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-MgF2 and KF-KBF4 at 880℃ 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%MgF2 molten salt,and the electrochemical reduction of B^3＋ is also a one-step reaction as B^3＋＋3e-→B in KF-KBF4 （1%,2% KBF4） 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-MgF2 molten salts and B^3＋ in KF-KBF4 molten salts are 6.8×10^-7 cm^2/s and 7.85×10^-7 cm^2/s,respectively.Moreover,the electrochemical synthesis of MgB2 by co-deposition of Mg and B was carried out in the KF-MgF2-KBF4 （molar ratio of 6：1：2） molten salt at 750℃.The X-ray diffraction analysis indicates that MgB2 can be deposited on graphite cathode in the KF-MgF2-KBF4 molten salt at 750℃.

Electrodeposition of Cu coating with high corrosion resistance on Mg-3.0Nd-0.2Zn-0.4Zr magnesium alloy

To improve the corrosion resistance, electrodeposition of Cu coating on Mg-3.0Nd-0.2Zn-0.4Zr （mass fraction, %NZ30K） magnesium alloy via an appropriate pretreatment was investigated. The surface morphologies, compositions and microstructures of the pretreated films and Cu coating were characterized in detail. The results show that the activation film consists of fluoride and phosphates and Zn immersion film forms preferentially on the eutectic compound Mg12Nd phase region. A smooth, uniform and dense Cu coating is successfully obtained. Potentiodynamic polarization tests reveal that Cu coating can greatly improve the corrosion resistance of NZ30K magnesium alloy. Open circuit potential （OCP） and electrochemical impedance spectroscopy （EIS） tests during long-term immersion further demonstrate that Cu coating can provide an effective protection for NZ30K magnesium alloy from corrosion up to ~60 h, due to its dense structure and a stable passive film formed. In addition, Cu coating exhibits good adhesion to substrate as confirmed by thermal shock test.

Preparation of porous Mg electrode by electrodeposition

In order to obtain a porous Mg electrode with a stable skeleton, organic Mg fuel cell （OMFC）, the electrochemical behavior of Mg deposition on Cu and Ni metallic substrates in 1 mol/L EtMgBr/THF solution was investigated by SEM, EDS and electrochemical methods. The experimental results show that Mg can be electrodeposited on both substrates, as a continuous layer on a Cu substrate. Accordingly, an approach for producing a porous Mg electrode with a stable skeleton of OMFC was proposed by means of electrodeposition of Mg on a foamed Ni substrate with a layer of Cu pre-plating. The discharge performance of this porous Mg electrode of OMFC is superior to that of a planar Mg electrode.

Electrochemical discharging performance of 3D porous magnesium electrode in organic electrolyte

A novel type of porous magnesium electrode with a stable 3D copper foam as current collectors for the organic magnesium-air battery was prepared by both amperostatic and pulsed electrodeposition of magnesium on copper foam substrates in an electrolyte of 1 mol/L EtMgBr/THF solution, respectively. Optimal parameters of the pulsed electrodeposition were obtained using a bending cathode at the right angle. The surface morphology of the porous electrode was investigated by SEM, and the discharging performance of the porous magnesium electrode was detected by the chronoamperometric measurement. The electrochemical stability of 3D copper foam current collectors was examined by cyclic voltammetry, SEM and ICP-OES analyses. The results show that the rate capability of the porous magnesium electrode with a stable 3D copper foam as a current collector is better than that of the planar magnesium electrode, and the rate capability of the porous magnesium electrode prepared by the pulsed electrodeposition is superior to that of the porous magnesium electrode prepared by the amperostatic electrodeposition. The 3D structure of copper foam current collectors of the porous magnesium electrode could keep stable during the discharging process.

