Sieverts-type Apparatus Research Articles

Hydrogen isotope effect of nanoporous palladium

Materials used in hydrogen isotopes separation are crucial in modern hydrogen energy field. In this article, a promising material nanoporous palladium was prepared and its relative properties were studied. Nanoporous palladium with pore scale of about 5 nm was fabricated by free dealloying corrosion. Its kinetic and PCT curves of hydrogen/deuterium adsorption at room temperature were tested using a Sievert-type volumetric apparatus. Microstructures were observed with Scanning Electron Microscopy and Atomic Force Microscopy. Crystalline structure was characterized with X-Ray Diffractometer before and after deuterium adsorption. Comparative experiments with spongy palladium that is commonly used in relative industry were also carried out. According to the results, nanoporous palladium shows faster hydrogen/deuterium adsorption rate than spongy palladium, which is due to its nanoporous structure that supplies a large amount of specific surface area. PCT curves of hydrogen/deuterium adsorption in nanoporous palladium among 298–338 K were tested and plateau pressures at different temperatures were obtained. Deuterium/hydrogen isotopes separation factors were calculated using plateau pressures above and were plotted with temperature. It's found that nanoporous palladium shows larger hydrogen isotope separation factors compared with spongy palladium at temperatures no higher than 323 K. These findings illustrate that nanoporous palladium would be an ideal material for hydrogen isotopes separation applications.

Experimental behaviour of a three-stage metal hydride hydrogen compressor

A three-stage metal hydride hydrogen compressor (MHHC) system based in AB2-type alloys has been set-up. Every stage can be considered as a Sieverts-type apparatus. The MHHC system can work in the pressure and temperature ranges comprised from vacuum to 250 bar and from RT to 200 °C, respectively. An efficient thermal management system was set up for the operational ranges of temperature desired. It drops temperature shifts due to hydrogen expansion during stage coupling and hydrogen absorption/desorption in the alloys. Each reactor consists of a single and thin stainless-steel tube to maximize heat transfer. These were filled with similar amount of AB2 alloy. The MHHC system was able to produce a compression ratio as high as 84.7 for inlet and outlet hydrogen pressures of 1.44 and 122 bar for a temperature span of 23 °C – 120 °C.

Fast hydrogen absorption/desorption kinetics in reactive milled Mg-8 mol% Fe nanocomposites

This study aims to better understand the Fe role in the hydrogen sorption kinetics of Mg–Fe composites. Mg-8 mol% Fe nanocomposites produced by high energy reactive milling (RM) for 10 h resulted in MgH2 mixed with free Fe and a low fraction of Mg2FeH6. Increasing milling time to 24 h allowed formation of a high fraction of Mg2FeH6 mixed with MgH2. The hydrogen absorption/desorption behavior of the nanocomposites reactive milled for 10 and 24 h was investigated by in-situ synchrotron X-ray diffraction, thermal analyses and kinetics measurements in Sieverts-type apparatus. It was found that both 10 and 24 h milled nanocomposites presents extremely fast hydrogen absorption/desorption kinetics in relatively mild conditions, i.e., 300–350 °C under 10 bar H2 for absorption and 0.13 bar H2 for desorption. Nanocomposites with MgH2, low Fe fraction and no Mg2FeH6 are suggested to be the most appropriate solution for hydrogen storage under the mild conditions studied.

