Cup-shaped functionally gradient NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript>-based cermet inert anodes for aluminum reduction

Application of inert anode and wet-table cathode technology for aluminum reduction will result in significant energy and environmental benefits, so it has been a research focus for several decades. The candidate as inert anode concentrates on oxide ceramic, cermet, and alloy. This paper reviews briefly the research progress and presents the achievements of Central South University, Changsha, China, in developing an NiFe₂O₄-based cermet inert anode, which includes the preparation and optimization of material performance, the joint between the cermet anode and metallic bar, as well as the results of electrolysis testing for a large inert anode group. At the same time, the problems for NiFe₂O₄-based cermet inert anode faced are discussed.     

Applying fundamental data to reduce the carbon dioxide footprint of aluminum smelters

The aluminum smelting process is a strong emitter of CO₂ with three major contributions: that arising from electrical energy generation and its utilization, the process conversion contribution linked with anode consumption and anode production, and the greenhouse gas equivalents of the intermittent perfluorocarbon (PFC) emissions. Fundamental studies of alumina solubility, the electrochemical mechanism for triggering the onset of PFC emissions, and the importance of both mixing and current density on the speed of termination of anode effects, help define better paths for process operation. In conjunction with advising prebake aluminum smelters on process optimization, the authors have successfully tested the differences in theory and practice, and applied fundamentals in the operating environment to change some of the installed control strategies, termination mechanisms, and work practices. These changes have improved performance and reduced the CO₂ footprint. The overall process reductions achieved exceed 2.24 million tonnes of CO₂ equivalents per year in smelters producing less than 3 million tonnes of aluminum per year. Barry Welch is a part-time visiting professor at the University of New South Wales as well as an industry consultant; Martin Iffert is managing director at Trimet Aluminum AG; and Maria Skyllas-Kazacos is Professor Emeritus of Chemical Sciences and Engineering at the University of New South Wales, where she continues to supervise research in aluminum reduction.     

Further Development on NiFe2O4-Based Cermet Inert Anodes for Aluminum Electrolysis

The new aluminum electrolysis technology based on inert electrodes has received much interest for several decades because of the environment and energy advantages. The key to realize this technique is the inert anode. This article presents China’s recent developments of NiFe₂O₄-based cermet inert anodes, which include the optimization of material performance, the joint between the cermet inert anode and metallic bar, as well as the results of 20 kA pilot testing for a large-size inert anode group. The problems NiFe₂O₄-based cermet inert anodes face are also discussed.     

固溶处理对Al-Zn-In-Mg-Ti-Mn合金电化学性能的影响

    研究了510℃×10 h固溶处理对Mn含量不同的Al-Zn-In-Mg-Ti-Mn合金在人造海水中的腐蚀电化学性能的影响.结果表明：固溶处理使该合金的电流效率下降,但对其自腐蚀电位影响不大;当合金中Mn含量较高时,固溶处理可改善其腐蚀过程中的表面腐蚀状况,降低工作电位,而电流效率下降不大;等效电路R_S(C₁(C₂R_t)(QR)(L₁R_ad1)(L₂R_ad2)(L₃R_ad3))能较好地拟合该合金在3%NaCl溶液中腐蚀的EIS谱,基本反映了其电化学腐蚀过程.     

Microscopic mechanism of perfluorocarbon gas formation in aluminum electrolysis process

In view of the unclear cause of perfluorocarbons (PFCs) emission in the anode effect stage of aluminum electrolysis, the microscopic formation mechanism of PFCs was studied by density functional theory calculation and X-ray photoelectron spectroscopy (XPS). It is found that the discharge of fluorine containing anions ([F]^?) on carbon anode first causes the substitution of C—H by C—F and further results in the saturation of aromatic C—C bonds, leading to the appearance of —CF₃ or —C₂F₅ group through six-carbon-ring opening. Elimination of —CF₃ and —C₂F₅ with F atom could be a likely mechanism of CF₄ and C₂F₆ formation. XPS results confirm that different types of —CF_x group can be formed on anode surface during electrolysis, and the possibility that [F]^? discharges continuously at the C edge and finally forms different C—F bonds in quantum mechanical calculation was verified.     

