Transformation Of Mg Research Articles

A model for the precipitate transformation of Mg–Si-rich clusters into Mg5Si6 β″ in Al–Mg–Si aluminum alloys

Abstract A model is developed that describes the kinetics of precipitate transformations in the course of natural and artificial aging of Al alloys containing Mg and Si additions. In our approach, the disordered Mg–Si-rich clusters, which form during natural aging in the highly supersaturated Al matrix, can directly transform into the monoclinic Mg5Si6 (β″), without prior dissolution of the clusters and independent nucleation of β″ in the Al matrix. The transformation rate is evaluated with classical nucleation theory (CNT), assuming that the clusters represent an infinitely large matrix phase in which the β″ precipitates can nucleate. The adapted CNT model is described, and the basic features of the precipitate transformation are discussed in a parameter study. The model can also account for the observation that, during natural aging, the parent clusters occur in a variety of Mg to Si ratios, all of which have a characteristic probability of either transforming into the β″ phase or dissolving.

Growth mechanism and corrosion resistance of layered double hydroxide film on magnesium alloy without external addition of magnesium and aluminum salts

This study first reports in-situ growth of layered double hydroxide (LDH) coatings on magnesium alloy surface without external adding magnesium (Mg2+) and aluminum (Al3+) salts with the aid of a chelating agent at ambient pressure and relatively low temperature (≤ 95 °C). The morphology, composition, and structure of the deposits on the magnesium alloy surface were analyzed using scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), etc. Combined with open-circuit potential (OCP)-time curves, the mechanism of growth and formation process of the LDH film was proposed. The process was divided into four stages, i.e., dissolution of the Mg substrate, formation of Mg(OH)2, nucleation of LDH by transformation of Mg(OH)2 phase, and growth of LDH phase. The corrosion resistance of the LDH coating before and after treatment with vanadate and tungstate was evaluated through electrochemical impedance spectroscopy (EIS), Tafel curves, and immersion measurements. Compared to bare magnesium alloy and pristine and vanadate-treated LDH, the LDH coating modified with tungstate exhibited the most effective corrosion protection for magnesium alloy AZ31, without obvious signs of corrosion after exposure to a 3.5 wt% NaCl solution for seven days.

Why Hydrogen Dissociation Catalysts do not Work for Hydrogenation of Magnesium.

Provision of atomic hydrogen by hydrogen dissociation catalysts only moderately accelerates the hydrogenation rate of magnesium. They shed light on this well-known but technically challenging fact through a combined approach using an unconventional surface science technique together with Density Functional Theory (DFT) calculations. The calculations demonstrate the drastic electronic structure changes during transformation of Mg to MgH2 , which make fractional hydrogen coverage on the surface, as well as substoichiometric hydrogen content in the bulk energetically unfavorable. Reflecting Electron Energy Loss Spectroscopy (REELS) is used to measure the surface and bulk plasmon during hydrogen sorption in magnesium. The measurements show that the hydrogenation proceeds via the growth of magnesium hydride without the presence of chemisorbed hydrogen on the metallic magnesium surface exactly as indicated by the calculations. This is due to the low stability of sub-stoichiometric amounts of chemisorbed H correlating with the unfavorable charge state of Mg. They are merely bound to the unchanged adjacent Mg layers, thereby explaining the failure of classical hydrogenation catalysts, which effectively only hydrogenate Mg in their direct vicinity. The acceleration of hydrogen sorption kinetics in Mg must affect the polarization in the interface between Mg and MgH2 during hydrogenation.

Effect of aging treatment on the mechanical property and precipitation transformation of Mg–Co–Y alloy

The strength and plasticity of magnesium (Mg) alloys have always been of significant concern. Here, it explores how the mechanical properties and precipitation transformation of the as-cast Mg-0.9Co-4.5Y (at.%) alloy are affected by aging hardening. The results demonstrate that the ultimate compressive strength (UCS) and compressive yield strength (CYS) of the as-cast Mg-0.9Co-4.5Y (at.%) alloy at peak hardness reach 604.8 MPa and 401.5 MPa respectively, while the compression rate (ε) of that after solution-treated reaches 21.9%. For the above changes in malleability and strength, we conduct an in-depth investigation of the impacts of phase composition, LPSO structure, and matrix precipitation. We find that the improvement of malleability is linked to the reduction of the volume fraction of LPSO phase after solution treatment, while the substantially increase of CYS after peak-aging is related to the dispersion strengthen of MgYCo4 phase and precipitation of β′ and β′′ phases, in which the precipitation of β′ and β′′ phases plays a leading role. This study uncovers the mechanical property and microstructure evolution of Mg-0.9Co-4.5Y (at.%) alloy in the aging response process and provides ideas for the performance regulation of Mg–Co–Y alloys.

