Hydrogen Thermal Desorption Research Articles

Thermal desorption of hydrogen from ammonia borane: unexpected role of homopolar B–H⋯H–B interactions

The solid-state structure of ammonia borane is held together by an intricate N-H···H-B proton-hydride bonding network. These intermolecular interactions have long been considered to mediate the release of hydrogen from this material. Here we reveal the silent but important role played by B-H···H-B interactions in the thermal decomposition of this leading hydrogen storage candidate.

Effects of the Hydrogen Absorption Conditions on the Hydrogen Embrittlement Behavior of Ni–Ti Superelastic Alloy

The present study has investigated whether the hydrogen embrittlement behavior of Ni–Ti superelastic alloy can be changed by modifying the hydrogen absorption conditions. Upon immersion in H2SO4 or H3PO4 solution, the stress plateau due to the stress-induced martensite transformation becomes unclear and forms a gentle slope. In addition, the superelastic strain decreases with increasing immersion time. The peripheral part of the fracture surface of the immersed specimens is flat as usual, whereas the center part of the fracture surface is rough compared with that under other hydrogen absorption conditions reported previously. For the specimens immersed in H3PO4 solution, hydrogen thermal desorption tends to be observed at higher temperatures compared with the specimens immersed in H2SO4 solution. Moreover, for a longer immersion time, a second peak of hydrogen desorption is observed at a high temperature, indicating that the hydrogen states change with the hydrogen absorption conditions. The results of this study suggest that changing the hydrogen embrittlement behavior by modifying the hydrogen absorption conditions may enable the determination of the embrittlement mechanism of the alloy.

Effect of Uniform Distribution of Fine Cementite on Hydrogen Embrittlement of Low Carbon Martensitic Steel Plates

The effect of uniform distribution of fine cementite on resistance of ultra-high strength steels to hydrogen embrittlement was studied. The materials used were directly-quenched and tempered 1000–1300 MPa class low carbon steel plates for welded structures with lath martensite structure. Cementite morphology was different at different heating rates to tempering temperatures. Finer cementite was distributed in rapidly-heated steels (20°C/s) than in slowly-heated steels (0.3°C/s). The rapidly-heated steels showed higher resistance to hydrogen embrittlement than the slowly-heated steels for a slow strain rate test (SSRT), whereas they showed almost the same resistance to hydrogen embrittlement for a constant load test (CLT). The specimens fractured in a plastic region for the SSRT, on the other hand, the CLT was conducted in an elastic region. The difference in hydrogen embrittlement resistance between plastic and elastic loading methods was concluded to result from a change in the hydrogen trap state at cementite in association with plasticity. Hydrogen is more strongly trapped at and/or around the strained interfaces between the matrix and cementite after plastic deformation. A close observation of fracture surfaces, hydrogen thermal desorption analysis and hydrogen microprint technique revealed that the high resistance of the rapidly-heated and tempered steels to hydrogen embrittlement for the SSRT is due to a shift of the fracture mode from quasi-cleavage fracture to ductile fracture. This shift was caused by the suppression of the quasi-cleavage fracture due to less hydrogen at lath boundaries accompanied by the uniform distribution of fine cementite.

Effect of microstructure on the phase composition and hydrogen absorption-desorption behaviour of melt-spun Mg-20Ni-8Mm alloys

The effect of microstructure on the phase composition and hydrogen absorption-desorption behaviour of Mg-based Mg-20Ni-8Mm (wt.%) (Mm = La-rich Mischmetal) alloys has been studied. Rapid solidification (RS) processing resulted in the formation of the high-temperature cubic modification of Mg2NiH4 and the solid solution hydride Mg2NiH0.3, in the disappearance of the monoclinic modification of Mg2NiH4, as well as in a decrease in the unit cell volumes of the constituent hydride phases. The above-mentioned tendencies became more pronounced in the order “as-cast < Cu-300 < Cu-1000 ≈ Cu-2000” (where the sample names Cu-#### denote the spinning velocity of the copper wheel in rpm), which is explained by an increase in the mechanical stresses in the materials and/or by an increased interfacial energy of the fine grains of the corresponding hydrides. The hydrogen absorption kinetics was improved in the order “Cu-300 < Cu-1000 < Cu-2000”. The temperature range of hydrogen thermal desorption from the hydrogenated alloys shrank in the order “Cu-300 > Cu-1000 >> Cu-2000”, which is explained by increased uniformity of the hydrides grain size in the hydrides with increasing solidification rate. During PCT (pressure composition temperature) tests, the Cu-1000 and Cu-2000 samples displayed the largest pressure hysteresis and the smallest slope of the higher Mg2NiH4 plateau, but also the lowest hydrogen storage capacity.

