Deposition Of Mg Research Articles

Analysis of the bone ultrastructure around biodegradable Mg–xGd implants using small angle X-ray scattering and X-ray diffraction

Magnesium alloys are increasingly researched as temporary biodegradable metal implants in bone applications due to their mechanical properties which are more similar to bone than conventional implant metals and the fact that Magnesium occurs naturally within the body. However, the degradation processes in vivo and in particular the interaction of the bone with the degrading material need to be further investigated. In this study we are presenting the first quantitative comparison of the bone ultrastructure formed at the interface of biodegradable Mg–5Gd and Mg–10Gd implants and titanium and PEEK implants after 4, 8 and 12 weeks healing time using two-dimensional small angle X-ray scattering and X-ray diffraction. Differences in mineralization, orientation and thickness of the hydroxyapatite are assessed. We find statistically significant (p < 0.05) differences for the lattice spacing of the (310)-reflex of hydroxyapatite between titanium and Mg–xGd materials, as well as for the (310) crystal size between titanium and Mg–5Gd, indicating a possible deposition of Mg within the bone matrix. The (310) lattice spacing and crystallite size further differ significantly between implant degradation layer and surrounding bone (p < 0.001 for Mg–10Gd), suggesting apatite formation with significant amounts of Gd and Mg within the degradation layer. Statement of significanceBiodegradable Magnesium-based alloys are emerging as a viable alternative for temporary bone implant applications. However, in order to understand if the degradation of the implant material influences the bone ultrastructure, it is necessary to study the bone structure using high-resolution techniques. We have therefore employed 2D small angle X-ray scattering and X-ray diffraction to study the bone ultrastructure surrounding Magnesium–Gadolinium alloys as well as Titanium and PEEK alloys at three different healing times. This is the first time, that the bone ultrastructure around these materials is directly compared and that a statistical evaluation is performed. We found differences indicating a possible deposition of Mg within the bone matrix as well as a local deposition of Mg and/or Gd at the implant site. Data availability statementThe raw/processed data required to reproduce these findings cannot be shared at this time as the data also forms part of an ongoing study.

Application of the Hybrid-Ion Battery Concept to Selected Oxide Systems

The success of Li-ion batteries led to a steady growth of applications that rely on this energy storage technology. However, the non-abundancy of necessary resources requires the establishment of successor technologies such as Na- or Mg-ion batteries. Both are still missing a breakthrough due to a variety of issues. Recently, the concept of hybrid batteries, which is based on a combined operation of two kinds of cations, has been proposed, bridging the gap between lithium and post-lithium energy storage [1]. Its main idea is to restrict chemical processes of one cation type to only one electrode while the other cation type takes part in processes on the other electrode. This results in the replacement or significant reduction of lithium amounts in a battery. Focusing on Li+, Na+ and Mg2+ ions as charge carriers, three types of hybrid batteries can be considered as Mg-Li, Mg-Na and Na-Li batteries. Currently, the main challenges are the search of a suitable electrolyte system compatible with both anodes and cathodes, as well as obtaining acceptable long-term cycling behavior, which is influenced strongly by many factors such as different SEI compositions. We studied different types of hybrid batteries with non-aqueous dual salt electrolytes using well-known electrode materials like Li4Ti5O12, TiNb2O7, LiFePO4 and LiV3O8 with the aim to evaluate issues concerning individual materials as well as general correlations referring to the certain type of a hybrid system. For example, we investigated LiV3O8 cathodes in mixed Na-Li electrolytes and found structural changes and the electrochemical behavior to be strongly influenced by the Li/Na ratio (Fig. 1). By obtaining higher capacities than in pure Na-ion batteries and better cycling behavior than in Li-ion batteries, we demonstrated that this concept represents a good compromise between these battery types. However, observed lithium plating on sodium anodes seems to be a general weakness of the hybrid Na-Li battery for the given electrolyte compositions, which has to be overcome [2]. Mg-Li batteries were studied using TiNb2O7 and Li4Ti5O12 operating at intermediate potentials that yielded promising results (Fig.2). A careful examination of structural evolution and the composition in a subsurface region revealed Li+ selectivity for bulk intercalation while Mg2+ is restricted to the anodic reaction. When aiming at higher voltages, electrolytes capable of depositing and stripping Mg become either unstable or reactive towards non-inert current collectors, but the applicability of LiFePO4 and LiV3O8 in dual salt electrolytes using special setups could be demonstrated. For the Mg-Na combination, we studied layered sodium oxides in a broad voltage range, and showed capability of desodiation of the layered structures and anodical deposition of Mg. However, the reverse reaction occurs at significantly lower discharge potentials with a large polarization. Figure 1

