Effect of AB5 alloy on Ti0.10Zr0.15V0.35Cr0.10Ni0.30 hydrogen storage alloy

The structure and electrochemical characteristics of melted composite Ti_0.10Zr_0.15V_0.35Cr_0.10Ni_0.30 + x% LaNi₄Al_0.4Mn_0.3Co_0.3 (x = 0, 1, 5) hydrogen storage alloys have been investigated systematically. XRD shows that though the main phase of the matrix alloy remains unchanged after LaNi₄Al_0.4Mn_0.3Co_0.3 alloy is added, a new specimen is formed. The amount of the new specimen increases with increasing x. SEM-EDS analysis indicates that the V-based solid solution phase is mainly composed of V, Cr and Ni; C14 Laves phase is mainly composed of Ni, Zr and V; the new specimen containing La is mainly composed of Zr, V and Ni. The electrochemical measurements suggest that the activation performance, the low temperature discharge ability, the high rate discharge ability and the cyclic stability of composite alloy electrodes increase greatly with the growth of x. The HRD is controlled by the charge-transfer reaction of hydrogen and the hydrogen diffusion in the bulk of the alloy under the present experimental conditions.     

Synthesis and characterization of high-energy ball milled nanostructured Fe50Ni50

Mechanical alloying is a non-equilibrium process for materials synthesis. It has been used to obtain nanocrystalline binary system FeNi.

Fe and Ni elemental powders have been ball milled in a planetary mill (Pulverisette 7, Fritsch) for various times up to several hours. The morphology of the powders was examined using scanning electron microscopy (SEM). X-ray diffraction (XRD) has been employed to follow the structural evolution during the ball milling process. The X-ray patterns were analysed by the MAUD procedure, which is based on the Rietveld method combined with a Fourier analysis, well adapted for broadened diffraction peaks. The grain size was found to be about 5 nm and the residual strain was about 0.021% after 322 h of milling. The as-milled samples, characterized by Mössbauer spectroscopy (MS) contain a mixture of (bcc) and γ (fcc) phases after 48 h of ball milling.     

The influence of Cu(OH)2 addition on the low-temperature electrochemical performance of La0.75Mg0.25Ni3.5 hydrogen storage alloy

The influence of Cu(OH)₂ addition in 7 mol/L KOH alkaline electrolyte on the electrochemical properties of La_0.75Mg_0.25Ni_3.5 hydrogen storage alloy electrode was investigated in the testing temperature range of from 25 °C to −40 °C in this paper. XRD Rietveld analyses shows that the La_0.75Mg_0.25Ni_3.5 hydrogen storage alloy consists of LaNi₅ phase, (La, Mg)₂Ni₇ phase and (La,Mg)Ni₃ phase. The maximum discharge capacity and the high-rate dischargeability (HRD) of the La_0.75 Mg_0.25Ni_3.5 alloy electrode both decrease with decreasing testing temperature, which mainly due to the slower hydrogen transfer in the bulk of the alloy and the lower electrocatalytic activity at lower temperatures. The scanning electron microscopy (SEM)/energy dispersive X-ray spectroscopy (EDS) analyses indicate that, with the addition of Cu(OH)₂ to the KOH alkaline electrolyte, fine particles of metal Cu can be coated on the La_0.75Mg_0.25Ni_3.5 alloy electrode surface during charging process by electrodeposition. The Cu powders deposited on the La_0.75Mg_0.25Ni_3.5 alloy electrode can improve the alloy’s low-temperature discharge properties by decreasing its charge-transfer resistance and increasing its exchange current density. The cyclic stability of the Cu-deposited La_0.75Mg_0.25Ni_3.5 alloy electrode can be also improved to a certain extent by increasing its corrosive resistance in KOH alkaline electrolyte.     

