Electrochemical behavior of Mg-Al-Pb alloy in 3.5% NaCl solution

An investigation on electrochemical behavior of Mg-5%Pb alloy, Mg-6%Al alloy and Mg-6%Al-5%Pb alloy(mass fraction) in 3.5% Na Cl(mass fraction) solution was conducted using electrochemical measurements and corroded morphology observation, in which solid solution and the as-aged state of each alloy were compared to discuss the influence mechanism of lead and aluminium on the electrochemical properties of alloys. The X-ray diffraction(XRD) analysis was performed to make microstructure characterization. The electrochemical results indicate that the corrosion of Mg-5%Pb alloy is predominated by homogeneous pitting and dissolution of PbCl_2 film due to Cl ions attack, while corrosion crevice propagates along grain boundaries in solid solution of Mg-6%Al alloy and the micro galvanic corrosion also plays vital role in Mg_(17)Al_(12) phase containing experimental alloys. The co-existence of lead and aluminium in magnesium alloy increases corrosion current density and electrochemical activity as well. The comparison between solid solution and the as-aged state demonstrates that Mg_2 Pb and Mg_(17)Al_(12) somewhat increase corrosion resistance but lighten anodic polarization by facilitating corrosion product flaking off.     

Corrosion mechanism and corrosion model of Mg-Y alloy in NaCl solution

Corrosion of Mg–Y alloy was studied using electrochemical evaluations, immersion tests and SEM observations. Corrosion mechanisms of Mg-(0.25 and 2.5) Y alloy and Mg-(5, 8, and 15) Y alloy were uniform corrosion and pitting corrosion respectively, and the content of Mg_(24)Y_5 phases determined its effect acting as cathode to accelerate the corrosion or corrosion barrier to inhibit the corrosion. Corrosion resistance of Mg-(0.25, 2.5, 5, 8, and 15) Y alloys was as follows: Rt(Mg-0.25Y) Rt(Mg-8Y) Rt(Mg-15Y) Rt(Mg-5Y) Rt(Mg-2.5Y). Y could significantly improve the corrosion resistance of the Mg-Y alloy, but the excess of Y deteriorated the corrosion resistance of the Mg-Y alloy. The optimum content of Y in the studied alloys was 2.5%.     

Microstructures, mechanical properties and compressive creep behaviors of as-cast Mg-5%Sn-（0-1 .0）%Pb alloys

The microstructures, tensile properties and compressive creep behaviors of Mg-5%Sn-(0–1.0)%Pb (mass fraction) alloys were studied. The microstructures of the Mg-Sn-Pb alloys consist of dendritic α-Mg and Mg₂Sn phase. The addition of Pb can refine the size of Mg₂Sn phase and grain size, reduce the amount of Mg₂Sn phase at grain or inter-dendrite boundaries and change the distribution of Mg₂Sn phase. Pb exists in the Mg₂Sn phase or dissolves in α-Mg matrix. The mechanical properties of the tested alloys at room temperature are improved with the addition of Pb. When the Pb content is over 0.5%, the mechanical properties are decreased gradually. The Mg-5%Sn-0.5%Pb shows the best ultimate tensile strength and elongation, 174 MPa and 14.3%, respectively. However, the compressive creep resistance of the Mg-Sn-Pb alloys is much lower than that of the Mg-Sn binary alloy at 175 °C with applied load of 55 MPa, which means that Pb has negative effects on the compressive creep resistance of the as-cast Mg-Sn alloys.     