Controlled synthesis of Mg(OH)2 thin films by chemical solution deposition and their thermal transformation to MgO thin films

The chemical solution deposition of Mg(OH)2 thin films on glass substrates and their transformation to MgO by annealing in air is presented. The chemical solution deposition consists of a chemical reaction employing an aqueous solution composed of magnesium sulfate, triethanolamine, ammonium hydroxide, and ammonium chloride. The as-deposited films were annealed at different temperatures ranging from 325 to 500 °C to identify the Mg(OH)2-to-MgO transition temperature, which resulted to be around 375 °C. Annealing the as-deposited Mg(OH)2 films at 500 °C results in homogeneous MgO thin films. The properties of the Mg(OH)2 and MgO thin films were analyzed by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, UV–Vis spectroscopy, and by circular transmission line model. Results by X-ray diffraction show that the as-deposited thin films have a brucite structure (Mg(OH)2), that transforms into the periclase phase (MgO) after annealing at 500 °C. For the as-deposited Mg(OH)2 thin film, a nanowall surface morphology is found; this morphology is maintained after the annealing to obtain MgO, which occurred with the evident formation of pores on the nanowall surface. The assessed chemical composition from X-ray photoelectron spectroscopy yields Mg0.36O0.64 (O/Mg ratio of 1.8) for the as-deposited Mg(OH)2 film, where the expected stoichiometric composition is Mg0.33O0.67 (O/Mg ratio of 2.0); the same assessment yields Mg0.60O0.40 (O/Mg ratio of 0.7) for the annealed thin film, which indicates the obtainment of a MgO material with oxygen vacancies, given the deviation from the stoichiometric composition of Mg0.50O0.50 (O/Mg ratio of 1.0). These results confirm the deposition of Mg(OH)2 films and the obtainment of MgO after the heat-treatment. The energy band gap of the films is found to be 4.64 and 5.10 eV for the as-deposited and the film annealed at 500 °C, respectively. The resistivity of both Mg(OH)2 and MgO thin films lies around 108 Ω·cm.

Silicide phase formation by Mg deposition on amorphous Si. Ab initio calculations, growth process and thermal stability

Formation of magnesium silicides on amorphous silicon by deposition of Mg at room temperature is studied by electron energy loss spectroscopy, differential reflectance spectroscopy and high resolution transmission electron microscopy. Optimal crystal structures of Mg silicides under high pressure are found by ab initio DFT calculations. These structures are related to the particular minima of enthalpy. Dielectric functions are calculated for these structures. The transitions from the cubic phase c-Mg2Si to orthorhombic o-Mg2Si at 5.6 GPa and then from o-Mg2Si to hexagonal h-Mg2Si at 22.3 GPa are predicted using the USPEX code. The experimental spectra and the data obtained from the calculated dielectric functions are mutually consistent. Optical reflectance is suitable for monitoring the growth and transformations of the phases during experiments. During Mg deposition onto amorphous Si, the o-Mg2Si phase forms first, then the c-Mg2Si phase grows upon it. The observed sequence of phase formation is related with the compression stress arising in the depth of the Mg-Si mixture.

Strengthening of paper by treatment with a suspension of alkaline nanoparticles stabilized by trimethylsilyl cellulose