Mechanical properties of SiCp/Al2O3 ceramic matrix composites prepared by directed oxidation of an aluminum alloy

Silicon carbide particulate reinforced alumina matrix composites were fabricated using DIrected Metal OXidation (DIMOX) process. Continuous oxidation of an Al-Si-Mg-Zn alloy with appropriate dopants along with a preform of silicon carbide has led to the formation of alumina matrix surrounding silicon carbide particulates. SiC_p/Al₂O₃ ceramic matrix composites fabricated by the DIMOX process, possess enhanced mechanical properties such as flexural strength, fracture toughness and wear resistance, all at an affordable cost of fabrication. SiC_p/Al₂O₃ matrix composites were investigated for mechanical properties such as flexural strength, fracture toughness and hardness; the composite specimens were evaluated using standard procedures recommended by the ASTM. The SiC_p/Al₂O₃ ceramic matrix composites with SiC volume fractions from 0.35 to 0.43 were found to possess average bend strength in range 158-230 MPa and fracture toughness was found to be in range of 5.61-4.01 MPa√m. The specimen fractured under three-point loading as observed under scanning electron microscope was found to fail in brittle manner being the dominant mode. Further the composites were found to possess lower levels of porosity, among those prepared by DIMOX process.     

Effect of milling method and time on the properties and electrochemical performance of LiFePO4/C composites prepared by ball milling and thermal treatment

Effects of ball milling way and time on the phase formation, particulate morphology, carbon content, and consequent electrode performance of LiFePO₄/C composite, prepared by high-energy ball milling of Li₂CO₃, NH₄H₂PO₄, FeC₂O₄ raw materials with citric acid as organic carbon source followed by thermal treatment, were investigated. Three ball milling ways and five different milling durations varied from 0 to 8 h were compared. LiFePO₄/C composites could be obtained from all synthesis processes. TEM examinations demonstrated LiFePO₄/C from ball milling in acetone resulted in sphere shape grains with a size of ∼60 nm, similar size was observed for LiFePO₄/C from dry ball milling but in a more irregular shape. The ball milling in benzene resulted in a much larger size of ∼250 nm. The LiFePO₄/C composites prepared from dry ball milling and ball milling in acetone showed much better electrochemical performance than that from ball milling in benzene. SEM examinations and BET measurements demonstrated that the high-energy ball milling effectively reduced the grain size. A ball milling for 4 h resulted in the best electrochemical performance, likely due to the proper amount of carbon and proper carbon structure were created.     

Complete oxidation of methane on Pd/YSZ and Pd/CeO2/YSZ by electrochemical promotion

In this work, methane combustion over Pd/YSZ and Pd/CeO₂/YSZ catalyst was investigated at a temperature range of 470–600 °C. For the first time, the feasibility of electrochemical promotion on palladium films prepared by wet impregnation was reported. The catalytic activity of palladium was found to increase over 160% via transference of oxygen ions from the solid electrolyte to the catalyst film. In addition, palladium supported over ceria and yttria-stabilized zirconia showed the highest activity. As expected, the presence of ceria allowed improving the oxygen storage capacity of the catalyst system.     

Crystallographic and electrochemical characteristics of Ti45Zr35Ni17Cu3 quasicrystalline alloy ball-milled with nickel powder

Crystallographic and electrochemical characteristics of ball-milled Ti₄₅Zr₃₅Ni₁₇Cu₃ + xNi (x = 0, 5, 10, 15 and 20 mass%) composite powders have been investigated. The powders are composed of amorphous, I- and Ni-phases when x increases from 5 to 20. With increasing x, the amount of Ni-phase increases but the quasi-lattice constant decreases. The maximum discharge capacity first increases as x increases from 0 to 15 and then decreases when x increases further from 15 to 20. The high-rate dischargeability and cycling stability increase monotonically with increasing x. The improvement of the electrochemical characteristics is ascribed to the metallic nickel particles highly dispersed in the alloys, which improves the electrochemical kinetic properties and prevents the oxidation of the alloy electrodes, as well as to the mixed structure of amorphous and icosahedral quasicrystalline phases, which enhances the hydrogen diffusivity in the bulk of the alloy electrodes and efficiently inhibits the pulverization of the alloy particles.     