The adaptable effect of Ru on hydrogen sorption characteristics of the MgH2 system

In this study, a MgH2–Ru composite is prepared by mechanical ball milling of MgH2 and Ru powders. The microstructural analysis revealed the uniform distribution of Ru nanoparticles in the MgH2 matrix and the formation of intermetallic compounds (i.e. Mg6.2Ru and Mg1.5Ru) after dehydrogenation of the composite. The substantial improvements in the de/hydrogenation properties of MgH2 are due to the adjustable catalytic role of Ru under low temperature and pressure conditions. MgH2–Ru composite started to release hydrogen at an onset temperature of 300 °C, much lower than the mechanically milled pure MgH2 (350 °C). Hydrogen absorption of the MgH2–Ru composite is relatively fast at 350 °C and stored 6.1 wt% in 5 min. At the same temperature, the hydrogenated MgH2–Ru composite released all stored hydrogen in less than 5 min. Compared with the catalyst-free MgH2, the hydrogenation and dehydrogenation activation energies of the MgH2–Ru composite are reduced to 65.12 ± 2.4 kJ/mol H2, and 97.46 ± 4.15 kJ/mol H2, respectively. In addition, it further demonstrated how the reversible transformation of Mg–Ru intermetallic phases induces the thermodynamic destabilization of the MgH2 system. The presence of Ru not only facilitated the breaking of the Mg–H bond but also provided very good catalytic interfaces for enhanced de/hydrogenation properties of MgH2.

MOF-derived Ni nanoparticles dispersed on monolayer MXene as catalyst for improved hydrogen storage kinetics of MgH

We designed a state-of-art catalyst Ni@C-MXene, which provides ample Ni and Ti active sites to significantly promote the hydrogen storage performance of MgH 2 . Experimental methods and theoretical calculations reveal that the in-situ formed Ti 0 facilitates the mutual transformation of Mg 2 Ni/Mg 2 NiH 4 , which is called “facilitated hydrogen pump” effect in this work. • Monolayer MXene was used as the functional carrier to undertake Ni nanoparticles derived from Ni-MOFs. • Striking improvements in hydrogen storage properties were achieved for MgH 2 when the catalyst was added. • DFT calculations revealed the effect of in-situ formed Ti 0 on the Mg 2 Ni/Mg 2 NiH 4 mutual transformation. • A concept of “facilitated hydrogen pump” effect was proposed. A novel catalyst—MOFs derived Ni nanoparticles dispersed on exfoliated monolayered MXene functional carrier was prepared and introduced into MgH 2 in this work. Striking improvements in hydrogen storage properties were achieved for MgH 2 when the catalyst was added. Concisely, the hydrogen releasing peak temperature of the MgH 2 + 10 wt% Ni@C-MXene is 241.1 °C, about 120.2 °C lower than that of the additive-free MgH 2 . According to Kissinger method, the dehydrogenation activation energy of the MgH 2 + 10 wt% Ni@C-MXene composite is calculated to be 54.79 kJ mol −1 , over 60% lower when compared with the pristine MgH 2 (145.08 kJ mol −1 ). At 300 °C, the MgH 2 + 10 wt% Ni@C-MXene composite releases about 5.6 wt% hydrogen within 2 min, while only 2 wt% hydrogen is desorbed even the dehydriding time prolongs to 60 min for the pure MgH 2 . In addition, the completely dehydrogenated MgH 2 + 10 wt% Ni@C-MXene exhibits eminent hydrogen absorption performance, with approximate 5 wt% hydrogen uptaken within 2 min under 3.2 MPa hydrogen pressure at 150 °C. Moreover, an excellent hydrogen cycling stability is achieved in the MgH 2 + 10 wt% Ni@C-MXene without decay for both capacity and kinetics after 10 cycles. Beside the regular XRD, XPS and TEM techniques to clarify the evolution of Ni and Ti during hydrogen de/absorption cycling, more importantly we performed the first principle based calculations to reveal how the in-situ formed Ti 0 would affect the Mg 2 Ni/Mg 2 NiH 4 mutual transformation. Apart from the nano confinement effect of MXene for Ni/Mg 2 Ni/Mg 2 NiH 4 , the in-situ formed Ti 0 from MXene also favors the “hydrogen pump” effect of Mg 2 NiH 4 due to the decreased formation energy E f under the assistance of Ti 0 . Through such a synergistic “nano-confinement and facilitated hydrogen pump” effect, the hydrogen de-/absorption kinetics of MgH 2 is significantly accelerated.

