Enhancing (de)hydrogenation kinetics properties of the Mg/MgH_2 system by adding ANi_5(A=Ce,Nd,Pr,Sm,and Y) alloys via ball milling

Magnesium(Mg)-based alloys have already been widely studied as the hydrogen storage materials because of their high reversible hydrogen storage capacity,low cost,light weight,etc.However,the poor de/hydrogenation kinetic properties dramatically hinder the practical applications.In this work,the MgH_2-ANi_5(A=Ce,Nd,Pr,Sm,and Y) composites were prepared by a high-energy ball milling method.which can effectively refine the particle size thus improving the kinetic properties.Experimental results reveal that the MgH_2-ANi_5 composites mainly consist of Mg_2 NiH_4,MgH_2 and rare earth(RE) hydride,which will be dehydrogenated to form Mg_2 Ni,Mg and stable RE hydride reversibly.Accordingly,the asmilled MgH_2-ANi_5(A=Ce,Nd,Pr,Sm,and Y) composites with various A-elements can respectively contribute to a reversible hydrogen storage capacity of 6.16 wt%,5.7 wt%,6.21 wt%,6.38 wt%,and 6.5 wt%at a temperature of 300℃,and show much better kinetic properties in comparison to the pure MgH_2 without any additive.In-situ formed Mg_2 Ni and stable RE hydride(such as CeH_(2.73) and YH_2) might act as effective catalysts to significantly improve the hydrogen storage properties of MgH_2.The present work provides a guideline on improving the kinetic properties of the Mg-based hydrogen storage alloys.     

Thermal stability of amorphous alloys Mg65Cu25Y10, Mg63Ni30Y7 after electrochemical hydrogen absorption

Thin ribbons of the metallic glass Mg₆₅Cu₂₅Y₁₀ and Mg₆₃Ni₃₀Y₇ obtained by melt spinning were saturated with atomic hydrogen during electrochemical decomposition of water. The amount of absorbed hydrogen was as high as 4 mass% for the alloy Mg₆₅Cu₂₅Y₁₀H_x and 1.5 mass% for the alloy Mg₆₃Ni₃₀Y₇H_x. As the hydrogen content increases up to 3.6 mass%, the amorphous structure of the copper-containing alloy is transformed to a nanocrystalline structure with formation of magnesium and yttrium hydrides and also the intermetallic Cu₂Mg at room temperature. The appearance of crystalline compounds during saturation with hydrogen leads to a decrease in the thermal stability of the amorphous alloy and a shift of the differential scanning calorimetry curves toward lower temperatures. In the presence of nickel, the thermal stability of the amorphous alloy Mg₆₃Ni₃₀Y₇H_x increases with hydrogen saturation. After heating up to the crystallization temperature, the compounds Mg₂NiH_0.3 and YH₂ appear. __________ Translated from Poroshkovaya Metallurgiya, Nos. 3–4(448), pp. 105–111, March–April, 2006.     

The formation and dissociation of magnesium alloy hydrides and their use for fuel storage in the hydrogen car

The formation of hydrides by the reaction of high-pressure hydrogen (300 to 800 psi) with Mg-10Al and Mg-25Ni was studied at 400 and 450°C. Although the reaction kinetics for both alloys can be described by the Johnson-Mehl relationship, the morphology and nature of the reaction products were very different for the two alloys. The temperature dependence of the rates suggests that an interfacial reaction, possibly the transfer of hydrogen from the metal to the hydride, may be the rate-controlling step. One hydride, MgH₂, formed internally in the Mg-10Al alloy as spherical particles of nearly constant size at any time, indicating that nucleation was rapid. The reaction involving Mg-25Ni resulted in two hydrides, MgH₂ and Mg₂NiH₄, the former being more stable and forming first by consuming the primary magnesium phase of the eutectic structure. The hydride advanced into the alloy as a “front”, after which the eutectic plates of Mg₂Ni reacted to form the ternary hydride. Finally, the larger primary plates of Mg₂Ni reacted. Dehydriding of the Mg-10Al alloy hydride also followed the Johnson-Mehl relationship and was found to be complete in 90 min at 300°C, these conditions being favorable for the use of this hydride in vehicles combusting hydrogen. On the other hand, dehydriding of the hydrided Mg-25Ni alloy occurred by a twostep process in which some of the Mg₂NiH₄ dissociated followed by complete dissociation of this hydride and of the MgH₂. Only a small fraction, 10 pct of the available hydrogen could be recovered in several hours at 300°C. The Mg-10Al alloy exhibited a much higher resistance to fragmentation during hydriding than did the Mg-25Ni alloy. An analysis of numerous factors required of hydrides for use in vehicular applications showed that Mg-10Al was much better than Mg-25Ni, although the charging time is much too long.     

