LaNi5 Powder Research Articles

Effective thermal conductivity of LaNi5 powder beds for hydrogen storage: Measurement and theoretical analysis

Accurately measuring and analyzing the effective thermal conductivity of metal hydride beds is critical to design the structure of solid-state hydrogen storage tanks. On the basis of the steady-state radial heat flow method, a measurement cell of effective thermal conductivity was manufactured. The effective thermal conductivities of nonactivated and activated LaNi5 powder beds were measured in helium, nitrogen, and argon atmospheres with the temperature changing from 20 to 60 °C and pressure from 0.1 to 4.0 MPa. Then, the effective thermal conductivities were further analyzed using the Zehner–Schlünder–Damköhler model. Results show that the effective thermal conductivities can be enhanced by increasing gas thermal conductivity, gas pressure, and bed temperature. In addition, the effective thermal conductivities can be accurately predicted using the modified Zehner–Schlünder–Damköhler model considering the Smoluchowski effect (error < ± 5 %). With the use of the modified Zehner–Schlünder–Damköhler model, the contributions of different heat transfer pathways to the entire heat transfer of LaNi5 powder beds were analyzed. Approximately 70 %–91 % of the effective thermal conductivity of LaNi5 powder beds is contributed by the conduction of the particle–gas–particle pathway.

Measurement and theoretical analysis of effective thermal conductivity of lanthanum pentanickel powder beds for hydrogen storage in different particle sizes and bed porosities

Particle diameter and bed porosity change due to the expansion and contraction of metal hydride particles during hydrogen absorption and desorption, which leads to variations in the effective thermal conductivity of metal hydride beds. Therefore, the effective thermal conductivity of the metal hydride beds under different bed porosities and particle diameters must be measured for the design of metal hydride-based hydrogen storage tanks. In this study, the effective thermal conductivities of four kinds of lanthanum pentanickel (LaNi5) powder beds with different bed porosities and particle diameters were measured in various gas atmospheres with gas pressure varying from 0.1 to 4.0 MPa. The volume mean diameters of the four kinds of LaNi5 powders equal 335.2, 196.4, 147.7, and 23.7 μm, respectively. Subsequently, the effects of bed porosity and particle diameter on the effective thermal conductivities were analyzed through the modified Zehner–Schlünder–Damköhler model considering the Smoluchowski effect. Experimental results show that particle diameter and bed porosity influence markedly the effective thermal conductivity of lanthanum pentanickel (LaNi5) powder beds. However, the findings of theoretical analysis based on the modified Zehner–Schlünder–Damköhler model reveal the considerably weaker effect of particle diameter on the effective thermal conductivity under identical bed porosity compared with the measurement results. Such a finding was observed because the variation in particle diameter inevitably changed bed porosity during the effective thermal conductivity measurement, which also affected the effective thermal conductivity of the beds. In addition, decreasing bed porosity and increasing particle diameter can remarkably improve the heat transport via the gas–solid mixture pathway, which improved the effective thermal conductivity of the beds and thus explained the experimental results.

Effect of expanded natural graphite addition and copper coating on reaction kinetics and hydrogen storage characteristics of metal hydride reactors

Experimental and numerical studies are carried out to determine the effects of copper coating and/or ENG (expanded natural graphite) addition on the hydrogen storage performance of ground LaNi5. The amounts of copper coating and/or ENG addition are also investigated. The results reveal that the thermal conductivity of ground LaNi5 can be improved by up to ∼6 and ∼12 times with copper coating and ENG addition, respectively. This results in enhanced hydrogen absorption kinetics thereby significantly reduced hydrogen charging times, compared to those determined for LaNi5 without any addition. On the other hand, the amount of hydrogen stored shows a decreasing trend with increasing copper coating and ENG addition since the weight of storage material loaded to the reactor is kept the same. Nevertheless, the optimum copper and ENG contents are determined regarding the amount of stored hydrogen and the corresponding charging time. Similar H/M values are obtained with the optimized powders with additives compared to that of ground LaNi5. Based on these results, various new samples are also prepared by mixing the decided copper coated LaNi5 and ENG added LaNi5 powders and examined to optimize the composition of these blended powders.