阀金属化合物在高比容铝电解电容器中的研究进展

为了适应近年来电子产品功能化和小型化的发展趋势,铝电解电容器正向着小型化、大容量的方向发展,制备高比容阳极箔的技术是实现这一目标的有效途径之一。本文系统介绍了制备高比容铝电解电容器用阳极箔表面阀金属化合物薄膜的沉积技术,从不同沉积技术制备出薄膜质量的角度,阐述了各种沉积技术在制备铝电解电容器用阳极箔时的优缺点;并分析了通过复合阀金属化合物薄膜的方法来提高阳极箔电性能的研究进展,探讨了高比容铝电解电容器用阳极箔制备技术未来的发展趋势。     

高纯铝箔在不同退火加热速率下的晶粒尺寸预测及生长动力学分析

基于电子背散射衍射技术（EBSD）和薄膜材料晶粒生长模型理论,对高压阳极铝箔在不同升温速率下退火的晶粒尺寸及其生长动力学进行了研究。结果表明：依据典型的等温晶粒生长方程,可以计算得出晶粒生长指数n=4,活化能Q_g=129 kJ/mol,速率常数K=1.28×10^-8 m⁴·s^-1。基于薄膜材料的晶粒生长模型和能量各向异性特性,解释了（001）取向晶粒得以快速生长的原因,且发现这些快速生长的晶粒与S晶粒呈40°<111>取向关系。     

Effect of aging time and temperature on exfoliation corrosion of aluminum alloys 2024‐T3 and 7075‐T6

Two types of aluminum alloys, 2024‐T3 and 7075‐T6, have been selected in this study to investigate the effect of metallurgical aspects on exfoliation corrosion. To determine and evaluate the metallurgical effects of heat treatments on corrosion behaviour of these alloys, G34 ASTM test was selected to investigate the exfoliation corrosion behaviour. The results showed that with increasing the aging time for the aluminum alloy type 2024‐T3 the susceptibility to exfoliation corrosion increases, while for type 7075‐T6 decreased. These results refer to precipitation of the intermetallic compound phases such as CuAl₂, and MgZn₂, in 2024‐T3 and 7075‐T6 respectively. The amount of these phases increases with increasing the aging time for both alloys. The investigations showed the phases that initiate in 2024‐T3 act as anode sites while in 7075‐T6 they act as cathode sites.     

Hall cell energy recovery and anode pre-heating, gauging the opportunity

Anode pre-heating was proposed as an alternative for recycling waste heat from smelting operations, which currently consume substantially more energy than the theoretical minimum required. Aside from direct electricity savings, anode pre-heating can provide extra metal production and reduce carbon dioxide emissions. Public data on energy and aluminum production is analyzed to examine the value of these three potential components and define a research development path. It is concluded that indirect process gains show the most potential value with economies on the order of 3 TWh per year in electricity, an avoidance of about 1.8 million metric tons of CO₂ emissions, and an increase in production capacity of about 200,000 metric tons of aluminum per year without any expansion of installed capacity.     

Investigation of β/γ-MnO2 in composite electrodes with carbon nanotubes in a redox reaction with lithium in a model accumulator

Balastless thin-layer MnO₂/Al electrodes without an electroconducting carbon additive in combination with multiwalled carbon nanotubes (MWCNT) MnO₂/Al-MWCNT, as well as bulk-modified paste electrodes MnO₂ (MWCNT) F4/18H12X9T stainless steel electrodes, have been studied in the redox reaction with lithium in a model accumulator on the basis of propylene carbonate (PC), dimetoxiethane (DME), and 1MLiClO₄ and ethyl carbonate (EC), dimethylcarbonate (DMC), and 1M LiClO₄ electrolytes. The window of the electrochemical stability of the anode oxidation on MnO₂-Al/electrodes in the work range of the potentials for the electrolytes under study is 2.0–4.1 and 2.0–4.2 V, respectively. Because of the high contact resistance between the particles of the thin-layer β/γ-MnO₂/Al electrode, its discharge capacity cannot exceed 110–120 mA h/g; however, it is stable through 180 cycles. The discharge capacity volume paste MnO₂, F4/18H12X9T electrodes during the first cycle reaches 265–280 mA h/g and that of the reversible capacity ranges up to 185–250 mA h/g during the first 50 cycles. The role of the aluminum collector in the electrochemical transformation of MnO₂ has been discussed in thin-layer MnO₂/Al electrodes obtained by the mechanical rubbing of the active component into the aluminum matrix. The lithium chemical diffusion coefficient D_Li established in the redox reaction of MnO₂ with lithium has been estimated in thin-layer composite MnO₂ MWCNT/Al electrodes at the current peak values (around 10^?12 cm²/s) by slow cyclic voltammetry.     