Phase equilibria and intermetallic phases in the Ni-Si-Mg ternary system

The Ni-Si-Mg ternary phase diagram has been established after homogenization and slow cooling to room temperature. The chemical compositions of the alloys and their phases were obtained using fully quantitative energy dispersive X-ray spectroscopy (EDS) with standard spectrum files created from intermetallic compounds Mg₂Ni and Ni₂Si. The following intermetallic phases have been observed: (a) four new ternary intermetallic phases, designated as ν, ω, μ, and τ, (b) a ternary intermediate phase Mg(Ni,Si)₂ based on the binary MgNi₂ phase containing Si; (c) three ternary intermetallic phases, η, κ, and ζ, previously reported by the present authors;[10] and (d) Mg₂SiNi₃ (Fe₂Tb type),^[9] previously reported by Noreus et al. ^[8] The MgNi₆Si₆ phase, which was also previously reported,^[7] was not observed at the corresponding composition in the present work. However, the MgNi₆Si₆ phase reported as being of hexagonal symmetry (Cu₇Tb type),^[9] with the lattice parameters a=0.4948 nm and c=0.3738 nm, possibly corresponds to the μ phase (Mg(Si_0.48Ni_0.52)₇) discovered in the present work. The lattice structure of the newly discovered ω phase was determined with the help of the X-ray indexing program TREOR (developed by Werner et al. ^[13]) to be a hexagonal structure of the Ag₇Te₄ type ((Mg_0.52Ni_0.48)₇Si₄) with the lattice parameters a=1.3511 nm and c=0.8267 nm.     

Synthesis of Mg-based composite material with in-situ formed LaH3 and its hydrogen storage characteristics

In this work, a Mg-based composite material with in-situ formed LaH₃, Mg₂NiH₄-LiBH₄ + 20 wt% LaH₃, was prepared by ball milling LiBH₄ and hydrogenated LaMg₂Ni and Mg₂Ni powder mixture, followed by heat treatment at 573 K. The onset dehydrogenation temperature of the composite is reduced by 50 K compared with that of Mg₂NiH₄-LiBH₄. The LaH₃-doped composite shows faster kinetics, absorbing 1.43 wt% hydrogen within 100 s at 423 K, which is 6.5 times faster than Mg₂NiH₄-LiBH₄. Moreover, the composite releases 1.24 wt% hydrogen within 500 s at 573 K, 0.69 wt% higher than Mg₂NiH₄-LiBH₄. The activation energy of the composite is reduced by 8.2 and 80 kJ/mol compared with that of Mg₂NiH₄-LiBH₄ and commercial MgH₂, respectively. The improvement in hydrogen storage properties is attributed to the fact that LaH₃ promotes the generation of nano-sized spongy Mg structure, which has good catalytic activity during the subsequent hydrogenation/dehydrogenation process.     