Temperature-induced solvent assisted single-crystal-to-single-crystal transformation of Mg(II)-Ln(III) heterometallic coordination polymers

Two new heterometallic coordination polymers (CPs) [Ln2 (pydc)6Mg3(H2O)6]·11H2O (Ln ​= ​Eu (1), Tb (2); H2pydc ​= ​pyridine-2,6-dicarbolylic acid) were synthesized by solvothermal method at 120 ​°C in 48 ​h. Interestingly, after being left in the mother liquor for 3 days at room temperature, the crystal structures of the coordination polymers transform into anionic complexes 2 [Mg(H2O)6]·2 [Ln (pydc)3]·2Him·im•8H2O (Ln ​= ​Eu (3), Tb (4); im ​= ​imidazole; Him ​= ​protonated imidazole) by single-crystal-to-single-crystal transformation. The four complexes were characterized by elemental analysis, IR, TG, XRD as well as single-crystal X-ray diffraction. Coordination polymers 1 and 2 exhibit three-dimensional network structure and their topology symbol is {44.62}3{49.66}2, whereas complexes 3 and 4 are zero dimensional molecules. The luminescence properties of the complexes were determined at solid state. They show characteristic emission spectra of Eu(III) and Tb(III) ions, respectively. The quantum yield Фtotal is 48.42 ​± ​10%, 95.65 ​± ​10%, 44.22 ​± ​10%, and 76.97 ​± ​10% for coordination polymers 1 (Mg–Eu), 2 (Mg–Tb), 3 (Mg–Eu), and 4 (Mg–Tb), respectively. The corresponding fluorescence decay lifetime of 1–4 is τobs1 ​= ​1884.72 ​± ​1.51, 1777.75 ​± ​1.45, 1625.17 ​± ​1.40, and 1487.75 ​± ​1.36 ​μs? The effect of Mg(II) on the fluorescence properties of the lanthanide coordination polymers was investigated.

Thermochemical transformation and reversible performance of Mg(NH2)2–NaMgH3 system

Reversible hydrogen uptake of Mg(NH2)2–MgH2 system has been achieved by the introduction of Na for the first time. The thermochemical and mechanochemical transformations of Mg(NH2)2-xNaMgH3 (x = 0.5, 1 and 2) composites have been investigated through structural characterizations and gas desorption analyses. The hydrogenation property and reaction mechanism of Mg(NH2)2–NaMgH3 have been discussed. Experimental results indicate that the replacement of NaMgH3 for MgH2 can extensively suppress ammonia emission and improve the hydrogen desorption property of Mg(NH2)2–MgH2 system. For Mg(NH2)2–NaMgH3 system, its thermochemical reaction at low temperature is quite similar to the reaction under mechanochemical process. At high temperature (190 °C), the formation of NaMg(NH2)(NH) is detected. The introduction of Na alters the reaction route and enhances the reaction enthalpy of Mg(NH2)2–MgH2 system. The compound of NaMg(NH2)(NH) is synthesized by the reaction of MgNH and NaNH2 and it can reversibly store 1.8 wt% of hydrogen at 10 atm and 190 °C. The reversible cycling between NaMg(NH2)(NH) and Mg(NH2)2 is responsible for the partial reversible hydrogenation of Mg(NH2)2–NaMgH3 system.