Experimental investigations of AB5-type alloys for hydrogen separation from biological gas streams

AB5-type intermetallic compounds are suitable materials for hydrogen separation due to their ability selectively absorb hydrogen from different gas streams, including biologically produced ones. Recent studies show that metal hydride-based purification systems can effectively extract hydrogen from biogas with high CO2 concentration. Alloys LaNi5-xMx (M = Fe, Al, Mn, Sn) are prepared and activated during several cycles of H2 sorption/desorption and their PCT properties are measured in Sievert's type apparatus. Two compositions LaNi4.4Fe0.3Al0.3 and LaNi4.6Mn0.2Al0.2 are chosen for further investigations because they meet the requirements for biohydrogen separation system. After PCT measurements of 50-g samples, metal hydride powders are investigated by means of Quantochrome Nova 1200 and scanning electron microscopy to determine porosity, average particle size, specific surface area and permeability of metal hydride bed. Powder bed permeabilities are defined as 9.08 × 10−13 m2 for LaNi4.4Fe0.3Al0.3 and 6.86 × 10−13 m2 for LaNi4.6Mn0.2Al0.2 by Kozeny-Carman equation. AB5 type LaNi4.4Fe0.3Al0.3 and LaNi4.6Mn0.2Al0.2 alloys show good characteristics: low equilibrium pressures 0.025–0.03 MPa and acceptable reversible hydrogen capacity 1.1 %wt. for stationary hydrogen separation system.

Improving the hydrogenation properties of AZ31-Mg alloys with different carbonaceous additives by high energy ball milling (HEBM) and equal channel angular pressing (ECAP)

In this study, the hydrogen storage performance of commercial AZ31-Mg alloys combined with various allotropes of carbon was investigated and the microstructural modifications with respect to plastic deformation and high energy milling techniques investigated, with the aim of obtaining enhanced hydrogen storage efficiency. The hydrogen storage performance of alloys prepared with different weight ratios of carbonaceous materials as a catalyst was monitored in order to explore the effective improvement in hydrogen storage performance through microstructural modification. Additionally, the effects of different processing methods such as equal channel angular pressing (ECAP) and high energy ball milling (HEBM) were also observed. AZ31 Mg based composites with various carbon additives were produced through gravity resistance casting and their micrographic structures examined through optical Microscopy (OM), X-ray diffraction (XRD) and scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS). The average particle size distributions of the sample powders were also measured. The rate of hydrogenation kinetics was calculated by a Sievert's type apparatus. Significant enhancement of the hydrogenation performance was obtained with the addition of carbonaceous materials. Overall, the hydrogen storage performance after ECAP deformation of the AZ31-3CB (carbon Black) composite showed a gain in the maximum capacity of 6.72 ± 0.05 wt%. Similar, after milling of the AZ31-3G (Graphene) composite materials, a maximum potential capacity of 6.83 ± 0.04 wt% was attained within 792 ± 144.34 s, with desorption of the entire H2 content in 143.2 ± 26.09 s. The obtained results revealed significant improvement in the hydrogen storage capacity of AZ31-Mg alloys with the addition of carbon materials and with respect to plastic deformation and milling techniques.

Improved cycle durability of hydrogen absorption and desorption in melt-spun Mg86Pr3Al11 alloy

Abstract In this work, the hydrogen absorption and desorption properties of a melt-spun Mg86Pr3Al11 alloy were studied using a Sieverts-type apparatus. It was found that the melt-spun Mg86Pr3Al11 alloy exhibits an enhanced cycle durability of hydrogen absorption and desorption. After fifty hydrogen absorption and desorption cycles at 300 °C, the capacity retention rate is about 97% and the hydrogen sorption kinetics undertakes only a slight degradation, which is related to the existence of PrAl2 and Pr3Al11 phases in the melt-spun Mg86Pr3Al11 alloy.

Effects of graphite addition and air exposure on ball-milled Mg–Al alloys for hydrogen storage

