As-milled Samples Research Articles

Li-Ion Conductivity of Single-Step Synthesized Glassy-Ceramic Li10GeP2S12 and Post-heated Highly Crystalline Li10GeP2S12.

Li10GeP2S12 is a phosphosulfide solid electrolyte that exhibits exceptionally high Li-ion conductivity, reaching a conductivity above 10-3 S cm-1 at room temperature, rivaling that of liquid electrolytes. Herein, a method to produce glassy-ceramic Li10GeP2S12 via a single-step utilizing high-energy ball milling was developed and systematically studied. During the high energy milling process, the precursors experience three different stages, namely, the 'Vitrification zone' where the precursors undergo homogenization and amorphization, 'Intermediary zone' where Li3PS4 and Li4GeS4 are formed, and the 'Product stage' where the desired glassy-ceramic Li10GeP2S12 is formed after 520 min of milling. At room temperature, the as-milled sample achieved a high ionic conductivity of 1.07 × 10-3 S cm-1. It was determined via quantitative phase analyses (QPA) of transmission X-ray diffraction results that the as-milled Li10GeP2S12 possessed a high degree of amorphization (44.4 wt %). To further improve the crystallinity and ionic conductivity of the Li10GeP2S12, heat treatment of the as-milled sample was carried out. The optimal heat-treated Li10GeP2S12 is almost fully crystalline and possesses a room temperature ionic conductivity of 3.27 × 10-3 S cm-1, an over 200% increase compared to the glassy-ceramic Li10GeP2S12. These findings help provide previously lacking insights into the controllable preparation of Li10GeP2S12 material.

In-situ synthesis and characterization of Cu/NbC, Cu/NbC-WxC, and Cu/WxC nanocomposites via mechanical alloying

In-situ Cu/NbC, Cu/NbC-WxC, and Cu/ WxC nanocomposites were synthesized by mechanical alloying (MA) at room temperature using high-purity premixed Cu(10-x)NbxW (x = 0, 5, 10 at%) elemental powders. The synthesized powders were then consolidated through Equal Channel Angular Pressing at 700 °C. The microstructure, phase constituent, and hardness of the as-milled and consolidated powders were investigated using scanning and transmission electron microscopy, X-ray diffraction, and microhardness measurements. The 80 h MA resulted in the formation of a Cu/NbC and Cu/NbC-W nanocomposite powder with an average copper matrix crystallite size of 8–11 nm and NbC and W particle sizes mainly less than 100 nm. Refinement of the powders was achieved through cracking at the work-hardened areas in the copper matrix and fracturing of the tungsten and niobium particles. During consolidation, the W converted into W2C and WC phases. Additionally, the Cu matrix crystallite size increased to 41 nm, 43.6 nm, and 65.3 nm for Cu10Nb, Cu5Nb5W, and Cu10W, respectively. While Cu10Nb showed the highest hardness among the as-milled samples, Cu5Nb5W attained the highest hardness value of 462 HV after consolidation, which is due to its smaller Cu matrix crystallite size and finer carbide particles compared to the Cu10Nb and Cu10W alloys and likely due to the synergistic strengthening effect of the NbC and WxC carbide particles. These findings demonstrate the successful synthesis of in-situ Cu-based nanocomposites with tailored microstructures and constituent phases through mechanical alloying.

An investigation of the magnetic, mechanical, and kinetic characteristics of CuCrFeTiNi high entropy alloy by mechanical alloying and spark plasma sintering