Effect of mechanical alloying on the structure and properties of NbCr2 Laves phase fabricated by hot pressing

NbCr₂ Laves phase intermetallics has been successfully made with mechanically alloyed powders with nominal compositions Cr—33.3 at.% Nb by hot pressing (HP). The effect of mechanical alloying (MA) on the structure and the properties of hot-pressed alloy has been investigated by X-ray diffraction, scanning electron microscopy, and bending test, etc. The results show that the NbCr₂ Laves phase prepared from milled powders exhibits high strength and low density in comparison with one prepared from elemental powders. The high density of defects brought during MA and deficiently eliminated by following HP led to the high hardness and low density. Fine grains and dispersion of fine precipitation caused by MA are related to the improvement of strength of alloy.     

An investigation on flowability and compressibility of AA 6061100 − x-x wt.% TiO2 micro and nanocomposite powder prepared by blending and mechanical alloying

This work investigates the relationships between the components of powders, namely, the powder surface morphology, the flow characteristics and the compressibility of low-energy (microcomposite) and high-energy (nanocomposite) ball milled powders of Al 6061 alloy reinforced with TiO₂ particles. The morphology of the above powder as the function of reinforcement and the milling time was studied by using the scanning electron microscope (SEM). The changes in powder characteristics such as the apparent density, tap density, true density and flow rate were examined by the percentage of reinforcement and milling time. The cohesive nature of the powder was also investigated in terms of Hausner ratio and Kawakita plot. Further, the particle/agglomerate size of low-energy and high-energy ball milled powders was explained by the laser particle size analyzer. X-ray peak broadening analysis was used to determine structural properties of mechanically alloyed powders. The compressibility behavior was examined by the compaction equation proposed by Panelli and Ambrosio Filho to investigate the deformation capacity of the powder. The compressibility behavior, namely, the densification parameter (A) of the microcomposite powder (irregular morphology) was decreased significantly with increasing TiO₂ content due to the disintegration of TiO₂ particles and the cluster formation followed by its agglomeration. The compressibility behavior, namely, the densification parameter (A) of the nanocomposite powder (equiaxed and almost spherical) was decreased slowly with increasing TiO₂ content due to work hardening on the matrix powder. With increased milling time, the compressibility behavior of AA 6061-10 wt.% TiO₂ composite powders increased up to 30 h of milling due to embedding of TiO₂ particles with matrix and changes in powder morphology and finally decreased after 40 h due to work hardening effect.     

Influence of carbon sources on LiFePO4/C composites synthesized by the high-temperature high-energy ball milling method

Carbon-coated LiFePO₄ composites were synthesized by a new method of high-temperature high-energy ball milling (HTHEBM). Fe₂O₃ and LiH₂PO₄ were used as raw materials. Glucose, sucrose, citric acid and active carbon were used as reducing agents and carbon sources, respectively. In this method, high-energy ball milling and carbon coating worked together and, therefore, fine and homogeneous LiFePO₄/C particles with excellent properties were obtained in a relatively short synthesis time of 9 h. Moreover, the synthesis process could be completely finished at a relatively lower temperature of 600 °C for high-energy ball milling transforming mechanical energy into thermal energy. The results of X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electrochemical performance tests indicated that carbon source had an important influence on the properties of LiFePO₄/C composites synthesized by the HTHEBM method. It was proved that the LiFePO₄ composites coated with glucose had the best properties with 1 μm geometric mean diameter and 150.3 mA h g⁻¹ initial discharge capacity at a current rate of 0.1 C. After the 20th cycle test, the reversible capacity was 148 mA h g⁻¹ at 0.1 C, showing a retention ratio to the initial capacity of 98.5%.     