Control over the mechanical properties of cellulose-based artifacts (e.g. paper) is highly important in cultural heritage science. Especially, a non-aqueous method that does not cause swelling but can be applied to either single paper sheets or bound cellulose items (e.g., books) without any preselection is currently needed. Herein, we present a new multilayer deposition method that can simultaneously deposit alkaline reserve and improve the mechanical properties of historic wood pulp (HWP) paper, which often suffers from high fragility and brittleness. Alkaline nanoparticles (magnesium hydroxide Mg(OH)2NPs) stabilized by hydrophobic cellulose derivative i.e., trimethylsilyl cellulose (TMSC) in hexamethyldisiloxane (HMDSO) are prepared and deposited in the form of multiple layers on HWP paper by a technically effortless dip coating procedure. An enhanced and irreversible deposition of Mg(OH)2 NPs–TMSC and an alkaline reserve (AR) up to 4% (139 meq[OH−]/100g) are achieved as revealed by infrared spectroscopy and back-titration measurement. The tensile strength of uncoated HWP paper (1.6 MPa) is increased to 5.5 MPa after coating with Mg(OH)2NPs/TMSC (before aging) and then to ca 9 MP (after accelerated aging). In the latter case, the TMSC is transformed to cellulose by cleaving of O–Si bonds. The surfaces are evenly covered with thin and transparent coatings of hydrophobized nanoparticles as demonstrated by electron scanning microscopy and contact angle measurements.

Dual Functional Electron‐Selective Contacts Based on Silicon Oxide/Magnesium: Tailoring Heterointerface Band Structures while Maintaining Surface Passivation

AbstractSilicon (Si)‐based dopant‐free heterojunction solar cells (SCs) featuring carrier‐selective contacts (CSCs) have attracted considerable interest due to the extreme simplifications in their device structure and manufacturing procedure. However, these SCs are limited by the unsatisfactory contact properties on both sides of the junction, and their efficiencies are not comparable with those of commercially available Si SCs. In this report, a high‐performance silicon‐oxide/magnesium (SiOx/Mg) electron‐selective contact (ESC) design is described. Combining an ultrathin SiOx and a low work function Mg layer, the novel ESC simultaneously yields low recombinative and resistive losses. In addition, deposition of Mg on SiOx relaxes the restriction on the threshold thickness of the SiOx for electron tunneling and therefore broadens the optimization space for rear‐sided passivation. Meanwhile, hole‐selective contact with boosted light harvesting and suppressed interfacial recombination is achieved by forming a fully conformal contact between the conducting poly(3,4‐ethylene dioxythiophene): poly(styrenesulfonate) (PEDOT: PSS) and periodic Si pyramid arrays. With the double‐sided carrier‐selective contact designs, PEDOT: PSS/Si/SiOx/Mg SCs with efficiency of 15% are finally obtained via a totally dopant‐free processing. Subsequent calculations further indicate a pathway for the improvement of these contacts toward an efficiency that is competitive with conventionally diffused pn junction SCs.

Formation of Mg2Si at high temperatures by fast deposition of Mg on Si(111) with wedge-shaped temperature distribution

• Mg 2 Si can be grown by fast (100 nm/s) deposition of Mg on Si(111) at 365–609 °C. • A simple way to study temperature-dependent processes in one experiment is shown. • Analysis of the Mg 2 Si growth process at high temperature is given. • High deposition rate is the crucial requirement for Mg 2 Si growth at high temperatures.

Degradation Mechanisms of Magnesium Metal Anodes in Electrolytes Based on (CF3SO2)2N- at High Current Densities.

The energy density of rechargeable batteries utilizing metals as anodes surpasses that of Li ion batteries, which employ carbon instead. Among possible metals, magnesium represents a potential alternative to the conventional choice, lithium, in terms of storage density, safety, stability, and cost. However, a major obstacle for metal-based batteries is the identification of electrolytes that show reversible deposition/dissolution of the metal anode and support reversible intercalation of ions into a cathode. Traditional Grignard-based Mg electrolytes are excellent with respect to the reversible deposition of Mg, but their limited anodic stability and compatibility with oxide cathodes hinder their applicability in Mg batteries with higher voltage. Non-Grignard electrolytes, which consist of ethereal solutions of magnesium(II) bis(trifluoromethanesulfonyl)imide (Mg(TFSI)2), remain fairly stable near the potential of Mg deposition. The slight reactivity of these electrolytes toward Mg metal can be remedied by the addition of surface-protecting agents, such as MgCl2. Hence, ethereal solutions of Mg(TFSI)2 salt with MgCl2 as an additive have been suggested as a representative non-Grignard Mg electrolyte. In this work, the degradation mechanisms of a Mg metal anode in the TFSI-based electrolyte were studied using a current density of 1 mA cm-2 and an areal capacity of ∼0.4 mAh cm-2, which is close to those used in practical applications. The degradation mechanisms identified include the corrosion of Mg metal, which causes the loss of electronic pathways and mechanical integrity, the nonuniform deposition of Mg, and the decomposition of TFSI- anions. This study not only represents an assessment of the behavior of Mg metal anodes at practical current density and areal capacity but also details the outcomes of interfacial passivation, which was detected by simple cyclic voltammetry experiments. This study also points out the absolute absence of any passivation at the electrode-electrolyte interface for the premise of developing electrolytes compatible with a metal anode.

