降低铝用炭阳极净消耗对铝电解参数的影响

介绍了炭阳极消耗机理.工业试验结果证明了降低炭阳极净消耗会提高电流效率和铝产量,降低铝电解电耗和电解质温度的理论;还会延长换炭阳极周期.这些理论和试验结果有利提高铝厂经济效益.     

Simulation of the Fluid Flow-Related Phenomena in the Electrolyte of an Aluminum Electrolysis Cell

A full-scale water model and mathematical simulation were used to study the fluid flow-related phenomena in a water model of an aluminum electrolysis cell. The time-dependent, multiphase fluid flow model was developed to represent the complex transient flow in the electrolysis bath. The accuracy of the mathematical model was validated by the ink dispersion and laser doppler velocimetry measurements in the water model. The shape, motion, release frequency of large-size bubbles, the fluid flow pattern, and the electrolyte–metal interface were predicted by the mathematical simulation. The design and operation of the anode were discussed, including the effect of the anode edge corner shape, the presence of a tilted bottom angle, and the magnitude of applied current density. The results indicated that coupling using a curved corner, with slot and with tilted angle at the anode, is effective for the release of bubbles and for the stability of the electrolyte–metal interface.     

Recent studies of convection in commercial aluminum reduction cells

Convection rates and patterns in the bath electrolyte and the cathode metal of 150 kA prebaked anode aluminum reduction cells have been studied by means of radioactive tracers. Gamma radiation probes have been used for a continuousin situ determination of the radiotracer activity in the bath and liquid metal. The measurements are compared with predicted convection patterns from model magnetodynamic calculations for both magnetically compensated and uncompensated reduction cells. The measurements give evidence of a strong coupling between the convection currents in the metal and bath phases. The recorded activity vs time data further allow an estimation of the degree of turbulence in the reduction cells. From these investigations attempts are made to correlate data from the convection studies with current efficiency, as determined by the method of isotope dilution. The same method has also been used to determine liquid bath volume and the melting-out of solid bath electrolyte during periods with anode effect.     

Metal Anode Performance in Low-Temperature Electrolytes for Aluminum Production

An investigation has been undertaken into the performance of metal alloy anodes used to produce aluminum via an electrochemical method. Alumina was electrolyzed in NaF/AlF₃ and KF/AlF₃ electrolytes and mixtures thereof with copper-nickel-iron (Cu:Ni:Fe) alloy anodes and titanium diboride (TiB₂) cathodes. The operating temperatures of the electrochemical cells ranged from 973 K to 1123 K (700 °C to 850 °C), with an anode current density of 5000 A/m². Cells ranged in current capacity from 10 to 300 amperes, with oxygen gas formed at the anode and molten aluminum collected from the cathode. Posttest anodes were sectioned, and elemental maps were performed to characterize the distribution of the chemical phases, including the metal electrodes, bath phases, and aluminum metal production, which were used to determine the reaction mechanisms of the cell. The metal alloy slowly corroded and formed an adherent, electronically conducting nickel ferrite plus copper scale during the operation of the cell. The proposed mechanisms of the anode performance are described herein.     

On convection in aluminum reduction cells

The convection pattern in the bath electrolyte and the cathode metal of 150 kamp prebaked anode aluminum reduction cells has been studied by means of radioactive tracers. The initial distribution of the tracers—²⁴Na for the bath and¹⁹⁸Au for the metal phase-indicates a fast circulating movement with vortices at the ends in both phases. Circulation rates up to 100 cm per sec were observed, and an average value seemed to be 10 cm per sec. The implications of the convection on the mechanism of the secondary reactions, the dissolution of alumina in the bath electrolyte and the distribution of carbon particles in the cell are discussed.     

大型预焙铝电解槽异常槽况下的电场特性研究

以某420kA大型预焙铝电解槽为对象,利用ANSYS平台建立铝电解槽在异常槽况下的电场有限元模型,计算并分析了生产过程中氧化铝沉淀和阳极更换过程对电场的影响。结果表明,大面积沉淀的产生会明显改变原有的钢棒电流的分布特性,而区域分散沉淀和小面积沉淀对钢棒电流分布影响较小;随着换极位置的改变,电解质层电场、铝液水平电流密度及钢棒电流均呈现大幅变化。本研究可为沉淀诊断分析及阳极更换制度的优化提供支撑。     

