Codeposition Of Mg Research Articles

Study on Electrochemical Behavior of La(III) and Preparation of Al−La Intermetallic Compound Whiskers in Chloride Melt

This paper exhibits a novel method to prepare the Al−La intermetallic compound whiskers on the liquid magnesium electrode at 1023 K. The electrochemical behavior of La (III) on a tungsten electrode in LiCl−KCl−MgCl2−AlCl3−LaCl3 melts was investigated by different electrochemical measurements. The result from chronopotentiometry shows that co-deposition of Mg(II), Li(I), Al(III) and La(III) ions occurs when the current intensity more than −190 mA. Quarternary Mg–Li–Al–La alloy was prepared by galvanostatic electrolysis, and the Al4La intermetallic compound was identified via X-ray diffraction (XRD). The microstructure and micro−zone chemical analysis of Mg−Li−Al−La alloy were accomplished by scanning electron microscopy (SEM) with energy dispersive spectrometry (EDS). The results illustrate that lots of needle-like precipitates are synthesized on magnesium substrate. The crystal structure of needle-like precipitates was certified by transmission electron microscopy (TEM) with electron diffraction pattern. The result exhibits that the needle-like precipitates are Al−La intermetallic compound whiskers. The micro hardness of Mg−Li−Al−La alloy is remarkable improved with the help of Al−La intermetallic compound whiskers.

Electrochemical Co-Deposition of Mg–Ca Alloys from KCl–CaCl2–MgCl2 Melts

This work reports the electrochemical fabrication of Mg–Ca alloys by co-deposition of Mg and Ca ions in KCl–CaCl2–MgCl2 melts at 943 K on tungsten electrodes. Cyclic voltammetry indicated that co-reduction of Mg(II) and Ca(II) ions occurs at about −2.23 V in KCl–CaCl2 eutectic melts at 943 K. The diffusion coefficient of Mg(II) in KCl–CaCl2 eutectic melts was determined by chronopotentiometry with Sand's equation. Open-circuit chronopotentiometry was applied to evaluate the equilibrium potential of Mg(II)/Mg(0) system. Bulk products of Mg–Ca alloys were obtained by galvanastatic electrolysis at 6.00 A cm−2 on tungsten electrodes. The compositions of obtained Mg–Ca alloys were analyzed by inductive coupled plasma atomic emission spectrometer (ICP-AES). X-ray diffraction (XRD) indicates that Mg–Ca alloys mainly comprise α-Mg and Mg2Ca phases. The microstructure and micro-zone chemical analysis of Mg–Ca alloys were characterized by scanning electron microscopy (SEM) with energy dispersive spectrometry (EDS) analysis.

Electrochemical Formation of Mg–Li–Sm Alloys by Codeposition from LiCl–KCl–MgCl2–SmCl3 Molten Salts

In this article, the electrochemical method of preparing Mg–Li–Sm alloys by codeposition in LiCl–KCl–MgCl2–SmCl3 melts was investigated. Transient electrochemical techniques, such as cyclic voltammetry, chronopotentiometry, and chronoamperometry were used to explore the electrochemical formation of Mg–Li–Sm alloys. Chronopotentiograms demonstrated that the codepositon of Mg, Li, and Sm occurred when current densities were more negative than −0.31 A cm−2. Chronoamperograms indicated that the onset potential for the codeposition of Mg, Li, and Sm was −2.40 V, and the codeposition of Mg, Li, and Sm was formed when the applied potentials were more negative than −2.40 V. The different phases of Mg–Li–Sm alloys were prepared by galvanostatic electrolysis and characterized by X–ray diffraction (XRD), optical microscope (OM), and scanning electron microscopy (SEM). An inductively coupled plasma (ICP) analysis showed that the lithium and samarium contents in Mg–Li–Sm alloys could be controlled by the concentrations of MgCl2 and SmCl3. The results demonstrated that Sm could refine the grains dramatically. When the Sm content was 0.8 wt pct, the grain size was the finest.