Electrochemical Synthesis Quaternary Mg−Li−Al−Pr Alloy with and without Whisker on Magnesium Cathode in LiCl−KCl−PrCl3−AlCl3 Melts

The electrochemical behavior of Pr(III) was firstly studied by different electrochemical measurements, and the Mg−Li−Al−Pr alloys with different alloy phases were prepared by galvanostatic electrolysis. Meanwhile, the electrochemical behavior of Mg(II) was also investigated by cyclic voltammetry and chronopotentiometry, and the diffusion coefficient of Mg(II) in LiCl–KCl melts was finally determined by chronopotentiometry. The results from different electrochemical measurements which were measured in LiCl−KCl−MgCl2−AlCl3−PrCl3 melts exhibited that two kinds of Al−Pr intermetallic compounds (Al2Pr and Al3Pr) and one kind of Mg−Pr intermetallic compound (Mg12Pr) were formed. Chronopotentiometry illustrated that the co−deposition of Mg(II), Li(I), Al(III) and Pr(III) ions will be realized when the current intensity is more than −200 mA (S = 0.322 cm2). Quaternary Mg−Li−Al−Pr alloys with and without whiskers were prepared on Mg cathodes by galvanostatic electrolysis in LiCl−KCl−AlCl3−PrCl3 melts. The deposits were finally analyzed by XRD, SEM and TEM with electron diffraction test. The result from the SEM analysis exhibited that the element aluminum existed in the form of Al−Pr intermetallic compound whiskers in the Mg−Li−Al−Pr alloy, which was obtained by galvanostatic electrolysis on liquid magnesium electrode. The micro hardness and corrosion resistance of Mg−Li−Al−Pr alloys were enhanced significantly with the assistance of Al−Pr intermetallic compound whiskers.

Deposition of dielectric films on silicon using a fore-vacuum plasma electron source

We describe an experiment on the use of a fore-vacuum-pressure, plasma-cathode, electron beam source with current up to 100 mA and beam energy up to 15 keV for deposition of Mg and Al oxide films on Si substrates in an oxygen atmosphere at a pressure of 10 Pa. The metals (Al and Mg) were evaporated and ionized using the electron beam with the formation of a gas-metal beam-plasma. The plasma was deposited on the surface of Si substrates. The elemental composition of the deposited films was analyzed.

Mechanically Stiff, Zinc Cross-Linked Nanocomposite Scaffolds with Improved Osteostimulation and Antibacterial Properties.

Nanocomposite scaffolds are studied widely due to their resemblance with the natural extracellular matrix of bone; but their use as a bone tissue engineered scaffold is clinically hampered due to low mechanical stiffness, inadequate osteoconduction, and graft associated infections. The purpose of the current study was the development of a mechanically stiff nanocomposite scaffold using biodegradable gellan and xanthan polymers reinforced with bioglass nanoparticles (nB) (Size: 20-120 nm). These nanocomposite scaffolds were cross-linked with zinc sulfate ions to improve their osteoconduction and antibacterial properties for the regeneration of a functional bone. The compressive strength and modulus of the optimized nanocomposite scaffold (1% w/v polymer reinforced with 4%w/v nB nanoparticles, cross-linked with 1.5 mM zinc sulfate) was 1.91 ± 0.31 MPa and 20.36 ± 1.08 MPa, respectively, which was comparable to the trabecular bone and very high compared to nanocomposite scaffolds reported in earlier studies. Further, in vitro simulated body fluid (SBF) study suggested deposition of biomimetic apatite on the surface of zinc cross-linked nanocomposite scaffolds confirming their bioactivity. MG 63 osteoblast-like cells cultured with the nanocomposite scaffolds responded to matrix stiffness with better adhesion, spreading and cellular interconnections compared to the polymeric gellan and xanthan scaffolds. Incorporation of bioglass nanoparticles and zinc cross-linker in nanocomposite scaffolds demonstrated 62% increment in expression of alkaline phosphatase activity (ALP) and 150% increment in calcium deposition of MG 63 osteoblast-like cells compared to just gellan and xanthan polymeric scaffolds. Furthermore, zinc cross-linked nanocomposite scaffolds significantly inhibited the growth of Gram-positive Bacillus subtilis (70% reduction) and Gram-negative Escherichia coli (81% reduction) bacteria. This study demonstrated a facile approach to tune the mechanical stiffness, bioactivity, osteoconduction potential and bacteriostatic properties of scaffolds, which marked it as a potential bone tissue engineered scaffold.

