Mg2Ni Phase Research Articles

Catalytic modification of MgH2 hydrogen storage properties by La–Ni catalysts

In this paper, it is experimentally demonstrated that the La–Ni catalyst contributes to the hydrogen storage performance of MgH2. Firstly, La–Ni (La: Ni = 1: 5.7) catalysts are prepared by CaH2 reduction method, and then MgH2+x wt.% La–Ni (x = 0, 3, 5, 7) composite alloys were prepared by ball milling method. The present work focuses on the structural and hydrogen ab/desorption properties of the composite alloys, and analysis the modulatory effect and influence mechanism of different La–Ni catalyst additions on the hydrogen storage properties of MgH2. The findings show that the composite alloys have the same diffraction peaks and that the main phase of the composite alloys is the MgH2 phase, with the addition of the LaNi5 phase, the Mg2Ni phase and a small amount of Mg phase. The mutual reversible transformations of LaH3 and Mg2Ni and Mg2NiH4 play a catalytic role in the hydrogen ab/desorption process. Moreover, the addition of La–Ni catalyst plays a dramatic improvement effect on the kinetic performance of MgH2 ab/desorption. When the addition of La–Ni catalyst is 5 wt.%, the composite alloy exhibits the most excellent hydrogen uptake and release kinetics. The MgH2+5 wt.% La–Ni composite alloy absorbs 4.2 wt.% H2 within 2 min at 473 K and releases 3.43 wt.% H2 within 150 min at 503 K. Fitting the hydrogen release activation energy of the composite alloys shows that the hydrogen release activation energy of the composite alloys decreases first and then increases, and there is a minimum hydrogen release activation energy of 101.81 kJ/mol H2 when the addition amount x = 5 wt.%.

Atomic reconstruction for realizing stable solar-driven reversible hydrogen storage of magnesium hydride

Reversible solid-state hydrogen storage of magnesium hydride, traditionally driven by external heating, is constrained by massive energy input and low systematic energy density. Herein, a single phase of Mg2Ni(Cu) alloy is designed via atomic reconstruction to achieve the ideal integration of photothermal and catalytic effects for stable solar-driven hydrogen storage of MgH2. With the intra/inter-band transitions of Mg2Ni(Cu) and its hydrogenated state, over 85% absorption in the entire spectrum is achieved, resulting in the temperature up to 261.8 °C under 2.6 W cm−2. Moreover, the hydrogen storage reaction of Mg2Ni(Cu) is thermodynamically and kinetically favored, and the imbalanced distribution of the light-induced hot electrons within CuNi and Mg2Ni(Cu) facilitates the weakening of Mg-H bonds of MgH2, enhancing the “hydrogen pump” effect of Mg2Ni(Cu)/Mg2Ni(Cu)H4. The reversible generation of Mg2Ni(Cu) upon repeated dehydrogenation process enables the continuous integration of photothermal and catalytic roles stably, ensuring the direct action of localized heat on the catalytic sites without any heat loss, thereby achieving a 6.1 wt.% H2 reversible capacity with 95% retention under 3.5 W cm−2.

The effect of Gd on the microstructure and electrochemical properties of Mg-Ni-based alloys

The Mg-Ni-based alloys have been extensively investigated as negative electrode materials in Nickel-Metal Hydride (Ni-MH) batteries. In this work, two Mg-Ni-based samples (Mg71Ni29 and Mg72.6Ni25.3Gd1.1) were prepared by means of melting. The X-ray diffraction (XRD), scanning electron microscope (SEM), galvanostatic charging/ discharging and other electrochemical measurements were used for the investigation. The results show that the Mg71Ni29 and Mg72.6Ni25.3Gd1.1 alloys include the characteristic peaks of Mg2Ni and the less strong characteristic peaks of Mg and MgNi2 phases. The diffraction peak of the major phase Mg2Ni of the Mg72.6Ni25.3Gd1.1 alloy is shifted to a small angle and its unit cell volume increases. With the addition of Gd, the alloy electrodes exhibits better cycling stability. After 50 charge/ discharge cycles, the capacity retention rate of the alloy electrode increase from 16% (Mg71Ni29) to 22% (Mg72.6Ni25.3Gd1.1). However, the maximum discharge capacity of the alloy electrode decrease from 134.3 mAh/g (Mg71Ni29) to 91.9 mAh/g (Mg72.6Ni25.3Gd1.1). The Mg72.6Ni25.3Gd1.1 alloy possess lower limiting current density IL and exhibit relatively high corrosion resistance against the alkaline solution. After Gd doping, the charge transfer capacity of the Mg72.6Ni25.3Gd1.1 alloy surface is increased.

