Hydrogen Desorption Profile Research Articles

Estimation of the spatial distribution of carbon edge sites in a carbon structure using H2 desorption kinetics in temperature programmed desorption

This study aims to elucidate the role of hydrogen desorption profiles obtained through temperature programmed desorption (TPD) analysis of carbon materials for revealing their carbon edge sites. Accordingly, the H2 desorption profiles of several carbon materials, such as activated carbon, carbon black, reduced graphene oxide (rGO), phenol resin carbon, graphite, high-temperature treated carbon, and carbon nanotubes (CNTs), were investigated. The kinetic analysis of the profiles revealed that H2 desorption is a second-order reaction initiated by the association of edge hydrogen. Furthermore, the relationship between the total number of edge hydrogens in a sample and the peak temperature of H2 desorption represents the spatial distribution of edge hydrogens in the carbon structure. Additionally, most of the activated carbons, carbon blacks, and rGOs exhibited a uniform distribution of edge hydrogen throughout their carbon structures. In contrast, the edge hydrogen in graphite, high-temperature treated carbon, and CNTs were heterogeneously distributed throughout their structures.

Hydrogen Desorption Behavior Trapped in Various Microstructures of High-Strength Steels Using Thermal Desorption Analysis

The relationship between different microstructures and hydrogen trapping states of cold-drawn pearlitic (CD-P) steel, medium-carbon martensitic (MC-M) steel, and high-carbon martensitic (HC-M) steel was studied based on the hydrogen desorption profile, activation energy of hydrogen desorption (Ea), and hydrogen release behavior at room temperature by means of thermal desorption analysis (TDA). The TDA results revealed that hydrogen in CD-P and HC-M was present as both Peak 1H and Peak 2H, but only as Peak 1H in MC-M. Hydrogen release behavior indicated that Peak 1H for all three types of steel was diffusible (Ea ≤ 34 kJ/mol). For CD-P, Peak 2H was non-diffusible (Ea = 62 kJ/mol), but diffusible for HC-M (Ea = 43 kJ/mol). TDA results combined with SEM and/or TEM observation and XRD analysis clarified that the former hydrogen was desorbed from strained incoherent α/θ interfaces in a detrapping-controlled process. The latter hydrogen was desorbed via trapping sites involved in retained austenite in a diffusion-controlled process. It is essential to judge hydrogen trapping states as either diffusible or non-diffusible by analyzing not only hydrogen desorption profiles but also hydrogen release behaviors and Ea values, taking into account microstructure characteristics related to hydrogen trapping and diffusion processes.

Microscopic defects formed during crack incubation, initiation and propagation processes causing hydrogen-related fracture of dual-phase steels

Factors promoting hydrogen embrittlement of dual-phase (DP) steels fractured in the elastic region have been investigated from the viewpoint of the relationship between hydrogen states present in the vicinity of a fracture surface and hydrogen embrittlement susceptibility. Hydrogen embrittlement susceptibility was evaluated using slow strain rate testing (SSRT) and constant load testing (CLT). The hydrogen states present in the vicinity of the fracture surface were analyzed using thermal desorption analysis (TDA). The results indicated that fracture strength significantly decreased only at higher hydrogen contents as the crosshead speed was reduced. Additionally, the hydrogen desorption profiles showed that the hydrogen content corresponding to each temperature peak markedly increased with decreasing crosshead speed at higher hydrogen content. Only specimens fractured at a lower crosshead speed at higher hydrogen contents showed both a lower-temperature peak and also a higher-temperature peak. Specimens fractured by CLT also showed a higher-temperature peak, which was detected before fracturing at the applied load for 20 h. This indicates that microscopic defects might have formed and grown to cause damage even in the elastic region. In addition, it was confirmed that microscopic defect formation changed depending on the hydrogen content, crosshead speed and loading time, and the states of defect formation significantly affected hydrogen embrittlement susceptibility.