Effect of Synthesizing Temperature on Microstructure and Electrochemical Property of the Hydrothermal Conversion Coating on Mg-2Zn-0.5Mn-Ca-Ce Alloy

Mg(OH)2 conversion coatings were formed on an Mg-2Zn-0.5Mn-Ca-Ce alloy via hydrothermal method at three different synthesizing temperatures (160, 170 and 180 °C). The effect of synthesizing temperature on microstructure and electrochemical property of the coatings were systematically studied. With increasing synthesizing temperature, the coating became thicker due to the faster reaction and deposition of Mg(OH)2 on the α-Mg phase and secondary phases of the substrate Mg alloy. Internal micro-cracks were also generated in the higher-temperature synthesized coatings due to the increased shrinking stress, but the cross-cutting micro-cracks were suppressed. Benefiting from the improved barrier effect against penetration of corrosive medium, the higher-temperature synthesized thicker coating presented significantly enhanced electrochemical property and anti-corrosion efficiency in Hanks’ solution.

Characteristics of Surface Films Formed on Mg–Sn Alloys in NaCl Solution

The electrochemical behavior and surface films of pure magnesium and Mg–xSn (x = 2, 5 wt%) alloys were characterized in detail in an NaCl solution for a better understanding of the role of Sn in the corrosion process and film formation. The cathodic hydrogen evolution rate decreased and the protectiveness of surface film increased with the increase of Sn content. All of the films were nanocrystalline and had a double-layered structure, which mainly consisted of Mg(OH)2 and MgO. The porous outer layer of the film became more compact after the addition of Sn. The laminar inner layer in the Mg–Sn alloys was enriched in metallic Sn, because of the preferential dissolution of Mg atoms and the outward growth of the film. Owing to higher Sn content in the film of the Mg–5Sn alloy compared to the Mg–2Sn alloy, the Sn-rich layer could lead to a lower cathodic hydrogen evolution rate because of the higher hydrogen-evolution overvoltage of Sn than Mg. The decreased hydrogen evolution was beneficial to the deposition of Mg(OH)2, which contributed to the increased compactness and corrosion resistance of the surface film.

Electrochemical Deposition of Magnesium on SiC Fibers from the LiCl-KCl-MgCl2 Molten Salt

The preparation of Mg/SiC fiber precursor is the key process for the application of SiC fiber in the Mg alloys. Electrochemical deposition method was firstly adopted for the preparation of Mg/SiC fiber precursor in the LiCl-KCl molten salt. However, metal Li will be deposited prior to the deposition of Mg to form Li-C alloys with the carbon layer on the surface of SiC fiber due to the under potential deposition of Li+ ion. A Cu intermediate layer was introduced to avoid the formation of Li-C alloys, so that SiC fiber could be stable in a wide electrochemical window in the LiCl-KCl molten salt. A thin Cu layer was coated on SiC fiber using chemical plating method. The effect of NaOH concentration on the Cu coating was investigated and bright Cu coating was obtained. The electrochemical deposition process of Mg2+ ion was investigated through cyclic voltammetry and the detailed deposition parameters were obtained. Mg/SiC fiber precursor was prepared using pulse current electrodeposition method following the deposition parameters obtained by cyclic voltammetry. The morphology and microstructure of SiC/Mg fiber were explored through SEM. After the optimization of electrodeposition condition, compact and even Mg layer were prepared on SiC fiber.