汽车用La0.79Mg0.21Ni3.95储氢合金的制备与电化学性能研究

为开发出高能量密度镍氢电池负极材料,采用真空感应熔炼的方法制备了La_0.79Mg_0.21Ni_3.95储氢合金,对比分析了铸态和退火态储氢合金的物相组成、显微形貌和电化学性能。结果表明,铸态和800 ℃/24 h退火态La_0.79Mg_0.21Ni_3.95储氢合金中都只含有LaNi₅和（La,Mg）₂Ni₇相;升高温度至900 ℃及以上时,储氢合金中形成了不同含量的（La,Mg）₅Ni₁₉和（La,Mg）₆Ni₂₄相。900 ℃/24 h退火态储氢合金的可逆吸放氢性能要高于950 ℃/48 h退火态储氢合金。铸态和退火态储氢合金都在前3周循环过程中到达了最大放电比容量,950 ℃/48 h退火态储氢合金中主要为（La,Mg）₆Ni₂₄相,其具有较高的循环稳定性。铸态和退火态La_0.79Mg_0.21Ni_3.95储氢合金具有良好的电化学活化性能,高倍率放电性能（HRD₁₅₀₀）从高至低的顺序依次为950 ℃/48 h、950 ℃/24 h、900 ℃/24 h、 800 ℃/24 h、铸态;储氢合金的HRD₁₅₀₀与氢扩散速率（D）和交换电流密度（I₀）的变化趋势相同,950 ℃/48 h退火态储氢合金具有最大的HRD₁₅₀₀,这主要与合金电极中含有61.8%（质量分数）的（La,Mg）₆Ni₂₄相、具有较高的D和I₀有关。     

Electrochemical properties of MmNi3.03Si0.85Co0.60Mn0.31Al0.08 hydrogen storage alloys in alkaline electrolytes—A cyclic voltammetric study at different temperatures

The cyclic voltammetric behavior of MmNi_3.03Si_0.85Co_0.60Mn_0.31Al_0.08-based metal hydride electrode was studied in alkaline electrolytes at various temperatures (303, 308, 318 and 328 K). Electrochemical parameters such as limiting current density and corrosion potential were determined at these temperatures. The corrosion potential became more negative with increasing temperature. Hydrogen diffusivity was also found to increase with increasing temperature. From electrochemical discharge experiments, it was concluded that the charge transfer process was the rate-determining step.     

The electrochemical reduction of PdCl4 and PdCl6 in polyaniline: Influence of Pd deposit morphology on methanol oxidation in alkaline solution

The controlled uptake and electrochemical reduction of metal precursors PdCl₄²⁻ and PdCl₆²⁻ in polyaniline (PANI) is demonstrated. The formation of PANI/Pd composites is achieved with a reduction in proton doping and an increase in the oxidation of the polymer with Pd deposits physically blocking the nitrogen groups. High surface area filaments (PdCl₄²⁻) or a rough encapsulation (PdCl₆²⁻) of Pd metal on PANI are obtained. The structural differences highlight the influence of the metal precursor oxidation state on the morphology of the Pd deposits in PANI. Thermal gravimetric analysis provides an estimate of the Pd content for each composite of ∼40%. X-ray Photoelectron Spectroscopy and X-ray-excited Auger Electron Spectroscopy analyses confirm the deposition of Pd metal. The catalytic oxidation of methanol was demonstrated for both PANI/Pd composites in alkaline solutions that prohibit proton doping of the polymer. The data indicates that Pd metal acts as a solid-state dopant that may delocalize the charge on the polymer backbone to maintain conductivity. Methanol oxidation at PANI/Pd composites produced using PdCl₄²⁻ was enhanced relative to the composite produced using PdCl₆²⁻ and a planar Pd electrode. Comparison of PANI/Pd composite produced using PdCl₄²⁻ with other Pd catalysts from the literature indicates surface poisoning is reduced when Pd is coupled with the polymer. The composite is robust and stable in alkaline solution with the charge density decreasing by 5% on the positive scan and 13% on the negative scan after 200 voltammetric cycles. The data also indicates that the reductive desorption of surface contaminants is possible, minimizing the catalytic loss due to surface poisoning.     

