, it is important to explore the fretting characteristic of a rubber seal in hydrogen atmosphere. In this work, a numerical model considering the effect of hydrogen swelling was presented to study the fretting behavior of a rubber seal. The fretting running condition was analyzed. Results showed that, the amplitude of reciprocating motion made a great effect on the fretting state of rubber seals, the O-ring seal in high-pressure hydrogen atmosphere exhibits a higher propensity to run in the sticking regime because of swelling effect. The fluctuation range of the peak Mises stress in hydrogen was much larger than that in air, leading to aggravating the fatigue failure of the rubber seal. It was more difficult to produce relative slip in hydrogen compared with in air, resulting in exacerbating the fretting wear of rubber seals.

Improved resistance to hydrogen environment embrittlement of warm-deformed 304 austenitic stainless steel in high-pressure hydrogen atmosphere

The resistance of warm-deformed 304 austenitic stainless steel to hydrogen environment embrittlement (HEE) was investigated by adjusting the deforming temperature and deforming strain in hydrogen atmosphere. Higher deforming temperatures (100∼300 °C) can improve the resistance to HEE, while higher deforming strains weakened the resistance to HEE. Higher deforming temperatures caused a more uniform distribution of the high-density dislocations and less deformation twins, which weakened hydrogen segregation to prevent hydrogen-induced cracking. As the deforming strain increased, more primary deformation twins formed, which promoted the formation of strain-induced α′ martensite and then accelerated the growth of hydrogen-induced cracks.

Improving the photocatalytic activity of graphitic carbon nitride by thermal treatment in a high-pressure hydrogen atmosphere

Extending visible light absorption range and suppressing the recombination of photogenerated charge carriers are always important topics in developing efficient solar-driven photocatalysts. In this study, the thermal treatment process at 400 °C in a high-pressure hydrogen atmosphere was applied to modify graphitic carbon nitride. Compared to the normal atmospheric hydrogen treatment process, this process has the merit of producing nitrogen deficient graphitic carbon nitride in high-yield. The optimal photocatalytic activity of modified graphitic carbon nitride was demonstrated by controlling the treatment duration in the hydrogen atmosphere. The changes in the crystal structure, microstructure and optical properties of carbon nitrides were investigated by several characterizations. The relationship between the photocatalytic activity and structures of graphitic carbon nitride was preliminarily established. The results obtained in this study could provide some new ways of improving the activity of graphitic carbon nitride based photocatalyst.

Quantitative evaluation of hydrogen atoms trapped at single vacancies in tungsten using positron annihilation lifetime measurements: Experiments and theoretical calculations

The change in the positron annihilation lifetime (PAL) of vacancies containing hydrogen atoms was investigated by taking PAL measurements in tungsten. The vacancies were introduced by electron irradiation, and hydrogen atoms were charged under a high-pressure hydrogen atmosphere (5.8 MPa). The PAL of single vacancies was measured to be approximately 175 ps, which decreased to approximately 155 ps after hydrogen charging. The PAL of single vacancies containing hydrogen atoms was calculated using the electron density obtained by a first principles calculation. The change in the PAL of vacancies containing hydrogen atoms was measured in experiments and calculated in simulations, and then, the two values were compared. It was found that one vacancy captured one or two hydrogen atoms (an average of 1.6 atoms). The binding energy of hydrogen to vacancies of 1.19 eV was obtained under the assumption of a thermal equilibrium state, which was slightly higher than the value determined by a previous study (1.06 eV). It is believed that the effect of impurities causes this discrepancy. The elucidation of the effect of impurities on the change in the PAL and the binding energy leads to greater accuracy in the quantitative evaluation of the hydrogen atoms trapped at single vacancies.

Dihydride formation in the palladium–rhodium alloys under high hydrogen pressure

Palladium, rhodium and their alloys were studied in a diamond anvil cell in a high pressure hydrogen atmosphere up to 20 GPa by X-ray diffraction at room temperature. Formation of a monohydride with H/(Rh + Pd) = 1 ratio was observed for each alloy at hydrogen pressures less than 3 GPa. The corresponding volume expansion of the metal lattice was 2.2–2.8 Å3 per metal atom. A formation of the dihydride with H/(Rh + Pd) = 2 was observed at a hydrogen pressure around 10 GPa for the alloys with rhodium content Rh/(Rh + Pd) ≥ 50 at.%. The dihydride formation is accompanied by a volume expansion of metal lattice by 3.2–3.9 Å3 per metal atom. For Pd-rich alloys with Rh/(Rh + Pd) ≤ 25 at.% and pure Pd the dihydride formation was not observed up to maximum reached hydrogen pressure. All observed phases had a fcc structure of metal lattice.