Microstructure and hydrogen storage properties of the Mg2−xYxNi0.9Co0.1 (x = 0, 0.2, 0.3, and 0.4) alloys

Rare earth elements have excellent catalytic effects on improving hydrogen storage properties of the Mg2Ni-based alloys. This study used a small amount of Y to substitute Mg partially in Mg2Ni0.9Co0.1 and characterized and discussed the effects of Y on the solidification and de-/hydrogenation behaviors. The Mg2−xYxNi0.9Co0.1 (x = 0, 0.2, 0.3, and 0.4) hydrogen storage alloys were prepared using a metallurgy method. The phase composition of the alloys was studied using X-ray diffraction (XRD). Additionally, their microstructure and chemical composition were studied using scanning electron microscopy and energy-dispersive X-ray spectroscopy, respectively. The hydrogen absorption and desorption properties of the alloys were studied using pressure-composition isotherms and differential scanning calorimetric (DSC) measurements. The structure of the as-cast Mg2Ni0.9Co0.1 alloy was composed of the peritectic Mg2Ni, eutectic Mg–Mg2Ni, and a small amount of pre-precipitated Mg–Ni–Co ternary phases, and was converted into the Mg2NiH4, Mg2Ni0.9Co0.1H4, and MgH2 phases after hydrogen absorption. Furthermore, the XRD patterns of the alloys showed the MgYNi4 phase and a trace amount of the Y2O3 phase along with the Mg and Mg2Ni phases after the addition of Y. After hydrogen absorption, the phase of the alloys was composed of the Mg2NiH4, MgH2, MgYNi4, YH3, Y2O3, and Mg2NiH0.3 phases. With the increase of Y addition, the area ratios of the peritectic Mg2Ni matrix phase in the Mg2−xYxNi0.9Co0.1 (x = 0, 0.2, 0.3, and 0.4) alloys gradually decreased until they disappeared. However, the eutectic structure gradually increased, and the microstructures of the alloys were obviously refined. The addition of Y improves the activation performance of the alloys. The alloy only needed one cycle of de-/hydrogenation to complete the activation for x = 0.4. The DSC curves showed that the initial dehydrogenation temperatures of Mg2Ni0.9Co0.1 and Mg1.8Y0.2Ni0.9Co0.1 were 200 and 156 °C, respectively. The desorption activation energies of the hydrides of the Mg2Ni0.9Co0.1 and Mg1.8Y0.2Ni0.9Co0.1 alloys calculated using the Kissinger method were 94.7 and 56.5 kJ/mol, respectively. Moreover, the addition of Y reduced the initial desorption temperature of the alloys and improved their kinetic properties.

Effects of Y substituting Gd on the microstructure evolution, mechanical properties and dissolution behaviors in the Mg-Gd-Ni alloys used as fracturing plugging tools