2D-axisymmetrical modeling and experimental study of hydrogen absorption in copper coated metal hydride

The storage of hydrogen in metal hydride reactors is examined experimentally and numerically in this paper. In this respect, as-received LaNi5 powders are coated with different amounts of copper by using copper sulphate solution to accelerate the hydrogen charging processes. The thermal conductivity of the copper-coated storage material is found to reach up to 8 times of the uncoated powders. A two-dimensional axisymmetric model regarding complex heat and mass transfer occurring during hydrogen charging process in metal hydride reactors is numerically solved at macro level. The developed model is validated by using experimental data related to the amount of hydrogen stored and the reactor temperatures. In accordance with the experimental results, the simulation results show that more homogenous temperature distribution in the reactor can be obtained with the copper coating due to improved thermal properties. Moreover, charging time is also improved by the copper coating. However, since the reactor is loaded with coated/uncoated LaNi5 powders at the same weight of 65 g, the total amount of hydrogen stored decreases with the copper coating due to reduced amount of LaNi5.

Effect of Dissolution Temperature on Purity of LaNi5 Powder Synthesized with the Combustion-Reduction Method

The LaNi5 intermetallic phase has been extensively investigated because of its excellent properties, such as attractive hydrogen storage, medium plateau pressure, and easy activation. LaNi5 phase is generally produced by a complicated method, which involves several steps, i.e. melting, alloying, casting, softening and making them into powder. This study aimed to develop a new LaNi5 synthesis process by modifying the combustion-reduction method. In this method it is very important to produce La2NiO4, because LaNi5 is formed from the process of reducing this phase. The precursor powders La(NO3)3.6H2O and Ni(NO3)2.6H2O were reacted with distilled water as a solvent medium and mixed using magnetic stirring. The synthesis process was carried out at room temperature, 60 °C, 70 °C, and 80 °C for 10 minutes until the solution became transparent green. The solution was then dried for 2 hours at 100 °C to form a transparent green gel. The gel was calcined at a temperature of 500 °C for 2 hours, producing a black powder. The optimal black powder was then reduced using CO gas at 600 °C for 2 hours. The powder samples were characterized using XRD, FTIR, and SEM-EDX. The analysis revealed that synthesis at room temperature was the most optimal method for the reduction process because it produced the most La2NiO4, at 12.135 wt%.

Experimental investigation on annular metal hydride reactor for medium to large-scale hydrogen storage applications

In the present study, an annular metal hydride reactor equipped with internal radial fins was designed, fabricated and experimented for absorption and desorption characteristics under different operating conditions. The reactor was filled with 9 kg LaNi5 powder. The alloy absorbed 105.57 g of hydrogen in 1184 s under a supply pressure of 10 bar while the inlet temperature and flow rate of the heat transfer fluid were maintained at 25°C and 2.5 lpm, respectively. At the same time, for a fixed absorption mass of 111 g of hydrogen, the alloy desorbed 110 g of hydrogen in 1590 s at an inlet temperature of 60°C. The developed metal hydride reactor offered a system gravimetric and volumetric storage densities of 0.73% and 20.4 kg of H2 per m3, respectively. Further, the performance of the new reactor was compared to published results for an embedded cooling tube reactor with an outer cooling jacket. The comparison results suggested that the internal heat transfer enhancement of the metal hydride bed resulted in a significant improvement in the absorption (about 56%) and desorption (about 44%) performance than the reactor with multiple cooling tubes. The results also revealed better absorption and desorption rates with the water flow rate of 2.5 lpm (annular metal hydride reactor) instead of a very high flow rate of 20 lpm (embedded cooling tube reactor with an outer cooling jacket), saving a significant amount of pumping power. Finally, a modular design based on the annular metal hydride reactor is proposed for medium to large-scale hydrogen storage applications.

Measurement and analysis of effective thermal conductivity of LaNi5 and its hydride under different gas atmospheres

In this work, an ETC measurement cell based on the steady-state radial heat flow method was fabricated, and its reliability was validated by a commercial instrument. The ETCs of unactuated and activated LaNi5 powder beds were measured under various filling gases in the pressure range from 0.1 to 1.5 MPa. The experimental results show that the ETC of activated LaNi5 powder is much lower than that of the unactuated material due to the pulverization effect. The ETCs of unactuated and activated LaNi5 powder in helium atmosphere lie in the ranges of 1.04–1.63 W m−1 K−1 and 0.49–0.85 W m−1 K−1, respectively. Furthermore, the ETC increases with the increasing pressure and thermal conductivity of filling gas. The effects of hydrogen absorption and desorption on the ETC were investigated by step-by-step reaction, which depend mainly on the hydrogen concentration and expansion/constriction of MH particles.