Hydrogen effects on mechanical performance of nodular cast iron

Abstract The KBS-3 method for long-term disposal of spent nuclear fuel is designed with an external self-standing copper shell, which provides the most important barrier against corrosion and escape of radionuclides, and an internal nodular cast iron insert, which provides the load-bearing structure against external loads. The material intended for the load-bearing insert is ferritic nodular cast iron EN 1563 grade EN-GJS-400-15U. In this paper, hydrogen uptake and sensitivity to hydrogen-induced cracking of the cast iron were studied using tensile testing under continuous electrochemical charging in 1 N H2SO4 solution. Hydrogen uptake was measured by using the thermal desorption method. It was found that the hydrogen desorption profile manifests three distinct peaks at initial locations of 400, 500, and 700 K with a heating rate of 6 K/min. Plastic deformation results in a remarkable increase of the 400 K peak, which indicates hydrogen uptake during deformation. In the constant extension rate tests (CERT) and the constant load tests (CLT), electrochemical hydrogen charging reduced markedly the elongation to fracture and time to fracture, respectively. In CLT, hydrogen charging increased dramatically the creep rate at the applied load of about 0.7 yield stress. Ligaments between the graphite nodules exhibit brittle cleavage facets in the presence of hydrogen, while the ligaments show a characteristic ductile appearance of shear and small dimples when testing in air or distilled water. The obtained results are discussed in terms of the known mechanisms of hydrogen-induced cracking and the role of the graphite nodules in the embrittlement of ductile cast iron.

Identification of lattice defects beneath fracture surfaces of cold-drawn pearlitic steel fractured in elastic/plastic regions in the presence of hydrogen

The kinds of lattice defects formed beneath fracture surfaces were analyzed using thermal desorption analysis (TDA) for cold-drawn pearlitic steel that was fractured in the elastic/plastic regions in the presence of hydrogen. A sample thickness of 0.3 mm made it possible to obtain two separate peaks: a low temperature peak and a high temperature peak. Tensile tests and constant load tests were conducted under various hydrogen charging conditions to prepare samples with different elongations and fracture times. Samples of 0.3 mm in thickness beneath fracture surfaces were charged with hydrogen to determine the kinds of lattice defects and hydrogen desorption profiles were obtained using TDA. For samples that were fractured in the plastic region, a broad hydrogen desorption profile continuing to around 180 °C was obtained compared to samples without hydrogen charging and straining. Since this broad desorption profile was disappeared by aging at 200 °C, it probably corresponded to desorption from vacancies. In contrast, for samples that were fractured in the elastic region, this broad desorption profile was not obtained. These findings indicate that one of the factors causing hydrogenin the plastic region is probably vacancies, whereas other factors cause it in the elastic region.

Changes in mechanical properties following cyclic prestressing of martensitic steel containing vanadium carbide in presence of nondiffusible hydrogen

Changes in the states of nondiffusible hydrogen and mechanical properties after cyclic prestressing in the presence of only nondiffusible hydrogen were examined for martensitic steel containing vanadium carbide. The relationship between the change in the state of nondiffusible hydrogen and mechanical properties was also investigated. The hydrogen desorption profile in the high-temperature range decreased and that in the low-temperature range increased with increasing stress amplitude during cyclic prestressing in the presence of only nondiffusible hydrogen. Thus, the application of cyclic prestressing changed the state of hydrogen from a stable to an unstable one because of vacancies and their clusters. Hydrogen embrittlement susceptibility after cyclic prestressing increased with increasing stress amplitude and number of prestressing cycles in the presence of only nondiffusible hydrogen. This relationship indicates that hydrogen embrittlement susceptibility increased with the increasing amount of hydrogen detrapped from trap sites of nondiffusible hydrogen during cyclic prestressing. These results revealed that nondiffusible hydrogen easily detrapped from vanadium carbide due to the application of cyclic prestress and probably interacted with vacancies and their clusters, thus increasing hydrogen embrittlement susceptibility. The change of nondiffusible hydrogen to diffusible hydrogen and accumulation of vacancies and their clusters during cyclic prestressing are concluded to be the dominant factors in hydrogen embrittlement after the application of cyclic prestress.

Shape-controlled synthesis of Pt-Ir nanocubes with preferential (100) orientation and their unusual enhanced electrocatalytic activities

Pt-Ir nanocubes with (100)-terminated facets were synthesized for the first time and their unusual high electrocatalytic activity for a model reaction (i.e., ammonia oxidation) was reported. The key parameters in controlling the shape of the Pt-Ir nanocubes were systematically investigated by transmission electron microscopy (TEM). The electrocatalytic activities of the prepared Pt-Ir and pure Pt nanoparticles (NPs) were characterized by cyclic voltammetry (CV). The results showed that the amount of W(CO)6 and the volume ratio of oleylamine and oleic acid play a significant role in the development of well-defined Pt-Ir nanocubes. The resultant Pt-Ir nanocubes exhibit (100) orientation, which has been confirmed by not only the structural characterization results from high-resolution TEM (HRTEM) and X-ray diffraction (XRD) but also hydrogen desorption profiles obtained from the CV measurements in H2SO4 solution. Lattice contraction of the Pt-Ir nanocubes were suggested by HRTEM and XRD measurements, and the electronic interactions between Pt and Ir in the Pt-Ir nanocubes were demonstrated by X-ray photoelectron spectroscopy. The Pt-Ir nanocubes show higher specific activity than pure Pt nanocubes and much higher specific activity than the polycrystalline Pt-Ir NPs. The much improved specific activity of the Pt-Ir nanocubes could be attributed to the reason that the introduction of Ir in the Pt-Ir nanocubes largely maintains the highly active Pt (100) sites and thus a positive synergistic effect through the addition of Ir to Pt could be achieved due to the possible bifunctional mechanism and the electronic effect.