Thermochemical Analysis of Phases Formed at the Interface of a Mg alloy-Ni-plated Steel Joint during Laser Brazing

The thermodynamic stability of precipitated phases at the steel-Ni-Mg alloy interface during laser brazing of Ni-plated steel to AZ31B magnesium sheet using AZ92 magnesium alloy filler wire has been evaluated using FactSage thermochemical software. Assuming local chemical equilibrium at the interface, the chemical activity–temperature–composition relationships of intermetallic compounds that might form in the steel-Ni interlayer-AZ92 magnesium alloy system in the temperature range of 873 K to 1373 K (600 °C to 1100 °C) were estimated using the Equilib module of FactSage. The results provided better understanding of the phases that might form at the interface of the dissimilar metal joints during the laser brazing process. The addition of a Ni interlayer between the steel and the Mg brazing alloy was predicted to result in the formation of the AlNi, Mg₂Ni, and Al₃Ni₂ intermetallic compounds at the interface, depending on the local maximum temperature. This was confirmed experimentally by laser brazing of Ni electro-plated steel to AZ31B-H24 magnesium alloy using AZ92 magnesium alloy filler wire. As predicted, the formation of just AlNi and Mg₂Ni from a monotectic and eutectic reaction, respectively, was observed near the interface.     

Leaching of nickel from supported nickel waste catalyst using aqueous sulfur dioxide solution

Waste nickel catalyst is an important secondary source for recovery of nickel. Nickel from the waste has been leached out using aqueous SO₂ solution. The initial leaching kinetics is controlled by reaction at the surface involving the adsorption of SO₂ and H⁺ resulting in the formation of product species. A kinetic model based on the above scheme has been presented. The X-ray photoelectron spectroscopy (XPS) studies indicate that easily soluble Ni(OH)₂ or NiO is initially leached out, leaving behind the other nickel species which dissolves at a slower rate.     

Studies on Photocatalytic Performance of MgO Nanoparticles Prepared by Wet Chemical Method

In the present article, we explore a cost-effective and an environmentally benign route to prepare magnesium oxide (MgO) nanoparticles through thermal decomposition of magnesium hydroxide (Mg(OH)₂) nanoparticles. Mg(OH)₂ nanoparticles were prepared using different solvents namely ethylenediamine (EDA) and triethanolamine (TEA) by wet chemical method, and subsequently the as-synthesized Mg(OH)₂ nanoparticles were calcinated at 400°C for 2 h in air to obtain MgO nanoparticles. XRD pattern revealed that as-synthesized Mg(OH)₂ nanoparticles are polycrystalline in nature with hexagonal structure, and after annealing it transforms to MgO nanoparticles with cubic structure. FTIR spectrum of as-synthesized Mg(OH)₂ nanoparticles indicated the OH⁻ antisymmetric stretching vibration of the Mg(OH)₂ and after annealing the sharp peak at 3686 cm⁻¹ disappears, which confirms the complete transformation of hexagonal Mg(OH)₂ to cubic MgO. SEM analysis showed the formation of interfused Mg(OH)₂ nanoflakes and coral-like hierarchical MgO nanostructure made up of stacked nanoflakes. Optical band gap energy of Mg(OH)₂ and MgO nanoparticles prepared using different solvent were estimated using UV–Vis DRS. Degradation of methyl orange was performed to investigate the photocatalytic activity of coral-like hierarchical MgO nanostructure. Results demonstrate that coral-like hierarchical MgO nanostructure possessing large surface area and porous morphology exhibited good photocatalytic degradation of methyl orange.     

Microstructure and phase constituents in the interface zone of Mg/Al diffusion bonding

The microstructure and phase constituent for the Mg/Al diffusion-bonded joint were studied via scanning electron microscope (SEM), microhardness test, electron probe microanalyzer (EPMA), and X-ray diffraction (XRD). The test results indicated that the new compact phase was formed near the transition region of the Mg/Al diffusion interface. There are three new phase layers in the transition region. The microhardness of the diffusion zone is higher than that of the Mg and Al substrate. The fracture morphology mainly consists of a coarse and gray fracture, and the fracture is mainly the mixed fracture of cleavage and intergranular. X-ray diffraction tests indicate that the diffusion zone of the Mg/Al diffusion-bonded joint consists of intermetallic compounds MgAl, Mg₃Al₂, and Mg₂Al₃. With the increase of temperature, the content of Mg₃Al₂ and Mg₂Al₃ phases with good stability was increased.     