Preparation and electrochemical properties of Pb-0.3wt%Ag/Pb-WC composite inert anodes

We prepared Pb-0.3wt%Ag/Pb-WC(WC stands for tungsten carbide,the same below) composite inert anodes by double-pulse electrodeposition on the surface of Pb-0.3wt%Ag substrates,and investigated the electrochemical properties of the composite inert anodes,which were obtained under different forward pulse average current densities from 2 A/dm~2 to 5 A/dm~2 and WC concentrations from 0 g/L to 40 g/L in bath.The kinetic parameters of oxygen evolution,corrosion potential and corrosion current of the composite inert anodes were obtained in a synthetic zinc electrowinning electrolyte of 50 g/L Zn~(2+) and 150 g/L H_2SO_4 at 35 ℃,by measuring the anodic polarization curves,Tafel polarization curves and cyclic voltammetry curves.The results show that Pb-0.3wt% Ag/Pb-WC composite inert anodes obtained under forward pulse average current density of 3 A/dm~2 and WC concentration of 30 g/L in an original acid plating bath,possess higher electrocatalytic activity of oxygen evolution,lower overpotential of oxygen evolution,better reversibility of electrode reaction and corrosion resistance in [ZnSO_4+H_2SO_4] solution.The overpotential of oxygen evolution of the composite inert anode is 0.926 V under 500 A/m~2 in [ZnSO_4+H_2SO_4] solution,and 245 mV lower than that of Pb-1% Ag alloy;the corrosion current of the composite inert anode is 0.95×10~(-4)A which is distinctly lower than that of Pb-1%Ag alloy,showing the excellent corrosion resistance.     

Mechanism of zinc electroplating in alkaline zincate solution

The cathodic deposition properties and mechanism of Zn in alkaline zincate solution were studied by electrochemical techniques. The results show that Zn2 exists in the alkaline solution in the form of Zn(OH)42-. The apparent activation energy of the electrode reaction is 38.93 kJ/mol, which indicates that the discharge of Zn(OH)42- on cathode is controlled by electrochemical polarization, and accompanied by a preceding chemical reaction. The diffusion coefficient of Zn(OH)42- is 2.452×10-6 cm2/s. Zn(OH)2 is the species directly discharged on the cathode surface. Based on the above results the mechanism of zinc electroplating in alkaline zincate solution was put forward. The discharged species is Zn(OH)2 formed from the preceding chemical reaction, which becomes Zn(OH)ad when gaining one electron, and then gaining the second electron to become Zn. The first electron gaining step is rate determining one.     

Preparation and electrochemical performance of MWCNTs@MnO2 nanocomposite for lithium ion batteries

Tubular nanocomposite with interconnected MnO2 nanoflakes coated on MWCNTs(MWCNTs@MnO2)was fabricated by an aqueous solution method at 80°C.Scanning electron microscopy,X-ray diffraction and galvanostatic charge-discharge tests were used to characterize the structures and electrochemical performances of the as-prepared nanocomposite.The capacity reaches 1233.6 mA h g-1 at a current density of 100 mA g-1 for the first discharge,and it can still maintain a capacity of 633.1mA h g-1 after 100 charge-discharge cycles.The results show that MWCNTs with good electrical conductivity as anchors of MnO2 can provide fast electron transport channels for MnO2 in the electrochemical reactions,and the as-prepared MWCNTs@MnO2 nanocomposite is a potential anode material for lithium ion batteries.     

NaCl 溶液中回收AZ31 镁合金的腐蚀和电化学特性

利用熔炼工艺,将回收镁合金型材(RMA)进行了制备。在回收过程中,添加适量的Al、MnCl_2,最终得到合金AZ31,其中各元素质量分数如下:Al 3.31%、Zn 0.82%、Mn 0.27%、Fe 0.002%、Cu 0.004%、Ni 0.000 7%,剩余为Mg。研究了RMA的结构、在NaCl溶液中的腐蚀和电化学特性,并与商业化镁合金(CMA)进行了对比。X射线衍射仪和金相显微镜表明, RMA和CMA主要由镁基底组成,另外还有少量的Mg_(17)Al_(12)第二相。在NaCl溶液中进行的腐蚀试验和电化学特性研究表明, RMA抗腐蚀特性差于CMA,这可能与RMA中有更多的第二相有关。将两种合金作为镁电池原型器件的负极材料,进行放电性能测试。结果表明, RMA的放电时间和放电容量优于CMA。当NaCl电解质溶液浓度从0.6 mol/L增加至0.9 mol/L时,两种合金材料的放电时间和放电容量都得到了增加。     

