Effects of ball milling time on the microstructure and hydrogen storage performances of Ti21.7Y0.3Fe16Mn3Cr alloy

TiFe alloy can store hydrogen at room temperature and low hydrogen pressure, and its theoretical hydrogen storage capacity is up to 1.8 wt%. However, TiFe alloy needs to be activated at high pressure (5 MPa hydrogen) and high temperature (673–723 K), which limits the practical application of TiFe alloy. The as-cast Ti_21.7Y_0.3Fe₁₆Mn₃Cr alloy was milled for 0, 0.5, 0.75, 1, and 3 h to study the effects of ball milling on phase structures and hydrogen storage performances. Emphasis was focused on the activation process of as-milled alloys at different temperatures, including the activation process at 483, 443, and 403 K. The results show that the alloys were consisted of TiFe phase, and [Fe, Cr] solid solution. The nanocrystalline boundary produced by milling and the phase boundary provided by the second phase provide a large number of channels for hydrogen diffusion and promote the improvement of hydrogen storage performances. The time required for activation process of as-milled alloys was significantly reduced, and the activation time of as-milled (0.75 h) was only 4 min, and its enthalpy variation for hydrogen absorption and desorption was 22.943 and 26.215 kJ mol⁻¹ H₂, respectively.     

Solidification microstructure-dependent hydrogen generation behavior of Al–Sn and Al–Fe alloys in alkaline medium

This work deals with the development of quantitative correlations of hydrogen evolution performance with solidification microstructural and thermal parameters in Al–1Sn, Al–2Sn, Al–1Fe, and Al-1.5Fe [wt.%] alloys. The cellular growth as a function of growth and cooling rates is evaluated using power type experimental laws, which allow determining representative intervals of microstructure length scale for comparison purposes with the results of immersion tests in 5 wt%NaOH solution. For both Al alloys systems, hydrogen evolution becomes slower as the alloy solute content increased. However, for a given alloy composition, whereas a more homogeneous distribution of Sn-rich particles promotes faster hydrogen generation using Al–Sn alloys, coarsening of Al₆Fe IMCs (intermetallic compounds) fibers favors hydrogen production using Al–Fe alloys. When solidification conditions that result in a range of cellular spacings within 16 and 19 μm are considered, the specific hydrogen production of the Al-1wt.%Fe alloy is higher than that of the other studied alloys.     

Dynamic process of hydrogen and heat generation from reaction of Al–Li alloy powders and water vapor at moderate temperatures

As one of the alternative clean fuels, aluminum is suitable for generating hydrogen and power via metal hydrolysis. The reaction process characteristics were studied in a cylindrical reactor with 5 g of Al–Li alloy powder as fuel at moderate temperatures. The test performed good results with 1,130 mL/g alloy of H₂ yield, 86% of the reaction efficiency, and 54.5% of usable heat ratio. The dynamic change of temperature distribution was measured by 12 thermocouples in the reactor, and the maximum was not beyond 892°C. On the basis of the temperature characteristics, the reaction propagation speed was calculated and in the range of 0.57–0.95 mm/s. Moreover, the micromorphology and ingredients presented obvious differences between top product and bottom product, which was resulted from water vapor diffusion. The reaction of Al–Li alloy and steam was determined by both water vapor diffusion and heat transfer, which led to the distinct temperature trends near the vapor inlet, away from the vapor inlet, on the top and at the bottom. On the basis of the results, a mild and controllable hydrogen generation can be achieved at moderate temperatures by optimizing vapor inlet arrangement.     

