Mg-based Material Research Articles

Hydrogen adsorption, dissociation, and diffusion on high-index Mg(10[formula omitted]3) and their comparisons with Mg(0001): A systematic first-principles study

We have systematically studied the hydrogen adsorption mechanism, hydrogen dissociation, and diffusion on the high-index experimentally-found Mg(101¯3) surface and made comparisons with the low-index Mg(0001) surface, using density-functional theory calculations. Various possible H adsorption sites and structures on the high-index Mg(101¯3) are considered with H coverage up to eight monolayers. Specifically, the hydrogen adsorption sequence is found to be A1-fcc, A2-fcc, A1-tetra Ⅱ, A2-tetra Ⅱ, A3-fcc, B1-hcp, B2-hcp and B1-octa. The HMgH trilayer with Mg1.60+ and H0.80− is found to be very stable during initial H uptake, while the H electron gain of 0.8 e (i.e., H0.80−) is shown to be a reliable indicator of H-adsorbed Mg(101¯3) stability. Interestingly, on the one hand, H2 dissociation is the role step during H uptake on Mg(101¯3) with an H2 dissociation energy barrier of 0.87 eV, which is consistent with the value on the low-index Mg(0001) from previous first principle calculations. On the other hand, the H diffusion barriers along the closed-packed planes are lower than those perpendicular to the planes, verifying that more feasible diffusion paths are available on the high-index Mg(101¯3). These theoretical findings rationalize the previous joint experimental finding that the high-index Mg(101¯3) dramatically decreases H sorption temperatures, and provide an H adsorption mechanism on high-index Mg surface very different from that on low-index Mg(0001), thus improving the foundation of Mg-based hydrogen storage material designs.

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.

A framework for drug delivery

Materials Chemistry Metal-organic frameworks (MOFs) are attractive candidates for drug delivery if they can be formed from low-toxicity materials. Levine et al. noted that olsalazine, a low-toxicity anti-inflammatory drug used in treatment of gastrointestinal diseases, is tolerated in multigram doses and structurally related to the ligands used to create M-MOF-74. One-dimensional hexagonal pore structures with diameters of 2.7 nm were formed from olsalazine and dications such as Mg2+ or Fe2+. These materials not only displayed a high capacity for H2 adsorption, but they could also be loaded with model drugs such as phenethylamine. Pressed pellets of the Mg-based material released 50% of the olsalazine and 95% of the phenethylamine after 3 hours in phosphate-buffered saline, suggesting applications for multidrug delivery. J. Am. Chem. Soc. 10.1021/jacs.6b03523 (2016).

Preparation, microstructure and thermal properties of Mg[sbnd]Bi alloys as phase change materials for thermal energy storage

Comparing with Al-based phase change material, Mg-based phase change material is getting more and more attention due to its high corrosion resistance with encapsulation materials based on iron. This study focuses on the characterization of Mg36%Bi, Mg54%Bi and Mg60%Bi (wt. %) alloys as phase change materials for thermal energy storage at high temperature. The phase compositions, microstructure and phase change temperatures were investigated by X-ray diffusion (XRD), electron probe micro-analysis (EPMA) and differential scanning calorimeter (DSC) analysis, respectively. The results indicates that the microstructure of Mg36%Bi and Mg54%Bi alloys are mainly composed of α-Mg matrix and α-Mg + Mg3Bi2 eutectic phases, Mg60%Bi alloy are mainly composed of the Mg3Bi2 phase and α-MgMg3Bi2 eutectic phases. The melting enthalpies of Mg36%Bi, Mg54%Bi and Mg60%Bi alloys are 138.2, 180.5 and 48.7 J/g, with the phase change temperatures of 547.6, 546.3 and 548.1 °C, respectively. The Mg54%Bi alloy has the highest melting enthalpy in three alloys. The main reason may be that it has more proportion of α-Mg + Mg3Bi2 eutectic phases. The thermal expansion of three alloys increases with increasing temperature. The values of the thermal conductivity decrease with increasing Bi content. Besides, the activation energy of Mg54%Bi was calculated by multiple DSC technology.