In this work, the effects of substituting 3 wt% Gd with 3 wt% Y on the microstructure, mechanical properties, and corrosion behaviors in the Mg-Gd-Ni alloys were investigated. By substituting Gd with Y, the area fraction of bulk-shaped long-period stacking ordered phases (LPSO) increases, while one of eutectic Mg2Ni phase decreases slightly. Moreover, it also promotes the precipitations of lamellar LPSO phase and nanoscale stacking faults (SFs). The tensile tests showed that the addition of Y increased the yield strength by about 40 MPa, mainly due to the strengthening of the kink deformation of the bulk shaped LPSO phase, the hindering effect of the lamellar LPSO and SF on dislocation movement, and the strengthening caused by grain refinement. As a result, the Mg-5Gd-3Y–5Ni (MGYN) alloy exhibits excellent mechanical properties with tensile yield strength (TYS) of 288 MPa, ultimate tensile strength (UTS) of 364 MPa, and elongation (EL) of 8.3 %. Moreover, although the fraction of Mg2Ni phase with high electrochemical potential is decreased, the reduction in dissolution rate is not significant because the discontinuous distribution of lamellar LPSO in the grains intensifies the galvanic corrosion by increasing the proportion of cathode phase. As a result, the coexistence of Mg2Ni and LPSO phases can observably improve the dissolution rate. Finally, the highest dissolution rate (234.56 mg cm−2 h−1 in 3 wt% KCl solution at 93 °C) reported so far for the dissoluble magnesium alloys can be attained for MGYN alloy in this study. This work provides an economical material selection with high dissolution rate and sufficient strength for the fabrication of the fracturing plugging tools.

In-situ precipitation of ultrafine Mg2Ni particles in Mg-Ni-Ag metal fibers and their hydrogen storage properties

The intermetallic compound Mg2Ni shows improved hydrogen de-/absorption kinetics and a lower desorption temperature compared to pure Mg. However, the coarse Mg2Ni phase and its limited hydrogenation capacity restrict the application of the Mg2Ni alloy. In this study, an attempt was made to prepare Mg-Ni alloy fibers with a higher Mg content and a well-distributed Mg2Ni catalytic phase using the melt extraction (ME) method, and a unique metallic glass fiber was formed. With pre-annealing at 350 °C in a vacuum, uniformly dispersed Mg2Ni nanoparticles are in-situ formed, the phase transition is revealed to be metallic glass → Mg6Ni → Mg2Ni + Mg. About 1.5 wt% of hydrogen can be absorbed by the Mg-Ni fibers at 50 °C, and it is completely released in 8.8 min at 225 °C. Both the JMA and Kissinger models were utilized to accurately characterize the dehydrogenation activation energy, and the values of 90.4 and 95.8 kJ/mol were obtained, respectively. The hydrogen desorption process involves two distinct processes, the decomposition of Mg2NiH4 nanoparticles and MgH2 hydride in sequence, with dehydrogenation enthalpy changes of 64.5 and 78.2 kJ/mol, respectively. After hydrogen absorption and desorption cycles, a loose structure forms around the Mg2Ni nanoparticles. This structure serves as an efficient nucleation site for hydrides and provides diffusion paths for H atoms.

