Hydrogen storage properties of Mg-doped Ti_(1.2)Fe alloys synthesized by mechanical alloying

1　INTRODUCTIONHydrogenstoragematerials ,usedinhydrogensourcesystemsforfuelcellshavebeeninvestigatedduetotheirhighvolumetricdensity ,safety ,easyminiaturizationandconvenientoperation .Consider ingallkindsofhydrogenalloysasawhole ,AB typeTiFealloysareknowntobemuchmoresuitableforusingin portableormobilePEMFCbecauseofitshighreversiblehydrogenstoragecapacity ,whichismuchhigherthanthatofAB5 typealloys.Ontheotherhand ,theactivationpropertiesoftheTiFeal loysare poor .Forexample ,typically ,…     

Hydrogen storage properties of nanocomposite Mg-Ni-MnO2 made by mechanical milling

The hydrogen storage properties of the nanocomposite MggsNi3(MnO2)2(maas fraction, % ) were studied.The temperature changes in hydriding/dehydriding process were investigated. The nanocomposite was fabricated by ball milling process of mixed demental Mg, Ni and oxide maganese MnCh under hydrogen pressure (approximately 0.6 MPa).The hydrogen absorption and desorption properties of the samples milled for various times were investigated. A remarkable enhancement of hydrogen absorption kinetics and low operational desorption temperature have been.found after the sample milled for over 57h. For example, this nanocomposite can absorb hydrogen more than 6.0% (mass fraction) in 60s at 200℃ under 2.0 MPa, and desorption capacity also exceeds 6.0 % (mass fraction) in 400 s at 310℃ under 0.1 MPa.The storage properties of samp1es milled for various times were studied and the kinetics of the samples were analyzed.     

Carbon nanocomposites synthesized by high-energy mechanical milling of graphite and magnesium for hydrogen storage

Nanocomposites obtained by mechanical milling of graphite and magnesium with organic additives (benzene, cyclohexene or cyclohexane) have been studied with the aim of preparing novel hydrogen storage materials. The organic additives were very important in the milling processes to determine the characteristics of the resulting carbon nanocomposites. The mechanical milling with high energy resulted in the generation of large amounts of dangling carbon bonds in graphite with simultaneous decomposition of graphite structure. Such dangling bonds of carbon acted as sites to take up hydrogen. It has been proved by temperature programmed desorption (TPD) and neutron diffraction measurements that the hydrogen taken up in the nanocomposites exists in at least two states; in the form of C–H bond formation in the graphite component and in the form of hydride in the magnesium component. The relative amounts of two types of hydrogen strongly depended upon differences in additives used (benzene, cyclohexene or cyclohexane). When C₆D₆ besides C₆H₆ was used as additive, the hydrogen taken up was discussed from the standpoint of isotope effects. Upon addition of titanium tetraisopropoxide, the features of hydrogen uptake by the nanocomposites changed completely.     

Hydrogen sorption properties of Ti–Cr alloys synthesized by ball milling and cold rolling

Three Ti–Cr alloys with nominal compositions of TiCr_x (x = 2, 1.8 and 1.5) were synthesized by cold rolling and ball milling of as-cast ingots, and their microstructures and hydrogenation properties were studied. X-ray diffraction showed that TiCr_x transformed from a mixture of C14 and C15 Laves phases to a metastable BCC phase after 5 h of ball milling under argon. Cold rolling did not lead to the formation of a metastable BCC phase but only to the reduction of TiCr_x size particles under 20 nm. Surprisingly, the hydrogen absorption/desorption curves of cold rolled and ball milled samples at 323 K were quite similar. This result proves that hydrogen storage properties do not depend only on microstructure and that cold rolling could be an interesting method to synthesize hydrogen storage materials.     

Fabrication of Ti-Cu-Ni-Al amorphous alloys by mechanical alloying and mechanical milling

Ti-based amorphous alloy powders were synthesized by the mechanical alloying (MA) of pure elements and the mechanical milling (MM) of intermetallic compounds. The amorphous alloy powders were examined by X-ray diffraction (XRD), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). Scanning electron micrographs revealed that the vein morphology of these alloy powders shows deformation during the milling. The energy-dispersive X-ray spectral maps confirm that each constituent is uniformly dispersed, including Fe and Cr. The XRD and DSC results showed that the milling time required for amorphization for the MA of pure elements was longer than that of the MM for intermetallic compounds. The activation energy and crystallization temperature of the MA powder are different from those of the MM powder.     