HYDROGEN ABSORPTION BEHAVIOR OF 1500 MPa--GRADE HIGH STRENGTH STEEL 42CrMoVNb

Hydrogen absorption behaviors of a newly developed 1500 MPa-grade high strength steel 42CrMoVNb at different austenitizing temperatures and tempering temperatures were studied using cathodic charging and hydrogen thermal desorption analysis,which were also compared with commercial structural steel 42CrMo.The results show that the hydrogen escape peak temperatures (θ_p) in hydrogen evolution curves of hydrogen charged 42CrMoVNb specimens are between 200℃to 300℃both at as-quenched condition and as-tempered condition.The absorbed hydrogen content of 42CrMoVNb specimen increases slowly with increasing tempering temperature up to 500℃.When the tempering temperature exceeded 500℃,the absorbed hydrogen content increases sharply and reaches its peak,6.6×10~(-6),for the specimen tempered at 600℃,which is 5 times as much as that of the as-quenched specimen.Thereafter the absorbed hydrogen content declines sharply as the tempering temperature was gone up sequentially.When the specimen was tempered at 400℃,the absorbed hydrogen content decreases slightly with austenitizing temperature increasing,and in the microstructure no fine dispersed(V,X)C carbide precipitated,while when the specimen was tempered at 600℃, the absorbed hydrogen content increases sharply with austenitizing temperature increasing,and more fine dispersed(V,X)C precipitated.These results indicate that fine dispersed(V,X)C precipitate could be regarded as a strong hydrogen trap,and the trap activation energy,E_a,is equal to about 28.7 kJ/mol,which was obtained by change heating rate.

Thermal desorption of hydrogen from magnesium hydride (MgH 2): An in situ microscopy study by environmental SEM and TEM

As-received magnesium hydride (MgH 2), and MgH 2 doped with lithium borohydride (LiBH 4) and titanium (III) chloride (TiCl 3) catalyst were heated – in situ – in an environmental scanning electron microscope (ESEM) and a transmission electron microscope (TEM). Morphological and structural changes during heating and hydrogen desorption were recorded in real time. The studies show that native MgH 2 undergoes dramatic and destructive structural changes upon heating, whereas the doped/catalyzed MgH 2 mixture showed a benign outgassing with little structural change. Videos of the morphological changes during heating can be viewed online at the McGrady group website: http://www.unb.ca/fredericton/science/chem/smcgrady/group/shanebeattie/InsituESEMandTEM-MgH2.html.

Low-temperature hydrogen desorption and the structural properties of spark discharge generated Mg nanoparticles

Mg nanoparticles were synthesized using spark discharge, resulting in large-scale structures of agglomerated nanoparticles with primary particle sizes of ∼10 nm, surrounded by MgO shells 1–2 nm thick. Thermal hydrogen desorption starts at remarkably low temperatures of ∼350 K, related to the small sizes of particles, and extends over a broad temperature range to beyond 700 K, caused by the presence of oxide shells acting as activation barriers. The hydrogen sorption kinetics is increased significantly by adding Pd nanoparticles in situ during synthesis, showing the versatility of spark discharge generation for the production of metal hydride nanocomposites.

Cyclic deformation behavior and low cycle fatigue life of normalized medium carbon steel with hydrogen charging

The effects of hydrogen on low cycle fatigue properties have been fundamentally examined using normalized JIS S45C steel. With the aid of hydrogen thermal desorption analysis, the influence of the increase in carbon content has been discussed. The S45C steel easily pick-up hydrogen. But it is relatively insensitive to hydrogen absorption. This increased amount of hydrogen pick-up is firstly caused by large amount of pearlite structure. Further sulfur takes an important role for hydrogen pick up during cathodic charging. Hydrogen plays two kinds of roles during fatigue tests. One is hydrogen in dislocation core and makes plastic deformation easier in the first monotonic tension stage. The other is hydrogen/vacancy pair, and suppresses dislocation motion and increases stress amplitudes. The latter should be the fundamental issue for fatigue life. The amount of absorbed hydrogen itself is not only important, but the difference of hydrogen concentration between surface and inside is more important. When the fatigue crack initiates inside, the fatigue life is severely damaged to less than 10% of non-charged one. Taking the lower limit value of hydrogen to form internal fish-eye type cracking, S45C is less sensitive to hydrogen in cyclic straining. This comes from the pearlite structure that resists crack propagation.