Investigation of Barrier-Layer Materials for Mg2Si/Ni Interfaces

The durability of Ni electrodes, which are often used for Mg2Si thermoelectric chips, is poor at high working temperatures because of deposition of Mg at the Mg2Si/Ni interface and on the surface. Hence, a “Mg2Si/barrier material/Ni” structure was adopted instead of direct adhesion of Ni to Mg2Si. Ti, TiSi2, and TiN were selected as candidate materials for the barrier layer between Mg2Si and Ni, and the barrier effect, adhesion, and contact resistance of each of these materials were evaluated. After the samples had been annealed at 873 K for 1 h, Mg appeared on the Ti surface and TiSi2 deposited on Mg2Si; however, no Mg was detected on the surface of TiN or in the inner part of the Ni electrode. Continuous, low contact resistance was also observed for Mg2Si/TiN/Ni samples. TiN does not adhere strongly to Mg2Si but is a promising barrier material for Mg2Si/Ni interfaces.

Study of Stripping and Deposition of Magnesium in Mg Batteries

Magnesium (Mg) is an attractive material for use in the battery systems for many reasons: it is cheap and abundant; it has high volumetric capacity (3832 mAh/cm3); an attractive negative reductive potential (-2.3 V vs. SHE) and it has less safety issues since Mg is not plagued by dendrite formation.[1]Those properties are a motivation for the development of Mg batteries, but still a lot of additional research must be done on the fields of the electrolytes, suitable cathode materials and understanding the reversibility of Mg stripping and deposition. Despite the results that Mg is not forming dendrites[2], we have noticed non homogenous stripping and deposition of Mg in the different electrolyte solutions. Such non homogenous deposition can overgrow the separator, leading to formation of short circuits. To better understand reasons and to control the parameters that are influencing different morphologies of Mg deposition, we have decided to perform a detailed and systematic study how different electrolyte solutions and impurities (particularly H2O) influence process of Mg stripping and deposition. All the electrochemical measurements were performed in a two electrode beaker cell inside the glove-box (Ar atmosphere). Morphology of Mg foil and nano Mg powder was checked by scanning electron microscope. Solvents with different quantity of water were used for preparation of the electrolyte solutions. We performed two different sets of the electrochemical measurements; cyclic voltammetry and potentiometric cycling. While cyclic voltammetry showed a reversible stripping and deposition process, the potentiometric cycling revealed more information about the efficiency and kinetics of the process. Figure 1a presents Mg stripping and deposition process at a constant current in the first few cycles, showing that the electrodeposition process is taking part at two different potentials. Those two steps can be only observed when the source of Mg is not infinitive (as a positive electrode we typically used copper foil). To better understand the electrochemical processes occurring during the stripping and the deposition, we performed a controlled experiment where Mg was galvanostatically deposited on the Cu (Cu1) positive electrode (charge used for stripping was 0.5 Ah). Then Mg negative electrode was replaced by a fresh Cu electrode (Cu2) and Mg, deposited on Cu1 electrode, was galvanostatically cycled between two Cu electrodes (Cu1 and Cu2), which were examined under SEM at various stages of Mg deposition. Mg deposits appear at two different particle sizes (Figure 1b) and we found that smaller particles are consumed at the beginning of galvanostatic cycling; for the stripping of larger particles a certain overpotenital is required, which is then observed as a second potential. Working with different current densities we additionally found out that the size of particles depends on the current density, used for galvanostatic experiment. Low current densities are leading to large spherical particles, while with high current densities we obtained numerous small spherical particles. We need to point out that non homogenous electrodeposition of Mg can lead to disintegration of the bigger Mg particles from Mg foil surface and consequently to lower Coulombic efficiency as it was observed from our experiments. Careful analyses of Mg foil reveal a pitting corrosion on the surface. The reason for pitting corrosion formation has been studied. Our focus was on the water content in the solvent, which was found to have a large effect on the surface density and size of corroded spots. Besides lower Coulombic efficiency, problems related with the corrosion can importantly influence Mg battery behavior. Although the Mg does not form dendrites, the use of the Mg foil has several restrictions, among them two are exposed in this work. The solution to overcome those can be use of an electrode, prepared from Mg nano powder. Nano Mg powder deposition and stripping follows similar mechanisms as Mg foil, but powder exhibits some improved kinetic properties, which are quite beneficial for overall battery performance and surface deposition seems more uniform than in the case of the foil. Mg foil and nano powder were also tested in the complete Mg battery and we can confirm superiority of Mg nano powder over Mg foil. [1] Aurbach, D.; Cohen, Y.; Moshkovich, M. Electrochem. Solid-State Lett. 2001, 4, A113. [2] Matsui, M. J. Power Sources 2011, 196, 7048. Figure 1