In this study, the effect of mechanical alloying on the formation of CuCrFeTiNi high entropy alloys (HEA) at different times was investigated. The alloys were milled for 60 h and a bulk sample was produced using spark plasma sintering (SPS). X-ray diffraction, scanning electron microscopy, transmission electron microscopy, hardness, and vibrating sample magnetometry techniques were used for investigating the microstructure and properties of the as-milled powders. As a result of the analysis, it was found that HEA consisting of a solid solution with a refined microstructure of less than 48 nm was obtained after 60 h milling containing FCC and BCC phases (91% FCC and 8% BCC) while in the bulk sample the same phases can be seen but with different ratio (21% FCC and 79% BCC). The saturation magnetization and coercivity of the as-milled sample after 60 h of milling are 19.12 emu/g and 13.4 Oe, respectively, while these values for the as-sintered sample are 64.38 emu/g and 4.63 Oe, respectively. Based on the magnetic data, the produced alloy can be classified as good soft magnetic material. Also, the bulk sample has a Vickers hardness of 725 Hv, a compressive strength of 2466 MPa, and a yield stress of 1525 MPa.

MnFe2O4-based spinels by mechanochemical and thermochemical reaction of siderite and MnO2 powder mixtures

The manganese ferrite has been processed by mechanosynthesis, using reactive siderite and MnO2 powder mixtures, with and without subsequent heat treatment. Taguchi planning was used to assess the impact of milling conditions (rotational speed and time) and subsequent calcination temperature on conversion of precursors, based on integrated intensities of the main XRD peaks of precursor phases FeCO3 (104) and MnO2 (110), and spinel phase (311), using Ni as internal pattern. Thermogravimetry provided additional information on the residual contents of reactants in the as-milled samples. The best conditions for complete conversion to spinel phase of as-milled samples were obtained by milling at 650 rpm, for 6 h (I311,sp/I111,Ni=2.41), and for calcined samples were obtained after milling at 650 rpm, for 3 h, and calcination at 650 °C (I311,sp/I111,Ni=2.35). The impact of processing conditions on structural features of the spinel phase was accounted by the contributions to variance of intensity of its (311) reflection, which were 90% ascribed to rotational speed and only 4% ascribed to milling time, for as-milled samples, or 58%, 15% and 16% ascribed to rotational speed, milling time and calcination temperature, for calcined samples. Readier conversion of FeCO3 relative to MnO2 occurred during the milling stage, at low or intermediate rotational speed, with impact on Mn:Fe ratio in the spinel phase, as revealed by changes in lattice parameter of as-milled samples, in the range of 0.8424–0.8464 nm. Subsequent calcination minimized or eliminated traces of secondary phases. The incorporation of magnesium oxide and possibly other secondary components of the siderite precursor also induced structural changes in the resulting spinel phase, mainly in calcined samples (ao = 0.8370–0.8434 nm). Partial oxidation also contributed to structural changes in calcined samples, as revealed by differences between samples calcined in inert and oxidising atmospheres.

Direct Mechanochemical Synthesis, Phase Stability, and Electrochemical Performance of α-NaFeO2.

To better understand polymorph control in transition metal oxides, the mechanochemical synthesis of NaFeO2 was explored. Herein, we report the direct synthesis of α-NaFeO2 through a mechanochemical process. By milling Na2O2 and γ-Fe2O3 for 5 h, α-NaFeO2 was prepared without high-temperature annealing needed in other synthesis methods. While investigating the mechanochemical synthesis, it was observed that changing the starting precursors and mass of precursors affects the resulting NaFeO2 structure. Density functional theory calculations on the phase stability of NaFeO2 phases show that the α phase is stabilized over the β phase in oxidizing environments, which is provided by the oxygen-rich reaction between Na2O2 and Fe2O3. This provides a possible route to understanding polymorph control in NaFeO2. Annealing the as-milled α-NaFeO2 at 700 °C has resulted in increased crystallinity and structural changes that improved electrochemical performance in terms of capacity over the as-milled sample.