大気および高圧水素ガス環境を模擬した低合金鋼の水素チャージ法

Appropriate hydrogen charging methods were investigated to simulate hydrogen absorption from actual environments where high strength steels are used. Both absorbed hydrogen concentrations and hydrogen desorption profiles were compared between various hydrogen charging tests - immersion tests, cathodic charging tests, cyclic corrosion tests (CCT) and exposure tests in high pressure gaseous hydrogen. Absorbed hydrogen was analyzed using thermal desorption analysis (TDA) after the hydrogen charging tests. It was confirmed that acid immersion tests or cathodic charging tests in NaCl solution were appropriate to simulate hydrogen absorption from CCT. Fédération Internationale de la Précontrainte (FIP) tests or cathodic charging tests in NaCl - NH4SCN solution could be used to simulate hydrogen absorption in high pressure hydrogen gas environments. Comparisons in TDA profiles showed that the ratio of strongly-trapped hydrogen and weakly-trapped hydrogen changed depending upon the total amount of absorbed hydrogen. This result means the state of hydrogen in steels, which affects hydrogen embrittlement, can change according to the amount of absorbed hydrogen. The above-mentioned hydrogen charging tests and hydrogen analysis were conducted in 15 laboratories to check the scatter of measured hydrogen concentration.

Suitability of various complex hydrides for foaming aluminum alloys

Abstract

Synthesis and characterisation of a mesoporous carbon/calcium borohydride nanocomposite for hydrogen storage

Abstract Borohydrides with high hydrogen content are being extensively studied as potential hydrogen storage systems placing particular emphasis on upturning their unfavourable kinetic and thermodynamic properties which give rise to significantly high dehydrogenation temperatures and slow hydrogen release far away from the desired application window. In this work the encapsulation of Ca(BH 4 ) 2 particles in the pores of a CMK-3 type ordered mesoporous carbon scaffold by wet chemistry routes, also employing the use of TiCl 3 as a catalyst, is shown to have a beneficial effect on the hydrogen desorption profile of the bulk hydride by shifting its decomposition to noticeable lower temperatures.

Quasi in situ Mössbauer and XAS studies on FeB nanoalloy for heterogeneous catalytic dehydrogenation of ammonia borane

In our previous report, about 1 equiv. H 2 can be evolved from a Fe-modified ammonia borane (AB) sample at a temperature as low as 60 °C with significant depression of induction period, sample foaming and toxic byproducts [1]. In this study, the effects of catalyst precursors and catalyst loading were investigated on the hydrogen desorption profile and the formation of crystalline polyaminoborane (PAB). The experimental results show that loading 2.0 mol.% FeCl 3 to solid-state AB gives the best performance of formation of crystalline PAB. The rate of hydrogen evolution from the Fe-modified AB is 5.8 times as that of neat AB at 60 °C. X-ray absorption spectroscopy (XAS) and quasi in situ 57Fe Mössbauer characterizations show that Fe–B nanoalloy, which functions as catalytic species in the dehydrogenation, is formed upon mixing AB with FeCl 3.

Modeling of Hydrogen Thermal Desorption Profile of Pure Iron and Eutectoid Steel

We have developed a numerical model to simulate the hydrogen desorption profiles for pure iron and eutectoid steel, which is obtained in thermal desorption analysis (TDA). Our model incorporates the equation of McNabb and Foster without the hydrogen diffusion term combined with the Oriani's local equilibrium theory. It is found that the present numerical model successfully simulates the hydrogen desorption profile using the concentration of hydrogen trapping sites which is inferred from experiments both for pure iron and for eutectoid steel. We further verify the model by discussing the trapping site concentration and the effect of hydrogen diffusion.

Modeling of Hydrogen Thermal Desorption Profile of Pure Iron and Eutectoid Steel

We have developed a numerical model to simulate the hydrogen desorption profiles for pure iron and eutectoid steel, which is obtained in thermal desorption analysis (TDA). Our model incorporates the equation of McNabb and Foster without the hydrogen diffusion term combined with the Oriani's local equilibrium theory. It is found that the present numerical model successfully simulates the hydrogen desorption profile both for pure iron and for eutectoid steel. We further verify the model by discussing the trapping site concentration and the effect of hydrogen diffusion.