Magnesium Metal Anode Interfaces and Performance in Chloride-Free Electrolytes

The development of rechargeable Mg batteries, driven by the desire to overcome the limiting specific energy density and high cost of Li ion batteries, is currently frustrated by the lack of stable, functional electrolytes compatible with high voltage cathodes. A functional electrolyte must deliver the Mg cation to the anode surface at nearly 100% Coulombic efficiency, requiring cation desolvation and accommodation without formation of a cation blocking film. Successful electrolytes have relied on Lewis acid – base reactions to form Mg cation-solvent complexes that include the traditional Grignard based and more recently reported inorganic MgCl2 based complex electrolytes containing either BR4 - or AlRxCl4-x - species.1 However, the stability of organometallic and chloroaluminate electrolytes against traditional current collectors and proposed oxide intercalation cathodes are of significant concern. Novel Mg battery electrolytes based on the weakly coordinating N(SO2CF3)2 (TFSI) anion have recently received interest due to their wide electrochemical window and general chemical compatibility while maintaining the ability to deposit and strip Mg, a feature previously unknown for “conventional” Mg salt solutions.2,3,4 However, Mg deposition in these systems is typically characterized by low coulombic efficiency (< 50%) and Mg surface passivation in the absence of chloride additives. In this presentation we describe Mg deposition and stripping from a chloride-free MgTFSI2-glyme electrolyte at nearly 90% coulombic efficiency, demonstrating that such “conventional” electrolytes have the ability to support reversible Mg deposition at application-relevant rates (> 1 mA/cm2). This finding proves that the use of weakly coordinating salts in glymes need not prevent Mg2+ transport across the anode/electrolyte interface. The MgTFSI2 system further teaches us that non-reducing, non-chloride electrolytes are highly sensitive to impurities, which regulate the interfacial processes governing deposition irreversibility. We will discuss the influence of specific impurities, identified through spectroscopic techniques including GC-MS, on the activity of MgTFSI2-glyme electrolytes and demonstrate the importance of impurity removal for attaining good performance (Figure 1a). Having addressed the problem of impurities we will further discuss the origins of the technologically insufficient coulombic efficiency (<99.9%) and the passivation of Mg in MgTFSI2-glyme electrolytes. Characterization of cycled electrolytes by ESI-MS and cycled electrode interfaces by XPS implicates TFSI decomposition during Mg deposition and stripping as the primary source of these problems. This finding corroborates previous computational work performed by our collaborators, which predicts an electrochemical-chemical TFSI decomposition mechanism involving S-C bond cleavage and liberation of a CF3 group.5 Finally, we observe that films formed on Mg surfaces in MgTFSI2-glyme electrolytes do not prevent the subsequent deposition of Mg. This surprising result argues that surface films formed in these electrolytes are not necessarily cation blocking layers in the classic sense, but instead exhibit rectifying behavior, facilitating cation transport during deposition and impeding cation transport during dissolution (Figure 1b). Characterization of these films via visualization and surface-sensitive spectroscopic techniques including ToF-SIMS will be presented, and the extent to which these films regulate Mg2+ transport to and from the anode surface will be discussed. This work is supported as part of the Joint Center for Energy Storage Research, an Energy Innovation Hub funded by the U.S. Department of Energy, Office of Science. Sandia is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Company, for the U.S. DOE’s NNSA under contract DE-AC04-94AL85000. 1. T. Liu, et al. J. Mater. Chem. A 2014, 2 3430 2. U.S. Patent #US 2013/0252112 A1 3. S.Y. Ha, et al. ACS Appl. Mater. Interfaces 2014, 6, 4063 4. Y. Orikasa, et al. Sci. Rep. 2014, 4, 5622 5. N. Rajput, et al. J. Amer. Chem. Soc. 2015, 137, 3411 Figure 1

The stability of aluminum‐manganese intermetallic phases under the microgalvanic coupling conditions anticipated in magnesium alloys