“Preliminary results of hydrogen production from water vapor decomposition using DBD plasma in a PMCR reactor”

The water decomposition is considered one of the most attractive chemical processes for the production of hydrogen. The present work describes the preliminary results obtained in the experimental study of the water vapor dissociation into hydrogen and oxygen species using Dielectric-Barrier Discharge (DBD) plasma in a plate micro-channel reactor (PMCR). The water vapor molecules are injected without using carrier gas into the PMCR reactor at pressure of 100 kPa and temperature of 573 K. The applied high voltage of the plasma was within range of 14–18 kV and different steam flow rates have been analyzed within range of 100–200 ml/h. The product gases have been separated in ice trap which it was connected directly to the PMCR reactor to prevent the recombination of hydrogen and oxygen species. The concentration of the outlet species has been measured in a gas phase chromatography (GC) instrument. The PMCR reactor heating temperature effect on the water vapor decomposition has been analyzed. It was found that the water vapor is dissociated into their constituent molecular elements of hydrogen and oxygen gas using plasma. The maximum obtained mole fraction, hydrogen flow rate and conversion rate were 2.3%, 9.42 g/h, 42.51% respectively, at steam temperature of 573 K, pressure 100 kPa, PMCR heating temperature 403 K, steam flow rate of 200 ml/h and the plasma discharge high voltage of 18 kV. It was observed that the amount of evolved hydrogen concentration increased with the increase of the PMCR reactor heating temperature. Also, the thermal efficiencies versus the heat supplied have been calculated and the maximum obtained efficiency was 49.32%. Consequently, the evolved hydrogen flow rate appears to depend mainly on the plasma voltage, PMCR reactor heating temperature and the separating temperature of outlet hydrogen and oxygen species. The steam dissociation experiment will be extended to separate hydrogen and oxygen species elements at high temperature conditions.     

Numerical investigation on chill-down and thermal stress characteristics of a LH2 tank during ground filling

To investigate the thermal and structural characteristics of a flight-scale LH₂ tank during ground fillings, a CFD model and a structural analysis model are established to simulated the chill-down process and the induced thermal stress behavior of the tank, respectively. Results show that, at the early stage of filling, a severe temperature gradient appears at the liquid level, leading to a remarkable local concentration of thermal stress, while the maximal thermal deformation is at the outlet region. After the local wall is chilled down sufficiently, the temperature jump at the interface vanishes as well as the local thermal stress, while the maximal thermal deformation is located at the middle height of tank. The thermal stress is most serious at the beginning stage of filling and the maximum appears at the tank bottom. Moreover, the non-uniformity of the temperature distribution and the average thermal stress level within the tank wall both increase with the filling rate. At a filling rate of 7.5 kg·s⁻¹, the maximal thermal stress and thermal deformation of the target tank are more than 70 MPa and 30 mm.     

Opportunity of metallic interconnects for ITSOFC: Reactivity and electrical property

Iron-base alloys (Fe–Cr) are proposed hereafter as materials for interconnect of planar-type intermediate temperature solid oxide fuel cell (ITSOFC); they are an alternative solution instead of the use of ceramic interconnects. These steels form an oxide layer (chromia) which protects the interconnect from the exterior environment, but is an electrical insulator. One solution envisaged in this work is the deposition of a reactive element oxide coating, that slows down the formation of the oxide layer and that increases its electric conductivity. The oxide layer, formed at high temperature on the uncoated alloys, is mainly composed of chromia; it grows in accordance with the parabolic rate law (k_p = 1.4 × 10⁻¹² g² cm⁻⁴ s⁻¹). On the reactive element oxide-coated alloy, the parabolic rate constant, k_p, decreases to 1.3 × 10⁻¹³ g² cm⁻⁴ s⁻¹. At 800 °C, the area-specific resistance of Fe–30Cr alloys is about 0.03 Ω cm² after 24 h in laboratory air under atmospheric pressure. The Y₂O₃ coating reduces the electrical resistance 10-fold. This indicates that the application of Y₂O₃ coatings on Fe–30Cr alloy allows to use it as an interconnect for SOFC.     