Investigations on hydrogen storage properties of LaMg8.52Ni2.23M0.15 （M=Ni, Cu, Cr） alloys

LaMg8.52Ni2.23M0.15 (M=Ni, Cu, Cr) alloys were prepared by induction melting. X-ray diffraction showed that all the three alloys had a multiphase structure, consisting of La2Mg17, LaMg2Ni and Mg2Ni phases. Energy dispersive X-ray spectrometer results revealed that most of Cu and Cr distributed in Mg2Ni phase. La2Mg17 and LaMg2Ni phases decomposed into MgH2, Mg2NiH4 and LaH3 phases during the hydrogenation process. Hydriding/dehydriding measurements indicated that the reversible hydrogen storage capacities of Mg2Ni phase in LaMg8.52Ni2.23M0.15 (M=Cu, Cr) alloys increased to 1.05 wt.% and 0.97 wt.% from 0.79 wt.% of Mg2Ni phase in LaMg8.52Ni2.38 alloy at 523 K. Partial substitution of Cu and Cr for Ni decreased the onset dehydrogenation temperature of the alloy hydrides and the temperature lowered by 18.20 and 5.50 K, respectively. The improvement in the dehydrogenation property of the alloys was attributed to that Cu and Cr decreased the stability of Mg2NiH4 phase.     

Design and Achievement of Metallurgical Bonding of Mg/Al Interface Prepared by Liquid–Liquid Compound Casting via a Co-deposited Cu–Ni Alloy Coating

The metallurgical bonding of Mg/Al bimetal by liquid–liquid compound casting was realized via co-deposition Cu–Ni alloy coating. The metallurgical layer of the Mg/Al bimetal consisted of Cu solid solution, Cu₂Mg and (Al0.7Cu1.3) Mg, Mg solid solution, Al₃Ni₂, and Mg₂Cu. Vickers hardness of the interface was between 149.9 and 209 HV, which was significantly lower than those of Al–Mg intermetallic compounds. The formation mechanism of the interface was attributed to interdiffusion among AZ91D, A356, and Cu–Ni alloy coating.

     

Thermodynamics of O,N, and S in liquid Fe equilibrated with CaO-AI2O3-MgO slags

Nitrogen and S distribution ratios between CaO-Al₂O₃-MgO slags and liquid Fe were measured at 1873 K as a function of Al (or Mg, Ca) content in metal, using CaO, MgO, and A1₂O₃ crucibles. Based on the results for the solubility product of MgO, the equilibrium constant,K _Mg , for the reaction MgO =Mg +O and the first-order interaction parameter,e _O ^Mg (e _Mg ^O ), were estimated to be logK _Mg = -7.8 ± 0.2 ande _O ^Mg = -190 ± 60 (e _Mg ^O = -290 ± 90), respectively. The activities of A1₂O₃ at the slag compositions double-saturated with CaO/MgO, MgO/ MgO A1₂O₃, and MgO Al₂O₃/CaO 2A1₂O₃ components were obtained from the S distribution ratios between slag and metal, coupled with the reported values of sulfide capacities. Nitride capacities were also estimated from the N distribution ratios and the activities of A1₂O₃.     

Fabrication of Al-3 Wt pct Mg matrix composites reinforced with Al2O3 and SiC particulates by the pressureless infiltration technique