Improving hydrogen storage thermodynamics and kinetics of Ce-Mg-Ni-based alloy by mechanical milling with TiF3

Mg-based hydrides are too stable and the kinetics of hydrogen absorption and desorption is not satisfactory. An efficient way to improve these shortcomings is to employ reactive ball milling to synthesize the nanocomposite materials of Mg and additives. In this experiment, TiF3 was selected as an additive, and the mechanical milling method was employed to prepare the experimental alloys. The alloys used in this experiment were the as-cast Ce5Mg85Ni10, as-milled Ce5Mg85Ni10 and Ce5Mg85Ni10 + 3 wt.% TiF3. The phase transformation, structural evolution, isothermal and non-isothermal hydrogenation and dehydrogenation performances of the alloys were inspected by XRD, SEM, TEM, Sievert apparatus, DSC and TGA. It revealed that nanocrystalline appeared in the as-milled samples. Compared with the as-cast alloy, ball milling made the particle dimension and grain size decrease dramatically and the defect density increase significantly. The addition of TiF3 made the surface of ball milling alloy particles markedly coarser and more irregular. Ball milling and adding TiF3 distinctly improved the activation and kinetics of the alloys. Moreover, ball milling along with TiF3 can decrease the onset dehydrogenation temperature of Mg-based hydrides and slightly ameliorate their thermodynamics.

Phase evolution characteristics, thermal stability, and strengthening processes of Fe–Ni based ODS invar steel produced by mechanical alloying and spark plasma sintering

In the present study, the base composition of Fe-42 wt% Ni invar was used to prepare three different oxide dispersion strengthened (ODS) steel compositions with addition of 2 wt% Y2O3 and a varying amount of Ti (0.3%, 1%, and 2% wt.%) by mechanical alloying (MA) using SPEX8000 M high energy ball mill. The mechanically alloyed samples were compacted first to make pellets, and batch-annealed at 400, 600, 800, and 1000 °C to verify its thermal stability. The hardness of the as-milled and annealed samples was estimated to apprehend the effect of Ti content and temperature on the mechanical properties. Phase evolution was studied by using the x-ray diffraction (XRD) technique of the as-milled and annealed samples of all the compositions. Then, all the milled samples were spark plasma sintered (SPSed) at 1000 °C for further investigation of sintering characteristic, microstructure, and mechanical properties. The SPSed samples were subjected to compression and Vickers hardness testing to study the change in mechanical properties of the different compositions after sintering. Yield strength values of the three compositions were theoretically calculated through strengthening mechanisms analysis using XRD data and microstructural information of the SPSed samples and correlated with the experimentally determined compressive yield strength. The microstructural study of the SPSed samples was performed using transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD) analysis. The relationship between microstructure and mechanical properties has been examined in the context of various strengthening processes such as dislocation strengthening, solid solution strengthening, grain size strengthening, and precipitation/dispersoid strengthening in the SPSed alloys.

Effect of the supersaturation with nitrogen on the structure refinement and magnetic properties of mechanically alloyed and heated Fe14Cr ferritic alloys

Nano-nitride reinforcement of Fe–Cr alloys are under intense investigations, e.g., along with oxide-strengthened, nitride-strengthened reduced activation steels with superior high temperature mechanical properties are developed as materials for nuclear energy applications. Fe14Cr alloy powders were produced by mechanical milling for up to 170 h under a nitrogen atmosphere followed by heating under an Ar5%H2 atmosphere to 600°C–1120 °C. The samples were investigated by means of X-ray diffraction, DTA/TG and magnetic measurements. CrN, detected after milling for 58 h, reached 39 wt % (5.3 wt.% total N) at 170 h milling. The ferrite supersaturated with nitrogen shows a strong decrease in grain size and saturation magnetization, an increase in lattice constant, microstrain and coercivity, Hc. Upon heating, the metastable ultrafine α-ferrite and CrN in the as-milled samples undergo transformations and recrystallization into ferrite grains free of supersaturation, whose microstructure follows a continuous relaxation. The supersaturation with nitrogen was retained upon heating in the relatively stable ferrite crystalized at the milling stage. This microstructure undergoes a discontinuous relaxation in the 800°C–1120 °C region: a pronounced decrease of grain size (down to ∼25 nm), an increase of lattice constant, microstrain and Hc. These improvements were associated with features of discontinuous precipitation reaction of coherent nitride precipitates (involving a new α”-phase with expanded lattice), in connection with the heating in the austenite phase field. Such microstructure refinement or (nitride) strengthening of Fe14Cr alloys can be achieved on powders milled for much less time as compared to previously reported (oxide dispersion) strengthening of Fe14Cr–W–Ti ferritic steels.