Design of LPSO Phases in Mg-Y-Ni Alloys to Impact Hydrogenation Kinetics

A series of Mg-Y-Ni alloys with different volume fractions of long-period stacking-ordered (LPSO) phase were prepared, by controlling the alloy composition, heat treatment, and single-pass extrusion, to assess the influence of increasing LPSO phase volume fraction on the hydrogen absorption and desorption properties of the extruded alloys. The LPSO phase volume fraction in the alloys increased with increasing solute concentration, from ~24% LPSO in Mg97Y2Ni1 (at.%) to ~60% LPSO in Mg93Y4Ni3 (at.%) up to ~92% LPSO in Mg91Y5Ni4 (at.%). The most refined microstructure was obtained in the alloy with highest volume fraction of LPSO phase. After 100 s at 300 °C, the Mg91Y5Ni4 alloy absorbed 4.6 ± 0.2 wt.% H while the Mg97Y2Ni1 and Mg93Y4Ni3 alloys each absorbed 3.8 ± 0.2 wt.% H. After 10,000 s at 300 °C, all three alloys had absorbed a maximum of 5.3 ± 0.2 wt.% H with no further significant difference in hydrogen absorption kinetics. The Mg91Y5Ni4 alloy desorbed 1.8 ± 0.2 wt.% H after 100 s at 300 °C against a vacuum while the Mg97Y2Ni1 and Mg93Y4Ni3 alloys desorbed 0.8 ± 0.2 wt. H and 0.6 ± 0.2 wt.% H, respectively. After 10,000 s at 300 °C, the Mg91Y5Ni4 and Mg97Y2Ni1 alloys completely desorbed 5.2 ± 0.2 wt.% H and 5.4 ± 0.2 wt.% H, respectively, but the Mg93Y4Ni3 alloy desorbed only 3.7 ± 0.2 wt.% H. Hydrogen absorption and desorption kinetics were fastest in the Mg91Y5Ni4 alloy with the highest LPSO volume fraction, but no consistent trend with LPSO phase volume fraction was observed with the Mg93Y4Ni3 alloy, which showed the slowest absorption and desorption kinetics. The hydrogen pressures corresponding to metal–hydride equilibrium did not vary with LPSO phase volume fraction or alloy composition, indicating that the (de)hydrogenation thermodynamics were not significantly changed in any of the alloys. Hydrogen absorption experiments with thin foils, made of extruded Mg91Y5Ni4 alloy with the highest LPSO phase fraction, demonstrated that the LPSO structures decompose into Mg phase, Mg2Ni phase, lamellar Mg/Mg-Y structures, and YHx particles. This study shows that hydrogen kinetics can be impacted in Mg-Y-Ni alloys by controlling the LPSO phases using common metallurgical techniques.

Revealing distinct corrosion mechanisms of soluble as-extruded Mg–Er–Ni alloy with LPSO and Mg2Ni phase in different orientations

The effects of Er and Ni content on the microstructure evolution, corrosion mechanism of Mg–Er–Ni alloys with different orientations were investigated. With the increase of Er and Ni content, the corrosion rate of extrusion direction (ED) increases, while transverse direction (TD) is reversed, which may be due to the distinct corrosion mechanism in different orientations, where ED and TD exhibit soluble and corrosion-resistant mechanism, respectively. Moreover, high content second phase alloy with a large deformation grain fraction and low levels second phase alloy with fully recrystallized grains have larger and smaller corrosion rate differences in ED and TD, respectively.

Hydrogen storage property improvement of ball-milled Mg2.3Y0.1Ni alloy with graphene

In this paper, Mg2.3Y0.1Ni + x wt.% graphene (x = 1, 3, 5, 7) composite hydrogen storage alloys were fabricated by mechanical ball milling of Mg2.3Y0.1Ni alloy powder and graphene. The experimental results show that the phases of the composite alloy consist mainly of Mg2Ni, Mg, MgNi2 and Ni3Y phases, and graphene tends to be distributed at the edges of the alloy, increasing the phase boundary resulting from the contact between the C-boundary and the Mg2.3Y0.1Ni alloy, providing more channels for the diffusion of H2. In which 7 wt.% of graphene is added, the gestation period of the composite alloy completely disappears. And the ball-milled alloy with 3 wt.% graphene at different temperatures has the highest hydrogen uptake in 2 min and the highest hydrogen release in 10 min. At 573 K, the composite alloy has a hydrogen absorption capacity of 3.251 wt.% H2 in 2 min and reaches 90.21% of the maximum hydrogen absorption, while it is able to release 3.389 wt.% H2 in 10 min and reaches 99.04% of the maximum hydrogen release. And the composite alloy with 3 wt.% graphene has the smallest dehydrogenation activation energy. The absolute value of the enthalpy change is reduced from 60.1 kJ/mol to 54.8 kJ/mol, and the desorption enthalpy change is reduced from 73.4 kJ/mol to 67.5 kJ/mol.