Selective hydrogenation of Ti–Zr–Ni alloys

We prepared series of Ti–Zr–Ni samples by melt-spinning and subsequent thermal treatment at 700 °C for 2 h in dynamic 10 −5 mbar vacuum in order to obtain mixture of crystalline C14 Laves and α, β-(Ti, Zr) phases. These samples were exposed to hydrogen gas at 300 °C and 50 bar for 1000 min. The mass% of H was obtained gravimetrically and volumetrically. When approximately 1% of air was present in the Sievert device we found relatively narrow area in Ti–Zr–Ni phase diagram, so-called zero-zone, where hydrogen amounts in crystalline samples varied between 0 and 0.8 mass%. Surprisingly, icosahedral quasicrystalline (i-QC) samples showed no selective hydrogenation and absorbed more than 1.5 mass% H in the interval of compositions, where the i-phase is formed. XPS analysis revealed that the oxide layer thickness is similar after melt-spinning and thermal treatment for both type of samples, i.e. from inside and outside of the zero-zone. However, after hydrogenation the zero-zone samples had 5-times thicker surface oxide layer. In order to find, whether this is correlated to different electronic structure, DOS near E F was examined by 1H NMR. In parallel, thermal desorption of hydrogen was performed in order to reveal, if H-bonding sites are correlated to different hydrogenation behaviour of various samples.

Hydrogen-sorption and thermodynamic characteristics of mechanically grinded TiH 1.9 as studied using thermal desorption spectroscopy

Isobaric thermal desorption spectroscopy and X-ray diffraction analysis were used to study the influence of mechanical dispersion during high-energy milling γ-TiH 1.9 hydride upon its hydrogen-sorption characteristics, temperature and enthalpy of the γ → β (TiH 1.9 → Ti[H] β) phase transition at isobaric heating the sample under hydrogen atmosphere with speed 3°/min. Isobars of hydrogen thermal desorption in the regions of the γ and β phases of the Ti–H 2 system at pressures of 0.1, 0.25, 0.315 and 0.45 MPa of hydrogen in the reactor have been derived. Experimental data obtained for initial titanium hydride and mechanically grinded for 20 min in a planetary ball mill have been used for construction of Van’t Hoff plots and for determination of enthalpy of formation of γ-hydride from solid solution of hydrogen in bcc titanium. Our experimental data reveal that 20 min high-energy influence on titanium hydride powder leads to increasing the specific surface of the samples from 0.13 to 8.58 m 2/g and to significant (more than 250°) decreasing the temperature of the beginning of hydrogen release when heating the sample (i.e., to a decrease of thermal stability of mechanically activated TiH 1.9). However, mechanical dispersion does not change the temperature of the γ → β phase transition. It has been established that high-energy milling TiH 1.9 powder causes the effect of a decrease of enthalpy of the formation of γ-hydride from 248 kJ/mole H 2 to 175 kJ/mole H 2.

A novel polymorph of gadolinium tetrahydroborate produced by mechanical milling

Gadolinium tetrahydroborate produced by mechanochemical processing of LiBH 4–3GdCl 3 mixture exhibits a structural transformation at 484 K. The high-temperature structure has a type cubic structure Gd(BH 4) 3 ( a = 11.418 Å), which is isostructural with the one recently reported for Ce(BH 4) 3. This new phase remains upon heating up to 503 K. Combination of thermal hydrogen desorption, DSC, PXRD and FTIR allows to determine that the thermal decomposition of high-temperature structure Gd(BH 4) 3 starts above 503 K and leads to 3.1 wt% of hydrogen release obtaining mainly GdH 2 as final decomposition product.