Electrodeposition of aluminum and aluminum-magnesium alloys at room temperature

Electrodeposition of aluminum from benzene-tetrahydrofuran-Al Cl3-Li Al H4 was studied at room temperature. Galvanostatic electrolysis was used to investigate the effect of various parameters on deposit morphology and crystal size, including current density, temperature, molar ratio of benzene/tetrahydrofuran and stirring speed. The deposit microstructure was adjusted by changing the parameters, and the optimum operating conditions were determined. Dense, bright and adherent aluminum coatings were obtained over a wide range of current densities(10-25 m A/cm2), molar ratio of benzene and tetrahydrofuran(4:1 to 7:8) and stirring speeds(200-500 r/min). Smaller grain sizes and well-adhered deposits were obtained at lower temperatures. Aluminum-magnesium alloys could potentially be used as hydrogen storage materials. A novel method for Al-Mg deposition was proposed by using pure Mg anodes in the organic solvents system benzene-tetrahydrofuran-Al Cl3-Li Al H4. XRD shows that the aluminum-magnesium alloys are mainly Al3Mg2 and Al12Mg17.

Micro arc oxidation and electrophoretic deposition effect on damping and sound transmission characteristics of AZ31B magnesium Alloy

Micro arc oxidation(MAO) and electrophoretic deposition(EPD) process are employed to fabricate a dense coating on magnesium alloy to protect it from corrosion in engineering application. The EPD film changes the damping characteristic of magnesium alloy, and both the MAO and EPD process change the bending stiffness of samples being treated. Damping loss factor(DLF) test and sound transmission experiments were carried out for AZ31 B magnesium alloy with coating fabricated by MAO and EPD processes. The results indicate that DLF is improved in frequency range from 0-850 Hz. Bending stiffness of the samples is improved with MAO and EPD treatment. As a result, the sound transmission loss(LST) is improved in the stiffness control stage of the sound transmission verse frequency curve. To the samples by electrophoresis process, the LST is improved in frequency range from 2500-3200 Hz, because the damping loss factor is improved with EPD process. The results are useful for the surface treatment to enhance the damping loss factor, LST and widespread application of magnesium alloy while improving the corrosion resistance.

Online evaluation of electroless deposition rate by electrochemical noise method

Continuous noise resistance calculation(CNRC)technique was used for online determination of the electroless nickel deposition rate on zirconium pretreated magnesium alloy.For this purpose,the noise resistance(R_n) variation with time was calculated for the pretreated alloy surface in the electroless plating solution.The CNRC results were described by energy dispersive X-ray spectroscopy(EDS)and scanning electron microscopy(SEM)techniques.Also,potentiodynamic polarization and gravimetric measurements were used for determination of the electroless deposition rate at the same time period and the results were compared with the CNRC results.The Rn variation with plating time shows that the electroless plating consists of different stages with various deposition rates.The results of the CNRC and polarization methods were not in acceptable agreement due to the limitations of the polarization method for online monitoring of the deposition rate.However,the results of the gravimetric measurements were in complete agreement with the CNRC technique and so,the CNRC can be considered as suitable tool for online evaluation of the electroless deposition rate.

High specific strength MWCNTs/Mg-14Li-1Al composite prepared by electrophoretic deposition, friction stir processing and cold rolling

Multi-wall carbon nanotubes reinforced Mg-14Li-1Al composite(MWCNTs/Mg-14Li-1Al) was prepared by the processes of electrophoretic deposition, friction stir processing, and cold rolling. The microstructure and mechanical properties of the composite were investigated. The results show that, the microhardness of the composite is up to HV 84.4, which is 91.38% higher than that of the as-cast matrix alloy(HV 44.1). The yield strength and ultimate tensile strength of the composite are 259 and 313 MPa, which are 135.45% and 115.86% higher than those of the as-cast matrix alloy, respectively, and a high specific strength of 221.98 k N·m/kg is obtained. In the composite, the MWCNTs serve as nucleation particles during the friction stir processing and cold rolling, causing dynamic recrystallization and grain refinement. Furthermore, MWCNTs hinder the movement of dislocations and transfer the load from the matrix alloy, thus improving the strength.