In Al-3 wt pct Mg/Al₂O_3p (or SiC _p ) composites fabricated by the pressureless infiltration method, the infiltration behavior of molten metal, the mechanical properties, and the interfacial reactions were investigated. The spontaneous infiltration of the molten Al-3 wt pct Mg alloy into the powder bed occurred at a relatively low temperature (700 °C for 1 hour under a nitrogen atmosphere). Spontaneous infiltration of the molten metal is related to the formation of Mg₃N₂ by the reaction of Mg and nitrogen. The tensile strength and 0.2 pct offset yield strength and elongation tend to decrease with increasing infiltration temperature and time, because of an increased interfacial reaction. In Al-3Mg/Al₂O₃ composites, MgAl₂O₄ was observed at interfaces between Al₂O₃ and the matrix, as well as at oxide films of the Al powder surface. In addition, MgO was observed at interfaces between Al₂O₃ and the matrix. On the other hand, Al₄C₃ was formed at interfaces between SiC and the matrix in Al-3Mg/SiC composites. In addition, MgAl₂O₄ was observed as a reaction product at the interfaces between oxide films of SiC and the matrix, as well as at oxide films of the Al powder surface. Since the Si released as a result of the interfacial reaction is combined with Mg, age hardening can occur by the precipitation of Mg₂Si via T6 treatment.     

Formation of metallic phase on reducing-gas injection in multicomponent oxide melt. Part 2. Density and surface properties

The density and surface tension of melts of ferronickel (0–100% Ni) and oxidized nickel ore are measured by the sessile-drop method, as well as the interface tension at their boundary in the temperature range 1550–1750°C. The composition of the nickel ore is as follows: 14.8 wt % Fetot, 7.1 wt % FeO, 13.2 wt % Fe₂O₃, 1.4 wt % CaO, 16.2 wt % MgO, 54.5 wt % SiO₂, 4.8 wt % Al₂O₃, 1.5 wt % NiO, and 1.2 wt % Cr₂O₃. In the given temperature range, the density of the alloys varies from 7700 to 6900 kg/m³; the surface tension from 1770 to 1570 mJ/m²; the interface tension from 1650 to 1450 mJ/m², the density of the oxide melt from 2250 to 1750 kg/m³; and its surface tension from 310 to 290 mJ/m². The results are in good agreement with literature data. Functional relationships of the density, surface tension, and interphase tension with the melt temperature and composition are derived. The dependence of the alloy density on the temperature and nickel content corresponds to a first-order equation. The temperature dependence of the surface tension and interphase tension is similar, whereas the dependence on the nickel content corresponds to a second-order equation. The density and surface tension of the oxide melt depend linearly on the temperature. The results may be used to describe the formation of metallic phase when carbon monoxide is bubbled into oxide melt.     

Effect of Mg on Solidification Microstructures of Homogenous and Functionally Graded A390 Aluminum Alloys

Hypereutectic Al?CSi alloys are used in components that require high resistance wear and corrosion, good mechanical properties, low thermal expansion and less density. The size and morphology of hard primary silicon particles present in Al?CSi alloys greatly influences the mechanical properties. Addition of Mg leads to formation of intermetallic Mg₂Si phases, which contributes towards the properties of high silicon alloy as well as alters the nature and quantity of primary silicon formed. The high silicon alloy subjected to centrifugal casting leads to the formation of functionally gradient material, which provides variation in spatial and continuous distribution of primary phases in a definite direction exhibiting selective properties and functions within a component. The present study is to evaluate the effect of Mg on solidification microstructures of homogenous and functionally graded A390 aluminium alloys. The addition of Mg from 3 to 5?% in A390 alloy using Al?C20Mg master alloy has shown a transformation from primary silicon rich matrix to Mg₂Si rich matrix. Centrifugal casting shows the gradient distribution of primary silicon and Mg₂Si phases towards the inner periphery of the casting.     

Microstructure Characteristics and Mechanical Properties of Al 413/Mg Joint in Compound Casting Process

Al 413/Mg couples were prepared by the compound casting process. Characterization of the interface by an optical microscope and scanning electron microscope (SEM) showed that a relatively uniform interface composed of three different layers is formed at the interface. The thickness of the interface depended on the melt/insert volume ratio (VR) significantly and was 80?and 470? ??m? in 1.25?and 3?VRs, respectively. The results of the energy dispersive X-ray spectroscopy (EDS), wavelength dispersive X-ray spectroscopy (WDS), and X-ray diffraction analysis showed that the interface layers are mainly composed of Al₃Mg₂, Al₁₂Mg₁₇, and Mg₂Si intermetallic compounds. An accumulation of magnesium oxide films was detected within the (Al₁₂Mg₁₇?+???) eutectic structure of the interface next to the magnesium base metal. Despite different thicknesses of the interface, shear strengths of the Al 413/Mg couples prepared in 1.25?and 3?VRs were almost same. The study of the fracture surfaces of the Al 413/Mg couples revealed that the accumulated magnesium oxide films act as a weak point for initiation of longitudinal cracks and failure of the joint.     