Development of a Mg-based hydrogen-storage material by addition of Ni and NbF5 via milling under hydrogen

Milling under hydrogen was used to prepare samples with a composition of 80 wt% Mg + 14 wt% Ni + 6 wt% NbF5 (named 80Mg + 14Ni + 6NbF5). 80Mg + 14Ni + 6NbF5 had a large effective storage capacity of hydrogen of approximately 5.6 wt% H. The activation of 80Mg + 14Ni + 6NbF5 was done after one storing-releasing cycle. At n = 2 at 593 K, 80Mg + 14Ni + 6NbF5 stored 3.92 and 5.57 wt% H after 2.5 and 60 min, respectively, under 12 bar H2, and released 2.34 and 4.81 wt% H after 10 and 60 min, respectively, under 1.0 bar H2. The following reaction happened during milling under hydrogen and at the early storing-releasing cycles: 14Mg + Ni + 4NbF5 + 7H2 → MgH2 + Mg2NiH4 + Mg + 10MgF2 + 4NbH2. At a fairly low temperature of 423 K, the sample stored 0.28, 0.34, and 0.57 wt% H after 5, 10, and 60 min, respectively. The initial storing rate of 80Mg + 14Ni + 6NbF5 increased as the temperature rose from the room temperature to 573 K since the effect of thermal activation is predominant, and fell as the temperature rose from 573 K to 623 K since the effect of decrease in the driving force for storing reaction is predominant.

气–固法合成制备氢化镁及热力学分析

氢能发展日益壮大，制氢、储氢、运氢成为关键的工程技术问题。氢化镁作为镁基储氢材料，因其储氢量大，密度小，氢气释放易于控制而成为氢燃料电池领域关注的焦点之一。本文采用气–固反应法制备氢化镁，并通过对不同状态的镁(镁蒸汽与固体镁粉)与氢气的在高温高压下的合成反应进行热力学计算和实验，从而论证其大规模生产的工业可行性。热力学分析和试验验证结果表明：相比于镁在蒸汽状态下与氢气反应制备氢化镁而言，工业高纯镁固体粉末与氢气反应制备氢化镁的温度和压强条件要求较低(673 K, 7 MPa, 72 h)，可工业化制备氢化镁。 With the rapid development of hydrogen energy, hydrogen production, storage and transport be-come key issues of engineering technology. MgH2, as an Mg-based hydrogen storage material, has become the center of attention in hydrogen fuel-cell area because it has a high hydrogen capacity with less dense and easy control in hydrogen releasing. In this paper, gas-solid reaction is adopted to prepare MgH2. And a feasibility study in industry is analyzed about reactions between hydrogen with magnesium vapor and powder, respectively, by considering their thermodynamics calculation. The thermodynamics analysis and experimental results show that the temperature and pressure conditions of the reaction between hydrogen and magnesium powder are more easily fulfilled (673 K, 7 MPa, 72 h) than that between hydrogen and magnesium vapor, and that this method can be used in industry.

<i>In Situ</i> Hydrogenation and Desulfurization of CS<sub>2</sub> by Mg-Based Hydrogen Storage Material:Products and Mechanism Analysis

Mg-based hydrogen storage material was prepared by ball milling, and then the material was used to react with CS2. The morphology and hydrogen desorption properties of the hydrogen storage material as well as the CS2hydrogenation product were analyzed. Results show that in situ hydrogenation and desulfurization of CS2happens with the MgH2in the hydrogen storage material as hydrogen donator and desulfurizer at 300 °C and ordinary pressure, and MgS, CH4and H2S are generated from the reaction. There is a coupling relationship between dehydrogenation of the hydrogen storage material and hydrogenation of CS2. The addition of nickel and molybdenum show negative effect on the sulfur fixation capability of the Mg-based hydrogen storage material though they could decrease the dehydrogenation temperature of the material.

Effect of Technological Parameters on Preparation of Mg-Based Foam Materials

As a novel material, Mg-based foam material not only has fantastic physical characteristics, such as low density, high specific surface area, high specific strength and stiffness, and good biocompatibility, but also has special functional properties, for example, electromagnetic wave shielding, vibration reduction, sound absorption, and so on. It can be widely applied to aeronautical and aerospace, military, shipbuilding, transportation, automotive and medical industries. Mg-based foam material was prepared by direct foaming in magnesium alloy liquid in this study, and the effect of technological parameters on the products, such as addition amount of and granularity of SiC particles and MgCO3 particles, stirring temperature, stirring time, stirring velocity, foaming temperature and foaming time, was investigated. The aim of this research was to develop a new technology which could fabricate large scale Mg-based foam material in air condition. The results showed that variations of technological parameters may affect preparation of the foam materials in some extent and resulted in the changes of the products in apparent density, porosity and structural uniformity. The light weight Mg-based foam with homogeneous pores could be obtained by suitable combination of the technological parameters.