Amorphization of Al---Cu---Fe quasicrystalline alloys by mechanical milling

The amorphous phase is formed from as-solidified Al---Cu---Fe alloy powder, which is mainly composed of the quasicrystalline phase, by mechanical milling. The structure and morphology of the milled powders were monitored by X-ray diffraction, scanning electron microscopy, and transition electron microscopy respectively. Experimental results indicate that quasicrystalline alloys are more easily amorphized than the corresponding crystalline alloys. No intermediate metastable phase appeared during the whole process. The crystallization behavior of the amorphous powders has been examined by thermal annealing and differential thermal analysis.     

Microstructural and mechanical study of nanocrystalline (Ti0.8W0.2)C synthesized by high-energy ball milling

The microstructural characteristics of nanocrystalline (Ti_0.8W_0.2)C elaborated by mechanical alloying process were investigated by using both X-ray diffraction and electron microscopy. The diffraction crystallite size (DCS) and the microstrain of (Ti_0.8W_0.2)C ball milled powders have been determined according to the Rietveld refinement method. The results obtained showed that the (Ti_0.8W_0.2)C diffraction crystallite size decreases and its microstrain increases as the milling duration increases. A transition from grain-size hardening to grain-size softening was observed at DCS = 8 nm. It is demonstrated that, as the grain size decreases, the plastic deformation mechanism undergoes a transition from an intragranular deformation by dislocation sliding to an intergranular deformation by grain boundary sliding, as a result of increasing volume fraction (39%) of the grain boundary (GB) zone.     

铸态及快淬态La-Mg-Ni系(PuNi3型)贮氢合金的循环稳定性

用铸造及快淬工艺制备了La-Mg-Ni系(PuNi3型)La2Mg(Ni0.85Co0.15)9Bx(x=0～0.2)贮氢合金,分析测试了铸态及快淬态合金的微观结构与循环稳定性,研究了硼及快淬工艺对合金微观结构及电化学循环稳定性的影响.结果表明,铸态合金具有多相结构,包括(La,Mg)Ni3相和LaNi5相,一定量的LaNi2相及微量的Ni2B相,经大于15 m/s淬速快淬处理后Ni2B相消失,并且其它相的相对量随淬速的变化而变化.硼的加入提高了铸态及快淬态合金的循环稳定性,但其作用机理完全不同.合金的循环寿命随淬速的增加而增加,但快淬工艺对La-Mg-Ni系贮氢合金循环寿命的改善非常有限.     

Hydrogen storage properties of V＋TiFe0.85Mn0.15 multi—phase alloys made by mechanical alloying

The mechanical alloying technique was used to make multi-phase alloys V TiFe0.85Mn0.15.Their hydrogen storage properties were characterized and compared with that of the polycrystalline alloys made by casting.It was found that the ball milled alloys can absorb hydrogen at room temperature in the first cycle without prior activation.The 40% V 60% TiFe0.85Mn0.15 alloy made by mechanical alloying shows the best hydrogen storage property with the valid hydrogen capacity up 50 220mL/g at 293K and 4.0MPa, and the P-C-T behavior is also improved.The XRD and EDX analyses also show that the phase of these alloys contains.V,TiFe,γ-TiMnx,TiFe2 and α-FeV.The composition of these phases affects significantly the hydrogen storage properties of alloys.     

Degradation behaviors of La–Mg–Ni-based metal hydride alloys:structural stability and influence on hydrogen storage performances

The present work focuses on the structural stability upon hydrogenation of three typical La–Mg–Ni-based alloys:La_(2-)Mg Ni_9,La_3Mg Ni_(14)and La_4Mg Ni_(19).Structural changes during gaseous and electrochemical cycles were characterized,and the influence of the structure distortion on the hydrogen storage properties was concerned.Hydrogen-induced amorphization(HIA)and disproportionation of the three alloys have occurred during both the gaseous and electrochemical cycles.Structural stability of the phase structures in the La–Mg–Ni system is found to follow the order:La Ni_(5-)[(La,Mg)_5Ni_(19)[(La,Mg)_2Ni_7[(La,Mg)Ni_3[(La,Mg)Ni_2.HIA increases thermal stability of the metal hydrides and difficulty to dehydrogenation and leads to degradation of both the gaseous and electrochemical capacities.Interestingly,La_2Mg Ni_9with poor stability presents elevated discharge capability even at 60°C which can be attributed to increase in the hydrogen desorption capability and inhibition of the self-discharge induced by severe HIA at higher temperatures.In addition,HIA in the electrochemical reactions is obviously weaker than the extent during the gaseous cycles,which is mainly due to the slower hydrogenation speed.The development of HIA in the gaseous and electrochemical process is considered to follow the direct and gradual modes,respectively.     