Effect of calcination temperature on morphology and electrochemical performance of PbLi2Ti6O14

As a promising anode material, PbLi₂Ti₆O₁₄ has attracted the attention of many researchers. In this work, a series of PbLi₂Ti₆O₁₄ are prepared by solid state method at five different calcination temperatures and used as anode materials in lithium ion batteries. Through a series of tests, the results show that the phase purity, morphology and electrochemical performance of PbLi₂Ti₆O₁₄ can be seriously influenced by calcination temperature. When the calcination temperature is 900?°C, the phase-pure PbLi₂Ti₆O₁₄ can be obtained with relatively small particle size, excellent cycle performance and outstanding lithium ion diffusion behavior. It provides an initial charge capacity of 151.3?mA?h?g^?1 at 100?mA?g^?1. After 100 cycles, it shows a reversible capacity of 142.0?mA?h?g^?1 with superior capacity retention of 93.85%. In contrast, PbLi₂Ti₆O₁₄ formed at 800?°C displays an unsatisfactory performance due to the presence of impurity, even though it has the smallest particle size and the largest lithium ion diffusion coefficient among the five samples. The reversible capacity is only 82.6?mA?h?g^?1 after 100 cycles with capacity retention of 53.9%. In order to further study the lithium ion diffusion behavior of PbLi₂Ti₆O₁₄, the in-situ X-ray diffraction technique is also implemented. It is found that during the lithiation/delithiation process, the stable framework can effectively inhibit the volume change and ensures the excellent electrochemical performance of PbLi₂Ti₆O₁₄.     

Phase structure and electrochemical properties of Ml1?xMgxNi2.78Co0.50Mn0.11Al0.11 hydrogen storage alloys

The effect of magnesium content on the phase structure and electrochemical properties of Ml_1−x Mg _x Ni_2.78Co_0.50Mn_0.11Al_0.11 (x = 0.05, 0.10, 0.20, 0.30) hydrogen storage alloys was investigated. The results of X-ray diffraction reveal that all the alloys consist of the major phase (La, Mg)Ni₃ and the secondary phase LaNi₅. With increase in x, the relative content of the (La, Mg)Ni₃ phase increases gradually, and the maximum capacity and low temperature dischargeability of the alloy electrodes first increase and then decrease. When x is 0.20, the discharge capacity of the alloy electrode reaches 363 mAh g⁻¹ at 293 K and 216 mAh g⁻¹ at 233 K, respectively. The high rate dischargeability of the alloy electrodes increases with increase in x. When the discharge current density is 1200 mA g⁻¹, the high rate dischargeability of the alloy electrodes increases from 22.0% to 50.4% with x increasing from 0.05 to 0.30. The cycling stability of the electrodes decreases gradually with increase in magnesium content.     

The effect of partial substitution of Ti with Zr, Cr or V in the Mg35Ti10Ni55 electrode alloy on its electrochemical performance