Magnesium Based Sol-Gel Derived Bioactive Glass Ceramics for Dental Tissue Regeneration

Scaffold-based tooth engineering is currently the most popular approach towards replacing dental tissues or even engineering a bio-tooth. Although, various scaffold materials have been employed in tooth regeneration, the scaffold-based tooth design has, until now, achieved only limited success. Recently, bioactive Mg-based ceramics have attracted interest as Mg plays an important role on skeletal metabolism and affects the quality and structure of hard dental tissues. Mg has been reported to improve the mechanical properties of calcium phosphate ceramics, control biodegradation rate and stabilize the cell-material interface improving cell attachment and growth. The aim of this study was the development of an experimental Mg-based ceramic material, with enhanced bioactivity and adequate mechanical properties, in order to be potentially used in dental tissue regeneration. The Mg-based ceramic was prepared by the sol-gel method, while the stabilization was performed at 1300, 1400 and 1450oC in order a fully crystalline material to be obtained. The characterization of the materials -before and after immersion is Simulated Body Fluid (SBF)- was performed by Fourier Tranform Infrared Spectroscopy (FTIR), X-Ray Diffractometry (XRD) and Scanning Electron Microscopy associated with an EDS analyzer (SEM-EDS), while the flexural strength of uniaxially pressed pellets was measured using a universal testing machine for 3- point bending tests (Instron 3344). FTIR spectra and XRD patterns of all powder samples before immersion in SBF solution confirmed the presence of three crystalline phases; akermanite, merwinite and diopside. The onset of apatite formation on the surface of all powders was observed even after three days of immersion, while the apatite formation on the surface of the sintered pellets was slightly delayed. Flexural strength values were in the range of 30Mpa. In conclusion, Mg-based glass-ceramics attain adequate mechanical integrity and high rate of bioactivity and could be potentially used in the construction of ceramic scaffolds for dental tissue regeneration.

Influence of yttrium addition on properties of Mg-based sacrificial anode

To improve lower current efficiency of Mg-based sacrificial anode, a Mg-based sacrificial anode material with yttrium addition was investigated. Its electrochemical properties were evaluated by the galvanostatic method, and its microstructure and constitution were characterized by metallurgical microscope and X-ray diffraction. The results showed that, the addition of yttrium refined dentrite grains, maximized current efficiency, and minimized potential of magnesium sacrificial anode. When 0.1% yttrium was doped, the anode showed the highest current efficiency, 62.5%, which improved its current efficiency by 14%.

Research and Development of Nano-Composite Materials for Hydrogen Storage

Hydrides with light elements such as MgH2, LiH, NH3 and NH3BH3 are known as high hydrogen containing materials. However, the high work temperature and the slow reaction rate limit the practical application of hydride systems. Those properties can be improved by the nano-composite materials. The nano-composite materials for hydrogen storage encompass a catalyst and composite hydrides at the nanometer scale. The catalyst increases reaction rate. The thermodynamic stability of the nano-composite materials can be controlled by the composite hydrides. In addition, the hydrogen absorption kinetics is accelerated by the nano-size materials and they may change the thermodynamic stability of the materials. In this study, we reviewed our experimental results on hydrogen storage properties of light weight nano-composite materials. The Mg-based nano-composite material with Nb2O5 showed excellent kinetics as compared with that of Mg. The Li-Mg-N-H system absorbed and desorbed above 5.5 mass % of H2 at 423K (8LiH ＋ 3Mg(NH2)2 3Li2.667MgN2H1.333＋8H2). We found that the H2 absorption and desorption of the MH-NH3 (M: Li, Na, K) system takes the following reaction path, MH + NH3  MNH2 + H2.