Immobilization of enzymes into nanofiber membranes via electrospinning and its application in natural sweetener production

Non-caloric artificial sweeteners (NAS) are currently the world's most widely used food additives, which are considered safe and contributed to good health. But recent research shows that there are still controversies. Therefore, natural sweeteners had gained much attention as NAS substitutes. Recently, the fastest growing market of natural sweetener is the sweeteners made from monk fruit, because its extracts are highest in sweetness among various natural sweeteners and parts of the sweetness compounds have significant anti-diabetic activity. However, one of the components in monk fruit extracts called Siamenoside I (S I), which found to be the most sweetness compound and taste most closely to sucrose, are relatively low in contents. In addition, the Mogroside III E (MG III E), which is lower in sweetness compared to S I but with significant anti-diabetic properties, are also low in contents in the natural monk fruit extracts. As the results, the developing of methods to enrich the contents of S I and MG III E in monk fruit extracts and related products are the goals for the current natural sweetener manufacturers. The bitter tastes and flavors of saponins containing functional foods and related beverages are still the issues to be addressed. For example, the modification of glycoside linkage patterns of saponins including oleuropeins, ginsenosides, and momordicosides could achieve the debittering purpose and meet the consumers' preferences. Therefore, the goals of this research are to immobilize specific enzymes using electrospinning. Together with the high throughput microreactor, and the continuous packed-bed column, we suppose that we could obtain a fair amount of S I and MG III E through enzyme transformation of MG V and improve the taste of monk fruit extracts as natural sweeteners. Support or Funding Information This research was supported by the by the National Science Council of Taiwan (NSC Grant 106-2218-E-029-002-MY2). The screening of yeast transformants having its exg1Δ::kanMX4 replaced by DbExg1-His-URA3 cassette which has S I bioconversion activity A. Ura− and G418 resistance selection. B. The genotype confirmation of yeast transformants. Successful transformants have 3523 b.p product. Numbers represent candidates relative to candidates in A. C. Screening of transformants with siamenoside I production specificity. Peak 1, mogroside V; 2, siamenoside I; 3, mogroside IV; 4, mogroside IIIE. SEM images and size distribution of electrospun nanofibrous membrane: (Upper panel) PVA; (Lower panel) cross-lined PVA. SEM images and size distribution of electrospun nanofibrous membrane: (Upper panel) PVA with 0.5% of the enzyme; (Lower panel) cross-lined PVA with 0.5% of the enzyme. SEM images and size distribution of electrospun nanofibrous membrane: (Upper panel) PVA with 2.0 % of the enzyme; (Lower panel) cross-lined PVA with 2.0% of the enzyme. This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Supported Ag Catalysts on Mg–Al Oxides toward Oxidant-Free Dehydrogenation Reaction of Benzyl Alcohol

Oxidant-free dehydrogenation of alcohols has attracted considerable attention, owing to the largely improved utility value of alcohols. Herein, mixed metal oxides (MMOs) via topological transformation of Mg–Al hydrotalcite precursors were prepared and used as support for the immobilization of metallic Ag nanoparticles. The resulting Ag/MgAl-MMO shows an excellent catalytic performance toward oxidant-free dehydrogenation of benzyl alcohol (conversion of benzyl alcohol: 95.9%; selectivity of benzaldehyde: 93.3%), which is close to platinum-group catalysts commonly used in this reaction. A combination study based on a series of characterization methods reveals a synergistic catalysis between Agδ+ and medium-strong acid/basic sites (Mgδ+–Oδ−) from support: Agδ+ facilitates the breakage of α-C–H bond while Mgδ+–Oδ− accelerates the cleavage of O–H bond. This work provides an effective approach to enhance catalytic behavior toward dehydrogenation reactions by virtue of metal–support interactions.