Effect of bimetallic nitride NiCoN on the hydrogen absorption and desorption properties of MgH2 and the catalytic effect of in situ formed Mg2Ni and Mg2Co phases

Magnesium hydroxide has attracted extensive attention in the past few years due to its excellent hydrogen storage capacity, good reversibility, and low cost, but its high thermodynamic stability and low rate of kinetic activity hinder its application. Therefore, in order to improve the hydrogen storage capacity of MgH2, we prepared ternary transition metal nitride NiCoN to catalyze MgH2 by hydrothermal and calcination techniques. Owing to the addition of 6 wt% NiCoN, the dehydrogenation process of MgH2 started at 164.4 °C (ball-milled MgH2 started dehydrogenation at 287.6 °C). At 285 °C, 4.95 wt% of hydrogen gas was desorption within 30 min, while 4.6 wt% of hydrogen gas was absorbed at 125 °C. And calculated by the Kissinger method, the activation energy required for the dehydrogenation reaction of MgH2-6NiCoN is reduced to 56.5 kJ/mol (ball-milled MgH2 is 127.3 kJ/mol). It is found that MgH2-6NiCoN forms Mg2Co/Mg2Ni in situ during the first dehydrogenation process, and then transforms into Mg2CoH5/Mg2NiH4 after rehydrogenation, implying a reversible phase transition between the Mg2Co/Mg2CoH5 and Mg2Ni/Mg2NiH4 phases. Due to the formation of intermediate products, it still maintains a good hydrogen desorption capacity after 40 cycles. The dehydrogenation retention rate is 94 %. The excellent behavior of MgH2 is attributed to the formation of Mg2Ni/Mg2NiH4 and Mg2Co/Mg2CoH5, which are responsible for the improved hydrogen absorption/desorption behavior of MgH2. These findings provide new insights into the hydrogen storage behavior of the catalytic MgH2 system.

Effect of interlayer and deposition temperature on the hydrogen storage properties of amorphous Mg-based thin films

In this work, the effect of different interlayers (including Mo, Nb, and Ti) and deposition temperatures (including 25 °C, 75 °C, 150 °C and 200 °C) on the hydrogen storage performance of MgNi amorphous alloy films are studied. On the one hand, the MgNi amorphous alloy films remain undestroyed after hydrogen absorption and desorption cycles with the help of Mo, Nb and Ti interlayers. However, the onset desorption temperature and peak desorption temperature of the MgNi amorphous alloy films are almost unchanged after inserting the interlayers. On the other hand, as the deposition temperature increases from 25 °C to 200 °C, there are nanocrystalline Mg2Ni and Mg phases formed in the amorphous MgNi alloy matrix. The crystalline-amorphous structure provides abundant nucleation sites for hydride formation, and accelerate the diffusion and dissociation of hydrogen.

Microstructure Characteristics and Hydrogen Storage Kinetics of Mg77+xNi20-xLa3 (x = 0, 5, 10, 15) Alloys.

Mg77+xNi20-xLa3 (x = 0, 5, 10, 15) alloys were successfully prepared by the vacuum induction melting method. The structural characterizations of the alloys were performed by using X-ray diffraction and scanning electron microscope. The effects of nickel content on the microstructure and hydrogen storage kinetic of the as-cast alloys were investigated. The results showed that the alloys are composed of a primary phase of Mg2Ni, lamella eutectic composites of Mg + Mg2Ni, and some amount of LaMg12 and La2Mg17. Nickel addition significantly improved the hydrogen-absorption kinetic performance of the alloy. At 683 K, Mg77Ni20La3 alloy and Mg82Ni15La3 alloy underwent hydrogen absorption and desorption reactions for 2 h, respectively, and their hydrogen absorption and desorption capacities were 4.16 wt.% and 4.1 wt.%, and 4.92 wt.% and 4.69 wt.%, respectively. Using the Kissinger equation, it was calculated that the activation energy values of Mg77Ni20La3, Mg82Ni15La3, Mg87Ni10La3 and Mg92Ni5La3 alloys were in the range of 68.5~75.2 kJ/mol, much lower than 150~160 kJ/mol of MgH2.

