Introduction Of Magnesium Research Articles

Enhanced near-infrared optical transmission in zinc germanium phosphide crystals via precise magnesium doping.

A zinc germanium phosphorus (ZnGeP2) crystal with a chalcopyrite structure is an efficient frequency converter in the mid-infrared region. However, point defect-induced optical absorption at the pumping wavelength (near infrared region) blocked the further application of ZnGeP2. To alleviate the absorption losses caused by point defects, in situ magnesium doping compensation was presented during the ZnGeP2 bulk crystal growth process via the vertical Bridgman method. Combined with theoretical calculations, the structural distortion of the magnesium-doped ZnGeP2 crystals in different orientations was illustrated. The thermodynamic and kinetic stability of the magnesium-doped ZnGeP2 structure were demonstrated. The transmission results indicated the improvement of transmittance within a wavelength range of 1.8-2.4 μm when doped with magnesium, which revealed the powerful ability of the appropriate dopant in optimizing near-infrared optical properties. Thus, the introduction of magnesium is a practical approach to improve the transmittance performance and extend the pumping source wavelengths of ZnGeP2 crystals.

Structural features of Cu2MgxZn1−xSnS4 solid solution films for third-generation solar cells

The paper studies the influence of the ratio of Mg/Zn molar concentrations in the precursor (0 ≤ y ≤ 0.5) on the structural, substructural, optical characteristics and chemical composition of Cu2MgxZn1−xSnS4 films deposited by the spray pyrolysis method from molecular solutions. The data of X-ray structural studies indicate the formation of single-phase films with the structure of kesterite. The single-phase structure is also confirmed by studies of Raman spectra for samples obtained at y ≤ 0.3. Chemical analysis of the films confirms the successful inclusion of Mg in thin layers up to the level of (5.5–6.7) at%. An increase in the total amount of Mg has little effect on the concentration of all elements except zinc. The introduction of magnesium changes the lattice constants of the material, the sizes of coherent scattering regions, the level of microdeformations, and the density of dislocations in the films. At the same time, the layers obtained at y = 0.1 have the minimum total concentration of dislocations (0.73·1017 lin/m−2). Thus, replacing zinc with magnesium increases the quality of the solid solution at concentrations y < 0.3. The band gap of the undoped Mg compound was found to be 1.47 eV, and for the Mg-doped samples it decreases from 1.28 eV (y = 0.1) to 1.22 eV (y = 0.5). Thus, based on the obtained results, the Cu2MgxZn1−xSnS4 solid solution can be considered as an inexpensive material for creating absorption layers of thin-film solar cells.

Detecting Cage Crossing and Filling Clusters of Magnesium and Carbon Atoms in Zeolite SSZ-13 with Atom Probe Tomography.

The conversion of methanol to valuable hydrocarbon molecules is of great commercial interest, as the process serves as a sustainable alternative for the production of, for instance, the base chemicals for plastics. The reaction is catalyzed by zeolite materials. By the introduction of magnesium as a cationic metal, the properties of the zeolite, and thereby the catalytic performance, are changed. With atom probe tomography (APT), nanoscale relations within zeolite materials can be revealed: i.e., crucial information for a fundamental mechanistic understanding. We show that magnesium forms clusters within the cages of zeolite SSZ-13, while the framework elements are homogeneously distributed. These clusters of just a few nanometers were analyzed and visualized in 3-D. Magnesium atoms seem to initially be directed to the aluminum sites, after which they aggregate and fill one or two cages in the zeolite SSZ-13 structure. The presence of magnesium in zeolite SSZ-13 increases the lifetime as well as the propylene selectivity. By using operando UV-vis spectroscopy and X-ray diffraction techniques, we are able to show that these findings are related to the suppression of aromatic intermediate products, while maintaining the formation of polyaromatic compounds. Further nanoscale analysis of the spent catalysts showed indications of magnesium redistribution after catalysis. Unlike zeolite H-SSZ-13, for which only a homogeneous distribution of carbon was found, carbon can be either homogeneously or heterogeneously distributed within zeolite Mg-SSZ-13 crystals as the magnesium decreases the coking rate. Carbon clusters were isolated, visualized, and analyzed and were assumed to be polyaromatic compounds. Small one-cage-filling polyaromatic compounds were identified; furthermore, large-cage-crossing aromatic molecules were found by isolating large coke clusters, demonstrating the unique coking mechanism in zeolite SSZ-13. Short-length-scale evidence for the formation of polyaromatic compounds at acid sites is discovered, as clear nanoscale relations between aluminum and carbon atoms exist.