Structural and electrochemical performance of additives-doped α-Ni(OH)2

The additives-doped α-nickel hydroxides were prepared by supersonic co-precipitation method. The crystal structure and grain size of the prepared samples were characterized by X-ray diffraction (XRD) and Particle size distribution (PSD), respectively. Cyclic voltammetry (CV) tests show that Al-Co-Y doped Ni(OH)2 has better reaction reversibility, higher proton diffusion coefficient than those of Al-Co doped Ni(OH)2. Al-Co-Y doped Ni(OH)2 also has lower charge-transfer resistance as shown by electrochemical impedance spectroscopy (EIS). Charge/discharge tests show that the discharge capacity of Al-Co-Y doped Ni(OH)2 reaches 328 mAh/g at 0.2 C and 306 mAh/g at 0.5 C, while Al-Co doped Ni(OH)2 can only discharge a capacity of 308 mAh/g at 0.2 C and 267 mAh/g at 0.5 C.     

Preparation of crystalline Mg(OH)_2 nanopowder from serpentinite mineral

In this paper we describe a route to produce crystalline Mg(OH)2 nanopowders from serpentinite ore distributed in the Halilovskiy array(Russia, Orenburg region). An efficient extraction route consisting of treatment on serpentinite in 40% HNO_3 at 80 °C followed by NH_4OH titration for Mg(OH)_2 precipitation was demonstrated. In this study, crystalline Mg(OH)2 nanopowders have been synthesized by solvothermal reaction method using(Mg(NO_3)_2á6H_2O) which were obtained from serpentinite, NH4 OH as a precipitator, and hydroxyethylated nonylphenol as surface-active substance. Microstructure and phase composition of samples were investigated employing scanning electron microscopy(SEM) and transmission electron microscopy(TEM), X-ray phase analysis(XRD), and inductively coupled plasma optical emission spectroscopy(ICP-OES). XRD reveals that Mg(OH)2 nanopowder with high purity has the brucite structure. It was found that crystalline Mg(OH)_2 nanopowders exclusively consist of lamellar-like structures and the sizes of Mg(OH)_2 are 30–265 nm length or width.     

A new perspective on the 5 V discharge capacity of Li/Al doped manganese spinels

A series of manganese spinels LiMn2-yMeyO4 (Me = Li, Al, Mg) were prepared and examined by XRD and electrochemical methods. The spinels doped with Li or high content of Al can exhibit discharge capacity in the 5 V region, but spinels doped with Mg do not exhibit any 5 V discharge capacity. It is also observed that the 5 V discharge capacity of Li/Al doped spinels will be greatly suppressed once calcinated at temperatures above 900 ℃ in preparation. It is suggested that the 5 V discharge capacity of Li/Al doped spinels may be originated from the special chemical/structural characteristics of spinel phases containing Li or high content of Al prepared at temperatures below 900 ℃.     

高温固相法合成尖晶石型Li4Ti5O12及其性能研究

以Li₂CO₃ 和TiO₂ 为原料,以乙醇为分散剂,采用高温固相方法合成Li₄Ti₅O₁₂锂离子电池负极材 料,利用XRD、SEM 和电化学测试等方法对合成材料的结构、形貌以及电化学性能进行了表征。系统考察了热处理 温度对Li₄Ti₅O₁₂负极材料结构及电化学性能的影响,同时也研究了锂的投料量对Li₄Ti₅O₁₂电化学性能的影响。在 1.0~2.2V(vs.Li/Li ⁺ )范围内,以0.1mA/cm² 的电流密度对最佳工艺条件下合成的Li₄Ti₅O₁₂负极材料进行了恒 电流充放电测试。其首次放电比容量为167mAh/g,经过30周充放电循环后放电比容量几乎没有衰减,表现出较 大的初始放电比容量和良好的循环性能。     

Effect of CaO doping on corrosion resistance of Cu/（NiFe2O4-10NiO） cermet inert anode for aluminum electrolysis