Magnesium hydride (MgH2) is a promising candidate as a hydrogen storage material. However, its hydrogenation kinetics and thermodynamic stability still have room for improvement. Alloying Mg with Al has been shown to reduce the heat of hydrogenation and improve air resistance, whereas graphite helps accelerating hydrogenation kinetics in pure Mg. In this study, the effects of simultaneous Al alloying and graphite addition on the kinetics and air-exposure resistance were investigated on the Mg60Al40 system. The alloys were pulverized through high-energy ball milling (hereinafter HEBM). We tested different conditions of milling energy, added graphite contents, and air exposure times. Structural characterization was conducted via X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). H2 absorption and desorption properties were obtained through volumetry in a Sieverts-type apparatus and Differential Scanning Calorimetry (DSC). The desorption activation energies were calculated using DSC curves through Kissinger analysis. Mg60Al40 with 10 wt% graphite addition showed fast activation kinetics, even after 2 years of air exposure. Graphite addition provided a catalytic effect on ball-milled Mg–Al alloys by improving both absorption and desorption kinetics and lowering the activation energy for desorption from 189 kJ/mol to 134 kJ/mol. The fast kinetics, reduced heat of reaction, and improved air resistance of these materials make them interesting candidates for potential application in hydride-based hydrogen storage tanks.

Synthesis, characterisation and hydrogen sorption properties of mechanically alloyed Mg(Ni1-xMnx)2

Hydrogen storage materials based on the stoichiometry Mg(Ni1-xMnx)2 have been synthesized by High Energy Ball Milling (HEBM) and studied as potential candidate materials for solid state hydrogen storage. The microstructures of the as-cast and the milled alloys were characterized by means of X-ray Powder Diffraction (XRD) and Scanning Electron Microscopy (SEM) both prior and after the hydrogenation process. The storage characteristics (Pressure-Composition-Temperature isotherms) and the sorption kinetics obtained by a commercial and automatically controlled Sievert-type apparatus. The X-ray results showed that the substitution of Mn over Ni could eliminate and inhibit the MgNi2 phase. The calculation of the average crystallite size showed that the increase of the amount of Mn can reduce the size at the early stages, but for Mn content higher than 0.25 the crystallite size increases, while the microstrain levels decreased monotonically. The hydrogenation and dehydrogenation measurements took place at several temperatures (150–200–250–300 °C). The results showed that the kinetics for both the hydrogenation and dehydrogenation can be fast for operation at temperatures between 250 and 300 °C, but for temperatures below 200 °C the hydrogenation process is very slow, and the dehydrogenation process cannot be achieved.

Study on nanostructured MgH2 with Fe and its oxides for hydrogen storage applications

Magnesium hydride is one of the most suitable candidates for hydrogen storage due to completely reversible hydrogen storage reactions. Moreover magnesium is a widespread element on the earth. In this work the preparation of nanostructured magnesium hydride has been realized by mechanical milling under inert gas in presence of iron and its oxides. The work presents a complete comparison between Fe and its oxides as catalyst for sorption kinetics. Fe is a suitable catalyst for hydrogen storage as it largely fastens kinetics respect to pure MgH2 and is a widespread and cheap material. The materials have been investigated by Sievert type apparatus (PCI), Differential Scanning Calorimetry (DSC), Scanning Electron Microscope (SEM) and X-Ray Diffraction (XRD).

CO₂ Adsorption Investigation on an Innovative Nanocomposite Material with Hierarchical Porosity.

A NaX nanozeolite-geopolymer monolith, with hierarchical porosity, has been produced by a one-pot hydrothermal synthesis using metakaolin as alluminosilicate source and a sodium silicate solution as activator. Its final composition, reported in terms of oxides, is 1.3-Na₂O-3.0SiO₂-1Al₂O₃-12H₂O. Its microstructural and chemical features and CO₂ adsorption performance have been investigated. The microstructure of the composite is characterized by NaX zeolite nanocrystals glued by the geopolymeric binder to form a complex three-dimensional network of pores. Overall porosity resulted ~23.5%, whereas compressive strength is 16±0.7 MPa. Monolith showed BET surface area of 350 m²/g, a micropore surface area of 280 m²/g and a mesopore volume, due to the geopolymeric binder, of 0.09 cm³/g. Its CO₂ adsorption capacity has been measured at the temperatures of 7, 25 and 42 °C up to 15 bar using an optimized Sievert-type (volumetric) apparatus. All the adsorption data were evaluated by Toth/Langmuir isotherm model and commercial pure NaX zeolite was used as reference. CO₂ adsorption isotherms show a maximum uptake value around 21 wt% at (~7 °C) that decrease to 18 wt% at high temperature (~42 °C) passing through 19 wt% at room temperature (~25 °C). The homogeneity grade of the surface, as obtained using Toth analysis performed on the adsorption isotherm, is close to t ≅ 0.40, lower than the 0.61 obtained for pure commercial NaX zeolite, as a consequence of the binder formation. Monolith exhibits a notably higher K values and quicker saturation with respect to reference that can be ascribed to the presence of mesoporosity that provides an easier and faster transport of CO₂ in the NaX nanozeolite framework. The produced composite is a potential solid adsorbent candidate in industrial process.

