Residual Hydrogen Content Research Articles

Effect of hydrogenation on fatigue crack growth resistance of diffusion bonded TC4 titanium alloy laminates

A method was proposed to improve the fatigue crack growth (FCG) resistance of TC4 (Ti6Al4V) titanium alloy laminate by hydrogenation/low-temperature diffusion bonding/dehydrogenation (H-DB-DH) combined process. Effects of hydrogen contents and different dehydrogenation temperatures on FCG behaviors and tensile properties as well as microstructures were investigated. Residual hydrogen contents beneath fatigue fracture surfaces were measured to determine the safe dehydrogenation temperature. The hydrogen content of 0.3 wt% and dehydrogenation temperature of 780 °C are optimal to produce TC4 laminate with a 9.87 % improvement of FCG life compared with the diffusion bonded one without hydrogenation. FCG rate decrease results from the comprehensive effect of recrystallization volume fraction increase, grain refinement, mean geometrically necessary dislocations (GNDs) density decrease and texture intensity weakness as well as texture diversity improvement. This paper provides theoretical support for fatigue property improvement of titanium alloy by hydrogen diffusion bonding process.

Fabrication of silicon nitride based high-Q microring resonators prepared by the hot-wire CVD method and their applications to frequency comb generation

Fabrication of silicon nitride (SiN) based high-Q microring resonators prepared by the hot-wire chemical vapor deposition (HWCVD) method is presented. By the virtue of low-stress HWCVD films, no special precautions against crack propagation were required for high confinement waveguide device fabrication. By using an additional annealing process, the intrinsic Q factor in excess of 5 × 105 was obtained in the telecommunication C band, and which allowed us to observe frequency comb generation. We also investigated into the anneal temperature dependence of the residual hydrogen concentration in the film as well as the optical properties of the microring resonators.

Hydrogen diffusion simulation of the X80 pipeline steel girth weld zone considering the synergistic effect of the structure–stress–concentration field

Hydrogen embrittlement failure, caused by hydrogen permeation and diffusion in the girth weld zone of pipelines, is the main obstacle to large-scale hydrogen blending transportation. Accordingly, a three-dimensional model of the girth weld zone of X80 pipeline steel was established. Considering the influence of structural inhomogeneity in the weld zone, multi-field sequential coupling simulation technology was used to analyze the diffusion process of hydrogen under the combined action of the residual stress and hydrogen concentration fields. A synergistic mechanism between hydrogen enrichment, structural characteristics, and residual stress in the weld zone was revealed. The results indicated that the structural inhomogeneity in the girth weld zone and residual stress field significantly influenced the hydrogen concentration distribution. Moreover, for the hydrogen diffusion process at the grain boundaries, the impact of the residual stress was greater than that of the structural inhomogeneity. This study further clarifies the spatial distribution of hydrogen atoms induced by multi-field coupling in the weld zone and provides a reference for the safety assessment of girth weld layers from an engineering perspective.

Residual hydrogen reduction and refining effect during two-step hydrogen-argon plasma arc melting of cerium

Herein, the two-step hydrogen-argon plasma arc melting technology (HPAM-APAM) namely hydrogen plasma arc melting (HPAM) followed by argon plasma arc melting (APAM), was put forward to successfully realize the application of HPAM on cerium refining. The residual hydrogen content was significantly decreased to 79 ppm with the increase of APAM time to 40 min. The contents of volatile impurities Li and Mg were greatly reduced to less than 0.1 ppm. Paradoxically, the contents of Ti and W with low vapor pressures could be reduced to 2 ppm, whereas the impurities Fe and Si with high vapor pressures were hardly removed. The analysis indicated that the reduction of W and Ti was ascribed to the formation of volatile WO3 and TiO, while the negligible reduction of Fe and Si was attributed to the strong interaction strength with cerium based on “alloy phase formation theory”. A new kinetic refining mechanism by the activated H during HPAM process was proposed. This work helps to extend HPAM to refine hydrogen absorbing metals and provides new insights into the removal mechanism of metallic impurities.

