Sieverts-type Apparatus Research Articles

Hydrogen Adsorption Properties of Lantern-Type Dinuclear M(BDC)(DABCO)1⁄2

Abstract The hydrogen adsorption properties and uptake capacities of three-dimensional microporous materials of lantern-type dinuclear M(BDC)(DABCO)1⁄2 (M=CoII, CuII, and ZnII; BDC = 1,4-benzenedicarboxylate, DABCO = 1,4-diazabicyclo[2.2.2]octane; Co(BDC)(DABCO)1⁄2 (1), Cu(BDC)(DABCO)1⁄2 (2), Zn(BDC)(DABCO)1⁄2 (3)) were investigated at various temperatures of 77–333 K and pressures up to 10 MPa using a PCT automatic measuring system (Sievert-type apparatus). The results indicated that uptake to 4.11, 2.70, and 3.17 wt % of hydrogen can be stored on 1, 2, and 3, respectively, at 77 K. The amounts of hydrogen are adsorbed by all complexes at around room temperature (293 K) and high-pressures are much lower (<0.5 wt %). Adsorption isotherms at around room temperature show a linear uptake relationship; all of them follow the Henry’s law. By measuring nitrogen gas adsorption/desorption, all complexes exhibit approximately Type-I isotherms according to the IUPAC classification and possess BET surface areas in the range of 1165 (for 3) to 1595 m2 g−1 (for 1). Further, the thermal stability of all complexes is high, in the range of about 500 K (for 3) to 600 K (for 1). These complexes were synthesized and characterized by X-ray powder diffraction pattern, TG/DTA, FT-IR, surface area analysis, and hydrogen adsorption measurements.

Influence of hydrogen absorption–desorption on structural properties ofDy1−xMmxCo2 alloys

The effect of hydrogen absorption–desorption on the structural properties of Laves phaseDy1−xMmxCo2 (x = 0.1, 0.3and 0.5; Mm = mischmetal, a natural mixture of the light rare earth metals containing 50 wt% Ce, 35 wt%La, 8 wt% Pr, 5 wt% Nd and 1.5 wt% of other rare earth elements and 0.5 wt%Fe) alloys has been investigated by means of hydrogen absorption–desorptionpressure-composition (PC) isotherms, kinetics of hydrogen absorption and powderx-ray diffraction (XRD). The PC isotherms and kinetics of hydrogen absorptionhave been studied in the pressure range 0.001–1 bar and temperature range50–200 °C using Sieverts-type apparatus. The experimental results of the kineticcurves are interpreted using the Johnson–Mehl–Avrami (JMA) modeland the reaction order and reaction rate have been determined. Theα-,(α+β)- and β-phase regions have been identified from the different slope regions of thePC isotherms and first-order type kinetic plots. The dependence of thereaction rate parameter upon hydriding pressure and temperature in the(α+β)-phase region has been discussed. The effect of hydrogenation pressure, temperatureand Mm concentration on the hydrogen-induced transformation from crystallineDy1−xMmxCo2–H toamorphous Dy1−xMmxCo2–H and decomposition into crystalline (Dy,Mm)H2 and Co have been discussed in detail. Further, the effect ofdehydrogenation on the recovery of the crystalline Laves phase structure ofDy1−xMmxCo2 fromits decomposed state is presented. This hydrogenation–disproportionation–desorption–recombination(HDDR) process can be conveniently used in powder metallurgy.

Thermodynamic and kinetic properties of Ho 1−xTi xCo 2-hydrogen system

The hydrogen absorption behavior of Laves phase Ho 1− x Ti x Co 2 ( x=0.1–0.6) alloys has been investigated by pressure-concentration (PC) isotherms and cyclic-, temperature- and pressure-dependent absorption kinetics. The PC isotherms and kinetics of hydrogen absorption have been studied in the pressure range 0.01–1 bar and temperature range 50–200 °C using Sievert's-type apparatus. The drastic changes in the induction period and particle size during the activation process have been discussed based on the kinetics of repeated hydrogenation cycles and scanning electron microscopy (SEM) images of the hydrides at different hydriding cycles, respectively. The experimental results of kinetic curves are interpreted using the Johnson–Mehl–Avrami (JMA) model, and the reaction order and reaction rate have been determined. The α-, ( α+ β)- and β-phase regions in Ho 1− x Ti x Co 2-H have been identified from the different slope regions of the first-order-type kinetic plots. The dependence of the reaction rate parameter on hydriding pressure and temperature in the ( α+ β)-phase region has been discussed.