Microstructure and hydrogen storage properties of Mg-Sn nanocomposite by mechanical milling

To improve the hydrogen storage properties, the composition and microstructure of Mg-Sn alloys were modified through fabricating Mg/Mg₂Sn nanocomposite by mechanical alloying. The microstructures were characterized by X-ray diffraction and scanning electron microscopy. It is found that Mg₂Sn instead of Mg(Sn) solid solution is preferably formed during milling process. Although Mg₂Sn is not a hydriding phase, the in situ formed nanosized Mg₂Sn facilitates hydrogen absorption/desorption of Mg by forming Mg/Mg₂Sn nanocomposite. The mechanically milled Mg-5 at.% Sn nanocomposite exhibits slightly elevated plateau pressure and destabilized thermodynamics due to the introduction of large amount of interface energy in Mg/Mg₂Sn nanocomposite.     

Hydrogen storage properties of Mg(Al) solid solution alloy doped with LaF3 by ball milling

LaF₃ was doped to the Mg(Al) solid solution alloy for enhancing the hydrogen absorption and desorption by ball milling. XRD was used to analyze the phases of the samples and the phase transition induced by hydrogenation and dehydrogenation. The microstructure and phase distribution were investigated by SEM and STEM. The hydrogen storage properties were measured by Sieverts method. For Mg_0.93Al_0.07-5wt.%LaF₃ nanocomposite, the hydrogen storage kinetic properties were significantly improved by reducing the hydriding and dehydriding activation energies to 65 and 78 kJ/mol, respectively, and the dehydriding enthalpy was calculated to be 69.7 kJ/mol. The improved hydrogen storage properties were mainly attributed to the catalytic effects of the in situ formed nanostructure Al₁₁La₃ and MgF₂ together with the dissolving of Al in Mg lattice.     

Ni（OH）2 particles synthesized by high energy ball milling

1 Introduction Ni(OH)2/NiOOH has been used as positive materials in alkaline secondary batteries for more than 100 years[1- 3]. The performance improvement of Ni(OH)2/NiOOH electrode is crucial for the application of these batteries as they are all positi…     

High strength nanocrystalline L12-Al3(Ti,Zr) intermetallic synthesized by mechanical alloying

Nanocrystalline L1₂-Al₃(Ti,Zr) intermetallic has been synthesized directly by mechanical alloying of elemental blends of the nominal composition Al₇₅(Ti_25−xZr_x) for x = 0, 5, 10, 15, 20 and 25. The long range order parameter is found to increase with the Zr content. The lattice parameter difference between the L1₂-Al₃(Ti,Zr) and Al was minimum for the alloy with 10% Zr. A very high hardness of 3.23 GPa was achieved for the L1₂ phase in the Al₇₅Ti₁₅Zr₁₀ composition in the green compact condition with a relative density of 77.6%.     

Hydriding/dehydriding properties of Mg-Ni-based ternary alloys synthesized by mechanical grinding

The Mg-Ni-based ternary alloys Mg2-xTixNi(x=0, 0.2, 0.4) and Mg2Ni1-xZrx(x=0, 0.2, 0.4) were successfully synthesized by mechanical grinding. The phases in the alloys and the hydriding/dehydriding properties of the alloys were investigated. Mg2Ni and Mg are the main hydrogen absorption phases in the alloys by XRD analysis. Hydriding kinetics curves of the alloys indicate that the hydrogen absorption rate increases after partial substitution of Ti for Mg and Zr for Ni. According to the measurement of pressure-concentration-isotherms and Van't Hoff equation, the relationship between ln p(H2) and 1 000/T was established. It is found that while increasing the content of correspondingly substituted elements at the same temperature, the equilibrium pressure of dehydriding increases, the enthalpy change and the stability of the alloy hydride decrease.     

Structure and electrochemical performances of Mg_(20-x)Y_xNi_(10)(x=0-4) alloys prepared by mechanical milling

Mg_2Ni-type Mg_(20-x)Y_xNi_(10)(x=0,1,2,3 and4) electrode alloys were fabricated by vacuum induction melting.Subsequently,the as-cast alloys were mechanically milled on a planetary-type ball mill.The effects of milling time and Y content on the microstructures and electrochemical performances of the alloys were investigated in detail.The results show that nanocrystalline and amorphous structure can be successfully obtained through mechanical milling.The substitution of Y for Mg facilitates the glass forming of the Mg_2Ni-type alloy and significantly enhances the electrochemical characteristics of the alloy electrodes.Moreover,the discharge capacity of Y-free alloy monotonously grows with the milling time prolonging,while that of the Y-substituted alloys has the maximum values in the same case.The milling time of obtaining the greatest discharge capacity markedly decreases with Y content increasing.The electrochemical kinetics of the alloys,including high rate discharge ability(HRD),diffusion coefficient(D),limiting current density(I_L) and charge transfer rate,monotonously increase with milling time extending.     