Hydrogen Desorption Properties of LiBH4/xLiAlH4 (x = 0.5, 1, 2) Composites.

A detailed analysis of the dehydrogenation mechanism of LiBH4/xLiAlH4 (x = 0.5, 1, 2) composites was performed by thermogravimetry (TG), differential scanning calorimetry (DSC), mass spectral analysis (MS), powder X-ray diffraction (XRD) and scanning electronic microscopy (SEM), along with kinetic investigations using a Sievert-type apparatus. The results show that the dehydrogenation pathway of LiBH4/xLiAlH4 had a four-step character. The experimental dehydrogenation amount did not reach the theoretical expectations, because the products such as AlB2 and LiAl formed a passivation layer on the surface of Al and the dehydrogenation reactions associated with Al could not be sufficiently carried out. Kinetic investigations discovered a nonlinear relationship between the activation energy (Ea) of dehydrogenation reactions associated with Al and the ratio x, indicating that the Ea was determined both by the concentration of Al produced by the decomposition of LiAlH4 and the amount of free surface of it. Therefore, the amount of effective contact surface of Al is the rate-determining factor for the overall dehydrogenation of the LiBH4/xLiAlH4 composites.

Low temperature de/hydrogenation in the partially crystallized Mg60Ce10Ni20Cu10 metallic glasses induced by milling with process control agents

Slow hydrogen de/absorption kinetics and high hydrogen desorption temperature are still great challenges for both crystalline and amorphous Mg-based alloys. In this work, through using ethanol (E) and ethylene glycol (EG) as milling process control agents (PCAs), partial and controllable crystallization of the melt-spun Mg60Ce10Ni20Cu10 metallic glass was achieved. The microstructure of the as-milled powders and corresponding hydrides was characterized by DSC, SEM, TEM and XRD. De/hydrogenation properties were measured by automatic Sieverts-type apparatus and TG-MS. It was found that the PCAs could lead to partial crystallization of the Mg60Ce10Ni20Cu10 metallic glass due to the dissolving of oxygen into the amorphous structure from PCAs. The introduction of a small amount of the nanocrystals promoted greatly hydrogen de/absorption properties of the melt-spun Mg60Ce10Ni20Cu10 alloy. The hydrogenation temperature could be decreased to below 100 °C and the initial hydrogen desorption temperature of the EG-added hydride could be decreased to below 150 °C. The structure evolution of the de/hydrogenated samples of the EG-added powder was also studied. The hydrogen-induced crystallization was evidently observed in the hydrogenated sample. The ethanol and ethylene glycol was found to be effective milling PCAs to create a composite structure of amorphous and crystalline, and the composite structure greatly enhanced the de/hydrogenation properties. However, the structural stability and reversibility of such composite structure during hydrogenation were still great challenges.