Hydrogen Storage Properties of Mg-Al Alloy Prepared by Super Lamination Technique

Microstructures and hydrogen storage properties of Mg-Al super laminate composite alloys were investigated. The laminated sample was made by alternately stacking Mg films and Al films. The laminate was subjected to repetition of stacking and cold-rolling under an ambient condition (super lamination technique), combined with final heat treatment under an argon gas atmosphere. The number of films and thickness was nearly 15000 layers and about 50μm, respectivery. Their microstructures and hydrogen storage properties were studied by scanning electron microscopy, X-ray diffractometry and volumetric method by use of a Sieverts-type apparatus. In heat treatment process at 673K, Mg17Al12 intermetallic compound was formed by interdiffusion. This compound absorbed and desorbed hydrogen reversibly through the disproportionation and recombination react at 673K.

The Effects of Oxidized and Oxide-Free Boron on the Mg-B-H Nanohydrides Transformation in the Nearly Nanosized Powders

In this work oxidized and oxide-free amorphous boron (a-B) powder and elemental Mg were used in an attempt to directly synthesize the Mg(BH4)2 complex hydride by controlled reactive mechanical alloying (CRMA) under hydrogen in a magneto-mill up to 200h. The particle size was refined to the 100-200nm range. Nanocrystalline MgH2 (~6nm crystallite size) was formed within the particles when an oxidized a-B is used. In contrast, a mixture of MgB2 and an amorphous hydride MgHx was formed when an oxide-free a-B was used. Differential scanning calorimetry (DSC) test up to 500°C produced a single endothermic heat event at 357.7°C due to hydrogen desorption. In addition, desorption conducted in a Sieverts-type apparatus revealed ~1.4wt.% of hydrogen release. The X-ray diffraction pattern after DSC test of the 200h milled sample made with oxide-free boron showed the presence of MgB2.

Studies on synthesis and dehydrogenation behavior of magnesium alanate and magnesium–sodium alanate mixture

Magnesium alanate ( Mg ( AlH 4 ) 2 ) has been synthesized by mechanochemically activated metathesis reaction involving MgCl 2 and NaAlH 4 . Its dehydrogenation kinetics and storage capacity has been studied by using Sievert's type apparatus. We have obtained dehydrogenation capacity of 2.7 wt% H 2 from Mg ( AlH 4 ) 2 + 2 NaCl during the first decomposition step at 140 ∘ C and 1.1 wt% H 2 during second step decomposition at 280 ∘ C . Efforts were carried out to reduce NaCl content from the product using Soxhlet extraction technique. The Soxhlet extracted product gives the total dehydrogenation capacity of 4.7 wt% H 2 . To enhance the storage capacity, we have synthesized a complex hydride consisting of mixture: x Mg ( AlH 4 ) 2 + y NaAlH 4 ( 0 < x < 1 , y ⩾ 1 ) . In the alanate mixture 0.5 Mg ( AlH 4 ) 2 + NaAlH 4 , the dehydriding temperature of NaAlH 4 gets lowered by ∼ 50 ∘ C (from 190 ∘ C to 140 ∘ C ) with 4 times faster desorption kinetics. The total hydrogen liberated in 180 min from NaAlH 4 + 0.5 Mg ( AlH 4 ) 2 ( + NaCl ) mixture at 140 ∘ C has been observed to be 3.7 wt% H 2 .

Synthesis, characterization and hydrogenation of [formula omitted][formula omitted] alloys

Hydrogen storage properties and structural properties in ZrFe 2 - x Ni x ( x = 0.2 , 0.4 , 0.6 , 0.8 ) alloys, prepared by arc melting in argon atmosphere, have been investigated. Powder XRD study shows that the lattice constants and the unit cell volume of ZrFe 2 - x Ni x ( x = 0.2 , 0.4 , 0.6 , 0.8 ) alloys having C15 Laves phase cubic structure decreases with increasing Ni content due to the smaller atomic radius of Ni compared to Fe. Surface morphology and elemental composition of the alloys were investigated by SEM and EDX. Hydrogen absorption pressure–composition ( P – C ) isotherms were investigated in the ranges 303 K ⩽ T ⩽ 373 K and 0.5 bar ⩽ P ⩽ 50 bar using a Sievert type apparatus. The P – C isotherms show the single plateau region in the temperature and pressure range studied. The plateau pressure increases with increasing Ni content for a given temperature. The entropy and enthalpy of dissolved hydrogen in ZrFe 2 - x Ni x – H ( x = 0.2 , 0.4 , 0.6 , 0.8 ) have been calculated by means of the vant Hoff plot and the variation of these parameters with hydrogen content is discussed with respect to the existence of α , α + β , and β phase regions in the P – C isotherms.