Metal degassing in vacuum-chamber of circulating vacuum degasser of JSC EVRAZ NTMK

For smelting of high-quality metal for transport purposes, it is necessary to limit the content of harmful impurities in it, including dissolved gases. For example, hydrogen content in the finished product should not exceed more than 2 ppm. In order to obtain low residual hydrogen content in steel in the converter shop of JSC EVRAZ NTMK, the transport metal is processed at circulating vacuuming plants. Circulating vacuum degasser is the last stage of steel processing before casting on continuous casting machine, so it is important to study and improve the technological processes in it. To investigate the physico-chemical processes occurring in this metallurgical unit, a hydrodynamic model of the system circulating vacuum degasser – steel ladle was created. Based on theoretical calculations and experiments conducted on a physical model, the main dependencies between the structural and technological parameters of the metallurgical unit were determined. The resulting equation makes it possible to determine the rate of metal circulation in vacuum chamber depending on gas flow rate supplied to inlet snorkel and its inner diameter at circulating vacuuming plants designed for metal processing in steel ladles with a capacity of 140 – 180 tons. Theoretical calculations were confirmed by practical smelting in a steelmaking unit. It is shown that during the wear of lining of the inlet snorkel vacuum chamber, in order to obtain stable residual hydrogen content, it is necessary to make changes in the technological process of vacuuming. Additionally, rational technological parameters of steel processing at the circulating vacuuming plant were determined on the basis of theoretical calculations.

Metal Degassing in Vacuum-Chamber of Circulating Vacuum Degasser of JSC EVRAZ NTMK

For smelting of high-quality metal for the applications in transport vehicles, it is necessary to limit the content of harmful impurities in it, including dissolved gases. For example, hydrogen content in the finished product should not exceed more than 2 ppm. In order to obtain low residual hydrogen content in steel in the converter shop of JSC EVRAZ NTMK, the transport metal is processed at circulating vacuuming plants. Circulating vacuum degasser is the last stage of steel processing before casting on continuous casting machine, so it is important to study and improve the technological processes in it. To investigate the physico-chemical processes occurring in this metallurgical unit, a hydrodynamic model was created for the system that includes the circulating vacuum degasser and the steel ladle. Based on theoretical calculations using physical model and experiments conducted, the main dependencies between the structural and technological parameters of the metallurgical unit were determined. The resulting equation makes it possible to determine the rate of metal circulation in vacuum chamber depending on the gas flow rate supplied to inlet snorkel and its inner diameter at circulating vacuuming plants designed for metal processing in steel ladles with a capacity of 140–180 tons. Theoretical calculations were confirmed by practical smelting in a steelmaking unit. It is shown that in order to obtain stable residual hydrogen content during the wear of lining of the inlet snorkel vacuum chamber, it is necessary to make changes in the technological process of vacuuming. Additionally, rational technological parameters of steel processing at the circulating vacuuming plant were determined on the basis of theoretical calculations.