Experimental investigation of mixing phenomena in a gas stirred liquid bath

Mixing phenomena in a room temperature water bath, agitated by injecting air through a straight circular nozzle fitted axially at the bottom of the vessel, were characterized by experimentally measuring mixing time(t _mix) by electrical conductivity technique. It was found thatt _mix defined at 99.5 pct homogenization did not depend on location and size of conductivity probe, location of tracer injection, and the amount of tracer injected. tpet decreased with increasing gas flow rate and bath height, but decreasing nozzle diameter. Visual observations of the two-phase plume and flow conditions in the bath revealed that the plume swirled above a certain gas flow rate which enhanced the mixing rates in the bath. The transitions in Int _mix vs In ε_b curves were found to correspond to onset of swirling; ε_b is the rate of buoyancy energy input per unit bath volume. Systematic analysis of experimental data revealed that a fraction of gas kinetic energy contributed to mixing in the bath. It was a function of bath height, being negligible at lower bath heights and almost 1 at larger bath heights. Further, it was experimentally found thatt _mix decreased with increasing bath height only up to a certain value, beyond which it started increasing. Visual observations of the bath revealed that the height at whicht _mix started increasing corresponded to a transition in which the bath was converted into a bubble column. The experimental data, for a particular bath height, were fitted into two separate straight lines of the formt _mix =cε ⁻ⁿ wherec andn are empirical constants and ε is the rate of energy input per unit bath volume. Formerly Graduate Student in the Department of Metallurgical Engineering at the Indian Institute of Technology, Kanpur, India     

掺杂TiO2的镍铁尖晶石的高温导电性

镍铁尖晶石基惰性阳极属于高温半导体材料,在铝电解过程中其电导率不能满足要求.为了提高其电导率,本文研究了在尖晶石中添加TiO2对电导率的影响,试验结果表明,添加TiO2以后,镍铁尖晶石材料的电导率有较大的提高.     

低温铝电解的研究

综述了低温铝电解的研究进展，分析了电解质组成对电解质物理化学性质的影响以及低温铝电解与节能的关系。指出氧化铝的溶解度小且溶解速度慢、电解质导电性差以及阴极结壳是实现低温铝电解所要解决的主要问题，提出了今后的研究方向。     

铝电解阳极开槽技术研究

本文通过深入分析铝电解工艺中阳极压降、阳极效应及阳极在电解质中排渣过程,从阳极外形、理化指标入手,优化阳极炭块结构。开槽阳极的使用,使阳极压降降低了60mV以上,吨铝节能180kwh/t.Al左右;开槽阳极使电解过程中阳极效应从0.20个/槽·日降低到0.05个/槽·日。降低了阳极压降、减少了阳极效应,原铝直流电耗进一步降低,产生更多经济效益和社会效益。     

The effect of quality of anodes on the process of electrolytic of manganese dioxide

During the electrosynthesis of manganese dioxide, the anode material and anode current density (i _a) exert the largest influence on the characteristics of electrolysis and the quality of the obtained material. The activation of anodes, which consists of the deposition of the titanium-manganese alloy on the titanium base of the electrode by the thermal-diffusion method, prevents passivation at i _a = 100 and 200 A/m². The electrochemical characteristics of electrolysis for NTMA (a built-up titanium-manganese activated anode) and ATDP (an experimental activated anode with thermodiffusion coating) anodes at i _a = 100 and 200 A/m² have close values. The voltage across the bath does not exceed 2.2–3.0 V, the current efficiency is 95–98%, and electrical power consumption is 1.33–1.80 (kW h)/kg. The chemical composition and the crystalline modification of electrical manganese dioxide corresponds to the requirements of GOST (State Standard) 25823-83. The activated ATDP anodes behave similarly to the known HTMA anodes. After electrolysis, no variations in the surface layer are found on them.     

电解槽中无铝液进行电解时阴极表面炭的侵蚀与脱落

研究了铝电解槽阴极碳块表面在电解过程中被电解质侵蚀而脱落的情况,探讨了其被侵蚀脱落的机理。得出电解过程中当阴极没有铝液存在时,电解槽的阴极表面被电解质严重侵蚀并脱落掉渣。电解时测定不同极距下的槽电压,研究了不同电解质高度上的电解质熔体导电性能的变化,得出:电解开始时槽内电解质熔体的导电性能是均一的;电解一段时间后电解质熔体的电阻改变很大。这是由电解过程中有金属产物从阴极表面溶解,脱落的炭渣以及阳极气体在电解质熔体中的溶解等综合因素引起的。     

The influence of the initial shape and position of an anode and the curvature of the aluminum on the current distribution in prebaked aluminum cells

Mathematical modeling of the secondary current distribution in prebaked aluminum cells was used to study the influence of (1) a modified anode shape, (2) the curvature of the metal, and (3) an anode being set too high or too low. The calculations show that, if the lower corners of a new anode are cut off by 5 cm (diagonally), the steady-state shape of the anode is reached after 3 days, as compared to 6 to 8 days for rectangular corners. If the metal curvature corresponds to a 3 cm difference in height per 100 cm of length, and the sloping metal is facing a newly set horizontal anode, the current density varies across the anode with a maximum of 125 pct of the normal value (0.75 A cm⁻²), and it takes 4 days until the anode is aligned with the metal. If a new anode is set 1 cm too low or too high, the initial current through that anode after heatup is 123 and 84 pct, respectively, of the normal value, and it takes 4.2 and 7.7 days, respectively, until the interpolar distance is correct (45 ± 1 mm).     