Novel magnesium matrix hybrid composites manufactured through powder metallurgy technique

In the present study, novel magnesium matrix hybrid composites have been developed through the addition of titanium and nickel micro particulates using the hot pressing technique which is one of the powder metallurgy methods. Titanium and nickel elements were first-time used in combination as reinforcing materials in the manufacture of hybrid composites. A clean interface was obtained free from porosity, oxide and unwanted secondary phases between the matrix and reinforcement in all produced samples. In addition to the matrix and reinforcement phases, the Mg2Ni phase was also observed in the microstructural characterizations. The existence of this phase was confirmed through XRD analyses, its peak intensity increased with the increasing amount of reinforcement. While the addition of Ti and Ni provided a mean of 33 % and 83 % improvement in the yield strength and compressive strength of pure magnesium at room temperature, respectively, they did not cause a serious decrease in ductility values compared to those of ceramic reinforcement materials. The yield and compressive strengths of hybrid composites were found to be greater than those of the reference sample at all test temperatures. The mechanical properties such as yield strength, compressive strength and ductility together with low densities have shown that produced hybrid materials constitute an important alternative to traditional materials such as iron, steel and even aluminum frequently used in the manufacture of automobile components.

Hydrogen storage thermodynamics and kinetics of the as-cast and milled Ce-Mg-Ni-based alloy

Aiming at investigating the improvement of hydrogen storage performance of the ternary Ce5Mg85Ni10 alloy after mechanical ball milling, the phase transformation and microstructure evolution of the milled alloys are observed by XRD, SEM and TEM. After ball milling, the alloys mainly exhibit nanocrystalline and amorphous structures and consist of Mg, Mg2Ni and CeMg12 phases. After hydrogen absorption, the milled alloys consist of MgH2, Mg2NiH4 and CeH2.73 phases. Isothermal and non-isothermal reaction curves of hydrogen absorption and desorption of the milled alloys are characterized by an Sievert apparatus, DSC and TGA. The Arrhenius and Kissinger equations are used to calculate the hydrogen desorption activation energy. For the Ce5Mg85Ni10 alloy, its structure and thermodynamics and kinetics performance of hydrogen storage strongly depend on the ball milling time. The results shows that ball milling for 5 h can achieve the optimal activation and kinetics performances but further prolonging the ball milling time lead to the impairment of hydrogen storage performance. Besides, ball milling time has little effect on thermodynamic property. Experiments results show that the 5 h-milled alloy after activation can absorb 4 wt% H2 in 18 s at 473 K and 3 MPa, and can desorb 3 wt% H2 in 906 s at 533 K and 1 × 10−4 MPa. In addition, the hydrogen desorption enthalpy change of the 5 h-milled alloy is 75.28 kJ/mol and the hydrogen desorption apparent activation energy of this alloy is 62.69 kJ/mol.

Investigation of ball-milling process on microstructure, thermodynamics and kinetics of Ce–Mg–Ni-based hydrogen storage alloy

Aiming at improving hydrogen storage performance of Mg-base alloy, the Mg90Ce3Ni7 alloy is prepared by medium-frequency induction melting and following mechanical ball-milling process. X-ray diffraction analysis reveals that the ball-milling Mg90Ce3Ni7 alloy is composed of Mg, Mg2Ni and CeMg12 phases, whereas subsequent milling induces grain refinement and the formation of amorphous phase. In addition, the extension of ball-milling time also not further improve the thermodynamic properties, whereas has a very significant effect on the kinetic properties, which is mainly attributed to the change of microstructure of the alloy by ball milling process. The ball-milling not only creates the nanocrystalline and amorphous structures, but also refines the particle size of the alloy. This is beneficial to the nucleation and diffusion of the alloy during reversible hydrogenation reaction. Concretely, the ball-milling time enhances the kinetics of hydrogen absorption at low temperature, especially for the alloy milled for 20 h, in which can absorb more than 3.5 wt % H2 over 30 min at 100 °C. Meanwhile, the ball-milling time enhances the kinetics of hydrogen desorption. It leads to effectively reducing the dehydrogenation activation energy to 72.2 kJ/mol H2, which allows the alloy can release more than 5 wt % H2 in 10 min at 280 °C. The work provides a scientific way to promote the practical application of Mg-based hydrogen storage alloy.