In-situ synthesis and purification of high grade titanium carbonitride powder via carbonitrothermic reduction of low grade titanium ore

This study reports the production of pure titanium carbonitride powder via carbonitrothermic reduction of low grade titanium ore. High temperature reduction of the as-milled samples in a nitrogen-containing atmosphere at 1400 °C for 20 min was maintained for the synthesis of the Fe – TiCN composite. An acid solution of 10% concentration, which contains HCl acid, was used to purify the Fe – TiCN composite, for the purpose of obtaining a high purity TiCN powder. The obtained TiCN powder was characterized using field emission scanning electron microscopy (FESEM), X-ray diffraction spectrometer (XRD), particle size analyser (PSA), LECO non – metal analyser, Raman spectroscopy, and high resolution transmission electron microscope (HRTEM) was used to study the powder lattice orientation and particle distribution. The overall results of these analyses confirm the formation of high grade TiCN powder, as the synthesized powder was free of iron and other impurities, and its mean particle size was found to be 4.687 μm.

Effect of Y addition on the structural transformation and thermal stability of Ti-22Al-25Nb alloy produced by mechanical alloying

Abstract In this study, a Ti-22Al-25Nb alloy with nanocrystalline structure was produced by high energy mechanical alloying (HEMA) and 1 at.-% yttrium was added as a thermal stabilizer. The as-milled samples were annealed at various temperatures up to 900 °C in a protective gas atmosphere, and the samples were allowed to cool to room temperature in the furnace. The phase transformations and microstructural changes as a function of the annealing temperatures and alloy compositions were studied using room- and high-temperature X-ray diffraction (XRD), focused ion beam microscopy (FIB), and scanning electron microscopy (SEM). The mechanical properties of the samples were interpreted based on the hardness results and their correlation with the microstructures. The results showed that the as-milled nanocrystalline structure of Ti-22Al-25Nb alloy increased from 3.4 nm to 350 nm after annealing at 800 °C due to the high driving force induced by the large grain boundary area. Consequently, the as-milled hardness of the Ti-22Al-25Nb alloy dropped from 7.63 ± 0.18 GPa to 5.37 ± 0.28 GPa. The grain size stability of the Ti-22Al-25Nb alloy after annealing at elevated temperature was ensured through the addition of yttrium. Thus, the grain size remained at the level of 125 nm, and the hardness value was maintained at around 6.98 ± 0.43 GPa after annealing at 800 °C.

Synergistic effects of La2Mg17/Ni/H system on hydrogen storage

Synergistic effects of La2Mg17/Ni system on the hydrogen storage are discussed in the paper. The surface microstructure transitions are studied. The new hydrides with the cotton-like structures which have the lower dehydrogenation temperatures are generated on the as-milled sample surface. The surface structures present the obvious stratification with the phases of Ni, Mg2Ni-H and La-Mg-based alloys from the surface to inside after the heat-treatment process. The special surface stratified configuration can improve the hydrogen storage properties. The hydrogen storage capacities and cycle stabilities have increased significantly compared with the original alloy. The −2%Ni sample has the best comprehensive property among them.

Ultrafast synthesis of the nanostructured Al59Cu25.5Fe12.5B3 quasicrystalline and crystalline phases by high-energy ball milling: Microhardness, electrical resistivity, and solar cell absorptance studies