Measurement of effective thermal conductivity of LaNi[formula omitted] powder packed bed

Effective thermal conductivity of LaNi5 powder packed bed was analyzed with a miniaturized guarded hot-plate (GHP) apparatus. Here, GHP was designed for precise measurement of effective thermal conductivity of metal-hydride powders even with small sample amounts (2.12×104 mm3). Dimensions of sample container and apparatus were determined through two-dimensional (2-D) steady-state heat conduction analysis. Calibration experiment and uncertainty analysis were conducted to validate the accuracy of the GHP. Based on the measurements of the residual thermal conductivity of the LaNi5 packed bed, effect of particle size on contact factor of LaNi5 packed bed was estimated. By applying the Yagi and Kunii (YK) model to the effective thermal conductivity of LaNi5 packed bed, effect of contact factor and gas thermal conductivity on characteristic length of gas film were newly analyzed. Factors of YK model were modified in present work and validated through comparison with experimental data from previous literature.

Mechanochemical CO2 methanation over LaNi-based alloys

We report that CH4 production occurs, when LaNi-based alloy powders are mechanically ball-milled in a mixture CO2 and H2 gases for several hours. In Gas Chromatography (GC) analysis after the milling, the CO2 peak disappeared and the CH4 peak emerged. Activated LaNi5 powder demonstrated even higher catalytic activity than pristine LaNi5 or Ni powder. Energy Dispersive X-Ray (EDX) analysis of these powders revealed Fe and Cr present in the powder, suggesting an alloying of the sample powders with elements from the ball-milling media occurred during the milling. Atom probe tomography (APT) analysis unveiled that the resulting microstructure mainly consists of disproportionated metallic La/Ni, and nanometer scale oxides of La, Fe, Cr and Ni. Moreover, LaFe-carboxides and a trace of hydrocarboxylic compounds were detected. Ball-milling of a similar compound, LaNi4.6Al0.4, under CO2 atmosphere resulted in complete disappearance of CO2 in the milling vial. Subsequent milling of this powder in H2 atmosphere generated CH4. The results obtained in this study suggest that finely dispersed carboxides of Fe and La could be intermediates to lead to mechanochemically activated CO2 methanation.

Suitability Evaluation of LaNi5 as Hydrogen-Storage-Alloy Actuator by In-Situ Displacement Measurement during Hydrogen Pressure Change.

The swelling ability of LaNi5 for application to hydrogen-storage-alloy (HSA) actuator is discussed through the measurement of the swelling ratio in hydrogen. The HSA actuator is driven by hydrogen pressure change causing the swelling of HSA. LaNi5 is one of the candidate materials for HSA actuators as well as palladium. Some prototypes of HSA actuators using LaNi5 have been fabricated; however, the kinetic swelling ability of LaNi5 itself has been not investigated. In this paper, the authors investigated the static and kinetic swelling ability of LaNi5 powder under hydrogen atmosphere. The results showed that the swelling ratio increased by 0.12 at the phase transition pressure. Response time decreased with an increase in the charged pressure during absorption, while it remained constant during discharge. Reaction kinetics revealed that these swelling behaviors were explained by hydrogen absorption and lattice expansion. The swelling ability of LaNi5 was also compared with that of palladium. The results show that LaNi5 swells 1.8 times more than palladium under 0.5 MPa. LaNi5 is suitable for an actuator driven repeatedly under more than the phase transition pressure. Palladium can be used for one-way-operation actuator even under 0.1 MPa since its response time during the evacuation was much longer than during the pressurization.

Measurements of expansion of LaNi5 compacted powder during hydrogen absorption/desorption cycles and their influences on the reactor wall

The volume expansion, which occurs during the storage of hydrogen by metal hydrides, is a phenomenon linked to the lattice swelling or structural transition some samples. An experimental study realized out in order to characterize the progressive swelling and shrinking observed during the hydrogen absorption and desorption cycles by the compacted LaNi5 powder. The sample LaNi5 compacted has been submitted to 30 hydrogen absorption/desorption cycles, at the same cooling temperature equal 40 °C, under pressure 0.2 bar for the description state and 6 bars for absorption. As expected, the experimental results clearly indicate that the cyclic hydrogenation causes pellet volume changes, i.e. an almost reversible swelling/shrinking in the radial direction. However, this phenomenon can generate major mechanical stresses on the cell containing the pellet. The deformations react on the tank wall tantamount to the initial pressure of hydrogen. The values of the amplitude of the displacement increase progressively up to the 30th cycle, then, the phenomenon is stabilized up to 35 cycles, and this is explained that the relaxation of the metal limited the radial expansion.