低钴AB_5型贮氢合金的制备及电化学性能

为了降低镍氢电池的原材料成本 ,研究了一系列多元、低钴和无钴AB5型贮氢合金 ,以及取代元素对贮氢合金电化学性质的影响。结果显示 ,用少量的铁、铜和铬部分取代贮氢合金La(NiMnCoAl) 5中的钴对改善贮氢合金电化学循环稳定性有效。贮氢合金La(NiMnAl) 4.6(FeCuCr) 0 .2 Co0 .2 具有满意的循环稳定性 ,它在 0 .2C放电条件下的最大放电容量为 2 96mAh/g-1,经过 30 0次循环容量衰减仅 2 1.8%。另外 ,还用X射线衍射检测了贮氢合金的微观结构     

Hydrogen storage characteristics of Ti2Ni alloy synthesized by the electro-deoxidation technique

Ti₂Ni alloy was synthesized in the molten CaCl₂ electrolyte by the electro-deoxidation method at 900 °C and the electrochemical hydrogen storage characteristics of the synthesized alloy was observed. The X-ray diffraction peaks indicated that stoichiometric oxides in TiO₂–ZrO₂–NiO mixture reduced to Ti₃O₅, CaTiO₃, CaZrO₃, Ni and Ti₂O₃ within 5 h electro-deoxidation process. Extension of the electro-deoxidation time to 10 h caused formations of TiO and equilibrium Ti₂Ni phase. After 24 h electro-deoxidation the target alloy with the equilibrium Ti₂Ni phase structure and the maximum amount of the dissolved Zr in it was obtained. It was observed that the synthesized alloy had maximum discharge capacity of 200 mA h g⁻¹. Upon increase in the charge/discharge cycles, however, the discharge capacity decayed sharply. According to the gathered EIS data at various DODs, the rapid degradation in the electrode performance of Ti₂Ni alloy was attributed to the developed barrier oxide layer on the electrode surface.     

Hydrogen storage properties of as-cast and annealed low-Co La_(1.8)Ti_(0.2)MgNi_(8.9)Co_(0.1) alloys

Low-Co La_(1.8)Ti_(0.2)MgNi_(8.9)Co_(0.1) alloys were prepared by magnetic levitation melting followed by annealing treatment. The effect of annealing on the hydrogen storage properties of the alloys was investigated systematically by X-ray diffraction(XRD), pressure-composition isotherm(PCI), and electrochemical measurements. The results show that all samples contain LaNi_5 and LaMg_2Ni_9 phases. LaCo_5 phase appears at 1,000 ℃. The enthalpy change of all hydrides is close to -30.6kJ·mol~(-1)H_2 of LaNi_5 compound. Annealing not only increases hydrogen capacity and improves cycling stability but also decreases plateau pressure at 800 and 900 ℃. After annealing, the contraction of cell volume and the increase of hydride stability cause the high rate dischargeability to reduce slightly. The optimum alloy is found to be one annealed at 900 ℃, with its hydrogen capacity reaching up to 1.53 wt%, and discharge capacity remaining 225.1mAh·g~(-1) after 140 charge–discharge cycles.     

Experimental and atomistic simulation based study of W based alloys synthesized by mechanical alloying

The present research work represents the synthesis of nanostructured W based alloys with the nominal compositions of W₉₀Mo₁₀ and W₈₀Ni₁₀Mo₁₀ (all in wt.%) by mechanical alloying and followed by conventional sintering at 1500 °C for 2 h in Ar atmosphere. The microstructure and evolution of phases during milling and consolidated products are investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Energy dispersive spectroscopy (EDS). Crystallite size of 38.7 nm and 40 nm and lattice strain of 0.41% and 0.33% are achieved in W₉₀Mo₁₀ and W₈₀Ni₁₀Mo₁₀ alloy respectively at 20 h of milling. The lattice parameter of all the investigated alloys shows initial expansion at 10 h of milling and then contraction at 20 h of milling. W₈₀Ni₁₀Mo₁₀ shows maximum sintered density of 94.8% as compared to W₉₀Mo₁₀. The hardness as well as the compressive strength of W₈₀Ni₁₀Mo₁₀ alloy records maximum value of 8.57 GPa and 1.18 GPa, respectively. The minimum wear depth is attained in W₈₀Ni₁₀Mo₁₀ alloy to that of W₉₀Mo₁₀. Molecular dynamic simulation based study is also performed to reveal the mechanisms responsible for deformation. Atomistic simulation shows that addition of nickel lowers the flow stress and increases ductility of W-Mo alloy studied at nanoscale. Results of atomistic simulation based study correlates well with experimental analysis.