A vacuum calcination route to high-surface-area MgO nanoplates for superior arsenate adsorption and catalytic properties

Porous MgO nanoplates with high surface area has been synthesized by a vacuum calcination route using industrially available Mg(OH)2 as the precursor. The vacuum calcination not only promoted the phase transformation of Mg(OH)2 to MgO at a low temperature (300 °C), but also inhibited the thermally-induced particle growth and pore coalescence, leading to the formation of MgO nanoplates with fine grain sizes (5.5 nm), ultrasmall pores (2–4 nm) and high surface area (390 m2 g−1). The as prepared MgO nanoplates exhibited superior arsenic adsorption properties with a maximum adsorption capacity of 481.0 mg g−1, as well as excellent catalytic activity for the Claisen-Schmidt condensation reaction.

In-Situ Atomic-Scale Phase Transformation of Mg under Hydrogen Conditions

The magnesium hydrogenation issue poses a serious obstacle to designing strong and reliable structural materials as well as offering a safe alternative for hydrogen applications. Understanding phase transformation of magnesium under hydrogen gas plays an essential role in developing high-performance structural materials and hydrogen-storage materials. Herein, we report in-situ atomic-scale observations of phase transformation of Mg and Mg-1 wt % Pd alloy under hydrogen conditions in an aberration-corrected environmental transmission electron microscope. Compared with the magnesium hydrogenation reaction, the magnesium oxidation reaction predominately occurs at room temperature even under pure hydrogen gas (99.9%). In comparison, magnesium hydrogenation is readily detected in the interface between Mg and Mg6Pd, due to the catalytic role of Mg6Pd. Note that the nanoscale MgH2 compound transfers into MgO spontaneously, and the interface strain remarkably varies during phase transformation. These atomic-level...

Syntheses of two coordination polymers with rutile-type topology and the single-crystal-to-single-crystal transformation of Mg(ii) complex induced by methanol

Two isomorphous 3D frameworks with rutile topology based on isonicotinate, [Mn(IN)2]·H2O (1) and [Mg(IN)2]·H2O (2), were prepared. Compound 1 shows excellent stability in alcohols, while compound 2 reveals a rare single-crystal-to-single-crystal transformation from a 3D structure to a mononuclear molecule of [Mg(IN)2(CH3OH)4] (3) by soaking in methanol.

Dynamic electrochemical impedance spectroscopy (DEIS) studies of AZ31 magnesium alloy in simulated body fluid solution

The change in impedance values as a function of potential indicated the transformation of Mg from its passive to active state.

Phase transformation of Mg–Li alloys induced by super-high pressure

The effect of superhigh pressure (4GPa) on phase transformation behavior and mechanical properties of a duplex phase Mg–7wt%Li alloy has been investigated in the temperature range from 450 to 1150°C. Hardness and tensile strength of Mg–7wt%Li alloy have been significantly improved by super-high pressure treatment at 700°C for 120min. The microstructural observation is confirmed that super-high pressure is of benefit for phase transformations from bcc-Li3Mg7 to hcp phases and hcp-Li3Mg17 to hcp-Li0.92Mg4.08. The improved mechanical properties are mainly associated with the reduction of bcc-Li3Mg7 phase and the formation of {10−11} compression twins in hcp-Li0.92Mg4.08 phase.

Molecular structural transformation regulated dynamic disordering of supramolecular vesicles as pH-responsive drug release systems

The spontaneous release of drug payloads in the whole body always results in the compromised drug bioavailability and ultimate therapeutic efficacy. To achieve enhanced therapeutic efficacy and reduced side effects, pH-responsive targeted drug delivery systems have been studied due to their enhanced tumor accumulation and controllable maximum drug release feature. The present study described a co-assembly constructed by a pH responsive molecule (i.e., malachite green carbinol base (MG)) and liposome for highly efficient doxorubicin (DOX) release in tumor cells (MG–DOX⊂L). The structural transformation of MG effectively regulates the drug release profile in acidic environment. The pH-responsive sensitivity of co-assembly can be fine-tuned by altering the mixing ratios of building blocks with pH responders (i.e., MG molecules). MG–DOX⊂L was beneficial for the DOX release at pH5.0 and showed a higher cytotoxicity in KB cells owing to the pH-responsive drug release in acidic organelles following endocytosis pathway. In vivo tumor targetability and growth inhibition were evaluated in KB cell-xenografted nude mice. We have demonstrated that effective tumor growth inhibition in vivo is attributed to the synergistic contributions from highly efficient cellular entry and responsive intracellular release of DOX from MG–DOX⊂L.