Effect of glidants on LaNi5 powder flowability

Tension accumulation in container walls is a matter of concern in hydride based hydrogen storage systems. As the hydrogen absorbing material swells during hydrogen absorption it will need to flow and accommodate within its container. Failure to do so will result in the build-up of tensions and, eventually, in the failure of the container after a number of absorption-desorption cycles. There have been several ways of avoiding the build-up of mechanical stresses: having a container geometry that allows the swelling of the hydride, combining the hydride forming alloys with other materials that can handle the volume increase or the stresses, and adding solid lubricants to improve the ability of the hydride to accommodate within the container. In the present study we explore the application of nanoscaled powders normally used in the industry as glidant agents for bulk powders. In particular, we address the influence of three different types of glidants in the flowability of LaNi5 powder: Aerosil R 805, molybdenum disulfide (MoS2) and Vulcan XC72 carbon black. For this purpose, we have used a pressurized rotating drum device that allows hydrogen pressure or vacuum to test LaNi5 in hydrogen absorbed or desorbed states. The angle of repose results indicate an improvement on powder flowability when using Aerosil in concentrations of approximately 0.05 wt% or MoS2 at concentrations of approximately 0.1 wt%. These results are in agreement with models that explain the reduction of interparticle forces when using small quantities of nanoscaled particles. Vulcan XC72 showed no effectiveness as glidant. This unexpected behavior is most likely related to its tendency to become trapped in the cracks of the larger LaNi5 particles and to form relatively large aggregates.

Microstructure and Hydrogen Storage Properties of LaNi5-Multi Wall Carbon Nanotubes (MWCNTs) Composite

The composites LaNi5-X wt% MWCNT (X = 1, 10, 20 and 30) were co-milled in a SPEX8000 under Ar atmosphere. Scanning electron microscopy (SEM) images confirmed the presence of multi-walled carbon nanotubes (MWCNTs) on the surface of LaNi5 powder. Moreover, SEM illustrated the relationship between milling time, MWCNTs concentration and state of coverage. Lattice micro-strain and apparent domain size were obtained by plotting the Williamson–Hall curve. It was observed that prolonging the milling resulted in enhancement of lattice micro-strain and reduction of grain size. On the basis of hydrogen ads- and des-orption kinetic, MWCNTs can properly protect the whole active surface of LaNi5 and form an easy passage route facilitating H atoms transport. Among the samples, LaNi5-10 wt% MWCNTs showed optimal hydrogen storage properties. The hydrogen storage properties of 15-min milled samples were approximately comparable to activated pure LaNi5 where prolonging the milling deteriorated the structure of the alloy and drastically decreased the amount of absorbed H2.

Effect of powder granulation on hydrogen transport rate and hydrogen solubility in LaNi5-paraffin composite material

On the basis of potentiostatic discharge method, the diffusion rate of atomic hydrogen as well as its solubility in LaNi5 crystal lattice have been evaluated for three LaNi5 powder - paraffin composite electrodes, with different LaNi5 powder particle diameters: 0 - 20 μm, 20 - 50 μm and 50 - 100 μm. The chronoamperommetric tests have been carried out in strong alkaline (6 M KOH), deaerated solution, at 25°C. Apparent hydrogen diffusion coefficients have been determined using Crank’s spherical diffusion model. It has been shown, that increase of particle size is prone to increase of hydrogen apparent diffusion coefficient and to decrease of hydrogen concentration in the solid phase. To explain the granulation effect on hydrogenation ability parameters, the inhibition of hydrogen transport by surfacial corrosion products present on powder particles has been assumed.

Evaluation of electrochemical hydrogenation and corrosion behavior of LaNi5-based materials using galvanostatic charge/discharge measurements

A detailed thermodynamic analysis of galvanostatic −i/+i characteristics of epoxy resin bonded, LaNi5 powder based electrodes enables not only alloy hydrogenation ability but also oxidation susceptibility of their constituents to be determined. It is shown that electrode cycling is prone to oxidation of nickel during discharging process, however, the NiO/Ni equilibrium is reversible and nickel oxides undergo reduction during charging. Similar behavior exhibits bismuth as Ni partial substitute. The way of determining alloy constituent oxidation/reduction times as well their corrosion rate in 6 M KOH is presented. The effects of substitution of 20 at% of nickel by Bi or Zn on hydrogen capacity, corrosion behavior and surface development are discussed. It is shown that multiphase LaNi4Bi alloy possesses much worse whereas monophase LaNi4Zn alloy possesses clearly better hydrogen absorption properties as compared with LaNi5 reference. The plots of charge curves allow to distinguish processes of atomic hydrogen absorption and evolution of molecular H2 for the tested alloys.