Performance of hydrogen trapping and phase transformation in hydrogenated duplex stainless steels

Duplex stainless steels (DSS) (SAF 2507) have outstanding mechanical properties and high levels of corrosion resistance (especially to SCC in chloride-containing environments). However in spite of this they are susceptible to hydrogen embrittlement.The interaction of hydrogen with the microstructure and defects in DSS (SAF 2507) was investigated in order to gain an in-depth understanding of the behaviour of hydrogen in this material. Hydrogen was introduced into the metal by means of electrochemical cathodic charging in acid solution.Using X-ray diffraction and SEM microscopy, the phase transformation was studied. γ→γ* was the major hydrogen-induced phase transformation in duplex steel. The pseudo hydride phase of γ* was unstable—disappearing during ageing, over a period of 24h at room temperature, and after thermal desorption (20–450°C). This is as a result of hydrogen evolution. A negligible amount of ɛ-martensite was further observed immediately after charging. Hydrogen desorption induced surface tensile stress provoking the phase transformation γ→ɛ→αM.A linear model was used to analyze thermal desorption of hydrogen, through the TDS spectrum, and resulted in the identification of trapping types in DSS. These include: the strain regions around the dislocations with activation energy of about 20kJ/mol; grain boundaries (22.5–28.5kJ/mol); the dislocations core (34.8–40.3kJ/mol), vacancies and austenite–ferrite interfaces (50.2–57.4kJ/mol).The relation of initial hydrogen concentration and heating rate to the thermal desorption process is discussed.

Hydrogen storage properties of spark generated palladium nanoparticles

Palladium nanoparticles of ∼4 nm were synthesized using spark discharge generation, and their hydrogen storage properties were determined using both thermal desorption spectroscopy (TDS) and Sievert’s (PCT) measurements. PCT measurements indicate that the thermodynamic properties of the nanoparticles towards hydrogen storage differ significantly from that of bulk Pd, even after sintering of the crystallites to 24 nm as determined using X-ray diffraction (XRD). Both the enthalpy and entropy of hydrogen absorption and desorption differ from bulk values, resulting in less hysteresis between absorption and desorption equilibrium plateau pressures and a lowering of the critical temperature of hydride formation T c by approximately 100 K. The TDS measurements indicate a transition from diffusion to surface-barrier limited hydrogen desorption when going from Pd foil to Pd nanoparticles. This results in a strong decrease in the hydrogen thermal desorption temperatures by ∼160 K during TDS. These results indicate that spark discharge is an interesting method for metal hydride nanoparticle generation.

Thermal desorption of hydrogen from graphane

The process of hydrogen desorption from graphane (graphene sheet saturated by hydrogen adsorbed from both sides) has been studied using the method of molecular dynamics. The temperature dependences of the time of desorption onset for various hydrogen coverages on graphene are calculated and the corresponding activation energies in the Arrhenius equation are determined. It is established that graphane exhibits a rather high thermal stability that makes possible its use in two-dimensional electronics even at room temperature. For the same reason, graphane can hardly be considered as a promising hydrogen storage material for fuel cells.

Evaluation of hydrogen absorption behaviour during acid etching for surface modification of commercial pure Ti, Ti–6Al–4V and Ni–Ti superelastic alloys

The hydrogen absorption behaviour during acid etching for the surface modification of commercial pure Ti, Ti–6Al–4V and Ni–Ti superelastic alloys has been investigated on the basis of the surface morphology, electrochemical behaviour and hydrogen thermal desorption analysis. To simulate the conventional acid etching for the improvement of the biocompatibility of Ti alloys, the specimens are immersed in 1 M HCl, 1 M H 2SO 4 or 0.5 M HCl + 0.5 M H 2SO 4 aqueous solution at 60 °C. Upon immersion, commercial pure Ti absorbs substantial amounts of hydrogen irrespective of the type of solution. In H 2SO 4 or HCl + H 2SO 4 solutions, the hydrogen absorption occurs for a short time (10 min). For Ti–6Al–4V alloy, no hydrogen absorption is observed in HCl solution, whereas hydrogen absorption occurs in other solutions. For Ni–Ti superelastic alloy, the amount of absorbed hydrogen is large, resulting in the pronounced degradation of the mechanical properties of the alloy even for an immersion time of 10 min, irrespective of the type of solution. The hydrogen absorption behaviour is not necessarily consistent with the morphologies of the surface subjected to corrosion and the shift of the corrosion potential. The hydrogen thermal desorption behaviour of commercial pure Ti and Ni–Ti superelastic alloy are sensitively changed by acid etching conditions. The present results suggest that the evaluation of hydrogen absorption is needed for each condition of acid etching, and that the conventional acid etching often leads to hydrogen embrittlement.

Effect of hydrogen on plastic strain localization in single crystals of austenitic stainless steel

Tensile tests accompanied with on-line in situ field emission gun-scanning electron microscopy observations were performed to study hydrogen effects on plastic strain localization in the form of slip lines in single crystals of austenitic stainless steel. It was found that the slip lines on the hydrogen-charged specimens were markedly shorter and more grouped together than the straight slip lines on the hydrogen-free specimens. Hydrogen thermal desorption and positron annihilation spectroscopy were applied to study the combined effect of hydrogen and plastic deformation on excessive generation of vacancies.