The CaO-doped Cu/（NiFe2O4-10NiO） cermet inert anodes were prepared by the cold isostatie pressing-sintering process, and their corrosion resistance to Na3AlF6-K3AlF6-Al203 melt was studied. The results show that the relative density of 5Cu/（NiFe2O4-10NiO） cermet sintered at 1 200 ℃ increases from 82.83% to 97.63% when 2% CaO （mass fraction） is added. During the electrolysis, the relative density of cermet inert anode descends owing to the chemical dissolution of additive CaO at ceramic grain boundary, which accelerates the penetration of electrolyte. Thus, the corrosion resistance to melts of Cu/（NiFe2O4-10NiO） cermet inert anode is reduced. To improve the corrosion resistance of the cermet inert anode, the content of CaO doped should be decreased and the technology of cleaning the ceramic grain boundary should be applied.     

Influence of Nd and Y additions on the corrosion behaviour of extruded Mg-Zn-Zr alloys

To improve the corrosion resistance of wrought magnesium alloys through rare earth (RE) additions, the corrosion behaviour of Mg-5Zn-0.3Zr-xNd (x=0, 1, and 2; wt%) and Mg-5Zn-0.3Zr-2Nd-yY (y=0.5 and 1; wt%) alloys in a 5wt% NaCl solution was investigated using immersion test and electrochemical measurements. The results of immersion test show that Mg-5Zn-0.3Zr-2Nd alloy exhibits the best corrosion resistance among the tested alloys. Electrochemical measurements show that secondary phases in RE-containing Mg...     

Mg<Subscript>2</Subscript>(OH)<Subscript>2</Subscript>CO<Subscript>3</Subscript>·3H<Subscript>2</Subscript>O whiskers growth mechanism

From the perspective of growth units, the growth mechanism of Mg₂(OH)₂CO₃·3H₂O whisker is investigated in this paper. Results show that the growth morphology of Mg₂(OH)₂CO₃·3H₂O whisker is consistent with the model of anion coordination polyhedron growth units. The growth solution Raman shift of Mg₂(OH)₂CO₃·3H₂O was monitored using Raman spectroscopy. The growth units are [Mg-(OH)₄]^2- and H₂CO₃. The growth process of Mg₂(OH)₂CO₃·3H₂O whisker is as follows: growth unit [Mg-(OH)₄]^2- first incorporates into the larger dimension [Mg-(OH)₄] _n ^2- , then the [Mg-(OH)₄] _n ^2- combines with H₂CO₃ into a linear skeleton Mg₂(OH)₂CO₃ in the same line. Mg₂(OH)₂CO₃ combines with H₂O by hydrogen bonds and ultimately transforms into Mg₂(OH)₂CO₃·3H₂O whisker. Magnesium carbonate whiskers have a layered structure, each of which is made of magnesium, carbon, oxygen, with H₂O in between each layer. When skeletons are superimposed within the same plane as a parallelepiped one, they grow into solid cuboid-shaped whiskers. When the parallelepiped skeletons planes combine with each other through the cascading links, they grow into hollow cylindrical whiskers.     

Effects of different iron sources on the performance of LiFePO4/C composite cathode materials

Olivine LiFePO₄/C composite cathode materials were synthesized by a solid state method in N₂ + 5vol% H₂ atmosphere. The effects of different iron sources, including Fe(OH)₃ and FeC₂O₄·2H₂O, on the performance of as-synthesized cathode materials were investigated and the causes were also analyzed. The crystal structure, the morphology, and the electrochemical performance of the prepared samples were characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM), laser particle-size distribution measurement, and other electrochemical techniques. The results demonstrate that the LiFePO₄/C materials obtained from Fe(OH)₃ at 800°C and FeC₂O₄·2H₂O at 700°C have the similar electrochemical performances. The initial discharge capacities of LiFePO₄/C synthesized from Fe(OH)₃ and FeC₂O₄·2H₂O are 134.5 mAh·g⁻¹ and 137.4 mAh·g⁻¹ at the C/5 rate, respectively. However, the tap density of the LiFePO₄/C materials obtained from Fe(OH)₃ are higher, which is significant for the improvement of the capacity of the battery.     