Effect of Y content on the hydrogen storage properties of ball-milled Mg2.4-xYxNi (x = 0.05, 0.1, 0.15, 0.2) alloys

Metal hydride hydrogen storage is currently the fastest growing and most promising method of hydrogen storage. In this paper, the Mg2.4-xYxNi (x = 0.05, 0.1, 0.15, 0.2) alloys were first melted by vacuum high-frequency induction melting furnace. Subsequently the alloy ingots were mechanically crushed and mechanically ball milled for the same time. And the microstructure and gaseous hydrogen storage properties of the ball-milled alloy were characterized thoroughly by varying the content of rare earth element Y. The results showed that the main phase of the alloy is the Mg2Ni phase, followed by the Ni3Y phase and a small amount of the Mg phase and MgNi2 phase. And the diffraction peaks of the Ni3Y phase are obviously enhanced with the increase of Y content, demonstrating that the exchange of Y for Mg promotes the formation of the Ni3Y phase, but the intermetallic compound Ni3Y phase was consistently present as a chemically inert material regardless of hydrogen absorption/desorption. Based on the hydrogen storage properties, the hydrogen storage alloys with different Y contents can be fully activated after one hydrogen absorption/desorption cycle, and the gestation period of the alloys with different Y contents showed a trend of decreasing and then increasing. For alloys with different Y contents, the Mg2.3Y0.1Ni alloy demands the shortest time for the initial activation of hydrogen absorption. And when the temperature is 573 K, the time taken to absorb 90% of the hydrogen capacity was 8 min, 6 min, 8 min and 12 min, and the time taken to release 90% of the hydrogen capacity was 4.6 min, 3.4 min, 5 min and 6 min for alloys with different Y contents, respectively. And the maximum values of hydrogen absorption/desorption saturation rate of Mg2.3Y0.1Ni alloy have reached 80.17% and 96.02%, respectively. The activation energy of hydrogen release of the alloys decreases from 123.9 kJ/mol to 113.1 kJ/mol. In contrast to the kinetic properties, there is no significant difference in the enthalpy and entropy changes for different Y contents, indicating that the addition of rare earth element Y has minimal effect on the thermodynamic properties of the alloy.

Theoretical and experimental study of the titanium substituted Mg2-xTixNi alloys and Mg2-xTixNiH4 hydrides

The formation of the Ti substituted Mg2Ni alloys, a promising hydrogen storage material for various applications is studied in detail. Mg1.95Ti0.05Ni alloy and ribbons are successfully prepared by vacuum arc melting and melt spinning methods. The phases, microstructures, and thermal behavior of the alloys and ribbons are characterized by XRD, SEM, TEM, DTA/TG. Sievert-type apparatus is used to study hydrogen sorption properties. Apart from the dominant Mg2Ni phase, the formation of MgNi2, Mg, and Ni3Ti phases is seen in both Mg1·95Ti0·05Ni alloy and ribbons. During the initial three cycles, Mg1·95Ti0·05Ni ribbons showed 2 wt % hydrogen storage capacity. To explain the atomic-scale influence of Ti dopant in the studied alloys and hydrides, FP(L)APW + lo method based on Density Functional Theory (DFT) is applied to Mg2-xTixNi (x = 0.25 and 0.5) alloys and Mg2-xTixNiH4 (x = 0.25 and 0.5) hydrides. An increase in the Ti dopant on the Mg site leads to the hydrides destabilization. Bader's charge density topology analysis provides insight into the charge transfer and bonding between the constituent atoms.