New DA white dwarf models for asteroseismology of ZZ Ceti stars

Context. Asteroseismology is a powerful tool used to infer the evolutionary status and chemical stratification of white dwarf stars and to gain insights into the physical processes that lead to their formation. This is particularly true for the variable hydrogen-rich atmosphere (DA) white dwarfs, known as DAV or ZZ Ceti stars. They constitute the most numerous class of pulsating white dwarfs. Aims. We present a new grid of white dwarf models that take into account advances made over the last decade in modeling and input physics of both the progenitor and the white dwarf stars. As a result, it is possible to avoid several shortcomings present in the set of white dwarf models employed in the asteroseismological analyses of ZZ Ceti stars that we carried out in our previous works. Methods. We generate white dwarf stellar models appropriate for ZZ Ceti stars with masses from ∼0.52 to ∼0.83 M⊙, resulting from the whole evolution of initially 1.5–4.0 M⊙ mass star models. These new models are derived from a self-consistent way with the changes in the internal chemical distribution that result from the mixing of all the core chemical components induced by mean molecular-weight inversions, from 22Ne diffusion, Coulomb sedimentation, and from residual nuclear burning. In addition, the expected nuclear-burning history and mixing events along the progenitor evolution are accounted for, in particular the occurrence of third dredge-up, which determines the properties of the core and envelope of post-AGB and white dwarf stars, as well as the white dwarf initial-final mass relation. The range of hydrogen envelopes of our new ZZ Ceti models extends from the maximum residual hydrogen content predicted by the progenitor history, log(MH/M⊙)∼ − 4 to −5, to log(MH/M⊙) = − 13.5, thus allowing for the first stellar models that would enable the search for seismological solutions for ZZ Ceti stars with extremely thin hydrogen envelopes – if, indeed, they do exist in nature. We computed the adiabatic gravity(g)-mode pulsation periods of these models. Calculations of our new evolutionary and pulsational ZZ Ceti models were performed with the LPCODE stellar evolution code and the LP-PUL stellar pulsation code. Results. Our new hydrogen-burning post-AGB models predict chemical structures for ZZ Ceti stars that are substantially different from those we used in our previous works, particularly in connection with the chemical profiles of oxygen and carbon near the stellar centre. We also discuss the implications of these new models for the pulsational spectrum of ZZ Ceti stars. Specifically, we find that the pulsation periods of g modes and the mode-trapping properties of the new models differ significantly from those characterizing the ZZ Ceti models of our previous works, particularly for long periods. Conclusions. The improvements in the modeling of ZZ Ceti stars we present here lead to substantial differences in the predicted pulsational properties of ZZ Ceti stars, which are expected to impact the asteroseismological inferences of these stars. This is extremely relevant in view of the abundant amount of photometric data from current and future space missions, resulting in discoveries of numerous ZZ Ceti stars.

Susceptibility of carbon pipeline steels operated in natural gas distribution network to hydrogen-induced cracking

The existing network of both transit and distribution gas pipelines has recently been proposed to be used for the transportation of hydrogen as an energy fuel in the multifaceted structure of the development of renewable energy sources. From this point of view, the paper considers the sensitivity of a long-term operated steel of distribution gas pipeline to hydrogen assisted cracking as a result of preliminary electrolytic hydrogenation of flat tensile specimens, followed by determination of strength and plasticity characteristics. The research methodology has two features: (i) the specimens are cut out from the pipe in the transverse direction to the pipe axis; in this case the fracture plane is parallel to the rolling direction of metal sheet from which the pipes were made; (ii) specimen thickness is 1.2 mm maximally providing through hydrogenation. The study additionally includes determination of hydrogen concentration in the steel, and fractographic analysis. It is shown that the low-carbon steel of the 52-year-old gas pipeline with high residual hydrogen content especially sensitive to hydrogen assisted cracking, indicated by signs of low-energy fracture at the micro scale.

Effect of Co substitution on hydrogenation behavior of GdNi3-xCox (x = 0, 0.2, 1.0) and crystal structure of its hydride phases

The effect of substituting Co for Ni in GdNi3 on the hydrogenation properties and phase transformation during the hydrogen absorption–desorption process of GdNi3-xCox (x = 0, 0.2, 1.0) was investigated using P–C isotherms and X-ray diffraction analysis (XRD). GdNi3 showed a residual hydrogen content of 0.6 H/M after the first desorption process. The maximum hydrogen capacity of GdNi3 was 1.0 H/M, while the reversible hydrogen capacity decreased to 0.4 H/M because of the residual hydrogen. The reversible hydrogen capacity was improved to 1.0 H/M in GdNi2.0Co1.0, and two plateaus were observed in the absorption–desorption process. The crystal structures of the full hydride phases GdNi3H3.8 and GdNi2.8Co0.2H3.8 could not be determined because of the heavy peak broadening in the XRD pattern, while the PuNi3-type structure of the original alloy was retained in the full hydride phase GdNi2.0Co1.0H3.6. The retention rates of GdNi3 and GdNi2.0Co1.0 at 100 cycles were 75% and 92%, respectively. The cyclic properties of GdNi2.0Co1.0, up to 100 cycles, favorably compared with those of LaNi5, which was found to be related to the small lattice strain formed during the first hydrogen absorption process.