In this study, the Al59Cu25.5Fe12.5B3 nanoquasicrystalline alloy and related crystalline phases were synthesized through mechanical alloying using a high-energy ball milling and consolidated by a cold isostatic pressing apparatus. This paper focuses on the synthesis, structural and microstructural evolutions, thermal stability, microhardness, and electrical and optical properties of the Al59Cu25.5Fe12.5B3 nanoquasicrystalline alloy for solar selective absorber usages. The structural evolutions of the mechanically alloyed and heat-treated AlCuFeB powders were investigated by X-ray diffractometry. Accordingly, the effect of milling time and heat treatment on the formation of quasicrystalline and related crystalline phases were studied in the AlCuFeB alloy system. The microstructure, morphology, and chemical microanalysis of the un-milled and as-milled powders were examined by field-emission scanning electron microscopy and energy-dispersive X-ray spectroscopy. The composition of the as-milled AlCuFeB powders was estimated employing inductively coupled plasma-atomic emission spectroscopy. The thermal stability of the AlCuFeB powders was recorded by differential thermal analysis, and the weight gain of the particles during annealing was investigated through thermogravimetric analysis. The nanostructured Al59Cu25.5Fe12.5B3 stable quasicrystalline phase and crystalline Al(Cu,Fe) solid-solution were synthesized by the ultrafast milling procedure in 1 h. The rationale behind using the term ultrafast synthesis is to synthesize the QC i-phase only by the high-energy ball milling procedure in short-term ball milling without subsequent annealing treatment. However, the single quasicrystalline phase could not be obtained even after the annealing treatment. The quasicrystalline size was calculated by the Williamson–Hall method and optimized by the Rietveld refinement procedure, and it was found that the size is varied between 53 and 61 nm. Furthermore, the particle size distribution of the as-milled AlCuFeB powders was measured using laser static light scattering, which ranges from 0.1 to 50 μm. The microhardness of the consolidated as-milled and heat-treated samples was estimated utilizing the Vickers microhardness indenter. At the same time, their electrical resistivity was assessed by the four-point probe method at room temperature. The spectral analyses of absorption on the consolidated as-milled samples were carried out in the ultraviolet, visible, and near-infrared regions. It was found that the presence of the quasicrystalline phase in the AlCuFeB alloy prominently improves the microhardness, electrical resistivity, and particularly sunlight absorptance.

Peculiarities of the Synthesis of Ternary Fe-Al-Sn Intermetallic Compound from Mechanically Alloyed Materials

A nanostructured Fe65Al30Sn5 alloy has been synthesized by mechanical alloying of elemental Fe, Al, and Sn powders in a planetary ball mill. The structure and phase composition of the as-milled sample and the samples after subsequent heat treatment at 400 °C, 500 °C, and 800 °C were investigated using X-ray diffraction, electron microscopy, 57Fe and 119mSn Mossbauer spectroscopy. We found that the as-milled sample is a nanocrystalline ternary bcc solid solution of the estimated composition Fe62Al32.6Sn5.4. The samples of Fe65Al30Sn5 after annealing are non-uniform materials that mainly comprise the ternary B2 ordered phase Fe65Al30Snx, xSn ≤ 1 at. pct. In addition to the dominant B2 ordered phase, we also identified chemically non-ordered regions, Sn and FeSn, FeSn2.

All-solid-state half-cell of Li/a-Si film using guest Li+ conductor 15NaI∙LiBH4 as a solid electrolyte

In the present study, an all-solid-state half-cell Li/ amorphous Si (a-Si) was fabricated using the guest Li+ ion conductor (15NaI∙LiBH4) as a solid electrolyte. Continuous lithiation/delithiation of the a-Si film was confirmed. At room temperature, the charge-discharge cycles were stable over 80 cycles with the high Coulombic efficiency of 99%. On the other hand, the poor rate performances are the problem; the capacities remained at approximately 1300 mAh/g at 12.7 μA/cm2. Heating the cell at 60 °C resulted in the improvement of the rate performance, which can be due to the improvement of the Li+ conductivity of 15NaI∙LiBH4. In order to understand the correlation between the microstructure and Li+ conductivity of 15NaI∙LiBH4, the as-milled sample was post-annealed and the variation in the microstructure was observed by transmission electron microscopy (TEM). It was indicated that the lattice defects, such as dislocation and lattice distortion, have a significant contribution for the Li+ ion conductivity of the 15NaI∙LiBH4.