Organic-free modulation of the framework Al distribution in ZSM-5 zeolite by magnesium participated synthesis and its impact on the catalytic cracking reaction of alkanes

Al distribution engineering is an effective way to tune the catalytic performance of ZSM-5 zeolite. In the present work, a series of [Al, Mg]-ZSM-5 with different Mg contents were obtained by hydrothermal synthesis method. For comparison, Mg/ZSM-5 with a comparable Mg content were also prepared using the conventional impregnation method. Characterizations of XPS-sputtering, H2-TPR and Py-IR indicated the distribution and coordination structures of Mg in the samples obtained by the two preparation methods were quite different. Besides, the introduction of magnesium by hydrothermal synthesis well regulates the location of framework Al, which is not possible by the impregnation method. 27Al MAS NMR and UV–vis-DRS of Co2+-exchanged zeolites demonstrated [Al,1.0 Mg]-ZSM-5 has less aluminum in the channel intersections compared to conventional HZSM-5. Finally, the significantly lower content of “Al pairs” in [Al,1.0 Mg]-ZSM-5 inhibits the hydride transfer process, resulting in higher yields of propylene in n-octane and crude oil catalytic cracking reactions.

Experimental and Theoretical Studies on Possibility of Void Filling by Magnesium in Mg-Doped Tetrahedrites.

Tetrahedrites, due to their promising thermoelectric properties, are one of the materials being investigated for use in thermoelectric generators. One problem is the lack of n-type tetrahedrites, which would be beneficial for the design of tetrahedrite thermoelectric modules. Preliminary theoretical studies have shown that elements from groups I and II can be introduced into the structural voids of tetrahedrite, acting as donor dopants, and should enable n-type conductivity. Therefore, in this work, an attempt was made to obtain and study magnesium-doped tetrahedrites. A series of samples, MgxCu12Sb4S13, with different magnesium contents were obtained and their phase and chemical compositions were characterized. It was observed that the structural changes occurring upon doping indicate that Mg atoms are likely to be embedded in the structural voids. The experimental studies have been supported by electronic structure calculations indicating that the most likely location of Mg is in the structural voids at the 6b Wyckoff position. Seebeck coefficient and resistivity measurements showed that doping with Mg reduces the concentration of holes, which is consistent with the predicted donor character of the dopant. However, the introduction of magnesium in sufficient amounts to achieve n-type conductivity was not successful.

Distinctive features of the crystal-chemical, thermal and luminescence properties of (Zn0.94Mg0.06)2SiO4:Mn phosphor

The effect of magnesium introduction on the structural, thermal, and luminescent characteristics of Zn2SiO4:Mn at the fixed magnesium concentration of 6 at% has been studied. Zn1.88–2xMn2xMg0.12SiO4 phosphors were synthesized by the solid phase method. The structural properties were studied using X-ray diffraction. The luminescent properties were characterized by the PLE and PL spectra. The charge state of manganese ions was determined by the XPS method. It was found that the Zn1.88–2xMn2xMg0.12SiO4 samples at x ≤ 0.14 were single-phase. The unit cell parameters of the solid solutions changed nonmonotonically with increasing x. The change in the linear trend of the parameters occurred at x = 0.06, and was caused by the oxidation of a part of the Mn2+ ions to Mn3+. The introduction of 6 at% magnesium into the Zn2–2xMn2xSiO4 structure caused an inversion of the crystallographic positions in which manganese was predominantly oxidized. It was shown that the melting temperatures of the Zn2–2xMn2xSiO4 and Zn1.88–2xMn2xMg0.12SiO4 solid solutions decreased with increasing manganese concentration, but were practically independent of the presence of magnesium. The structural phase transition α→β was recorded in the premelting region for all Zn2–2xMn2xSiO4 compositions. For the Zn1.88–2xMn2xMg0.12SiO4 solid solutions, the α→β transition was registered only for x˂0.06. The optimal photoluminescence intensity of Zn2–2xMn2xSiO4 shifted to the region of lower values of x with the introduction of magnesium and turned out to be maximum for Zn1.76Mn0.12Mg0.12SiO4. The introduction of 6 at% magnesium reduced the decay time by almost a factor of two; for the sample with x = 0.06 the decay time was 0.654 ms.