Effects of dl-alanine fuel and annealing on auto-combustion derived MgFe2O4 powder with low carbon content and improved magnetic properties

Structural and magnetic properties of as-prepared and annealed MgFe2O4 nano-powders prepared by auto-combustion method using dl-alanine fuel have been investigated. Nanoparticles with single-crystal electron diffraction patterns are analyzed, and phase purity is confirmed by X-ray diffraction and Raman and infrared spectroscopy. Residual carbon (C), hydrogen (H) and nitrogen (N) content in as-prepared powders is found to reduce by annealing the powders at 900 °C in air. Annealing the as-prepared powders in the range (600–1200 °C) increases the crystallite size from 35 to 46 nm, and increases saturation magnetization to 36 emu/g with low coercivity of ~ 33 Oe. Variations in the magnetic properties are correlated with changes in cation distribution in the octahedral and tetrahedral sites estimated from X-ray diffraction and magnetic studies.

Minimization of hydrogen concentration in the superheated mixture at steam turbine working fluid overheating by mixing with high-temperature products of hydrogen in oxygen combustion at nuclear power plant

A new design of hydrogen-oxygen superheater with hybrid cooling of the combustion chamber with feed water and low-temperature steam is proposed for smoothening the cooling process in order to reduce the residual hydrogen content in the process steam. The combustion chamber at this design consists of two parts. In the first part, external cooling with feed water is used for smooth cooling of combustion products to 1900 … 2100 K in the most thermally stressed zone. In the second part, low-temperature steam is used as coolant for external cooling, the temperature of the generated high-temperature steam is reduced down to 1400 … 1500 K. Finally, the obtained high-temperature steam is mixed with the working fluid.

Application of pyrolysis to remove hydrogen from an organic nuclear waste

The work deals with the removal by slow pyrolysis of epoxy resin from samples of spent nuclear fuel embedded in this polymer. Beyond the nuclear field, epoxy resin removal by pyrolysis is a typical issue for the recovery of metals in electronic waste. The main objective is to find the optimal conditions to remove hydrogen in the residual solid waste, in order to avoid hydrogen production by radiolysis during storage and so to prevent any risk of overpressure and explosion. The condensable pyrolysis products (tar-water mixture) and the char were characterised and quantified by elemental analyses, while the permanent gases were quantified by gas chromatography. A data reconciliation method was applied to adjust the values of raw measurements in order to complete the mass balances for both C, H, O and N elements and pyrolysis products. After studying the impact of temperature on the pyrolysis balance, experiments on a pilot furnace were conducted at 450 °C, in the frame of a parametric study of the heating rate, argon gas flow rate, resin mass and plateau time. At fixed temperature, we show that the plateau time is the only significant parameter for minimizing the residual hydrogen content in the char.

Effect of residual hydrogen content on the tensile properties and crack propagation behavior of a type 316 stainless steel

The tensile properties and crack propagation rate in a type 316 austenitic stainless steel prepared by vacuum induction melting method with different residual hydrogen contents (1.1–11.5 × 10−6) were systematically investigated in this research work. The room temperature tensile properties were measured under both regular tensile (12 mm/min) and slow tensile (0.01 mm/min) conditions, and the fracture properties of the tensile fractures with both rates were analyzed. It shows that the hydrogen induced plasticity loss of stainless steel strongly depends on the tensile rate. Under regular tensile condition, there is no plastic loss even when the hydrogen content is up to 11.5 × 10−6 while in the slow tensile condition, the plastic loss can be clearly identified rising with the increasing H contents. The fatigue crack propagation rate was tested at room temperature, and the crack growth rate formula (Paris) of the 316 stainless steels with varied H contents were obtained. The fatigue crack propagation rate test shows that the crack growth rate of the 316 stainless steel with 8.0–11.5 × 10−6 hydrogen is significantly higher than that of benchmark steel.