Electrochemical hydrogen storage behaviors of as-milled Mg–Ti–Ni–Co–Al-based alloys applied to Ni-MH battery

In the study, the hydrogen storing materials Mg–Ni-based Mg50-xTixNi45Al3Co2 (x = 0, 1, 2, 3, 4) + 50 wt% Ni (named Mg50-xTixNi45Al3Co2 (x = 0–4) + 50Ni) with nanocrystalline and amorphous structures were fabricated by the method of mechanical milling and designed for the negative electrode of Ni–MH batteries. The investigation aims at researching the function of Ti dosage on the electrochemical hydrogen storing characteristics and microstructure of the experimental specimens. The analysis of X-ray diffraction profiles and Scanning Electron Microscope images determines that the experiment specimens contain the major phase Mg2Ni and the minor phase MgNi2. The observation of TEM images reveals a fact that the specimens after ball-milling treatment consist of the nanocrystal and amorphism structures. The electrochemical tests show that as for the samples after ball-milling treatment, the discharge capacities of them gain the utmost value at the first circulate without activation treatment, and the increase of Ti dosage brings on an evident rise in the specimens’ discharge capacity and cycle stability. Concretely, as the Ti content alters from 0 to 4, the discharge capacities of the as-milled (20 h) sample increase from 405.0 to 519.4 mAh/g and capacity retention rate of 100th circulate (S100 = C100/Cmax) augments from 45% to 72%. What’s more, a series of measurements, such as the high rate discharge ability (HRD), the electrochemical impedance spectrum (EIS) as well as Tafel polarization curves etc. show that the electrochemical kinetics performances of as-milled specimens in this experiment have a trend of increasing first and then decreasing with the addition of Ti element.

Study of the effect of mechanical alloying on the structure of Ni-Mn-Sn Heusler alloy

The formation process of nanocrystalline Ni-Mn-Sn Heusler alloy was investigated using mechanical alloying route. Powder samples of this alloy were fabricated using high milling energy technology of planetary ball mill in an argon atmosphere. The effects of selected milling time (0 hr, 5 hr, 10 hr and 15 hr) on the crystallite size, lattice strain, morphology and chemical composition of as-milled powder samples were studied using X-ray diffraction (XRD) and scanning electron microscope (SEM) attached with energy-dispersive Xray spectroscopy (EDX). Thermal behavior of the samples was analyzed by differential scanning caloorimetry (DSC). Results indicated that the formation of single phase Ni2MnSn Heusler alloy was obtained after 15 hr of milling through the balance between particle coalescence and fracture accompanied by uniform grain refinement. The optimum milling time resulted from the proper selection of milling parameters. Compositional analysis of 15 hr asmilled sample revealed stoichiometric Heusler composition (X2YZ) of Ni-Mn-Sn alloy with no impurities. The subsequent heating of the powder particles in DSC showed crystallization of Ni-Mn-Sn alloy. The obtained results provide an understanding of the fabrication of Ni-Mn based Heusler alloy powders by mechanical alloying technique by using laboratory scale ball mill with the aim to bring out structural and thermal aspects of the alloy.

Fabrication of bulk nanostructured silver by spark plasma sintering from nanostructured silver powders

In this research, bulk nanostructured silver was successfully fabricated from nanocrystalled powder by mechanical alloying (MA) and spark plasma sintering (SPS). Mechanical Alloying behavior, changes in structural parameter, and crystal sizes were investigated by XRD. The initial powder and as-milled powder were subsequently consolidated by spark plasma sintering at 700 °C. During MA process, the crystal size decreased from 47 nm to 26 nm. After SPS process, the crystallite size increased to 6 and 21 percent for the samples produced from initial powder and as-milled samples respectively. The highest microhardness was obtained as 102 HV for the sample produced by as-milled powder, with the crystallite size of 50 nm and density of 93%.