Synthesis,Corrosion and Bioactivity Evaluation of Gelatin/Silicon and Magnesium Co-Doped Fluorapatite Nanocomposite Coating Applied on AZ31 Mg Alloy

In this study, a nano-composite composed of gelatin as the matrix and Si-Mg-FA nano-particles as an additive was deposited on the AZ31 Mg alloy via dip coating method. In addition, a coating composed of MgO, MgSiO₃ and Mg₂SiO₄ phases was applied on the AZ31 Mg alloy by anodizing process. It was found that the Nano-composite coating with a uniform distribution of nano-particles within the gelatin matrix with the thickness of about 9 µm was dense, crack-free and uniform whereas the surface of anodized layer was relatively coarse due to the presence of flaws and micro-cracks. The surface morphology, EDS analysis and FTIR results revealed the ability of nano-composite coated specimen to form the bone-like apatite. Due to the presence of aforementioned phases and special surface features, the anodized specimen possessed higher and lower corrosion resistance than uncoated and nano-composite coated specimens, respectively. The passive coating resistances (R_CT) of nano-composite, anodized specimen and uncoated samples were 2164, 1449 and 1024 Ω cm², respectively.     

The effects of Mg2+, Mn2+, Zn2+, and Al3+ on the nickel deposit during electrowinning from sulfate bath

The presence of impurities like Mg²⁺, Mn²⁺, Zn²⁺, and Al³⁺ during electrowinning of nickel shows several effects. The effects include current efficiency, deposit quality, purity, crystallographic orientation, surface morphology, and polarization behavior. Addition of the impurities did not change the current efficiency significantly but did change the quality and purity of the electrodeposited nickel. Based on the quality of the deposits obtained, the tolerance limits of these impurities in nickel bath were obtained. Although no deviation of nickel structure from fee was observed, the peak height values for different orientations changed with all of the impurities and the values varied with impurity concentration. The surface morphologies of electrodeposited nickel in the presence of impurities also showed changes. The potentiodynamic scan curves for nickel deposition showed deviations in the presence of all the impurities studied. Based on the results, an attempt was made to correlate the various effects.     

A Comprehensive Study of Diffusion Bonding of Mg AZ31 to Al 5754, Al 6061 and Al 7039 Alloys

In the present study, microstructural and mechanical properties of diffusion bonding of AZ31–Mg with Al 5754, Al 6061, and Al 7039 alloys were compared under same conditions. The vacuum diffusion processes were performed at a temperature of 440 °C, the pressure of 29 MPa, and a vacuum of 1?×?10^?4 torr for 60 min. The microstructural characterizations were investigated using optical microscopy and scanning electron microscopy equipped with EDS analysis and linear scanner. The XRD analysis was performed to study phase figures near the interface zone. The results revealed the formation of brittle intermetallic compounds like Al₁₂Mg₁₇, Al₃Mg₂, and their other combinations at bonding interfaces of all samples. Additionally, the hardness of Al alloys seemed to play a key role in increasing diffusion rate of magnesium atoms toward the aluminum atoms, with Al 6061 alloy having the highest diffusion rate. It consequently led to an increase in diffusion rate and thus formation of a strong diffusion bonding between magnesium and aluminum alloys. The highest strength was about 42 MPa for the diffusion bonding between Mg AZ31 and Al 6061. Further investigations on surfaces indicated that the brittle phases especially Al₃Mg₂ caused brittle fracturing.