A novel process for fabricating electrical contact SnO<Subscript>2</Subscript>/Ag composites by reciprocating extrusion

Reciprocating extrusion combined with simple powder compaction was used to produce electrical contact SnO₂/Ag composites from Ag and SnO₂ powders with improved properties. The SnO₂ particles were uniformly dispersed in the Ag matrix after 20 passes of extrusion. The hardness of the composites increased with extrusion passes and leveled off after ten passes, whereas the electrical conductivity decreased slowly after five passes. The variation of the coefficient of thermal expansion with temperature revealed that SnO₂/Ag interface strength increased with extrusion passes and was greatest after 20 passes. The SnO₂/Ag composites with 20 passes showed the best electrical contact properties in which there was no mass loss through mass transfer from cathode to anode during the make-break erosion test at both low and high current conditions. On the other hand, SnO₂/Ag composites with one pass and commercial SnO₂-In₂O₃/Ag specimens had an apparent mass loss under the same condition. Electrical contact composites produced by the present method are promising in electrical contact applications in consideration of cost and performance.     

基于线性规划算法的磷生铁最优化成分设计

铝电解槽阳极组装用磷生铁在使用过程中需要的特性与其本体材料的物理性能息息相关。运用材料热力学的方法计算出五大元素(C,Si,P,Mn,S)的含量变化对磷生铁电导率和热膨胀系数的影响,并通过线性回归建立电导率和热膨胀系数与五大元素含量和温度的函数关系,最后利用线性规划最优化算法对某铝厂现行磷生铁成分进行有目的性的优化。通过优化后,磷生铁电导率最大优化率为14.50%,热膨胀系数最大优化率为5.99%。     

Long-term material balance of iron in aluminum reduction cells

The distribution of iron was evaluated using the total material balance of iron in aluminum cells. The data on the Fe₂O₃ content in primary and secondary alumina, in aluminum fluoride, and in melted and crushed baths, and the data on the iron content in prebaked anodes, anode butts, and produced aluminum in the period 1998 through 2002 were determined using statistical analysis. The average content for the standard deviation of iron oxide, with respect to the iron in each material, was studied for each year, and a trend was calculated for the entire period. From a statistical point of view, the content of Fe in aluminum systematically increased during the years 1998 through 2002. Conversely, it was observed that the content of Fe₂O₃ in the crushed bath decreased during the same period. The crushed bath seems to be a very important flow in the process, since it accumulates most of the iron content. One can expect that a substantial part of the iron is distributed directly into the aluminum and the dry scrubbers. Based on the statistical analysis, the material balance of the iron in the prebaked anode cells resulted in the production of 1 t of aluminum. The total iron material balance (for both input and output materials) in the whole period of investigation totaled −642 g Fe. This value was approximately the same for each year. The higher content of Fe in the output materials is most probably caused by secondary sources of iron, which were not incorporated into the balance.     

Experimental Study of the Morphology and Dynamics of Gas-Laden Layers Under the Anodes in an Air–Water Model of Aluminum Reduction Cells

The bubble layer formed under an anode and the bubble-induced flow play a significant role in the aluminum electrolysis process. The bubbles covering the anode bottom reduce the efficient surface that can carry current. In our experiments, we filmed and studied the bubble layer under the anode in a real-size air?Cwater electrolysis cell model. Three different flow regimes were found depending on the gas generation rate. The covering factor was found to be proportional to the gas generation rate and inversely proportional to the angle of inclination. A correlation between the average height of the entire bubble layer and the position under the anode was determined. From this correlation and the measured contact sizes, the volume of the accumulated gas was calculated. The sweeping effect of large bubbles was observed. Moreover, the small bubbles under the inner edge of the anode were observed to move backward as a result of the escape of huge gas pockets, which means large momentum transport occurs in the bath.     

甲苯对AlCl_3-TEBAC离子液体中电沉积铝的影响

在含有甲苯添加剂的酸性三氯化铝—苄基三乙基氯化铵(AlCl_3-TEBAC)离子液体中进行铝的电沉积。考察甲苯加入量对离子液体电导率的影响,研究金属铝在离子液体中的电沉积行为,并用直流和脉冲电源进行铝电沉积。结果表明,离子液体电导率随甲苯摩尔分数x的增加而升高,但在x大于7.5%后,电导率趋于稳定;铝沉积反应为扩散控制的准可逆过程,在玻碳电极上的沉积是三维瞬时形核过程;电沉积得到的铝镀层为银灰色,而且脉冲电沉积得到的镀层要优于直流电沉积。