In this paper, Zr, Cr and V were selected as the partial substitution elements for Ti to form Mg₃₅Ti₅M₅Ni₅₅ quaternary alloys prepared by means of mechanical alloying on the basis of the ternary Mg₃₅Ti₁₀Ni₅₅ electrode alloy previously studied by the authors. It is found that all the three quaternary alloys possess an amorphous main phase and exhibit improved cycling stability than the original ternary Mg₃₅Ti₁₀Ni₅₅. The Zr-substituted alloy has also a higher discharge capacity. X-ray photoelectron spectroscopy (XPS) surface analysis reveals that on the surface of each alloy a multi-component oxide composite film is formed, which is more compact and corrosion resistant than the Mg(OH)₂ film and the (TiO₂)_x(NiO)_y(Mg(OH)₂)_z composite films reported previously. Auger electron spectroscopy (AES) analysis shows that the substituting elements tend to reduce the thickness of the passivation films. The thickness of composite oxide film on the alloys is in the following order: Mg₃₅Ti₁₀Ni₅₅>Mg₃₅Ti₅V₅Ni₅₅>Mg₃₅Ti₅Zr₅Ni₅₅>Mg₃₅Ti₅Cr₅Ni₅₅. The result agrees well with that of the polarization resistances (R_P) values obtained from the electrochemical impedance spectroscopy (EIS) Nyquist diagrams. It demonstrates that the thicker the passivation film is, the higher the R_P is and the more difficultly the charge transfer reaction proceeds. Anodic polarization curves indicate that the addition of Cr and Zr decreases effectively the corrosion current. However, the corrosion of the electrode alloys in the electrolyte is still high and proceeds constantly as the corrosion current remains almost constant during further cycles.     

Structural and electrochemical studies of (SnxCo1−x)60C40 alloys prepared by mechanical attriting

Using a vertical-axis attritor, samples of (Sn_xCo_1−x)₆₀C₄₀ for 0 ≤ x ≤ 0.7 have been prepared in increments of Δx = 0.1. The effect of Sn content on the structure and performance of the Sn-Co-C nanocomposites was examined by X-ray diffraction (XRD), ¹¹⁹Sn Mössbauer effect spectroscopy and electrochemical methods. XRD shows a diffraction pattern characteristic of a nanostructured material having amorphous CoSn grains in a carbon matrix for x = 0.5. Broad Bragg peaks of Co₃C, SnCo₃C_0.7 and CoSn₂ were observed for samples with 0 ≤ x ≤ 0.1, 0.1 ≤ x ≤ 0.4 and 0.5 < x ≤ 0.7, respectively. ¹¹⁹Sn Mössbauer effect spectroscopy shows the presence of an amorphous CoSn component in samples with 0.3 ≤ x ≤ 0.6. Samples with a large amount of the SnCo₃C_0.7 phase showed small capacity for lithium. Therefore, SnCo₃C_0.7 is best described as an inactive phase. The sample with x = 0.7 shows the highest specific capacity (about 600 mAh/g) of all samples prepared but exhibited poor capacity retention after cycle 45. Excellent charge-discharge capacity retention, reasonable specific capacity (>450 mAh/g) along with stable differential capacities were observed for samples near x = 0.5.     

Characterization and magnetic coercivity of nanostructured (Fe50Co50)100-XVX= 0,2,4 powders containing a small amount of Co3V intermetallic obtained by mechanical alloying

(Fe₅₀Co₅₀)_100−XV_X = 0,2,4 alloy powders were prepared by mechanical alloying. The milling times were 4 h, 8 h, 16 h, 24 h, 36 h, 55 h and 125 h, respectively. Structural, micro-structural and magnetic studies were carried out by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and a Vibration Sample Magnetometer (VSM). The XRD results showed that the inter-metallic compound (Co₃V) appears during milling and affects the coercivity, lattice parameter and micro-strain. Crystallite size decreases and reaches approximately 10 nm at 125 h. The coercivity increases during the milling and reaches a maximum at 55 h and then decreases slightly.     

Study of the electrochemical hydrogen storage properties of the proton-conductive perovskite-type oxide LaCrO3 as negative electrode for Ni/MH batteries

LaCrO₃ was prepared by glycine combustion method and investigated as negative electrode for Ni/MH batteries. The structures of the as-calcined powder and the 20th charge-discharge cycle sample were characterized by XRD. The electrochemical experimental results demonstrated that the LaCrO₃ electrode showed excellent electrochemical reversibility and considerably high charge-discharge capacity at various temperatures. Except for the charge-discharge cycle at 298 K, the discharge capacities of LaCrO₃ electrode keep steady at 107.1 mA h g⁻¹and 285 mA h g⁻¹ at 313 K and 333 K after 5 cycles, respectively.