Hydrogen diffusion studies in Zr-based Laves phase AB 2 alloys

The diffusion of hydrogen in the tetrahedral interstitials of bulk spherical Laves phase ZrMn 0.85Cr 0.1V 0.05Fe 0.5Ni 0.5 and ZrMn 0.85Cr 0.1V 0.05Fe 0.5Ni 0.5 + 1 wt% B alloys has been studied in the α-phase (solid-solution) region over the temperature range 450–650 °C, for hydrogen pressures up to 100 mbar using Sieverts-type apparatus. The diffusion constants have been determined from the gas–solid reaction, where the gas pressure dependence on time has been measured at fixed temperature. The results have been discussed on the basis of Fick's law of diffusion. The dependence of diffusion constant on alloy composition and initial pressure has been evaluated. Activation energy has been obtained from the temperature dependence of diffusion using Arrhenius relation.

Hydriding and electrical resistivity properties of MmTM 3-hydrogen ( [formula omitted], Co and Ni) system

Hydrogen absorption pressure-composition (PC) isotherms and kinetics of rhombohedral MmTM 3 ( TM = Ni , Fe and Co) alloys have been carried out using Sieverts type apparatus. The variations in plateau pressure, hydride stability and kinetics upon partial substitution of Fe or Co for Ni in MmNi 3 have been discussed. The absorption kinetics have been analyzed based on the Johnson–Mehl–Avrami (JMA) model. The reaction order and rate constants have been determined from the fit of the JMA model to the experimental data. The existence of different hydride phases and the hydriding reaction process in the different phase regions have been identified and explained. Further, the temperature dependent electrical resistivity of alloys and their hydrides have been studied and the variations in the resistivity with hydrogen concentration have been discussed.

Hydrogen sorption properties of MgH 2–LiBH 4 composites

A detailed analysis of the reaction mechanism of the reactive hydride composite (RHC) MgH 2 + 2LiBH 4 ↔ MgB 2 + 2LiH + 4H 2 was performed using high-pressure differential scanning calorimetry (HP-DSC) measurements and in situ synchrotron powder X-ray diffraction (XRD) measurements along with kinetic investigations using a Sievert-type apparatus. For the desorption the following two-step reaction has been observed: MgH 2 + 2LiBH 4 ↔ Mg + 2LiBH 4 + H 2 ↔ MgB 2 + 2LiH + 4H 2. However, this reaction is kinetically restricted and proceeds only at elevated temperatures. In contrast to the desorption reaction, LiBH 4 and MgH 2 are found to form simultaneously under fairly moderate conditions of 50 bar hydrogen pressure in the temperature range of 250–300°C. As found in pure light metal hydrides, significant improvement of sorption kinetics is possible if suitable additives are used.

Hydrogen-induced and A-site substitution-dependent structural properties of AB 2-type (Ho 1− xA x)Co 2–hydrogen system (A = Mm and Ti)

The structural changes of the Laves phases pseudo-binary (Ho 1− x A x )Co 2 alloys (A = Mm and Ti) upon hydrogen absorption have been investigated by means of powder X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The hydrogenation of alloys at different hydrogenation pressure and temperature has been performed using Sieverts-type apparatus. The effect of dehydrogenation and formation of hydride phases on the structural properties have been studied and results are interpreted with respect to their unhydrogentaed alloys. The pressure and temperature-dependent hydrogen-induced transformation from crystalline to amorphous and decomposition into constituents have been studied and discussed. The preferential occupancy of tetrahedral interstitial sites for hydrogen and relative stability of crystalline, amorphous and elemental hydrides have been reported. Further, the effect of Mm and Ti substitution upon amorphization conditions has been discussed.