Microstructure and mechanical properties of Mg–Ni–Gd alloy synthesised by powder metallurgy

ABSTRACT The hexagonal close-packed structure renders magnesium weak at room and high temperatures for structural applications despite its low density. Inducing thermally stable and coherent second phases would enhance/retain the strength of Mg-based alloys even at high temperatures. This paper aims to develop a high-strength Mg-based nanocomposite. A master alloy composed of Ni and Gd was cast and the composition of Mg97.56Ni1.22Gd1.22 (at.-%) was prepared using ball milling for 150 h. XRD plots of the as-milled powder having nano-size crystallites confirm the partial dissolution of the master alloy. Consolidation through sintering with 5, 7 and 9 h of exposure at 550°C and extrusion at 500°C resulted in the formation of Mg5Gd, Mg2Ni, Gd2O3 and MgO phases. The extruded samples possessed a high strength of 804 MPa, which can be attributed to ultra-fine grains and dispersoid strengthening by homogeneously distributed second-phase particles in the 100–200 nm range.

Effect of Mn on microstructure, mechanical properties, and corrosion behaviour of Mg-Ni alloys

Previous research on Mg-Ni alloys focused on the mechanical characteristics and damping behaviour in the presence of Zn and rare Earth elements. There has not been much research on the Mg-Ni-Mn alloy’s microstructure, mechanical properties, and corrosion behaviour. The present research work fulfills this gap by concentrating on the microstructure, mechanical, and corrosion characteristics of Mg-Ni-Mn alloys. Here, different Mg-Ni-Mn alloys were developed by varying the nickel and manganese content. The microstructure of the developed alloys was studied using an optical microscope and scanning electron microscope. Ultimate tensile strength and microhardness of all alloys were performed on a tensometer (room temperature), and Vickers hardness tester respectively. The corrosion rate of Mg-Ni and Mg-Ni-Mn alloys was measured at 3.5 wt% NaCl solution by immersion test. The result shows that the nickel and manganese presence refine the grain size of magnesium. XRD analysis confirmed the presence of α-Mg and Mg2Ni phases in Mg-Ni alloys. Along with these phases, the Mn phase was observed in Mg-Ni-Mn alloys. Mechanical properties such as ultimate tensile strength and hardness of pure magnesium were increased in the presence of Ni and Mn. However, the presence of manganese in Mg-Ni alloy shows an adverse effect on corrosion behaviour. The corrosion rate of the Mg-Ni alloy was accelerated in the presence of manganese.

Comparative study on the hydrogen storage performance of as-milled MgRENi rapid quenched alloy catalyzed by metal sulfides

The composites of Mg20Pr1Sm3Y1Ni10 as-quenched alloy and 3 wt.% M (M = CoS, CoS2, MoS2) catalyst were prepared by high-speed vibration ball mill. The effects of metal sulfides on the hydrogenation and dehydrogenation dynamics of alloys were compared. The results show that the as-milled composites contain a large number of amorphous embedded by a small amount of nanocrystals, and there are many point defects. After ball milling, the crystal grain size in the composites containing CoS is relatively larger, followed by CoS2 and MoS2 again. After hydrogenation, the amorphous phase is crystallized to form Mg2NiH4, YH3, Pr8H18.96, Sm3H7, Mg, Co or Mo phases, however, Mg2Ni, YH2, PrH2 and Ni3Y phases appeared after dehydrogenation. The maximum hydrogenation capacity of the composites containing CoS, CoS2 and MoS2 are 3.939, 4.265 and 4.507 wt.%, respectively. The hydrogenation saturation ratio of composite containing MoS2 is higher than that of the composites containing CoS and CoS2. The dehydrogenation activation energy of the composites containing CoS, CoS2 and MoS2 is 107.76, 68.43 and 63.28 kJ.mol−1.H2. On the improvement of hydrogen storage performance of Mg20Pr1Sm3Y1Ni10 alloy, the catalytic effect of MoS2 sulfide is better than that of CoS2 sulfide, and which is better than CoS sulfide.