Relationship between the structure and properties for an example of the thermal desorption of hydrogen from selected intermetallic hydrides based on zirconium and rare-earth metals

On the basis of the data of neutron diffraction analyses, it is shown that the temperature of hydrogen release in the process of thermal desorption from some interstices of the metal matrix depends not only on the type of their faceting but also on some other structural factors including, first of all, the sizes of interstices and the presence of short H – H distances.

SIMS analysis of low content hydrogen in commercially pure titanium

Due to their excellent specific strength and environmental resistance, titanium and its alloys have been widely used as structural components. However, titanium is very active, so that not only oxygen and nitrogen, but also hydrogen may be readily introduced into the material during manufacturing. Titanium usually contains a specific amount of hydrogen, and it exists in the titanium as a hydride or solid solution dependent on the hydrogen content. The hydrogen solid solubility limit of pure titanium (a-phase titanium) seems to be higher than 10 ppm [1], although some values are reported. That is to say, if the hydrogen content of pure titanium is less than 10 ppm, all the hydrogen is thought to be a solid solution in the titanium. On the other hand, when the hydrogen content is more than the solid solubility limit, hydrides would appear. As the hydride is brittle, it weakens the strength of the titanium. Therefore, the hydrogen content in commercially pure titanium (CP-Ti) is within 150 ppm [2]. The present authors carried out a fatigue strength evaluation of titanium samples using the hydrogen removed sample (hydrogen content is 2.7 ppm) and normal sample (34 ppm) [3, 4]. On the surface of the 2.7 ppm one, the hydride did not exist, while on the 34 ppm one, the hydride was present. It was found that the fatigue crack nucleation life of the 34 ppm one is greater than that of the 2.7 ppm one, and the fatigue crack propagation life of the 34 ppm one is the same as the 2.7 ppm one. This specific observation of the crack propagation indicated that the material behavior near the grain boundary is important for the crack propagation [3, 4]. It is then important to understand the actual state of hydrogen near the grain boundary for the CP-Ti applications. There are some methods to detect hydrogen in materials, and each method has some merits and demerits. The hydrogen thermal desorption analysis method (TDS and TDA) can be used for the average hydrogen content and energy state analysis [5]. As already mentioned, hydrogen in the CP-Ti exists as a solid solution or hydride, and the hydrogen localized around the grain boundary should be evaluated. The localized hydrogen can then be visualized by the following method.

Electron-stimulated defect formation in single-walled carbon nanotubes studied by hydrogen thermal desorption spectroscopy

Defects in single-walled carbon nanotubes introduced by low-energy electron irradiation at 8 K were sensitively detected by cryogenic thermal desorption of hydrogen molecules H 2 in the temperature range of 10–40 K. The thermal desorption spectrum was found to change significantly with sample annealing at temperatures as low as 40–70 K. Experimental results suggest that the H 2 physisorption sites responsible for the ‘defect’ peak at 28 K are interstitial channel space between nanotubes closely packed in bundles which becomes more easily accessible on damage. It is also suggested that the disordering provides groove sites for H 2 physisorption with smaller binding energy causing the damage-induced spectral component around 16 K, slightly lower than the desorption peak at 20 K that is observed in undamaged samples. The spectral change at 40–70 K could be interpreted by migration of adatoms at the low temperatures.

Anelastic mechanical loss spectrometry of hydrogen in austenitic stainless steels

Atomic distribution of hydrogen, its elemental diffusion jumps and its interaction with dislocations in a number of austenitic stainless steels are studied with anelastic mechanical loss (AML) spectrometry in combination with the hydrogen thermal desorption method. Austenitic stainless steels of different chemical composition, namely, AISI 310, AISI 201, and AISI 301LN, as well as LDX 2101 duplex stainless steel are studied to clarify the role of different alloying elements on the hydrogen behavior. Activation analyses of the hydrogen Snoek-like peaks are performed with their decomposition to sets of Gaussian components. Fine structure of the composite hydrogen peaks is analyzed under the assumption that each component corresponds to diffusion transfer of hydrogen between octahedral positions with certain atomic compositions of the nearest neighbouring lattice sites. An additional component originating from hydrogen-dislocation interaction is considered. Binding energies for hydrogen-dislocation interaction are also estimated for the studied austenitic stainless steels.