Mechanochemical synthesis of the α-AlH3/LiCl nano-composites by reaction of LiH and AlCl3: Kinetics modeling and reaction mechanism

Mechanochemical activation-assisted synthesis, compared to conventional wet methods, exhibits advantages such as higher chemical homogeneity and better quality of the resulting nano-crystals, in preparing nano-sized aluminum hydride (AlH3). Solid/liquid state milling is effective and convenient for production of α-AlH3/LiCl nano-composites through a mechanochemical reaction of LiH and AlCl3 in [2-Eim] OAc. However, the kinetics of this process has not been thoroughly studied. In this work, we studied the kinetics of mechanochemical synthesis of α-AlH3/LiCl nano-composite to understand the reaction process and find the optimum milling parameters (including shortest time to achieve high-quality product). We performed isothermal desorption tests for as-milled samples at 80 °C. Structures of the products were analyzed using X-ray powder diffraction. Johnson-Mehl-Avrami (JMA) model was adopted to describe the process, which contains transformation fraction and chemical reaction controlled regime. Kinetics of mechanochemical reaction at the beginning was limited by diffusion rate of the reagent, and later controlled by nucleation of AlH3. By fitting the experimental data, apparent activation energy for the mechanochemical reaction was calculated as 39.6 kJ/mol.

Study on the gaseous and electrochemical hydrogen storage properties of as-milled Ce[sbnd]Mg[sbnd]Ni-based alloys

For gaining further insight into the involvement of the gaseous and electrochemical hydrogen storage properties of CeMg12-type alloys, partial substitution and ball milling were both used to synthesize the nanocrystalline and amorphous CeMg11Ni + x wt.% Ni (x = 100, 200) samples. This research aims at elucidating the functional roles of Ni content and milling time on samples' structure and hydrogen storage performance. X-Ray diffraction and high-resolution transmission electron microscope were used to reveal the micro constructions of alloys. To determine the gaseous hydrogen storage property, Sievert's apparatus and a thermal gravity analysis bonded with a H2 probe were adopted. The dehydrogenation activation energy was computed in the Kissinger method. The electrochemical performances of the as-milled samples were measured through a constant current system. Further researches showed that the electrochemical performance of as-milled samples had been dramatically improved by increasing Ni content. With milling duration lengthens, the gaseous hydrogen absorption capacity, gaseous hydriding rate and high rate discharge capability of samples reached the maximal values, but electrochemical discharge capacity and gaseous dehydriding rate always increased. The dehydrogenation activation energy decrease resulted by improving Ni percent and milling duration was deemed as the cause of the excellent gaseous kinetics of samples.

Hydrogen Storage Performances of Nanocrystalline and Amorphous NdMg11Ni + x wt% Ni (x = 100, 200) Alloys Synthesized by Mechanical Milling

Nanocrystalline and amorphous NdMg12-type NdMg11Ni + x wt% Ni (x = 100, 200) alloys were successfully prepared through ball milling (BM). The microstructures and electrochemical properties were systematically studied to get a more comprehensive understanding of the sample alloys. The maximum discharging capacity could be obtained at only two cycles, indicating that as-milled alloys have superior activation capability. The more the Ni content, the better the electrochemical properties of the as-milled samples. To be specific, the discharge capacities of x = 100 and x = 200 (BM 20 h) samples are 128.2 and 1030.6 mAh/g at 60 mAh/g current density, respectively, revealing that enhancement of Ni content could significantly improve the discharging capacities of the samples. Additionally, milling duration obviously influences the electrochemical properties of the samples. The discharging capacity always rises with milling duration prolonging for the x = 100 sample, but that of the (x = 200) sample shows a trend of first augment and then decrease. The cycling stability of the (x = 100) alloy clearly decreases with extending milling duration, whereas that of the (x = 200) alloy first declines and then augments under the same conditions. In addition, the high rate discharge (HRD) abilities of the sample display the maximal values as milling duration changes. The HRD (HRD = C300/C60 × 100%) values of the as-milled alloys (x = 100, 200) are 80.24% and 85.17%, respectively.