磷酸铁锂与碳复合材料的电化学制备及性能研究

利用电化学沉积法在铝箔上制备了掺杂导电碳的磷酸铁锂与碳复合的正极材料.通过对比磷酸铁锂市售样品、电化学沉积法制得的样品、电镀液询问沉淀样品这3种样品的物理表面形貌、电化学性能曲线,组装电池后的循环充放电性能曲线,研究了电化学沉积法掺碳对于磷酸铁锂正极材料结构和电化学性能的影响,得出了电化学沉积法制备LiFePO_4/C复合材料的可行性.     

Electrochemical properties of Co-S/x wt.% AB_5 composite materials

The Co-S/x wt.% AB5(x=0,10,20,30) composite materials were prepared by simply mixing Co-S material fabricated by hydrothermal method and AB5 alloy.The structure and morphology of the composite materials were characterized by XRD and SEM,respectively.The electrochemical properties of the composite electrodes were studied by the galvanostatic charge,discharge test and electrochemical impedance spectroscopy.The results showed that the Co-S/20 wt.% AB5 composite electrode showed the highest discharge capacity and the best cycling stability.The existence of the AB5 alloy improved the electrochemical activity of composite electrodes,reduced the electrochemical polarization resistances and promoted the electrochemical conversion reaction between Co and Co(OH)2.In order to improve the utilization rate of active materials,0.01 mol/L Na2S2O3 was added into the electrolyte.The electrochemical properties of the composite electrode were significantly enhanced.After fifty cycles,the discharge capacity of the composite electrode increased from 407 to 481.7 m Ah/g and the capacity retention increased from 79.7% to 91.2%.     

Influence of thickness on the properties of solution-derived LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> thin films

LiMn₂O₄ thin films of different thickness were derived from solution deposition and heat treated by rapid thermal annealing. The phase identification and surface morphology were studied by X-ray diffraction and scanning electron microscopy. The electrochemical properties of the films were examined by galvanostatic charge-discharge experiments and electrochemical impedance spectroscopy. LiMn₂O₄ thin films of different thickness derived from solution deposition and rapid thermal annealing are homogeneous and crack free with the grain size between 20 nm and 50 nm. The specific capacity of these films is between 42 and 47 μAh·cm²·μm⁻¹. The capacity decreases with the increase of discharge current density. The capacity loss per cycle increases from 0.012% to 0.16% after being cycled 50 times as the film thickness increases from 0.18 μm to 1.04 μm. The lithium diffusion coefficients of these films are in the same order of 10⁻¹¹ cm²·s⁻¹.     

Surface films formed on SnO<Subscript>2</Subscript> anode in lithium secondary batteries by FTIR spectroscopy

The chemical composition of the passivating layer formed on nano SnO2 anodes in 1 M LiClO4＋ （ethylene carbonate）EC ＋ （dimethyl carbonate）DMC at different charge/discharge states in lithium secondary batteries was studied using extra reflectance FTIR spectra. Results show that solvent decomposition reaction that generally occurs on the surface of carbon and alkali metal electrodes also takes place on nano-SnO2 anode, and the major constituent of the passivating layer is Li2CO3 and ROCO2Li. Formation of the passivating layer would certainly lead to the irreversible capacity loss.     

Preparation and electrochemical performance of spherical Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> as anode materials for Li-ion batteries

Fe₃O₄ nano-powder was prepared by the hydrothermal method. The structure and morphology of the product were characterized by X-ray diffraction (XRD) and scanning electronic microscopy (SEM). The as-prepared powder has regularly spherical morphology, and the average size of product is about 25 nm. The possible application use of this material as the active mass of anode for rechargeable Li batteries was examined by cyclic voltammeter (CV), galvanostatic charge/discharge. The experimental results showed that this material exhibited large specific capacity at the first cycle, and the discharge and charge capacity retention of this electrode are 37.04% and 48.76%, respectively. Furthermore, the impedance change of Fe₃O₄ electrode under different cycle number and potential was examined.