通过水热法合成的纳米铁酸镍/石墨复合阳极材料具有优异的电化学性能

作为锂离子电池阳极材料的铁酸镍及其相关材料,由于其具有较高的理论比容量,近来受到广泛关注。为了克服在充放电过程中的较低导电性与较大的体积膨胀等不良因素,本文通过水热法合成了纳米铁酸镍钉扎在石墨表面而形成的复合物。该纳米铁酸镍/石墨复合物表现出了较高的比容量以及优异的循环性能。其初始放电容量接近1478mAh g-1,并且在100 mA g-1的电流密度下循环50周之后,其可逆容量依然高达1109 mAh g-1。在1000 mA g-1的充电电流情况下,该复合材料的充电容量也能保持750 mA g-1。这优异的电化学性能主要归功于纳米铁酸镍能够稳定的钉扎在石墨表面上,这种特殊的结构增强了材料的导电性同时也增大了材料的表面比容量。     

2219铝合金焊接接头晶间腐蚀行为

采用晶间腐蚀试验及极化曲线测试方法对2219铝合金母材、搅拌摩擦焊（FSW）及钨极氩弧焊（TIG）接头的腐蚀行为进行分析,借助金相显微镜、激光共聚焦显微镜、体视显微镜、扫描电镜及能谱仪分析腐蚀形貌及腐蚀产物.结果表明,2219铝合金母材及焊接接头的腐蚀行为主要与析出相有关,Al₂Cu的析出导致贫铜的无沉淀带作为阳极优先溶解.母材的抗晶间腐蚀能力最差,由表面点蚀开始,沿轧制方向逐渐发展为剥落腐蚀;TIG焊次之,表现为网状晶间腐蚀;FSW焊最低,焊核表现为点蚀,散落分布于表面.     

Optimizing efficiency of polycrystalline p-Si anode organic light-emitting diode

Optimizing efficiencies of organic light-emitting diodes (OLEDs) with a structure of Al/glass/nanometer-thick polycrystalline p-Si (NPPS) anode/SiO₂/N′-bis-(1-naphthl)-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB)/tris (8-hydroxyquinoline) aluminum (Alq₃)/4,7-diphenyl-1,10-phenanthroline (BPhen):Cs₂CO₃/Sm/Au were studied. The NPPS anodes were fabricated by magnetron sputtering (MS) Si and Ni layers followed by Ni-induced crystallization of the amorphous Si layers. By adjusting the resistivity of the p-Si target adopted in MS, the electroluminescent efficiency of the OLED was optimized. When the resistivity of the p-Si target is 0.01 Ω·cm, the current and power efficiencies of the NPPS anode OLED reach maximum values of 6.7 cd·A^?1 and 4.64 lm·W^?1, respectively, which are 2.7 and 3.1 times those of the resistivity-optimized bulk p-Si anode counterpart and 2.9 and 3.7 times those of the indium tin oxide (ITO) anode counterpart, and then, the physical reasons were discussed.     

Depolarised gas anodes for aluminium electrowinning

Consumable carbon anodes are used in the electrowinning of aluminium by the Hall-Heroult process.Emissions of CO2 may be eliminated by introducing an inert oxygen evolving anode,which however will require a higher anode potential.An alternative approach is to use a natural gas or hydrogen gas anode to reduce the CO2 emissions and lower the anode potential.Preliminary laboratory experiments were carried out in an alternative molten salt electrolyte consisting of CaCl2-CaO-NaCl at 680 °C.Porous anodes of platinum and tin oxide were tested during electrolysis at constant current.The behaviour of inert anode candidate materials such as tin oxide and nickel ferrite were also studied.     

The effect of Ca,Ba, and V<Subscript>2</Subscript>O<Subscript>5</Subscript> on oxide-film stability and the mechanism of oxidation of disperse aluminum

The results of a reactivity study of aluminum powders modified with surfactants of different natures allowing one to decrease the protective properties of an oxide film on a particle surface during heating in the oxidizing medium are given. Ca, Ba, and V₂O₅ used as modifiers were shown to allow considerably increasing the completeness and rate of oxidation of ASD-4-type aluminum powders used as fuels in composite propellant compositions. The mechanism of action of modifiers on the oxidation and combustion of disperse aluminum was established.     