Degradation of Creep Resistant Ni - Alloy During Aging at Elevated Temperature Part II: Structure Investigations

Abstract The results of structure observations of Ni base superalloy subjected to long-term influence of high pressure hydrogen atmosphere at 750K and 850K are presented. The structure investigation were carried out using conventional light-, scanning- (SEM) and transmission electron microscopy (TEM). The results presented here are supplementary to the mechanical studies given in part I of this investigations. The results of study concerning mechanical properties degradation and structure observations show that the differences in mechanical properties of alloy subjected different temperature are caused by more advanced processes of structure degradation during long-term aging at 850K, compare to that at 750K. Higher service temperature leads to formation of large precipitates of δ phase. The nucleation and growth of needle- and/or plate-like, relative large delta precipitates proceed probably at expense strengthening γʺ phases. Moreover, it can’t be excluded that the least stable γʺ phase is replaced with more stable γʹ precipitates. TEM observations have disclosed differences in dislocation structure of alloy aged at 750K and 850K. The dislocation observed in alloy subjected to 750K are were seldom observed only, while in that serviced at high stress and 850K dislocation array and dislocation cell structure was typical.

Tensile properties of precracked tempered martensitic steel specimens tested at ultralow strain rates in high-pressure hydrogen atmosphere

Tensile tests were performed on precracked Cr–Mo martensitic steel (C: 0.38, Si: 0.22, Mn: 0.84, P: 0.024, S: 0.021, Ni: 0.08, Cr: 1.11, Mo: 0.15, Cu: 0.12, Fe: bal. (wt%)) specimens at various strain rates (ranging from 6.5 × 10−8 s−1 to 1.0 × 10−4 s−1) in high-pressure (95 MPa) hydrogen and helium atmospheres. Irrespective of the strain rate, the tensile strength in the helium atmosphere was 1400 MPa. In the hydrogen atmosphere, the tensile strength decreased to less than 600 MPa at a strain rate of 2.0 × 10−5 s−1. However, the tensile strength increased to 900 MPa when the strain rate was decreased to 6.5 × 10−8 s−1. This recovery of the tensile strength was because of the decrease in the local stress in the vicinity of the precrack because of hydrogen.

Critical findings during the optimisation of hydrogen storage in vapour grown carbon fibres

The storage of hydrogen in vapour grown carbon fibres samples, according to different well known manufacturing processes, is studied. The main differences between the samples are: the precursor gases composition; the application of an annealing treatment in different atmospheres; charging by absorption in a high pressure hydrogen atmosphere; and finally, chemical and electrochemical treatments. The techniques used for the fibres characterization were: Rutherford backscattering and elastic recoil detection analysis with 2 MeV He+ ions.The study shows that the absorption of hydrogen in over-pressurized hydrogen atmosphere is more effective, than chemical treatment and charge by electrolytic processes. The formation of hydrogen hosting sites occurs even with the standard fabrication method, without the need of any of the above mentioned treatments. Annealing under different inert gases are of theoretical interest also, since we show evidence of different translational movement restrictions according to the nature of the inert gas. Even more important, we show that in some circumstances, the anode–cathode current used to measure the stored hydrogen in vapour grown carbon fibres, may not constitute a reliable methodology.

Crystal Structure Characterization and Catalytic Application of Novel Route Prepared Ru3(CO)9 DPAM (Diphenyl Arsino Methane)-tri Phenyl Phosphine Derivatives

Triruthenium dodecacarbonyl-Ru3(CO)12 based diphenylarsino methane-triphenyl phosphine derivatives, such as Ru3(CO)9-dpam-tris (methyl phenyl) phosphine (1), Ru3(CO)9-dpam-tris (methoxy phenyl) phosphine (2), and Ru3(CO)9-dpam-tris (fluro phenyl) phosphine (3) are synthesized by two step modified method. The catalytic hydrogenation of cyclohexene, styrene, and phenyl acetylene, on above mentioned Ru-based organometallic catalysts, has been studied under high pressure hydrogen atmosphere. The high pressure hydrogenation of cyclohexene and phenyl acetylene on Complex (1–3), showed good catalytic activity under pressurized condition. Hydrogenation of cyclohexene on Complex (3) showed better (50–65%) conversion in the presence of toluene than hexane solvent. The effect of temperature, role of solvent, and pressure conditions have also been studied.