Influence of the ECAP and HEBM processes and the addition of Ni catalyst on the hydrogen storage properties of AZ31-x Ni (x=0,2,4) alloy

In this work, the hydrogen sorption properties of AZ31 magnesium alloys with various additions of nickel (Ni) (i.e., Ni (X = 0, 2, 4) wt.%) were investigated. Cast ingots with different AZ31/NiP compositions were fabricated using a gravitating mechanical stir casting (GMSC) method. Two different processes, namely, equal channel angular pressing (ECAP) and high energy ball milling (HEBM) were performed to improve its hydrogen storage properties. The particle size of the sample powders were measured by laser diffraction analysis. The microstructures, powder morphologies, and phase transformation were characterized by optical microscopy (OM), scanning electron microscopy (SEM) and x-ray diffraction (XRD) analysis. The hydrogen sorption kinetics were measured by a Sievert's type apparatus. The results showing the impact of the ECAP and HEBM processes on the hydrogen storage properties were compared. The AZ31-4 Ni ECAP processed sample showed a maximum hydrogen storage capacity of 7.0 wt.% at 2322 s with complete desorption of all the hydrogen in less than 5 min at a temperature of 375 °C. On the other hand, the pure AZ31 alloy which was treated with the HEBM process showed the maximum hydrogen capacity of 6.5 wt.% at 2393 s with desorption of all the hydrogen within 6 min. In addition, the activation energy, as illustrated by the Kissinger plot, revealed that the activation energy of the ECAP processed AZ31-4 Ni was 104.73 (KJ/mol), obviously lower than the material processed by HEBM and pure MgH2.

Low Pressure Methane Storage in Pinecone-Derived Activated Carbons

The methane adsorption properties of activated carbon samples from pinecones using chemical activation with different KOH/precursor ratio were estimated at room temperature (≅298 K) and pressure up to 35 bar using a volumetric Sievert-type apparatus. A complete and detailed characterization of the synthesized activated carbon samples was obtained using nitrogen adsorption/desorption measurements at liquid nitrogen temperature (77 K), for the textural properties analysis, by scanning electron microscopy and X-ray diffraction for topography and long-range order estimation, and by wavelenght-dispersive spectrometry for chemical composition, respectively. All the adsorption data were analyzed by the Toth isotherm model. The probed activated carbon samples show both higher methane storage values for pressures up to 35 bar (the maximum value reached is 15 wt%) and totally reversible methane uptake up to many cycles without any treatment in between indication of very stable properties. The experimental work repo...

Low-cost Sieverts-type apparatus for the study of hydriding/dehydriding reactions

Abstract The design and construction of a low-cost equipment for the study of hydriding/dehydriding reactions of different materials are presented. This is a Sieverts-type apparatus where a small amount (0.2–1 g) of solid hydrogen storage materials can be characterized. The apparatus combines the features of double lines (sample and reference) to eliminate small thermal effects on the reservoir and sample-holder volumes, with a Δp = Δpsample − Δpreference approach to eliminate the need of a differential pressure transducer and to reduce costs. This apparatus can work from vacuum to 10 MPa hydrogen pressure and from room temperature to 673 K. Pressure, temperature and volume data are transformed by a real gases equation state and mass balance into hydrogen uptake or release in wt%. Characterization of typical hydrogen storage materials such as LiAlH4 and Mg is presented to validate the performance of the apparatus.

Microstructure and hydrogen absorption/desorption properties of Mg24Y3M (M = Ni, Co, Cu, Al) alloys

Ternary alloys with the nominal composition of Mg24Y3M (M = Ni, Co, Cu, Al) have been fabricated by using vacuum induction melting method. Their microstructure and phase composition are characterized by using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The isothermal hydrogen absorption and desorption kinetics are measured by a Sievert's-type apparatus. The dehydrogenation behaviors of the full hydrogenated alloys are also analyzed by differential scanning calorimetry (DSC) method. Results show that each and every alloy has a distinct multiphase structure containing the main phase Mg24Y5 and some amount of Mg. Intermetallic compounds of YCo2 and Al2Y are detected in the M = Co and M = Al alloy, while long-period stacking ordered (LPSO) phase can be also observed in M = Ni and M = Cu alloy. The hydrogen absorption and desorption kinetics shows a decreased trend in the following order: (M = Ni) > (M = Al) > (M = Co) > (M = Cu). The M = Ni alloy has the best hydrogen storage performance among the investigated alloys. The dehydrogenation activation energy (Ea) of the M = Ni alloy decreases to 66 kJ/mol, and its decomposition peak temperature is also reduced to 313 °C. Moreover, the p–c–T (pressure-composition isotherms) curves of the studied alloys are also discussed.