Development of a high-pressure microbalance for hydrogen storage materials

Pressure–composition isotherms (PCI's) help to determine thermodynamic properties related to hydrogen uptake of materials. PCI's are normally obtained volumetrically with a Sieverts type apparatus or gravimetrically with a microbalance. A potential problem with the gravimetric technique is that the sample is momentarily exposed to air when transferring it to the system often causing unwanted changes such as oxidation and reaction with moisture in the air. In this study, a high-pressure microbalance was built from scratch inside a glove box with inert atmosphere. The system consists of an electromagnetic microbalance, pressure resistant casing for up to 100 bar hydrogen, a flow system for hydrogen and inert gas, heating elements for temperature control, and software for controlling the system. Thermal convection effects are observed and dampened by heating on both the sample and a counterweight. The precision of the mass measurements for a 1 g sample was ±5 μg, and this range proved to be the same independent of pressure and temperature.

Diffusion of hydrogen in cubic Laves phase [formula omitted] ( [formula omitted], 0.2 and 0.4) alloys

The diffusion of hydrogen in cubic (C15-type) Laves phase Ho 1 - x Mm x Co 2 ( x = 0 , 0.2 and 0.4, Mm = mischmetal ) alloys was measured in the α -phase (solid solution) region over the temperature range of 500 – 800 ∘ C using Sieverts-type apparatus. The alloys and its hydrides have been characterized by powder X-ray diffraction (XRD) Rietveld method. The diffusion constants have been determined from the gas–solid reaction, where the gas pressure dependence on time has been measured at fixed temperature. The results have been discussed on the basis of Fick's law of diffusion. The dependence of diffusion constant on alloy composition and initial pressure has been evaluated. Activation energy is obtained from the temperature dependence of diffusion using Arrhenius relation.

Microstructural development in nanocrystalline [formula omitted] during H-absorption/desorption cycling

Repeated dehydriding/hydriding cycles of ball-milled nanocrystalline MgH 2 powders were carried out in a Sievert's-type apparatus. The microstructural changes during cycling were characterized by X-ray diffraction. Using the convolutional multiple whole profile fitting procedure, several microstructural parameters, i.e. the average grain size and the grain-size distribution of the as-milled and treated samples were determined. Based on the shrinking core model, the significant difference between the microstructures obtained after the first and repeated cyclings was explained.

Thermodynamic and hydrogen-induced structural properties of Ho1−xMmxCo2-hydrides

Thermodynamic and hydrogen-induced structural properties of hydrogenated Ho1−xMmxCo2 (x = 0, 0.1, 0.2, 0.3 and 0.4, Mm = mischmetal) alloys have been investigated. The hydrogen absorption pressure-composition isotherms were studied in the temperature range 50–200 °C and pressure range 0.001–1 bar using a Sieverts-type apparatus. The effect of Mm on the equilibrium plateau pressure and hydride stability has been discussed. Structural analyses and hydrogen-induced amorphization of Ho1−xMmxCo2hydrides were performed using powder x-ray diffraction. The structural stability of these alloys upon repeated hydrogenation and dehydrogenation cycles has been investigated. At lower hydriding pressure and temperatures, Ho1−xMmxCo2-hydrides retain their Laves C15 structure; however, the large lattice volume expansion about 24% is observed in the β-phase. The effect of hydrogenation pressure and temperature and Mm concentration on the hydrogen-induced transformation from crystalline Ho1−xMmxCo2-H to amorphous Ho1−xMmxCo2-H and recrystallization into elemental hydrides have been studied and discussed.

Hydrogen interactions with the PdCu ordered B2 alloy

Combined experimental and modeling studies on hydrogen interactions with PdCu ordered body-centered cubic (B2) alloys have set the stage for membrane alloy development for advanced water gas shift membrane reactors that separate pure hydrogen from coal gasifier exhaust or syngas. First principles potential energy surface and ground state minimization calculations were used to profile the surface site selectivity of H 2 and H 2S adsorption on the lowest energy PdCu B2 (1 1 0) surface. Finite temperature surface energy calculations for varying H 2 and H 2S coverages were used to estimate the potential for blocking of H 2 adsorption by H 2S physisorption under coal gasification partial pressure and temperature conditions. Experimental measurements of hydrogen solubility in the Pd 0.44Cu 0.56 B2 alloy were made with a Sievert's type apparatus. This data was assessed, along with existing experimental data and first principles predicted finite temperature data for hypothetical end-member phases, to develop a thermodynamic description of the ternary Pd–Cu–H system encompassing the PdCu B2 phase. First principles ground state and lattice dynamics simulations were used to predict favorable pathways for thermally activated hydrogen diffusion within the B2 lattice. The newly derived solubility and diffusivity parameters were evaluated within a mass transfer model to predict the ideal bulk permeability in the absence of other mass transfer contributions.