Synthesis and formation process of Al2CuHx: A new class of interstitial aluminum-based alloy hydride

Aluminum-based alloy hydride Al2CuHx (x ∼ 1) is synthesized by hydrogenating Al2Cu alloy using high-temperature and high-pressure hydrogen atmosphere. Al8Cu square antiprisms in Al2Cu twist around the c axis of a tetragonal unit cell by hydrogenation. The twist enlarges the interstitial spaces for accommodating hydrogen atoms which align linearly parallel to the c axis in Al2CuHx. Thermodynamic stability of Al2CuHx results from the balance of stabilization by H 1s and Al 3sp hybridization and destabilization owing to the Fermi-level lifting upon hydrogenation. The crystal and electronic structures of Al2CuHx illustrate the formation of an interstitial hydride of aluminum-based alloy.

Hydrogen environment embrittlement of stable austenitic steels

Seven stable austenitic steels (stable with respect to γ → α′ transformation at room temperature) of different alloy compositions (18Cr–12.5Ni, 18Cr–35Ni, 18Cr–8Ni–6Mn–0.25N, 0.6C–23Mn, 1.3C–12Mn, 1C–31Mn–9Al, 18Cr–19Mn–0.8N) were tensile tested in high-pressure hydrogen atmosphere to assess the role of austenite stability on hydrogen environment embrittlement (HEE). The influence of hydrogen on tensile ductility was small in steels that are believed to have a high initial portion of dislocation cross slip (18Cr–12.5Ni, 18Cr–35Ni, 18Cr–8Ni–6Mn–0.25N), while the effects of hydrogen were significantly greater in steels with other primary deformation modes (planar slip in 18Cr–19Mn–0.8N and 1C–31Mn–9Al or mechanical twinning in 0.6C–23Mn and 1.3C–12Mn) despite comparable austenite stability at the given test conditions. It appears that initial deformation mode is one important parameter controlling susceptibility to HEE and that martensitic transformation is not a sufficient explanation for HEE of austenitic steels.

Impact of High Pressure Hydrogen Atmosphere on the Mechanical Properties of Haynes 282 Superalloy

Abstract Haynes 282 alloy is a newly developed nickel-base superalloy, with properties focussed on high creep strength, thermal stability, good weldability and fabricability, which might qualify it as a substitute for established materials like Hastelloy-X or René-41 e.g. in aerospace applications. However, so far no information on the sensitivity for hydrogen environment embrittlement (HEE) has been published for this material. In the present work, tensile tests under hydrogen atmosphere have been carried out at room temperature and the results have been compared to those from tests under argon. Haynes 282 is found to show significant hydrogen embrittlement.

Analysis of martensitic transformation in 304 type stainless steels tensile tested in high pressure hydrogen atmosphere by means of XRD and magnetic induction

Tensile specimen of several 304 type stainless steels tested under pressurized hydrogen and helium atmospheres were investigated with the focus on the γ → α′ transformation as a function of Ni content. Martensite contents on the fracture surfaces increased with decreasing Ni content and were independent of the test atmosphere (He or H2) despite different macroscopic plastic deformations. This was attributed to similar plastic deformations at the crack tip which governs the γ → α′ transformation at the fracture surface. The severity of hydrogen environment embrittlement was quantified by RA measurements which is a measure of the maximum macroscopic plastic deformation. RA values in H2 decrease with decreasing Ni content and RA is almost exactly inverse proportional to the martensite content measured by Feritscope in the uniform elongation area. This implies that the influence of hydrogen of the steels investigated here is dominated by surface effects.

Effects of grain size on hydrogen environment embrittlement of high strength low alloy steel in 45 MPa gaseous hydrogen

The effect of grain size on the susceptibility of high-strength low alloy steels to hydrogen environment embrittlement in a 45 MPa gaseous hydrogen atmosphere was examined in term of the hydrogen content penetrating the specimen during the deformation. Notch tensile tests were performed in a 45 MPa hydrogen environment using specimens with different prior austenite grain size numbers varying from 2.5 to 5.4. The hydrogen content was measured by thermal desorption analysis with a quadrupole mass spectrometer before and after the tensile test. The fracture stress of the notch tensile test increased with increasing grain size number; this showed that grain refinement was effective in reducing the susceptibility of the specimens to hydrogen environment embrittlement in a high-pressure hydrogen atmosphere. The addition of nickel did not affect the fracture stress. A remarkable increase in the content of diffusive hydrogen was observed after the notch tensile test. Assuming that part of the diffusive hydrogen desorbed from grain boundaries, it can be inferred that grain refinement can reduce the mass of hydrogen in the unit grain boundary area, and the susceptibility to high-pressure hydrogen environment embrittlement. [doi:10.2320/matertrans.M2009241]