Electrochemical behaviors of Mg 2+ and B 3+ deposition in fluoride molten salts

By using cyclic and linear sweep voltammetry, the electrochemical deposition behaviors of Mg 2+ and B 3+ in fluorides molten salts of KF-MgF 2 and KF-KBF 4 at 880 °C were investigated, respectively. The results show that the electrochemical reduction of Mg 2+ is a one-step reaction as Mg 2++2e −→Mg in KF-1%MgF 2 molten salt, and the electrochemical reduction of B 3+ is also a one-step reaction as B 3++3e −→B in KF-KBF 4 (1%, 2% KBF 4) molten salts. Both the cathodic reduction reactions of Mg 2+ and B 3+ are controlled by diffusion process. The diffusion coefficients of Mg 2+ in KF-MgF 2 molten salts and B 3+ in KF-KBF 4 molten salts are 6.8×10 −7 cm 2/s and 7.85×10 −7 cm 2/s, respectively. Moreover, the electrochemical synthesis of MgB 2 by co-deposition of Mg and B was carried out in the KF-MgF 2-KBF 4 (molar ratio of 6:1:2) molten salt at 750 °C. The X-ray diffraction analysis indicates that MgB 2 can be deposited on graphite cathode in the KF-MgF 2-KBF 4 molten salt at 750 °C.

Electrochemical behavior of antimony and electrodeposition of Mg–Li–Sb alloys from chloride melts

The electrochemical behavior of Sb(III) ions was investigated in LiCl–KCl molten salt at 673 K. The reaction mechanism and transport parameters of electroactive species were determined by transient electrochemical techniques (such as cyclic voltammetry, square wave voltammetry, chronopotentiometry and chronoamperometry) at a molybdenum electrode. The results showed that electrochemical reduction of Sb(III) in LiCl–KCl melts occurred in a reaction step with an exchange of three electrons. A voltammogram with a different scan rate in LiCl–KCl containing 1.45 × 10 −4 mol cm −3 SbCl 3 showed that the deposition/dissolution reaction of Sb(III) ions was not completely reversible. The diffusion coefficient of Sb(III) ions was 1.65(±0.01) × 10 −5 cm −2 s −1 at 673 K. The electroreduction of Sb(III) ions at an Al electrode was also studied by cyclic voltammetry and open circuit chronopotentiometry in the temperature range of 668–742 K. The redox potential of Sb(III)/Sb at an Al electrode was observed at the more positive potentials values than those at an inert electrode. This potential shift due to the formation of intermetallic compound with Al electrode. AlSb alloys were prepared in LiCl–KCl–SbCl 3 melts at 742 K by potentiostatic electrolysis at an Al electrode. The activity of Sb and the Gibbs energy of AlSb formation were also calculated. Mg–Li–Sb alloys were obtained by galvanostatic electrolysis at 673 K and the electrochemical codeposition of Mg, Li and Sb was investigated on a molybdenum electrode in LiCl–KCl containing MgCl 2 and SbCl 3 melts at 673 K by cyclic voltammetry, chronopotentiometry and chronoamperometry. Cyclic voltammograms, chronopotentiometry and chronoamperometry measurements indicated that the electrochemical codeposition of Mg, Li and Sb metal occurred at current densities lower than −0.466 A cm −2 or at an applied potential more negative than −2.350 V vs. Ag/AgCl. X-ray diffraction (XRD) suggested that Mg 3Sb 2 and Li 3Sb were formed in Mg–Li–Sb alloys. The distribution of Sb element in Mg–Li–Sb alloys from the analysis of scan electron micrograph (SEM) and energy dispersive spectrometry (EDS) indicated that Sb metal showed a distribution which resembled an interlaced network.

Growth and Characterization of Thermoelectric Mg2Si Thin Films

ABSTRACTIn this work, room temperature co-deposition of Mg and Si was used to successfully fabricate Mg2Si thin films on Si substrate by dual cathode magnetron sputtering (DCMS). Films were annealed at 380°C. Various Mg/Si sputtering power ratios have been examined. XRD, SEM and IR reflectivity measurements on grown and annealed films, reveal that annealing is enhancing the formation of crystalline Mg2Si.