Effect of residual hydrogen on microstructure and magnetic properties of Sm(Co0.647Fe0.28Cu0.053Zr0.02)7.84 magnets

Magnetic properties and microstructure of Sm(Co0.647Fe0.28Cu0.053Zr0.02)7.84 magnets prepared by HD powder with different residual hydrogen content (25, 715, 1512 ppm) have been investigated. The squareness and coercivity increase from 0.56 to 0.63 and 24.03 to 26.37 kOe as the hydrogen content increased from 25 to 1512 ppm. TEM results show that similar cellular structure and lamellar structures are formed in these magnets. Due to superabundant vacancies induced by hydrogen, the average grain size of final magnets increases from 50.22 to 62.29 μm with the increase of hydrogen in HD powder. Larger grain size results in fewer grain boundary areas where no clear cellular structure formed. The kerr observation indicate that the reversal domain formed at the grain boundary areas is easier to grow up, while the reversal of in-grain domain shows much harder.

Quantitative investigation of the lateral diffusion of hydrogen in p-type GaN layers having NPN structures

This work quantitatively examined lateral diffusion of hydrogen in the (0001) in-plane direction in a Mg-doped p-type GaN layer sandwiched between n-type layers, based on the preparation and annealing of circular mesa structures having different radius values. Capacitance–voltage analyses and secondary ion mass spectrometry confirmed a decrease in the effective acceptor concentration along with an increase in the residual hydrogen concentration with increasing radius values, indicating hydrogen desorption through the sidewall and lateral diffusion. Considering the surface barrier to desorption, we estimated a lateral diffusion coefficient of 7 × 10−8 cm2 s−1 at 1123 K, reasonably reproducing the effect of the mesa radius.

A Model for Predicting Residual Hydrogen Content in Blooms and Billets Stacked in Large Industrial Piles

Hydrogen is highly detrimental for mechanical properties and internal quality of steel products. Hydrogen is captured in liquid steel from different sources, also depending on the different stages of the manufacturing process. During the liquid stages, the most effective countermeasure to reduce the hydrogen content is vacuum degassing. Nonetheless, not all the products undergo this process and then the cooling stage becomes fundamental to avoid hydrogen embrittlement phenomena. To be effective for hydrogen release, the cooling path needs to be suitably slow without abrupt temperature gradients. In industry, products are piled according to strategies following logistic rather than metallurgical logics, with very poor control of the cooling strategy. The paper presents a simplified and practical model, which predicts the final hydrogen content in blooms and billets with square or rectangular section after the slow cooling in a large pile by computing the cooling path of each product. The model allows identifying those products, where the residual hydrogen content after cooling is excessive, which are therefore more likely to show hydrogen embrittlement‐related problems. It allows simulation of different piling strategies for each specific product and is therefore useful in order to preliminarily identify the best piling procedure to avoid hydrogen embrittlement.

Nanoscale Probing of Local Hydrogen Heterogeneity in Disordered Carbon Nitrides with Vibrational Electron Energy-Loss Spectroscopy.

In graphitic carbon nitrides, (photo)catalytic functionality is underpinned by the effect that residual hydrogen content, manifesting in amine (N-H x) defects, has on its optoelectronic properties. Therefore, a detailed understanding of the variation in the local structure of graphitic carbon nitrides is key for understanding structure-activity relationships. Here, we apply aloof-beam vibrational electron energy-loss spectroscopy in the scanning transmission electron microscope (STEM) to locally detect variations in hydrogen content in two different layered carbon nitrides with nanometer resolution. Through low dose rate TEM, we obtain atomically resolved images from crystalline and disordered carbon nitrides. By employing an aloof-beam configuration in a monochromated STEM, radiation damage can be dramatically reduced, yielding vibrational spectra from carbon nitrides to be assessed on 10's of nanometer length scales. We find that in disordered graphitic carbon nitrides the relative amine content can vary locally up to 27%. Cyano (C≡N) defects originating from uncondensed precursor are also revealed by probing small volumes, which cannot be detected by infrared absorption or Raman scattering spectroscopies. The utility of this technique is realized for heterogeneous soft materials, such as disordered graphitic carbon nitrides, in which methods to probe catalytically active sites remain elusive.

