Alumina solubility in molten salt systems of interest for aluminum electrolysis and related phase diagram data

The solubility of alumina in molten Na₃AlF₆ containing various amounts of AlF₃, CaF₂, and LiF was determined by measuring the weight loss of a rotating sintered corundum disc. The results were fitted to the following empirical expression: 1 $$ [Al_2 O_3 ]_{sat} = A\left( {\frac{t} {{1000}}} \right)^B $$ where 2 $$ \begin{gathered} A = 11.9 - 0.062[AlF_3 ] - 0.003[AlF_3 ]^2 - 0.50[LiF] \hfill \\ - 0.20[CaF_2 ] - 0.30[MgF_2 ] + \frac{{42[LiF] \cdot [AlF_3 ]}} {{2000 + [LiF] \cdot [AlF_3 ]}} \hfill \\ B = 4.8 - 0.048[AlF_3 ] + \frac{{2.2[LiF]^{1.5} }} {{10 + [LiF] + 0.001[AlF_3 ]^3 }} \hfill \\ \end{gathered} $$ where the square brackets denote weight percent of components in the system Na₃AlF₆-Al₂O₃ (sat)-AlF₃-CaF₂-MgF₂-LiF and t is the temperature in degree Celsius. The standard deviation between the equation and the experimental points in the temperature range from 1050 °C to about 850 °C was found to be 0.29 wt pct Al₂O₃. A series of revised phase diagram data of interest for aluminum electrolysis was derived based on the present work and recently published data for primary crystallization of Na₃AlF₆ in the same systems.     

Liquidus temperatures in calcium ferrite slags in equilibrium with molten copper

Experimental laboratory methods have been developed that enable phase-equilibria studies to be carried out on slags in the system Ca-Cu-Fe-O in equilibrium with metallic copper. These techniques involve equilibration at temperature, rapid quenching, and chemical analysis of the phases using electron-probe X-ray microanalysis (EPMA). Equilibration experiments have been carried out in the temperature range of 1150 °C to 1250 °C (1423 to 1523 K) and in the composition range of 4 to 80 wt pct “Cu₂O,” 0 to 25 wt pct CaO, and 20 to 75 wt pct “Fe₂O₃” in equilibrium with metallic copper. Liquidus and solidus data are reported for the primary-phase fields of spinel (magnetite) and dicalcium ferrite. The resulting data have been used to construct liquidus isotherms of the CaO-“Cu₂O”-“Fe₂O₃” system at metallic copper saturation.     

Electrodeposition of magnesium-yttrium alloys by molten salt electrolysis

Electrodeposition of magnesium-yttrium alloys from molten salts was studied by electrochemical techniques.LiF-YF3 was electrolyte system with magnesium oxide and Yttrium oxide as raw materials.It was proved that Mg2+ and Y3+was deposited more prior than other ions during cyclic voltammetry and potential step measurement at 1050 °C.Voltammograms showed Mg2+ could be deposited at-0.5 V,and Y3+ could be deposited at-0.7 V on tungsten electrode compared with platinum electrode.The sedimentation of Mg2+ was more positive about 230 mV than that of other ions in electrolyte.The electrolytic codeposition of yttrium and magnesium was 0.58 V on condition that the weight ratio of Y2O3/MgO was 4:1.Chronopotentiogram indicated that the process of electrodeposition of magnesium-yttrium alloys on tungsten electrode was controlled by diffusion of ions from electrolyte to electrode interface.It was feasible to prepare Magnesium-Yttrium alloys by controlling content of ions in molten salt electrolyte.     

Electrodeposition of magnesium-yttrium alloys by molten salt electrolysis

Electrodeposition of magnesium-yttrium alloys from molten salts was studied by electrochemical techniques. LiF-YF₃ was electrolyte system with magnesium oxide and Yttrium oxide as raw materials. It was proved that Mg²⁺ and Y³⁺was deposited more prior than other ions during cyclic voltammetry and potential step measurement at 1050 °C. Voltammograms showed Mg²⁺ could be deposited at ?0.5 V, and Y³⁺ could be deposited at ?0.7 V on tungsten electrode compared with platinum electrode. The sedimentation of Mg²⁺ was more positive about 230 mV than that of other ions in electrolyte. The electrolytic codeposition of yttrium and magnesium was 0.58 V on condition that the weight ratio of Y₂O₃/MgO was 4:1. Chronopotentiogram indicated that the process of electrodeposition of magnesium-yttrium alloys on tungsten electrode was controlled by diffusion of ions from electrolyte to electrode interface. It was feasible to prepare Magnesium-Yttrium alloys by controlling content of ions in molten salt electrolyte.     