Electrochemical Codeposition of Al-Li-Mg Alloys at Solid Aluminum Electrode from LiCl-KCl-MgCl2 Molten Salt System

The electrochemical codeposition of Mg and Li at an aluminium electrode in LiCl-KCl (50:50 wt pct) melts containing different concentrations of MgCl2 at 893 K (620 °C) to form Al-Li-Mg alloys was investigated. Cyclic voltammograms showed that the potential of Li metal deposition at an Al electrode, before the addition of MgCl2, is more positive than that of Li metal deposition at an Mo electrode, which indicated the formation of an Al-Li alloy. The underpotential deposition of magnesium at an aluminium electrode leads to the formation of Al-Mg alloys, and the succeeding underpotential deposition of lithium on predeposited Al-Mg alloys leads to the formation of Al-Li-Mg alloys. Chronopotentiometric measurements indicated that the codeposition of Mg and Li occurs at current densities lower than −0.668 A cm−2 in LiCl-KCl-MgCl2 (8 wt pct) melts at an aluminium electrode. The chronoamperometric studies indicated that the onset potential for the codeposition of Mg and Li is −2.000 V, and the codeposition of Mg and Li at an aluminium electrode is formed into Al-Li-Mg alloys when the applied potentials are more negative than −2.000 V. X-ray diffraction and inductively coupled plasma analysis indicated that Al-Li-Mg alloys with different lithium and magnesium contents were prepared via potentiostatic and galvanostatic electrolysis. The microstructure of typical dual phases of the Al-Li-Mg alloy was characterized by an optical microscope and by scanning electron microscopy. The analysis of energy dispersive spectrometry showed that the elements of Al and Mg distribute homogeneously in the Al-Li-Mg alloy. The lithium and magnesium contents of Al-Li-Mg alloys can be controlled by MgCl2 concentrations and by electrolytic parameters.

Study on the preparation of Mg–Li–Mn alloys by electrochemical codeposition from LiCl–KCl–MgCl2–MnCl2 molten salt

This study presents a novel electrochemical study on the codeposition of Mg, Li, and Mn on a molybdenum electrode in LiCl–KCl–MgCl2–MnCl2 melts at 893 K to form different phases Mg–Li–Mn alloys. Transient electrochemical techniques such as cyclic voltammetry, chronopotentiometry, and chronoamperometry have been used in order to investigate the codeposition behavior of Mg, Li, and Mn ions. The results obtained show that the potential of Li metal deposition, after the addition of MgCl2 and MnCl2, is more positive than the one of Li metal deposition before the addition. The codeposition of Mg, Li, and Mn occurs at current densities lower than −1.43 A cm−2 in LiCl–KCl–MgCl2 (8 wt%) melts containing 2 wt% MnCl2. The onset potential for the codeposition of Mg, Li, and Mn is −2.100 V. α, α + β, and β phases Mg–Li–Mn alloys with different lithium and manganese contents were obtained via galvanostatic electrolysis from LiCl–KCl melts with different concentrations of MgCl2 and MnCl2. The microstructures of typical α and β phases of Mg–Li–Mn alloys were characterized by X-ray diffraction (XRD), optical microscopy (OM), and scanning electron microscopy (SEM). The analysis of energy dispersive spectrometry (EDS) and EPMA area analysis showed that the elements of Mg and Mn distribute homogeneously in the Mg–Li–Mn alloys. The results of inductively coupled plasma analysis determined that the chemical compositions of Mg–Li–Mn alloys correspond with the phase structures of XRD patterns, and lithium and manganese contents of Mg–Li–Mn alloys depend on the concentrations of MgCl2 and MnCl2.

Study on the preparation of Mg–Li–Zn alloys by electrochemical codeposition from LiCl–KCl–MgCl 2–ZnCl 2 melts