Preparation of nanocrystalline metal (Cr,Al, Mn,Ce, Ni,Co and Cu) modified ferrite catalysts for the high temperature water gas shift reaction

Water gas shift reaction is an essential process of hydrogen production and carbon monoxide removal from syngas. Fe–Cr–Cu catalysts are typical industrial catalysts for high temperature water gas shift reaction but have environmental and safety concerns related to chromium content. In this work nanocrystalline metal (M)-modified ferrite catalysts (M = Cr, Al, Mn, Ce, Ni, Co and Cu) for replacement of chromium were prepared by coprecipitation method and the effects of promoters on the structural and catalytic properties of the iron based catalysts were studied. Prepared catalysts were characterized using X-ray diffraction (XRD), N₂ adsorption (BET), temperature-programmed reduction (TPR) and transmission electron microscopies (TEM) techniques. Temperature-programmed reduction measurements inferred that copper favors the active phase formation and significantly decreased the reduction temperature of hematite to magnetite. In addition, water gas shift activity results revealed that Fe–Al–Cu catalyst with Fe/Al = 10 and Fe/Cu = 5 weight ratios showed the highest catalytic activity among the prepared catalysts. Moreover, the effect of calcination temperature, GHSV and steam/gas ratio on the catalytic performance of this catalyst was investigated.     

Effect of hydrogen on the microstructure and mechanical properties of high temperature deformation of Ti6Al4V additive manufactured

The additive manufactured Ti6Al4V-xH titanium alloy was compressed at 600°C–750 °C on a Gleeble 3800 testing machine, and the compression rates were 1s⁻¹ and 0.01s⁻¹, respectively. The experimental results show that with the increase of hydrogen content, the flow stress of the alloy decreases firstly and then increases gradually. When the hydrogen content is 0.27 wt%, the flow stress of titanium alloy is the smallest. EBSD and TEM analysis were carried out and show that the α lamellar microstructure became larger at 0.27H, the corresponding flow stress also decreased, and slip bands appeared in the alloy. Dislocation slip was an important deformation mechanism of the alloy. When the hydrogen content continued to increase, the α phase in the alloy gradually decreased, and α″ appeared at 0.81H. Therefore, adding appropriate hydrogen can reduce the alloy flow stress and improve the performance of titanium alloy during hot deformation.     

Hydrogen-induced softening of Ti–44Al–6Nb–1Cr–2V alloy during hot deformation

The effect of hydrogen on the hot deformation behavior and microstructural evolution of Ti–44Al–6Nb–1Cr–2V (at.%) alloys were investigated at temperature range of 1373–1523 K under strain rate of 0.01 s^?1. The true stress–strain curves show that the peak stress decreases from 323 MPa to 97 MPa when deformation temperature increases from 1373 K to 1523 K. The peak stress is decreased by 30% after hydrogenation with 2% H, which corresponds to the decrease of deformation temperature by about 50 K, it denotes that hydrogen can promote a solution softening effect in TiAl alloys. This is attributed to hydrogen-promoted the dynamic recrystallization, hydrogen-induced dislocation movement and hydrogen-stabilized the B2 phase. For dynamic recrystallization, the calculated results show that hydrogen accelerates the onset of dynamic recrystallization, which means that hydrogen promotes the dynamic recrystallization kinetics. For dislocation movement, EBSD results show that the fraction of low-density dislocation region increases from 59.6% to 79.7% after hydrogenation with 2% H, which indicates that hydrogen reduces the dislocation tangles and dislocation density. For B2 phase, more softening B2 phases are observed in hydrogenated alloy compared with that in unhydrogenated alloy, which results from hydrogen-promoted the transition of L (α₂/γ) → γ + B2. The positive effect of hydrogen on TiAl alloys provides an effective method to improve the hot workability of TiAl alloys.     

Influence of Mn or Mn plus Fe on the hydrogen storage properties of the Ti-Cr-V alloy

To increase the hydrogen storage capacity and the plateau pressure of the Ti_0.32Cr_0.43V_0.25 alloy, a fraction of the Cr was replaced with Mn or a combination of Mn and Fe. When Mn was used alone, the effective hydrogen storage capacity increased to about 2.5 wt% though the plateau pressure showed no significant change. When Fe was added with Mn, however, both the effective hydrogen storage capacity and the plateau pressure increased. The BCC (body centered cubic) lattice parameter of the alloy decreased linearly with the Fe content, but it was not affected by Mn alone. The effective hydrogen storage capacity of the Ti_0.32Cr_0.32V_0.25Fe_0.03Mn_0.08 alloy was about 2.5 wt%, higher than 2.35 wt% in the original alloy. The estimated usable hydrogen stored in the Ti_0.32Cr_0.32V_0.25Fe_0.03Mn_0.08 alloy was 2.71 wt% in the temperature and pressure range of 293–353 K and 5–0.002 MPa, respectively.     