The electrochemical behaviour of two Al‐Mn materials (Al‐ 5.5 at % Mn and Al‐ 13.5 at % Mn) has been studied in 0.275 M NaCl and 0.138 M MgCl2 solutions to simulate the cathodic environment of Al‐Mn particles during the corrosion of a Mg alloy. Upon polarization in NaCl solution to a potential in the range expected on a corroding Mg alloy, the Al‐5.5 at % Mn alloy proved unstable undergoing de‐alloying (loss of Al) and delamination of layers of the Al(OH)3 formed. This leads to a steady increase H2O reduction current. When polarized in MgCl2 solution the surface was partially protected from de‐alloying and the current for H2O reduction suppressed by the deposition of Mg(OH)2. The Al‐13.5 at % Mn alloy was considerably more stable when cathodically polarized. This increased stability was attributed to the higher density of Mn‐enriched areas in the alloy surface. This simulation of the microgalvanic cathodic behaviour of Al‐Mn intermetallic particles confirms that the appearance of corrosion product domes on the Al‐Mn intermetallic particles during the corrosion of Mg alloys as an indication of their cathodic behaviour and that Al‐Mn intermetallic particles are efficient, yet unstable cathodes.

The dynamics of calcium and magnesium inputs by throughfall in a forest ecosystem on base poor soil are very slow and conservative: evidence from an isotopic tracing experiment (26Mg and 44Ca)

Using nutrient budgets, it has been proven that atmospheric deposition of Mg and Ca sustains the fertility of forest ecosystems on base-poor soils. However the fate of this nutrient input within the ecosystem was presently unknown. Our hypothesis is that the biological cycling of these nutrients is very rapid and conservative to prevent further Mg and Ca losses most especially in ecosystems on base-poor soils. Stable isotopes of magnesium and calcium (26Mg and 44Ca) were used to trace the dynamics of throughfall Mg and Ca in the forest soil of a 35-year-old beech stand. The aim of the present study was to (1) understand the processes and the velocity of the incorporation of tracers in the biogeochemical cycles and (2) compute Mg and Ca budgets for the ecosystem by isotope dilution. Rainfall Mg and Ca were strongly and rapidly retained mainly by ion exchange in the thin OL litter-layer. However, Ca was much more strongly retained in the litter-layer than Mg. As a result, 2 years after the application of tracers (2012), 92 % of 26Mg and 67 % of 44Ca was released and transferred to the soil or taken up by trees. The vertical transfer of Mg was very slow only 15 % of 26Mg was found below 15 cm depth in 2012. Ca was slower than 26Mg only 9 % of 44Ca was found below 5 cm depth. Although matrix flow was the main vertical transfer process of Ca and Mg, preferential transfer in macropores occurred. Overall, Mg was more rapidly leached through the soil profile than Ca because the soil CEC was mainly composed of organic charges which affinity for Ca is much higher than for Mg. 27 % of 26Mg and 20 % of 44Ca was found in tree biomass and total tracer recovery was close to 100 %. These results suggest that no tracers were lost to drainage over the 2 years. Finally, applying the isotopic dilution theory to the whole-ecosystem enabled us to estimate Mg and Ca budgets −0.9 kg ha−1 year−1 for Mg, which was close to computed input–output budgets −0.8 and 0 kg ha−1 year−1 for Ca, which was very different from input–output budgets (−3.1 kg ha−1 year−1). Our results suggest that a Ca source is underestimated or not taken into account. Over all, organic matter of the litter-layer and in the soil profile played an essential role in the retention of throughfall Mg and Ca and their cycling within the forest ecosystem.

Mg Capping Inside p-Tert-butylcalix[4]arene Adsorbed on a Ge(100) Surface

The Mg capping inside p-tert-butylcalix[4]arene (p-TBCA) adsorbed onto a Ge(100) surface was investigated using high-resolution photoemission spectroscopy (HRPES) and their corresponding DFT calculation results. After 0.10 ML p-TBCA molecules had been adsorbed onto a Ge(100) surface, subsequent adsorption of a small amount of metallic Mg (∼0.10 ML) resulted in the formation of a capped structure inside the preadsorbed p-TBCA molecules. The adsorption structures resulting from further deposition of Mg (∼0.50 ML) onto the Ge(100) surface were monitored based on the surface charge state obtained from Mg 2s core level spectrum. We also clarified the evidence of the Mg capped inside p-TBCA adsorbed onto the Ge(100) surface as we monitored the work function change. Moreover, we confirmed that three different adsorption structures are experimentally favorable at room temperature through DFT calculation results.