Electrochemical codeposition of Mg, Li, and Zn on a molybdenum electrode in LiCl–KCl–MgCl 2–ZnCl 2 melts at 943 K to form Mg–Li–Zn alloys was investigated. Cyclic voltammograms (CVs) showed that the potential of Li metal deposition, after the addition of MgCl 2 and ZnCl 2, is more positive than the one of Li metal deposition before the addition. Chronopotentiometry measurements indicated that the codeposition of Mg, Li, and Zn occurs at current densities lower than −0.78 A cm −2 in LiCl–KCl–MgCl 2 (8 wt.%) melts containing 1 wt.% ZnCl 2. Chronoamperograms demonstrated that the onset potential for the codeposition of Mg, Li, and Zn is −2.000 V, and the codeposition of Mg, Li, and Zn is formed when the applied potentials are more negative than −2.000 V. X-ray diffraction (XRD) indicated that Mg–Li–Zn alloys with different phases were prepared via galvanostatic electrolysis. The microstructure of typical α + β phase of Mg–Li–Zn alloy was characterized by optical microscope (OM) and scanning electron microscopy (SEM). The analysis of energy dispersive spectrometry (EDS) showed that the elements of Mg and Zn distribute homogeneously in the Mg–Li–Zn alloy. The results of inductively coupled plasma analysis showed that the chemical compositions of Mg–Li–Zn alloys are consistent with the phase structures of the XRD patterns, and that the lithium and zincum contents of Mg–Li–Zn alloys depend on the concentrations of MgCl 2 and ZnCl 2.

Electrochemical formation of Mg–Li–Ca alloys by codeposition of Mg, Li and Ca from LiCl–KCl–MgCl2–CaCl2 melts

This work presents electrochemical formation of Mg-Li-Ca alloys via codeposition of Mg, Li and Ca on a molybdenum electrode in KCl-LiCl-MgCl(2)-CaCl(2) melts at 943 K. Cyclic voltammograms (CVs) showed that the underpotential deposition (UPD) of calcium on pre-deposited magnesium leads to the formation of a liquid Mg-Ca alloy, and the succeeding underpotential deposition of lithium on pre-deposited Mg-Ca alloy leads to the formation of a liquid Mg-Li-Ca solution. Chronopotentiometric measurements indicated that the codepositon of Mg, Li and Ca occurs at current densities more negative than -0.31 A cm(-2) in LiCl-KCl-MgCl(2) (5 wt%) melts containing 1 wt% CaCl(2). Chronoamperograms demonstrated that the onset potential for the codeposition of Mg, Li and Ca is -2.200 V, and the codeposition of Mg, Li and Ca is formed when the applied potentials are more negative than -2.200 V. X-Ray diffraction (XRD) indicated that Mg-Li-Ca alloys with different phases were formed via galvanostatic electrolysis. The microstructures of typical alpha and beta phases of Mg-Li-Ca alloys were characterized by optical microscope (OM) and scanning electron microscopy (SEM). The analysis of energy dispersive spectrometry (EDS) showed that the element Ca mainly distributes along grain boundary in Mg-Li-Ca alloys. The results of inductively coupled plasma analysis determined that the chemical compositions of Mg-Li-Ca alloys correspond with the phase structures of XRD patterns, and the lithium and calcium contents of Mg-Li-Ca alloys depend on the concentrations of MgCl(2) and CaCl(2).

Electrochemical Preparation of Mg-Li-Y Alloys by Codeposition from LiCl-KCl-MgCl2-YCl3 Melts

This work presents an electrochemical preparation routine of Mg-Li-Y alloys by codeposition of Mg, Li, and Y on a molybdenum electrode in LiCl-KCl-MgCl2-YCl3 melts at 943 K. Cyclic voltammograms (CVs) showed that the underpotential deposition (UPD) of yttrium on pre-deposited magnesium leads to the formation of a liquid Mg-Y solution. Chronopotentiometric measurements indicated that the codeposition of Mg, Li, and Y occurs at current density more negative −0.47 A cm−2. Mg-Li-Y alloys with different lithium contents were obtained via galvanostatic electrolysis.

Electrochemical study of the codeposition of Mg–Li–Al alloys from LiCl–KCl–MgCl2–AlCl3 melts

This work presents a novel electrochemical study on the codeposition of Mg, Li and Al on a molybdenum electrode in LiCl–KCl–MgCl2–AlCl3 melts at 943 K to form Mg–Li–Al alloys. Cyclic voltammograms (CVs) showed that the underpotential deposition (UPD) of magnesium on pre-deposited aluminum leads to the formation of a liquid Mg–Al solution, and the succeeding underpotential deposition of lithium on pre-deposited Mg–Al leads to the formation of a liquid Mg–Li–Al solution. Chronopotentiometric measurements indicated that the codeposition of Mg, Li and Al occurs at current densities lower than −0.47 A cm−2 in LiCl–KCl–MgCl2 (0.525 mol kg−1) melts containing 0.075 mol kg−1 AlCl3. Chronoamperograms demonstrated that the onset potential for the codeposition of Mg, Li and Al is −2.100 V, and the codeposition of Mg, Li and Al is formed when the applied potentials are more negative than −2.100 V. The diffusion coefficient of aluminum ions in the melts was determined by different electrochemical techniques. X-ray diffraction and inductively coupled plasma analysis indicated that α, α + β and β Mg–Li–Al alloys with different lithium and aluminum contents were obtained via potentiostatic and galvanostatic electrolysis.