Study on the influence of Mg content on the risk of hydrogen production from waste alloy dust in wet dust collector

We use a proprietary automatic Al–Mg alloy–water reaction test apparatus to compare the hydrogen evolution profiles of Al-xMg (x = 10%,20%) with different particle sizes, characterize the waste Al-xMg alloy dust particles before and after reaction through SEM, EDS, and XRD, and present a three-stage four-step hydrogen evolution model of Al-xMg (x ≤ 35%) alloy dust particles. It is discovered that the reaction of the Al–Mg alloy in water is a hydrogen evolution–adsorption–slow diffusion process. The particular β-Al₃Mg₂ in Al-xMg (x ≤ 35%) will adsorb the resulting hydrogen to form MgH⁺ and adhere to the surface of the particles. As the Mg content in the alloy increases, the hydrogen evolution reduces. The entire process lasts around 5–6 h, with maximum hydrogen conversion rate of 54% (Al–10%Mg, d (50) = 12 μm, α = 0.544). Our hydrogen evolution model provides very useful theoretical references for avoiding hydrogen explosion in Al–Mg alloy manufacturing facilities.     

The potential for using high chromium ferritic alloys for hydroprocessing reactors

This paper outlines the development of hydroprocessing reactors and the parallel development of applicable steels for their high temperature and high pressure process environments. Trends in the development of newer processes for severe hydroprocessing applications have been increasing in operating hydrogen partial pressures and operating temperatures that require the development of new alloys to meet these more severe process environments.The paper outlines the properties of conventional hydroprocessing reactor materials and discusses the advantages of the advanced high chromium ferritic steel alloy Grade 91 (9Cr–1Mo–V) for high temperature hydroprocessing applications. Additionally, the alloys permitted for ASME Section I and Section VIII Division I construction, Grade 92 (Code Case 2179), and what will probably be called Grade 122 (Code Case 2180) are briefly introduced as possible future choices for hydroprocessing reactor construction. These three alloys contain 9–12% Cr and have time independent allowable stress values above 566 °C.These high, time independent, strength values provide materials that will in some cases permit extending hydroprocessing temperature limits by 112 °C. The paper provides room temperature and elevated temperature mechanical and toughness properties for the low chrome and Grade 91 materials and discusses the effects of hydrogen attack, and hydrogen and isothermal embrittlement. Fabrication aspects, including forming and welding are addressed.The paper discusses the environmental resistance of these alloys and investigates the possibility of utilizing excess wall metal thickness in these materials in less severe applications in lieu of the deposition of a higher chromium alloy weld overlay to overcome the corrosive effects of the process environment.     

Improved hydrogen storage properties of Ti2CrV alloy by Mo substitutional doping

Controllable hydrogen release is of great importance to the practical application of hydrogen storage materials. Ti₂CrV alloy possesses the maximum hydrogen absorption capacity in the Ti–Cr–V series alloys, however, can hardly meet the reversible storage capacity of practical applications due to its stable dihydride. Here we report an advancement in hydrogen storage property of the Ti₂CrV alloy by Mo partial substitution for Ti. Although the hydrogen absorption kinetics slightly decreased with the increase of Mo content, the Mo substitution alloy achieves an effective hydrogen capacity of 2.23 wt% cutting-off at 0.1 MPa, much higher than Ti₂CrV alloy (0.8 wt%). It is ascribed that Mo partial substitution for Ti significantly decreased the dihydride stability as well as the enthalpy change value. The cyclic property of Ti₂CrV alloy drastically decreased, while Mo substitution alloy with smaller FWHM value can maintain 90% storage capacity after 20 cycles. Because lattice strain and distortion of the Ti₂CrV alloy were decreased by Mo doping.     