The influence of hydrogen desorption on micromechanical properties and tribological behavior of iron and carbon steels

The influence of the previous electrolytic hydrogenation on the micromechanical properties and tribological behavior of the surface layers of iron and carbon steels has been studied.The concentrations of diffusion-moving and residual hydrogen in steels are determined depending on the carbon content. It is shown that the amount of sorbed hydrogen is determined by the density of dislocations and the relative volume of cementite. After desorption of diffusion-moving hydrogen the microhardness increases and materials plasticity decreases. The change of these characteristics decreases with the increase of carbon content in the steels. Internal stresses increase and redistribute under hydrogen desorption. Fragmentation of ferrite and perlite occurs as a result of electrolytic hydrogenation. Ferrite is characterized by the structure fragmentation and change of the crystallographic orientation of planes. The perlite structure shows the crushing of cementite plates and their destruction. The influence of hydrogen desorption on the microhardness of structural components of ferrite-perlite steels is shown. Large scattering of microhardness ​​is found in perlite, due to different diffusion rates of hydrogen because of the unequally oriented cementite plates. It was found that the tendency of materials to blister formation is reduced with the increase of carbon content. The influence of hydrogen on the tribological behaviour of steels under dry and boundary friction has been studied. It is shown that hydrogen desorption intensifies the materials wear. After hydrogen desorption, tribological behaviour is determined by the adhesion interaction between the contacting pairs.

Effect of hydrogen content on hydrogen desorption kinetics of titanium hydride

Abstract Thermal desorption behaviours of titanium hydride powders with different hydrogen contents were studied using simultaneous TG-TDS measurements at a heating rate of 10 °C/min. The as-received TiH 2 powders were pre-heated to different temperatures and subsequently cooled to room temperature in argon. The XPS depth profile analysis demonstrated that after heat treatments, the relative oxygen concentrations decreased slightly compared with that of as-received TiH 2 powder. The changes in the TDS spectra for the pre-heat treated TiH 2 powders were primarily associated with the residual hydrogen contents. The origins of the observed TDS peaks and shoulders were attributed to the equilibrium hydrogen pressures of the phase regions that the decomposition reaction passed through. The hydrogen content was demonstrated to be essential for the phase transformation sequence during titanium hydride decomposition.

Removal of hydrogen in the vacuum treatment of steel

The degassing of 09Г2C steel produced in an arc furnace and treated in a ladle–furnace unit at AO Uralskaya Stal is analyzed. The vacuum-treatment parameters that determine the effectiveness of hydrogen removal from the steel are identified: the depth and duration of vacuum treatment; the argon flow rate; the steel temperature; the thickness of the slag layer; and the free board in the vacuum chamber. The hydrogen content changes most significantly when the degassing time is increased to 20 min. Longer treatment is not recommended. The greatest effect of the residual pressure in degassing is observed with simultaneous decrease in the minimum pressure to 2 mbar. Vacuum treatment of the steel is considerably impaired with increase in the residual pressure. Hydrogen removal is improved with increase in the steel temperature to 1600–1620°C, but slows considerably at higher temperatures. The influence of the vacuum-treatment parameters is established quantitatively, and a regression equation is derived for predicting the results of hydrogen removal and selecting the parameter values corresponding to specified hydrogen content in the steel. Vacuum-treatment parameters that permit the economical production of steel with 2.1 ppm are determined: steel heating before vacuum treatment by 100–110°C; vacuum treatment for 20 min at a pressure no higher than 1.5 mbar in the vacuum chamber; argon flow rate 0.05 m3/t. The temperature losses of the metal are determined by the total treatment time, consisting of the active degassing time and the auxiliary time (the preliminary evacuation time), which depends on the capabilities of the equipment and the organization of the process. The minimum residual hydrogen content in the steel for the given equipment (1.6 ppm) is ensured by vacuum treatment for 40 min at a pressure no higher than 1 mbar in the vacuum chamber, with preliminary heating of the steel by 120–125 °C and with an argon flow rate up to 0.072 m3/t.