Dynamic surface barrier effects on hydrogen storage capacity in Mg–Ni films

Hydrogen distribution profiles in Mg–Ni films deposited on quartz substrate by the magnetron-sputter co-deposition of Mg and Ni atoms have been investigated after hydrogenation at 8 × 10 5 Pa hydrogen pressure at temperatures 210, 230 and 250 °C during 1, 3, 6 and 72 h using elastic recoil detection analysis (ERDA) and nuclear reaction analysis (NRA) methods. Oxygen distribution profiles in the near-surface region have been measured by ERDA. It is shown that hydrogen storage capacity decreases as hydrogenation temperature increases from 210 to 250 °C for fixed hydrogenation duration and changes not monotonously as function of hydrogenation time for a fixed temperature. To explain variations of storage capacity as function of hydrogenation temperature and time, the structural film changes have been studied by X-ray diffraction technique, and surface topography was analysed using scanning electron microscopy. We suggest that registered results may be explained on the basis of assumption about the dynamic properties of surfaces which modify the hydrogen uptake mechanism.

Effects of heating on superconducting properties of amorphous Mg xB 1− x films

By simple codeposition of Mg and B at room temperature we have previously succeeded in preparing a thick amorphous (a-)Mg x B 1− x film ( x ≈ 0.33) with high resistivity which exhibits superconductivity at T c = 6.1 K. Here, we study the effects of heating on superconducting properties of the a-Mg x B 1− x film to seek the possibility to increase T c. We find that, by simply heating the film in vacuum up to 750 K for 10 min, both T c and the critical field B c at 2 K increase from 6 to 9 K and 4 to 8 T, respectively, while the resistance R increases slightly. The results raise basic questions concerning the roles of disorder on R, T c, and B c in amorphous superconducting films. Also, we discuss whether different interpretations of the data may be possible.

Electrochemical Codeposition of Mg–Li Alloys from a Molten KCl–LiCl–MgCl2 System

Abstract This work presents a novel study on electrochemical codeposition of Mg–Li alloys on molybdenum in KCl–LiCl (50:50 wt %) melts containing different concentrations MgCl2 at 943 K. Cyclic voltammograms showed that the underpotential deposition (UPD) of lithium on pre-deposited magnesium leads to the formation of liquid Mg–Li alloys. The codepositon of Mg and Li happens when the current intensity exceeds 0.59 A cm−2 in KCl–LiCl melts containing 5 wt % MgCl2. α, α + β, and β phases Mg–Li alloys with different lithium contents were obtained by galvanostatic electrolysis from KCl–LiCl melts with different concentrations MgCl2.

Epitaxial growth of MgB2(0001) thin films on magnesium single-crystals

Phase-pure MgB2 thin films have been grown in ultrahigh-vacuum conditions on Mg(0001) and Mg(101¯0) at low-temperature (185–220°C) via molecular beam epitaxy. By depositing B on the Mg substrate a maximum film thickness of ∼4ML can be achieved, while thicker layers can be obtained by codeposition of Mg and B. Thick films grown on Mg(0001) show a sharp hexagonal low energy electron diffraction pattern, as well as the angle resolved photoemission band structure and x-ray absorption features of MgB2(0001) surface. Poor long-range order can be achieved by codeposition on Mg(101¯0). This method allows important in situ measurements, may enable the controlled doping of MgB2, and could be used to realize MgB2-based superconducting devices.