Enhanced multi-cycle CO2 capture and tar reforming via a hybrid CaO-based absorbent/catalyst: Effects of preparation,reaction conditions and application for hydrogen production

A hybrid CaO-based absorbent/catalyst (Ca–Al–Fe) for calcium looping gasification (CLG) is prepared by a two-step sol-gel method. The effects of preparation and “carbonation-calcination” conditions on cyclic carbonation performance of Ca–Al–Fe are investigated. Calcination temperature of 900 °C and calcination time of 4 h are suitable parameters for absorbent preparation. The CaO conversion of Ca–Al–Fe increases with increasing carbonation temperature below 750 °C. Under severe calcination conditions such as high temperature, high CO₂ concentration and long-term up to 40 cycles, Ca–Al–Fe still shows good cyclic CO₂ capture reactivity. Moreover, the effect of Ca–Al–Fe on tar removal enhancement is investigated in comparison with three candidate absorbents (Ca、Ca–Fe and Ca–Al). During five toluene reforming cycles, Ca–Al–Fe presents the highest average H₂ yield and the least deposited coke with an average hydrogen concentration of about 68.8%. The average toluene conversion with Ca–Al–Fe is about 26.41% higher than that using conventional CaO.     

Effect of Cr addition on room temperature hydrogenation of TiFe alloys

This paper discusses the effect of AB₂ (Ti(Cr, Fe)₂) phase on the hydrogenation properties of a Ti–Fe–Cr alloy system. Five Ti–Fe–Cr based alloys were fabricated by varying the Cr content. The microstructural analysis results revealed that the fraction of the Ti(Cr, Fe)₂ phase increased with the increasing Cr content. The first hydrogenation test results indicated that all the alloys could absorb a significant amount of hydrogen at room temperature (30 °C) without a separate activation process. This behavior improved when the Ti(Cr, Fe)₂ phase existed in the AB phase; the kinetics of the first hydrogenation tended to increase with the fraction of Ti(Cr, Fe)₂ phase. The enhancement in the first hydrogenation kinetics of the Ti–Fe–Cr based alloys was attributed to the synergetic effect of the interface between the AB and Ti(Cr, Fe)₂ phases and the inherent fast hydrogenation of the Ti(Cr, Fe)₂ phase. However, the total hydrogen storage capacity decreased when the fraction of Ti(Cr, Fe)₂ phase increased.     

Effect of 0.3 wt%H addition on the high temperature deformation behaviors of Ti–6Al–4V alloy

The high temperature deformation behaviors of Ti–6Al–4V alloy and the alloy hydrogenated with 0.3 wt%H were studied. Comparing with the unhydrogenated alloy, the hydrogenated alloy exhibited higher plasticity and lower flow stress. The possibilities of hydrogen-induced plasticity were attributed to the effect of hydrogen on dislocation density, stacking fault energy in starting microstructure and dislocation mobility, dynamic recrystallization during high temperature deformation.     

Formation and properties of titanium-manganese alloy hydrides

Hydride formation and hydriding properties of Ti-Mn alloy systems, which have a hexagonal structure of MgZn₂(C14)-type known as the Laves phase, were studied by measuring pressure-composition isotherms in the temperature range 0–80°C. It was found that the Ti-Mn binary alloys whose Ti contents were less than 36 at % absorbed almost no hydrogen (P ? 4.5 MPa), but the alloys containing more Ti did react readily with hydrogen at room temperature without any activation treatment. The maximum absorbed hydrogen content of every Ti-Mn alloy was H/M ～ 1.The TiMn_1.5 hydride showed the most desirable properties of all the Ti-Mn binary alloy hydrides; the dissociation plateau pressure is approximately 0.7 MPa, the maximum amount of absorbed hydrogen is 228 ml g^?1 the maximum amount of released hydrogen is 190 ml g^?1 at 20°C, and ΔHΔH is the molar enthalpy change of hydrogen (i.e. the heat of formation).= ?28.7 kJ(mol H₂)^?1. Also, hydriding properties of TiMn₂ based Ti-Mn multi-component alloys containing other transition metals, such as Zr, V, Cr, Fe, Co, Ni, Cu, Nb, Mo, Ta, La and Ce, were studied. The dissociation plateau pressure at 20°C was obtained in a range from 0.01 MPa (for Ti_0.5Zr_0.5 Mn₂-H) to 1 MPa (for Ti_0.9Zr_0.1Mn_1.4V_0.2Cr_0.4-H).     