Cyclohexanethiol adsorption and reaction on the Ni(100) surface

The adsorption and reactions of cyclohexanethiol (CHT) have been characterized on the Ni(100) surface in the presence and absence of coadsorbed hydrogen. Cyclohexanethiol adsorbs at 120 K on the Ni(100) surface primarily as cyclohexylthiolate and surface hydrogen. Saturation coverage of CHT on the Ni(100) surface (0.25 ML) is very similar to other thiols on this surface, and indicates that an upright orientation is dominant. CS bond scission was observed at 240 K, as evidenced by sulfur X-ray photoelectron spectroscopy (XPS). However, no desorbing products are observed at this temperature due to strong interactions with the surface. The CHT CS bond scission temperature is 30 K lower than the CS bond breaking temperature for benzenethiol. Therefore, the energetics for CS bond activation correlate with bond strength, suggesting a radical mechanism. The reaction limited cyclohexane peak at 320 K is the first desulfurized hydrocarbon product which desorbs. Increasing dehydrogenation with increasing temperature results in benzene desorption at 360 K. The complex hydrogen desorption profile over the 320 to 360 K temperature range indicates significant stepwise dehydrogenation of surface intermediates. No carbon containing compounds desorb after the 360 K benzene peak. The amount of hydrogen desorbed indicates that approximately 60% of the CHT undergoes complete dehydrogenation for a saturated monolayer. Preadsorbed hydrogen does not influence CS bond activation, since free hydrogen desorbs below the CS bond scission temperature. However, additional coadsorbed hydrogen decreases the total product yield by blocking adsorption of the thiol. For small CHT coverages, complete decomposition dominates on the Ni(100) surface, yielding only gas phase hydrogen and surface bound sulfur and carbon. It is interesting to note that a small fraction of the CHT remains molecular and interacts primarily through the cyclohexyl ring, producing a molecular CHT peak at 180 K even at low coverages. The CS bond activation temperature is independent of surface hydrogen concentration, indicating that CS bond activation involves direct interaction of the metal with the CS bond, as observed previously for benzenethiol on this surface.

Particle size effect in supported platinum: Methylcyclohexane dehydrogenation

Dehydrogenation of methylcyclohexane has been studied over a platinum monometallic catalyst supported on α-Al 2O 3. Physical and chemical properties of platinum crystallites were studied by TPR and TPD/H 2 techniques. The hydrogen desorption profile was found to be particle size dependent. A tightly-bonded hydrogen fixed on platinum particles after high-temperature reduction was revealed by TPD/H 2. In the methylcyclohexane dehydrogenation, it was found that the reactivity of platinum crystallites is related to the activation process performed before the catalytic test. The dehydrogenation rate increased by at least a factor of 2.0 when a desorption following high-temperature reduction was performed. These results were consistent with the hydrogen desorption profiles observed by TPD/H 2.

Coated silica as support for platinum catalyst: II. Hydrogen chemisorption and activity for combustion

Samples of 0.5 wt.-% platinum supported on silica, alumina, titania and lanthana, and on coated supports (Al 2O 3/SiO 2, TiO 2/SiO 2 and La 2O 3/SiO 2) with threshold monolayer loadings, were characterized by hydrogen-oxygen titration, temperature-programmed desorption (TPD) of hydrogen and catalytic combustion of methane. All the samples show depressed chemisorption when reduced at 773 K, compared to reduction at 573 K. Surface platinum atom concentrations for Pt/TiO 2 and Pt/La 2O 3 are around one order of magnitude higher than those for Pt/SiO 2 and Pt/Al 2O 3. But when coated on silica, the oxide coatings caused greatly depressed surface platinum atom concentrations even lower than that on pure silica support. With Pt/Al 2O 3/SiO 2 and Pt/La 2O 3/SiO 2, hydrogen desorption profiles can be attributed to hydrogen spilt over onto alumina and lanthana, respectively. But for Pt/TiO 2/SiO 2, the desorbed hydrogen seems to originate from spilt over hydrogen on silica. This may imply full or nearly full coverage of silica by the oxides in the former two cases, and partial coverage in the latter case. Differences in TPD profiles of LTR and HTR samples agree well with chemisorption data. Titania and lanthana supported catalysts have much higher specific activity and TOF than silica and alumina supported platinum catalysts for methane combustion. When coated on silica, TOFs were increased while specific activities were lowered relative to those of pure oxides. Titania and titania coated silica, when used as supports for platinum, yield the most active catalysts for catalytic combustion of methane.