Preparation of LaNi&lt;sub&gt;5&lt;/sub&gt; by FFC Cambridge Process

A new technique was proposed for preparation of LaNi5 powder by direct electrolytic deoxidation of solid La2O3–NiO mixture oxides in molten CaCl2–NaCl. Oxides pellets was sintered and used as cathode. High – density graphite was used as anode. Electrolysis was performed. Current change during electrolysis was recorded. XRD was used to analyse the composition of products. SEM was used to analysis surface and cross section of pellets before sintering, after sintering and after electrolysis. The preparation mechanism and the influences of sintering temperature and cell voltage on electrolytic deoxidation was studied. Results show that the optimum conditions to prepare LaNi5 are：NiO-La2O3（Ni:La=5:1）pellets are formed at 30MPa, sintered at 850°C for 5h, electrolyzed under 3.2V in CaCl2–NaCl melt at 850°C for more than 12 hours.

Giant Bending Strain of Reversible Motion of Uni-Morph Soft Mover Composites Driven by Hydrogen Storage Alloy Powders Dispersed in Polyurethane Sheet

In order to generate the bending motion operated by pressure change in hydrogen gas, soft uni-morph composites were prepared, in which composites dispersed with not only driving particles of LaNi5 hydrogen storage alloy with Pd-Al2O3 catalyst powders to get high responsiveness, were piled up on a simple polyurethane sheet. Since the highest values of irreversible bending strain at the first hydrogenation ( 1 ) under 0.3 MPa H2 gas and the maximum irreversible bending strain during hydrogenation cycles ( m ) were remarkably obtained at the 35 vol% of LaNi5 powders dispersed in polyurethane composites, the bending strain of reversible motion was detected from the first to the 8th hydrogenation (r 1 and r 8 ) under 0.2 MPa H2 gas. The bending strain of reversible motion of polyurethane composites sheet is more than 2000 ppm, which was approximately equal to that of silicone rubber composites and is extremely larger than that (300 ppm) of ABS resin composites. Responsiveness (d=dt) of cyclic motion of elastic deformed mover composites, which were constructed with 35 vol%LaNi5 dispersed powder and matrix of polyurethane or silicone rubber, were more than 10 times higher than that of ABS composite. [doi:10.2320/matertrans.M2009178]

Carbon nanomaterials synthesized using liquid petroleum gas: Analysis toward applications in hydrogen storage and production

A chemical vapor deposition (CVD) technique was developed to synthesize carbon nanomaterials using liquid petroleum gas (LPG) as the carbon source. Multi-walled carbon nanotubes (CNTs) were produced using commercial hydrogen storage materials (LaNi5 and TiFe) powders as the catalyst. Nickel micro-wire arrays were synthesized using a template technique, and were subsequently used to synthesize a CNT mat. Nanomaterials were thoroughly characterized by one or more of the following methods; scanning electron microscopy, transmission electron microscopy, X-ray diffraction, cyclic voltammetry, and thermogravimetric analysis. CNTs with magnesium and/or palladium nanoparticles deposited using sono-chemical methods had a hydrogen storage capacity above 3.0wt%. The nickel micro-wire and CNT composite was found to be more active for hydrogen production when compared to nickel foils, and bare nickel micro-wires.

Properties of Zr0.5Ti0.5V0.75Ni1.25 alloy ball-milled with nanocrystalline LaNi5 powder

A type of composite powder was prepared by ball-milling Zr0.5Ti0.5V0.75Ni1.25 alloy with a small amount of (2 wt%) nanocrystalline LaNi5 which was synthesized by mechanical alloying. SEM and EDX results show that the surface of Zr0.5Ti0.5V0.75Ni1.25 alloy was coated with fine nanocrystalline LaNi5 particles after ball-milling. Electrochemical measurement revealed that electrochemical activity of this composite powder was higher than that of as-cast Zr0.5Ti0.5V0.75Ni1.25 powder. The mechanism of this improvement was also discussed.

ＬａＮｉ５の微粉化における耐大気酸化特性向上の為の処理の影響

Air exposure of LaNi5, which yields the growth of surface oxide layer, results in the decreased H2 absorption rate and the accelerated pulverization of the sample at the subsequent hydriding cycles. Recently effect of alkaline pretreatment and/or of Pd catalysis addition onto the LaNi5 powder were reported. Accelated molecular dessociation on the oxide surface by these treatments improve the absorption kinetics drastically even after significant oxidation.In this report the effect of these treatments on the sample pulverization was investigated. The existence of surface alkaline hydroxide (LiOH) layer accelerated the pulverization, while no difference was observed at the addition of Pd catalysis.