Single-crystal MgS nanotubes: synthesis and properties

The synthesis of the (rocksalt phase) single-crystal square-like cross-sectional MgS nanotubes via a thermal reaction process was reported for the first time in the family of II–VI sulfide semiconductors, which enriches the wide spectrum of diverse inorganic nanotubular structures. As-grown MgS nanotubes are structurally uniform single-crystals; an individual faceted tube is enclosed by four {020} crystal planes and grows along the [001] orientation. The MgS nanotubes exhibited efficient hydrogen-storage capacity of ∼ 2.2 wt% at room temperature under hydrogen pressure of 33.6 atm and one intensive cathodoluminescence emission band centered at ∼ 688 nm. The new concept established here will be very helpful in developing other types of Mg-based material nanotubes with high a hydrogen-storage capacity. Moreover, the MgS nanotubes' cavity could be filled with different semiconducting materials with various band gaps to give interesting electrical and optical nanodevices.

Boron nitride nanotubes as nanocrucibles for morphology and phase transformations in encapsulated nanowires of the Mg–O system

Boron nitride (BN) nanotubes were filled with nanowires made of Mg-containing compounds: a metallic Mg-based material; a MgO-based phase; and a thermally and chemically unstable oxygen-rich MgO 2-based phase. Crystallography of the tubes and their fillings was studied using high-resolution transmission electron microscopy, electron energy loss spectroscopy and energy dispersive X-ray analysis. These compounds displayed markedly different behavior inside BN nanotube channels during in situ TEM electron-irradiation-induced and thermal heating. The interplay between phases, their morphology and phase transformations were observed under heating. Thus the applicability of chemically and thermally stable BN nanotubes as one-dimensional nanocrucibles for novel nanoscale metallurgy/chemistry in the practically important Mg–O system has been thoroughly documented. This opens up a pathway for BN nanotube-channel-confined reactions in other inorganic systems.

Fabrication of Bulk Mg–Cu–Ag–Y Glassy Alloy by Squeeze Casting

A new Mg 65 Cu 15 Y 10 Ag 10 alloy having large glass-forming ability has been developed to produce bulk Mg-based glass material. Partial replacement of Ag with Cu in a Mg 65 Cu 25 Ag 10 alloy led to a significant improvement of glass-forming ability. The addition of Ag significantly decreases the melting temperature and also satisfies conditions of a multi-element system with a deep eutectic, large atomic-size difference between its components and a large electronegativity difference between the components for good glass-forming ability. Injection casting produced bulk metallic glass of Mg 65 Cu 15 Y 10 Ag 10 alloy having a diameter up to 6 mm. Squeeze casting was able to produce larger bulk metallic glass with Mg 65 Cu 15 Y 10 Ag 10 alloy having diameter of 10 mm, due to the rapid heat extraction and undercooling of the liquid alloy, by applying pressure during solidification.

5614684 Superplastic Mg-based composite material and method for production thereof

Data declustering is an important issue for reducing query response times in multi-disk database systems. In this paper, we propose a declustering method that utilizes the available information on query distribution, data distribution, data-item sizes, and disk capacity constraints. The proposed method exploits the natural correspondence between a data set with a given query distribution and a hypergraph. We define an objective function that exactly represents the aggregate parallel query-response time for the declustering problem and adapt the iterative-improvement-based heuristics successfully used in hypergraph partitioning to this objective function. We propose a two-phase algorithm that first obtains an initial K-way declustering by recursively bipartitioning the data set, then applies multi-way refinement on this declustering. We provide effective gain models and efficient implementation schemes for both phases. The experimental results on a wide range of realistic data sets show that the proposed method provides a significant performance improvement compared with the state-of-the-art declustering strategy based on similarity-graph partitioning.

Attenuation of glass dissolution in the presence of natural additives

The dissolution kinetics of silicate glasses in aqueous environments in systems which included a variety of natural crystalline solids in addition to the glass itself and the aqueous phase are reported. The results demonstrate the possibility of a dramatic decrease in the rate of dissolution of silicate glass in the presence of certain varieties of olivine-based materials. This decrease in dissolution rate was shown to be due to the fact that these additives consist mostly of Mg-based material but also contain minor amounts of Al and Ca. The combined presence of Mg with these minor species affected the corrosion rate of the glass as a whole, including its most soluble components such as boron. This study has potentially important implications to the durability of glasses exposed to natural environments. The results may be relevant to the use of active backfill materials in burial sites for nuclear waste glasses, as well as to better understanding of the environmental degradation of natural and ancient glasses.