Hydriding characteristics of [formula omitted] prepared by mechanical milling of the product of hydriding combustion synthesis

Hydriding combustion synthesis (HCS) and mechanical milling (MM) are both well-known methods for production of magnesium-based hydrogen storage alloys. The former can produce high active hydride by a simple process, and the latter can synthesis various metastable hydrogen storage materials such as nanocrystalline, amorphous and extended solid solutions phases with excellent hydrogen sorption properties. In the present study, HCS and MM were combined, aiming to decrease sorption temperature for Mg 2 Ni . The high active Mg 2 NiH 4 , synthesized by HCS, was mechanically milled for 0.5, 6, 40 and 80 h with 5 wt% of graphite under argon atmosphere. The effect of the milling process on the morphology and crystal structural of Mg 2 NiH 4 were investigated by means of scanning electron microscopy (SEM) and X-ray diffraction (XRD). The hydrogen storage properties were examined by a Sieverts type apparatus. The nanocrystalline Mg 2 NiH 4 milled for 40 h has the best sorption kinetics, which can absorb 2.4 wt% hydrogen at 303 K within 100 s in the first cycle. Several reasons are considered to explain the improvement in hydriding kinetics.

Hydrogen absorption and desorption properties of [formula omitted] alloys

The hydrogen absorption–desorption pressure-composition (PC) isotherms and kinetics of Ho 1 - x Mm x Co 2 ( x = 0 , 0.1 , 0.2 , 0.3 and 0.4, Mm = mischmetal ) have been carried out in the temperature and pressure ranges 50– 200 ∘ C and 0.001–1 bar using Sieverts-type apparatus. The effect of Mm on the equilibrium plateau pressure and hydrides stability has been discussed. The kinetics of hydrogen absorption at near equilibrium plateau region have been analyzed by a rate function. The reaction rate constants in the two-phase coexistence region and diffusion coefficient in the hydride phase region were calculated and its pressure and temperature dependence have been discussed. The hydrogen desorption from interstitial sites of Ho 1 - x Mm x Co 2 H has been performed using differential scanning calorimetry (DSC) and thermogravimetry (TG) analysis. The results are explored to identify the preferential occupation of different interstitial sites of hydrogen atoms and complete desorption temperature. The observed phase transformations as a function of hydrogen concentration and temperature have been discussed.

H-sorption behaviour of mechanically activated Mg–Zn powders

We report here on powder mixtures, with nominal compositions Mg 7Zn and Mg 7Zn 3, which were ball milled (i) at room temperature in an inert Ar atmosphere, (ii) at liquid nitrogen temperature (cryomilling), and (iii) at room temperature in a reactive H 2 atmosphere (reactive milling). In all cases, ball milling results in the formation of an amorphous Mg–Zn phase with a likely composition of about Mg 45Zn 55. A fraction of Mg is left unreacted and transforms to MgH 2 if ball milling is carried out in a reactive H 2 atmosphere. Hydrogen-absorption (H-absorption) in a Sievert-type apparatus for the powders ball milled in Ar results in the partial conversion of the Mg into MgH 2. The amorphous Mg–Zn phase appears not to play any significant role in the hydrogen-sorption (H-sorption) behaviour and crystallizes into Mg 21Zn 25. The latter partially decomposes into MgH 2 and MgZn 2, provided the hydrogenation reaction is extended for sufficiently long times.

Improvement in hydrogen cycling properties of magnesium through added graphite

Magnesium was milled under hydrogen with three types of carbon allotropes: carbon black, graphite, and multi-walled carbon nanotubes, respectively, using a special low-energy shearing mill. Structural and phase evolution were investigated using X-ray diffractometry (XRD) and morphology was investigated by scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS). Raman spectroscopy was used to investigate the changes in the nature of carbon–carbon bonding and differential scanning calorimetry (DSC) to investigate desorption characteristics. A Sieverts-type apparatus was applied to characterize the hydrogen absorption and desorption properties. It was found that graphite not only improved the hydrogen absorption, but also the desorption kinetics.