Zebra-Striped Fibers in Relation to the H2 Sorption Properties for MgH2 Nanofibers Produced by a Vapor–Solid Process

MgH2 is a promising candidate for solid-state H2 storage applications. To improve the H2 sorption kinetics, highly pure MgH2 nanofibers were synthesized by a vapor–solid process. The fibers showed improved sorption kinetics compared with bulk MgH2, which were investigated by a volumetric pressure–composition–temperature method. To choose a meaningful kinetic model that represented the physical reality and intrinsic kinetic parameters for the unique fiber structure, theoretical modeling of the sorption data and metallographic examinations of the in situ dehydrogenation process and partially hydrogenated samples were carried out. The Johnson–Mehl–Avrami (JMA) model, which is based on the theory of nucleation and growth transformation, was selected for the kinetic mechanism analysis of the hydrogenation/dehydrogenation of the fibers. The theoretical modeling by the JMA model indicated that the phase transformation of Mg to MgH2 (or of MgH2 to Mg) in the individual fibers proceeded one-dimensionally along the...

Photodegradation of malachite green using UV–vis light from two microwave-powered electrodeless discharge lamps (MPEDL-2): Further investigation on products, dominant routes and mechanism

In this research, we choose photolysis degradation (PD) course and H2O2-enhanced PD (HPD) course using UV–vis light from two microwave-powered electrodeless discharge lamps (MPEDL-2) as simplified models. The results verified that (1) ∼70% and 99.7% of MG were removed in PD and HPD courses within 5min irradiation, and PD course was proved to be dependent on OH and O2-, (2) major routes were related to transformation of MG into malachite green carbinol base (MGCB), which could be further decomposed into 4-dimethylaminobenzophenone (DLBP), and (3) after 0.5min irradiation, PD course verified that ∼30% and 1% of MG was converted into MGCB and DLBP; for comparison, HPD course demonstrated that ∼12.9% and 28.5% of MG was transformed into MGCB and DLBP. Accordingly, we draw conclusions that degradation mechanism of MG could be revised as seven steps with MGCB as a key product and pH variation of aqueous dyes solution played minor role. Additionally, these conclusions were also enlightened for degradation of MG by advanced oxidation process.

Investigation of the optical properties of Mg(OH)2 and MgO nanostructures obtained by microwave-assisted methods

Two simple methods for the synthesis of Mg(OH)2 nanostructures, MgO nanoflakes and MgO/Mg(OH)2 nanocomposite using a conventional microwave oven are reported. The first method includes the preparation of Mg(OH)2 by a simple reaction of magnesium powder with deionized water under microwave radiation. The second approach relates to the transformation of Mg(OH)2 to MgO nanoflakes and grass-like nanostructures by rapid microwave hybrid heating using a SiC-based composite susceptor. The as-synthesized samples have been characterized by X-ray diffraction (XRD) and Field Emission Scanning Electron Microscope (FESEM) The optical properties of the samples are investigated using UV–visible spectroscopy to study the reflective index and optical dielectric constant.

Effect of Pulse Frequency on Corrosion Behavior of AZ91 Mg Alloy Treated by Microarc Discharge Oxidation Coating

The paper demonstrated the anti-corrosion properties of an AZ91 Mg alloy fabricated via microarc discharge oxidation under an AC condition with various pulse frequencies ranging from 60 Hz to 2000 Hz. The structural features and phase compositions of the coating layers were characterized by utilizing scanning electron microscope and X-ray photoelectron spectroscopy. The optimum frequency for the coating layers with thick, uniform thicknesses was found to be 500 Hz for the conditions used in this study. This fact was explained by the change in the mode of spark discharge during coating, resulting in the occurrence of surface cracks as well as the transformation of Mg(OH)2 to MgO. Potentio dynamic polarization tests in 3.5 mass% NaCl solution revealed that the sample coated at a frequency of 500 Hz exhibited a corrosion potential of −1.42 V (vs. Ag/AgCl), suggesting a better corrosion resistance as compared to the other conditions.