Hydrogenation and Dehydrogenation of the Clathrate Na x Si136

Samples of the clathrate Na x Si136 were saturated with hydrogen to 100 atm at 25°C in a Sievertstype apparatus and at pressures of 6 and 28 kbar in lentil-type high-pressure apparatuses at 100 and 250°C. X-ray powder diffraction analysis and Raman spectroscopy of the samples quenched after the saturation with hydrogen showed that the phase composition of the clathrates did not change. Heating of the quenched samples to room temperature in a thermal desorption setup produced not hydrogen, but hydrogen-containing gases, as we assumed, silanes. Heating to 650°C leads to decomposition of these compounds to form hydrogen.

Improved hydrogen absorption and desorption kinetics of magnesium-based alloy via addition of yttrium

Yttrium (Y) is selected to modify the microstructure of magnesium (Mg) to improve the hydrogen storage performance. Thereby, binary alloys with the nominal compositions of Mg24Yx (x = 1–5) are fabricated by inexpensive casting technique. Their microstructure and phase transformation during hydriding and dehydriding process are characterized by using X-ray diffraction, scanning electron microscopy, and high-resolution transmission electron microscopy analysis. The isothermal hydrogen absorption and desorption kinetics are also measured by a Sievert's-type apparatus at various temperatures. Typical multiphase structures of binary alloy can be clearly observed. All of these alloys can reversibly absorb and desorb large amount of hydrogen at proper temperatures. The addition of Y markedly promotes the hydrogen absorption kinetics. However, it results in a reduction of reversible hydrogen storage capacity. A maximum value of dehydrogenation rate is observed with the increase of Y content. The Mg24Y3 alloy has the optimal desorption kinetic performance, and it can desorb about 5.4 wt% of hydrogen at 380 °C within 12 min. Combining Johnson–Mehl–Avrami kinetic model and Arrhenius equation, the dehydrogenation activation energy of the alloys are evaluated. The Mg24Y3 alloy also has the lowest dehydrogenation activation energy (119 kJ mol−1).

Magnetic phase diagrams of Gd-H, Tb-H, Dy-H systems

We study the impact of hydrogen impurity on the magnetic phase transition temperatures of the high purity rare-earth metals Gd, Tb and Dy. Prior to hydrogenation, the rare earths were purified by the vacuum distillation method. Hydrogenation was carried out using a Sievert-type apparatus. Magnetic phase diagrams were constructed based on the thermomagnetic analysis.

Magnetocaloric properties of hydrogenated Gd, Tb and Dy

The influence of hydrogen on magnetocaloric properties of three high purity heavy rare earths (R), gadolinium, terbium and dysprosium is studied. Hydrogenation procedure is performed using high purity hydrogen in a Sievert-type apparatus. In addition to the main α-RHx phase (where x is the hydrogen concentration), appearance of the second phase RH2 or its traces is detected in nearly all hydrogenated samples. In the samples where the main α-RHx phase prevails and only traces of the dihydride phase are found, the magnetocaloric effect (MCE) remains of the same magnitude as in the hydrogen-free samples. With the increase of hydrogen concentration (and with a corresponding increase of the RH2 phase content), the MCE values decrease. Only Gd samples demonstrate the increased Curie temperatures (TC = 291 and 296 K for Gd and GdH0.2, respectively) related to the increase of exchange interactions in the Gd-Gd pairs. At the same time, the Néel temperatures of Tb and Dy retain their values after hydrogenation.