Effect of magnesium on the catalytic properties of polymetallic zeolite catalysts for conversion of dimethyl ether to light olefins

Abstract The effects of magnesium modification of mono- and bimetallic zeolite catalysts (La-НZSM-5, Zr-НZSM-5, and La–Zr-НZSM-5) and high-temperature steam treatment of these catalysts on the conversion of dimethyl ether to light olefins were studied. The additional introduction of magnesium resulted in higher catalyst activity and selectivity to light olefins. The high-temperature steam treatment of the catalysts not only increased the catalyst activity, but also resulted in higher selectivity to propylene, which is most likely due to higher contribution of the alkene cycle. The developed magnesium-containing zeolite catalysts can be used for the synthesis of light olefins from dimethyl ether with dilution of dimethyl ether in the feed with steam or synthesis gas of different compositions.

Enhanced Magnetic Squareness in Manganese-Bismuth Mechanical Alloys Incorporating Magnesium Oxide

Manganese-bismuth (MnBi) mechanical alloys have been under development for novel permanent magnets without rare-earth elements. The ball-milling of bismuth (III) oxide and manganese powders in this work leads to soft magnetic MnBi alloys with rod-like MnO impurity and highly unbalanced compositions. Interestingly, the introduction of magnesium (Mg) as reducing element during the milling gives rise to unique magnetic properties. The obtained MnBi alloys incorporating plate-like MgO has an enhanced magnetic squareness but minimal coercive field. The magnetic squareness remains high after the heat treatment and washing. The washing in ammonia also brings about a balanced composition between Mn and Bi.

Polyolefin‐Magnesium Interactions Performing Powder Injection Molding Process

The introduction of magnesium into the metal injection molding (MIM) process has shown that sintering results are drastically influenced by the selection of the backbone polymer of the binder system. The polymer is needed to ensure the shape stability after injection molding until the sintering process begins. Using polyethylene (PE) based polymers result in a strong sintering inhibiting effect while polypropylene (PP) based polymers do not show such a negative influence on the sintering of the magnesium powder. This work displays a systematic investigation why these two polyolefins show such a strong difference when used as backbone polymers for MIM of magnesium. According to the literature, PE decomposes mainly into 1‐alkenes and n‐alkanes while PP decomposes into branched iso‐alkenes and iso‐alkanes. The different thermal decomposition products of PE react with magnesium forming metastable carbides that decompose into carbon. Carbon can act as a barrier between neighboring powder particles inhibiting the sintering process. The decomposition products of PP do not react in the same extent leading to the fact that sintering is still possible. The negative effect of the carbon can be reversed when hydrogen is used as a sintering atmosphere resulting in improved sintering even when PE is used.

Supported MgO–V2O5/Al2O3 catalysts for oxidative propane dehydration: Effect of the molar Mg : V ratio on the phase composition and catalytic properties of samples

The physicochemical properties of V2O5/Al2O3 and MgO–V2O5/Al2O3 supported catalysts (Mg : V = 1 : 1, 2 : 1, and 3 : 2) obtained by consecutive impregnation of the support with solutions of vanadium and magnesium precursors are studied using a complex of mutually complementary methods (XRD, Raman spectroscopy, UV–Vis spectrometry, and TPR-H2). The effect of the formation of surface magnesium vanadates of various composition and structure on the catalytic properties of the supported vanadium oxide catalysts in the oxidative dehydrogenation of propane is studied. The introduction of magnesium in the samples and an increase in its content, accompanied by a change in the structure of the surface vanadium oxide phases from polymeric VO6/VO5 species to surface metavanadate species, magnesium metavanadate, and further to magnesium divanadate, significantly affects their catalytic properties in the reaction of the oxidative dehydrogenation of propane to propylene.