Properties of MgB2 thin films made by radio frequency magnetron co-sputtering

We have studied properties of the superconducting MgB2 thin films made on sapphire substrates by radio frequency (rf) magnetron co-sputtering of Mg and B. The effects of annealing temperature and Mg:B ratio on the superconducting properties of the film were investigated. Films were prepared by room-temperature co-deposition of Mg and B using two guns and annealed in situ to form the superconducting MgB2 phase. Ar sputtering pressure was 20 mtorr with 5% of hydrogen gas to trap remnant oxygen gas in the deposition chamber. Average rf power density of Mg target was varied from 2 to 4 W cm−2 with that of B fixed at 12 W cm−2. An additional Mg layer was deposited on top to make up for Mg loss during in situ annealing. Films were heated up to 500–750 °C at the rate of 60 °C min−1, annealed for 20 min, and naturally cooled down by turning off the heater. The best results were obtained for films deposited with the rf power of Mg target at 50 W and annealed at 700 °C. The mechanism for MgB2 formation in low-pressure annealing is believed to be that during annealing the local Mg vapour pressure inside the film falls within the thermodynamic window.

Correlation between the superconducting and structural properties in MgB2 thin films prepared by molecular-beam epitaxy

Superconducting MgB2 films were prepared on an Al2O3(0001) substrate by codeposition of Mg and B using the molecular-beam epitaxy technique and the effects of the growth conditions on the structural and the superconducting properties were extensively investigated. The superconducting transition temperature Tc shows a peak as a function of the deposition-rate ratio of Mg to B2 and the stoichiometric composition is likely realized at the Tc peak. The optimum substrate temperature Ts was found to be 330 °C. Detailed structural characterizations indicate the strong suppression of structural coherence in the stoichiometric and Mg-rich films. This accounts for the fact that optimized Tc (26.6 K) is still lower than bulk Tc like in previous molecular-beam epitaxy studies. We argue that such structural disorder originates from epitaxial strain due to the lattice mismatch between the film and the substrate.

RBS characterization of MgB2 superconducting films annealed ex situ and in situ

The elemental composition and depth profiles of MgB2 films prepared by successive e-beam evaporation as well as by thermal co-deposition of Mg and B components were investigated by Rutherford backscattering spectrometry (RBS). In the case of films deposited by e-beam evaporation we studied both Mg-B precursors and appropriate MgB2 films grown on glassy carbon, Si(100) and J-sapphire substrates annealed in situ. For the films co-deposited by thermal evaporation on R-sapphire substrates and annealed ex situ we investigated superconducting MgB2 films only. The Tco values of all MgB2 films ranged from 21 to 30 K. Because of a very fine granular structure of the annealed films, confirmed also by SEM observations, we could not identify any MgB2 phase from x-ray diffraction (XRD) patterns. On the other hand, Mg2Si phase has been detected by XRD on the film–substrate interface for the superconducting film deposited on Si(100) substrate. The RBS measurements were performed with a 3.1 MeV 4He+ beam. Under these conditions, the 16O(α,α)16 elastic resonance allowed us to detect oxygen in all studied samples especially in B layers. The depth profiles of precursors prepared by successive e-beam evaporation showed clearly the multilayer film structure consisting of B and Mg layers. A strong interdiffusion between B and Mg layers may be observed after an in situ annealing, but still some degree of non-homogeneous component distribution may be observed. On the other hand, the MgB2 films co-deposited by thermal evaporation and annealed ex situ are much more homogeneous, but a higher content of oxygen is present.

Superconducting properties of MgB2 thin films prepared on flexible plastic substrates

Superconducting MgB2 thin films were prepared on 50-μm-thick, flexible polyamide Kapton-E foils by vacuum co-deposition of Mg and B precursors with nominal thickness of about 100 nm and a subsequent ex situ rapid annealing process in an Ar or vacuum atmosphere. In the optimal annealing process, the Mg–B films were heated to approximately 600 °C, but, at the same time, the backside of the structures was attached to a water-cooled radiator to avoid overheating of the plastic substrate. The resulting MgB2 films were amorphous with the onset of the superconducting transition at Tc,on≈29 K and a transition width of approximately 3 K. The critical current density was >7×105 A/cm2 at 4.2 K, and its temperature dependence indicated a granular film composition with a network of intergranular weak links. The films could be deposited on large-area foils (up to 400 cm2) and, after processing, cut into any shape (e.g., strips) with scissors, or bent multiple times, without any observed degradation of their superconducting properties.