Fast start-up of microchannel fuel processor integrated with an igniter for hydrogen combustion

A Pt–Zr catalyst coated FeCrAlY mesh is introduced into the combustion outlet conduit of a newly designed microchannel reactor (MCR) as an igniter of hydrogen combustion to decrease the start-up time. The catalyst is coated using a wash-coating method. After installing the Pt–Zr/FeCrAlY mesh, the reactor is heated to its running temperature within 1 min with hydrogen combustion. Two plate-type heat-exchangers are introduced at the combustion outlet and reforming outlet conduits of the microchannel reactor in order to recover the heat of the combustion gas and reformed gas, respectively. Using these heat-exchangers, methane steam reforming is carried out with hydrogen combustion and the reforming capacity and energy efficiency are enhanced by up to 3.4 and 1.7 times, respectively. A compact fuel processor and fuel-cell system using this reactor concept is expected to show considerable advancement.     

Porous Ni–Co surface formation and analysis of hydrogen generation by gas sensor

A Ni–Co alloy was used as the test piece. The porous Ni–Co alloy surface was prepared by Al electrodeposition at ?1.4 V and ?1.8 V and Al dissolution at ?0.5 V in a NaCl–KCl-3.5 mol% AlF₃ molten salt. The bath temperature was 750 °C and 900 °C. As a result, a porous Ni–Co alloy could be prepared by Al electrodeposition and Al dissolution on the Ni–Co alloy in the molten salt. It was clarified that a denser surface was formed at the bath temperature of 750 °C than at the bath temperature of 900 °C. Furthermore, it was clarified that the porous layer became thicker when the electrodeposition potential was ?1.8 V than when it was ?1.4 V. The formed porous Ni–Co alloy was evaluated for cathode performance in a 10 mass% KOH solution. Furthermore, the amount of generated hydrogen was measured by a constant voltage and constant current test with a gas sensor using a solid electrolyte. In the cathode polarization curve, the porous Ni–Co alloy showed a higher current density at a lower potential than the untreated Ni–Co alloy. It was shown that the Ni–Co alloy formed under the electrodeposition conditions at the electrodeposition potential of ?1.4 V and bath temperature of 750 °C is a very excellent cathode material. Furthermore, based on the constant voltage test, it was revealed that the porous treated sample generates a higher amount of hydrogen than the untreated sample.     

Design of ternary Al-Sn-Fe alloy for fast on-board hydrogen production, and its application to PEM fuel cell

An Al-Sn-Fe alloy is designed to increase the hydrogen generation rate even in weak alkaline water through the effective removal of Al oxide. Al-1wt.%Sn-1wt.%Fe alloy exhibits the hydrogen generation rate about 6 times higher than pure Al and 1.6 times higher than Al-1wt.%Fe alloy. Increases in exchange current density of Al alloys are in good accordance with increases in hydrogen generation rate. The addition of Sn in Al-Fe alloy can increase the hydrolysis rate by accelerating the breakdown of passive film (Al(OH)₃ and Al₂O₃) in an alkaline solution. Hence, the Al-1wt.%Sn-1wt%Fe alloy shows a much higher hydrogen generation rate than pure Al and Al-1wt.%Fe alloy in relatively weak alkaline water. In the hydrolysis of Al-1wt.%Sn-1wt%Fe, Fe accelerates the hydrogen production by inducing simultaneously both inter-granular and galvanic corrosion, whereas Sn increases the hydrogen generation rate by breaking the Al oxide down effectively. Based on the increase in the hydrogen generation rate of Al-1wt.%Fe and Al-1wt.%Sn-1wt%Fe alloys over pure Al, the contribution to the increase of Fe and Sn are calculated to be 63% and 27%, respectively. Because the same amount of power is obtained by PEMFC using 6 times less Al-Sn-Fe alloy than pure Al, the weight and volume of on-board hydrogen production reactor can be reduced significantly by alloying Al with a small amount of Fe and Sn.