Hydrogenation properties and crystal structure of YMgT4 (Т = Co, Ni, Cu) compounds

New two ternary YMgCo4 and YMgCu4 and one quaternary YMgCo2Ni2 compounds have been synthesized by mechanical alloying with further annealing. The hydrogenation capacity of YMgCo4 reaches 6.8at.H/f.u. The Pressure-Composition-Temperature studies of YMgCo4–H2 and YMgNi4–H2 systems revealed that introduction of magnesium, accompanied by shrinking of the unit cell, decreases the stability of hydrides comparing to binary YCo2 and YNi2 compounds. The values of heat and entropy of the YMgCo4H6.8 hydride formation were calculated: ΔH=−27.9±0.8kJmol–1H2 and ΔS=−93.4±2.6Jmol−1H2K−1. The YMgCo2Ni2–H2 system shows intermediate thermodynamic properties compared to the ternary hydrides (ΔH=−28.8±0.2kJmol–1H2 and ΔS=−117.6±2.4Jmol–1H2K−1). The YMgCo4H6.8 and YMgCo2Ni2H4.9 hydrides keep the cubic structure of the parent compounds with a cell volume expansion of 23 and 14.4% respectively. It is shown that the YMgCu4 compound does not interact with hydrogen under normal conditions.

Elucidating Restriction Endonucleases Reaction Mechanisms via Dwell-Time Distribution Analysis

We have developed a Total Internal Reflection Fluorescence (TIRF) microscopy based assay that allows us to simultaneously measure the length of the catalytic cycle for hundreds of restriction endonuclease molecules in one experiment. We stably attach thousands of short duplex DNA molecules, each labeled with a single quantum dot semiconductor nanocrystal, to a passivated glass surface within a flow channel. The disappearance of a quantum dot indicates that its DNA tether has been cleaved. We introduce restriction endonuclease molecules into the channel in the absence of magnesium, which permits binding to, but not cleavage of the surface immobilized DNA substrate. When buffer containing magnesium is introduced into the flow channel, DNA cleavage by the pre-bound restriction endonuclease molecules is initiated. This synchronization allows us to measure the lag time between the introduction of magnesium and the completion of DNA cleavage for the entire population of enzymes. Analysis of the dwell-time distributions can provide insights into the DNA cleavage mechanism. Our observations suggest that EcoRV, a dimeric Type II restriction endonuclease that cleaves the palindromic sequence GAT↓ATC (where ↓ is the cut site), requires two kinetic steps to complete duplex cleavage after prebinding. However, dwell-time distributions suggest that BcnI, which is active as a monomer and cleaves the pseudopalindromic sequence 5'-CC↓SGG-5' (where S stands for C or G), requires more than four kinetic steps to complete duplex cleavage. Furthermore, experiments performed with strand-specific DNA substrates suggest that the number of steps indicated by the dwell-time distribution depends on which strand of the recognition site must be cleaved to result in quantum dot release. By designing additional substrates that mimic the various intermediate states, we plan to dissect the mechanism by which BcnI cleaves each strand of the intact restriction site.

Introduction of manganese in pellet batch as a means of increasing the efficiency of blast-furnace smelting

Laboratory tests are conducted to determine how manganese-bearing additives affect the metallurgical properties of pellet and sinter batch based on titanium-magnetite concentrates from Kachkanar enrichment facility. The results show that such additives are more effective in pellet batch than in sinter batch. Moreover, the introduction of magnesium in pellet batch permits the formation of a fluxed product, without impairment of the metallurgical properties. This increases blast-furnace productivity by 1.0–1.5%, with analogous decrease in coke consumption.