Electrochemical performance of aluminum niobium oxide as anode for lithium-ion batteries

AlNbO_4,as lithium-ion batteries(LIBs) anode,has a high theoretical capacity of 291.5 m Ah g~(-1).Here,AlNbO_4 anode materials were synthesized through a simple solid-state method.The structure,morphology and electrochemical performances of AlNbO_4 anode were systematically investigated.The results show that AlNbO_4 is monoclinic with C2/m space group.The scanning electron microscopy(SEM) and transmission electron microscopy(TEM) characterizations reveal the AlNbO_4 particles with the size of 100 nm~(–2) lm.As a lithium-ion batteries anode,AlNbO_4 delivers a high reversible capacity and good rate capability.The discharge capacity is as high as 151.0 m Ah g~(-1)after 50 charge and discharge cycles at 0.1 C corresponding to capacity retention of 90.7 %.When the current density increases to 5.0C,AlNbO_4 anode displays reversible discharge capacity of 73.6 m Ah g~(-1)at the50 th cycle.     

Aluminum extraction from aluminum industrial wastes

Aluminum dross tailings, an industrial waste from the Egyptian Aluminum Company (Egyptalum), was used to produce two types of alums: aluminum sulfate alum (Al₂(SO₄)₃·12H₂O) and ammonium aluminum alum {(NH₄)₂SO₄AL₂ (SO₄)₃·24H₂O}. This was carried out in two processes. The first involves leaching the impurities using diluted H₂SO₄ with different solid/liquid ratios at different temperatures to dissolve the impurities present in the starting material in the form of aluminum sulfates. The second process is the extraction of aluminum (as aluminum sulfate) from the purified aluminum dross tailings thus produced. This was carried out in an autoclave. The effects of temperature, time of reaction, and acid concentration on pressure leaching and extraction processes were studied in order to specify the optimum conditions to be applied in the bench scale production as well as the kinetics of leaching process.     

Evaluation of the effects of variations in chemical composition on the quality of Al-Si-Mg,Al-Cu,and Al-Zn-Mg cast aluminum alloys

The effect of slight variations in chemical composition on the quality of cast aluminum alloys from three different major alloy systems was evaluated. For the evaluation of the alloy quality, an index Q _D adjusted to damage tolerance requirements that are currently involved for the design of advanced lightweight structures is used. The quality index Q _D accounts for tensile strength and ductility as well as for material failure through yielding or fracture. For this investigation, experimental results obtained for variations in chemical composition of the alloy systems Al-Si-Mg, Al-Cu, and Al-Zn-Mg were exploited. In total, castings from 37 different batches from 10 aluminum alloys, varying in chemical composition, were evaluated. Quality characterization and alloy quality ranking were made by evaluating results of 512 tensile tests using the index Q _D as well as, for comparison, the quality index Q, which is currently used by the industry. The results obtained involving the index Q _D seem to be more realistic, from the viewpoint of damage tolerance design requirements.     

Aluminum matrix composites reinforced by in situ Al2O3 and Al3Zr particles fabricated via magnetochemistry reaction

Aluminum matrix composites reinforced by in situ Al₂O₃ and Al₃Zr particles are fabricated from A356-Zr(CO₃)₂ system via magnetochemistry reaction, and the morphologies, sizes and distributions of the in situ particles as well as the microstructures, mechanical mechanisms of the composites are investigated by XRD, SEM, TEM and in situ tensile tests. The results indicate that with the pulsed magnetic field assistance, the morphologies of the in situ particles are mainly with ball-shape, the sizes are in nanometer scale and the distributions in the matrix are uniform. The interfaces between the in situ particles and the aluminum matrix are net and no interfacial outgrowth is observed. These are due to the strong vibration induced by the applied magnetic field in the aluminum melt, which in turn, accelerates the melt reactions. The effects of the magnetic field on the above contributions are discussed in detail.     

Anodizing and corrosion behaviour of aluminium

In this study, aluminum was anodized in 0.4 M H₂SO₄ + 0.145 M H₃BO₃ solution by means of potentiostatic method. In first step, the most appropriate conditions (anodizing voltage and period) were determined. The voltage-current behavior was investigated between 0 to 30 V and oxide formation potential (15 V) was determined. Then chorono-amperometric measurement was obtained at this potential during 2 hours. Therefore, anodizing process was applied at 15 V between aluminium anode and mild steel cathode. In the second step, the corrosion performance of non-anodized (Al) and anodized samples (Al₂O₃) have been investigated in 3.5% NaCl solution by using electrochemical impedance spectroscopy and polarization techniques. The interface between metal and solution was modeled with the equivalent circuit successfully. The circuit’s elements were calculated with Ivium Soft fitting program. The polarization curves were obtained between −1.8 V and 0.5 V potential ranges. The experimental results proved that the thickness and quality of oxide film was improved with help of anodizing process. Thus the corrosion resistance of anodized aluminum is significantly increased.