Impact of cation concentrations on fouling in membrane bioreactors

In this study, the interaction of calcium, magnesium, and sodium as well as impact of monovalent to divalent (M/D) cation ratio and magnesium to calcium (Mg/Ca) ratio in the feed wastewater on membrane fouling in submerged membrane bioreactor (MBR) was investigated. The protein and carbohydrate content of soluble microbial products (SMP) and extracellular polymeric substances (EPS) as well as their relative hydrophobicities was examined. The mixed liquor and its components (soluble and suspended solids) were analyzed for their filtration resistance, as reflected by the modified fouling index (MFI). Based on the findings of this study, the optimum conditions with respect to fouling rate were calcium and sodium concentrations of 36 and 140 mg/L, respectively, M/D of 1:1 and Mg/Ca of 5:1, with all parameters on an equivalent basis. High sodium concentration at high M/D ratio was found to decrease the floc size and increase the fouling rate. At the low M/D ratio of 1:1, introduction of magnesium was beneficial in reducing the fouling rate by increasing the EPS concentration and floc size and decreasing the SMP concentration and relative hydrophobicity in the supernatant. The fouling rate was found to be statistically correlated with the concentrations of Ca, Mg, and Na, with both Ca and Na adversely impacting fouling and Mg alleviating fouling propensity.

Impact of magnesium on membrane fouling in membrane bioreactors

The characteristics of membrane fouling were compared in submerged membrane bioreactors at three Mg:Ca molar ratios (1:5, 1:1, and 5:1), constant calcium concentration of around 1.7 mM and a solids retention time (SRT) of 15 d. Permeability, extracellular polymeric substances (EPS), soluble microbial products (SMP), Ca 2+ and Mg 2+ concentrations were measured regularly in the reactors to investigate the cause of membrane fouling. Molecular weight fractionation and relative hydrophobicity of EPS and SMP were also measured. In terms of membrane fouling rate, no differences were observed between Mg:Ca ratios of 1:5 and 1:1. The increase in the EPS and the concomitant decrease in SMP concentrations, both as protein and carbohydrates, due to divalent cation binding and enhanced bioflocculation were not significant enough to change the membrane permeability. More hydrophobic EPS was formed due to lower divalent cations at the low Mg:Ca ratio, resulting in higher EPS deposition on the membrane surface and membrane fouling. Comparison of the reactors with Mg:Ca ratios of 5:1 and 1:5 showed that the fouling rate is lower in the reactor with the higher Mg:Ca ratio. The introduction of magnesium at the higher Mg:Ca ratios proved that magnesium is beneficial in reducing membrane fouling due to changes in EPS and SMP characteristics as well as molecular weights.

Influence of different modified β zeolite on skeletal isomerization of n-hexene in the presence of hydrogen

Zeolite β was modified via treating with oxalic acid and doping with magnesium, and the influence of different modified zeolite β on skeletal isomerization of n-hexene in the presence of hydrogen was investigated. Moreover, parent β and modified β were characterized by XRD, N 2 physisorption, IR, NH 3–TPD, 27Al MAS NMR and 29Si MAS NMR, respectively. The results indicated, compared with parent β, β treated by oxalic acid was found that non-framework aluminum was removed effectively, and surface aluminum and framework aluminum were eliminated partly, which resulted in considerable decrease in the amount of acid sites. In contrast, the introduction of magnesium has little effect on crystalline structure of β, but it can reduce the amount of strong Brönsted acid sites. Noticeably, when β was modified by the combination of oxalic acid treatment and Mg dope, it can not only remove non-framework aluminum and reduce the amount of acid sites, but also facilitate the stability of crystalline structure of β and further eliminate strong Brönsted acid sites due to the introduction of Mg. The evaluation results of skeletal isomerization of n-hexene in the presence of hydrogen showed that, compared with parent β, β modified by the combination of oxalic acid treatment and Mg dope exhibits better activity and stability.

Effects of Mg and Zn on the surface of doped melt-derived glass for biomaterials applications

Bioactive glasses in the system SiO 2–CaO–Na 2O–P 2O 5 were synthesized pure and doped with magnesium or zinc by melt-derived method. The bioactivity was studied during in vitro assays: the ability of hydroxycarbonate apatite (HCA) layer to form on the glass surface was examined after contact with simulated body fluid (SBF). The X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) studies were performed before and after immersion in vitro assays. The SBF solutions were also analyzed using inductively coupled plasma-optical emission spectroscopy (ICP-OES). Introduction of magnesium and zinc as trace element induces several modifications on the observed phenomena at the glass surface and in SBF solution after immersion of the samples. The chemical durability of the glasses, the formation of the silica-rich layer and the crystallization of the HCA layer were affected, but not present the same modifications as the introduced doping element.

Enhancement of Pb (II) ions adsorption onto magnesium loaded activated carbon in aqueous solution

Magnesium loaded activated carbon was prepared to increase the adsorption capacity of lead (II) ions from aqueous solution. In case of sufficient amounts of surface acidic functional groups existing on the carbon, no significant improvement of heavy metal removal was observed even if the magnesium was loaded on it, but removing surface oxygen compounds by out-gassing in helium flow at 1173 K before magnesium loading, considerable enhancement of the heavy metal adsorption affinity onto the activated carbon could be observed. The amount of magnesium impregnation in the aqueous solution was also increased using the out-gassed carbon in the preparation. Any detrimental effect was not observed for aromatics adsorption by the introduction of magnesium. All adsorption equilibrium results at 293 K obeyed Langmuir isotherms. Heavy metal ions adsorption onto the magnesium loaded activated carbons progressed via ion exchange mechanism. Based on the Boehm titration surface analysis, the strong heavy metal adsorption sites might be generated forming the magnesium bound to carbon surface via oxygen bridge by means of calcining the magnesium nitrate impregnated out-gassing carbon in air at 653 K.

Optical Transmission Measurements on MOCVD Grown GaMnN Films on Sapphire

ABSTRACTWe demonstrate optical transmission measurements performed on 1.2 μm thick GaMnN films grown by metalorganic chemical vapor deposition on (0001) sapphire substrates. According to the data acquired from these measurements, Mn forms a deep acceptor band at 1.4 eV above the valance band of GaMnN. Full width at half maximum of this absorption band increases from 107 meV to 198meV as the Mn concentration increases from 0.3% to 1.6 %; which indicates that this band becomes wider as the concentration of Mn increases in the lattice. A broad absorption band starting at 1.9eV and extending to the band edge of GaMnN was also determined. This was attributed to the transition from the Mn energy band to the conduction band edge of GaMnN. Absorption at both of these bands scales with the Mn concentration and thickness of the films. The effect of co-doping of GaMnN films with magnesium on the transmission spectra was also investigated. The absorption band initially observed at 1.4 eV was shifted to 1.6 eV as a result of introduction of Magnesium into the lattice of GaMnN. From these results we conclude that Mn is incorporated in the lattice and forms an energy band in the bandgap of GaMnN. The width of this energy band is also a function of the Mn concentration in GaMnN.

Der Einbau von Magnesium in Liganden der Chlorophyll‐Reihe mit (2,6‐Di‐t‐butyl‐4‐methylphenoxy)magnesiumjodid

Introduction of Magnesium into Ligands of the Chlorophyll Series by (2,6‐Di‐t‐butyl‐4‐methylphenoxy)magnesium IodideExperimental details are given for the new method of introducing magnesium into porphinoid ligands by (2,6‐di‐t‐butyl‐4‐methylphenoxy)magnesium iodide (1), previously published in preliminary form [1]. Besides magnesium octaethylporphyrinate (14), methyl pyrochlorophyllide a (10), methyl chlorophyllide a (8), and methyl bacteriochlorophyllide a (12), the complexation of pheophytin a (2) to chlorophyll a (3) and of pheophytin b (4) to chlorophyll b (5) are described.