Dissolution of alumina in molten cryolite

Alumina powder dissolves rapidly in molten cryolite,i.e. in 4 to 8 seconds, provided that the particles are effectively dispersed in the melt. At alumina contents well below saturation the time of dissolution is independent of the alumina concentration, and it is not appreciably affected by additions of NaF, A1F₃, or CaF₂. Coarse grains dissolve more slowly than fine grains and α-Al₂O₃ (floury) dissolves more slowly than γ-Al₂O₃ (sandy). The rate-controlling step appears to be a slow chemical reaction. Bottom sludge in industrial cells contains about 40 pct A1₂O₃. This material has a higher α/γ-ratio than the alumina being fed to the cells, while the grain size is smaller due to disintegration of aggregates. The time of dissolution is identical to that of any other alumina with the same α/γ-ratio.     

Influence of Al2O3 on the reoxidation of aluminum in molten cryolite

The influence of Al₂O₃ content on the reoxidation reaction at 1293 K between CO₂ and Al dissolved in molten cryolite was examined. The rate and extent of the reaction were evaluated as the concentration of Al₂O₃ was varied from 0 to 12 wt pct at 4 pct intervals. The cryolite, under an argon atmosphere, was saturated with Al before CO₂ was introduced. High initial reaction rates were observed with a quasisteady state condition established 30 to 60 min after beginning an experiment. Increasing the Al₂O₃ content of the melt significantly reduced the initial rate, but it was not found to alter the steady rate for a given flow system. This phenomenon was observed for systems where CO₂ was passed over or bubbled through the molten cryolite. Bubbling the CO₂ through the molten cryolite led to increases in both the initial and steady state rates. M. K. Han, formerly a Graduate Fellow with the University of Washington.     

Solutions of iron oxides in molten cryolite

All the iron oxides (FeO, Fe₃O₄, Fe₂O₃, and FeAl₂O₄) dissolve in cryolite-alumina melts to give solutions containing both Fe(II) and Fe(III). The factor controlling the Fe(II)/Fe(III) ratio is the oxygen pressure, and experimental results are interpreted on that basis. Predictions are made of the variation of solubility with oxygen pressure, and the standard potential of the Fe²⁺/Fe³⁺ redox couple is calculated. The anode and anode gas of an industrial Hall-Heroult cell appear to be insufficiently oxidizing to cause significant conversion of Fe(II) to Fe(III). An anomaly in the liquidus diagrams for FeF₂ – Na₃AlF₆ and FeO – Na₃AlF₆ is accounted for in terms of solid solution of FeF₂ in cryolite. This article is based on a presentation made at “The Milton Blander Symposium on Thermodynamic Predictions and Applications” at the TMS Annual Meeting in San Diego, California, on March 1–2, 1999, under the auspices of the TMS Extraction and Processing Division and the ASM Thermodynamics and Phase Equilibrium Committee.     

熔盐电解法制备铝钙合金中的反电动势

研究了在CaCl2-CaF2纯钙盐体系中下沉式铝液槽结构熔盐电解法生产Al-Ca合金新工艺,采用连续脉冲-示波器法测定电解过程的反电动势,研究了在实验室条件下电解温度、电流密度、电解时问和极距对熔盐电解法制取铝钙合金的反电动势的影响.用熔盐电解法并采用铝阴极生产Al-Ca合金比对掺法更加节省电能,降低了Al-Ca合金的生产成本,是一种有经济价值的生产方法,有很好的发展前景.     

熔盐电解制备钨铜合金粉体槽内温场条件分析

在熔盐电解法由Na2WO4和CuO制取钨铜合金粉体的研究基础上,分析电解槽内的温度场分布,特别是电极区域的温度分布情况对电解行为的影响.通过位移法测量,采取比较法分析实验误差,结果表明:电解过程中2个主要的外部条件,即电解槽内温场分布与电场分布是联动的;温度条件影响着电极电位;同时,外部槽电压通过电流扰动槽内温场,使电极区域温场分布不均.     

熔盐预电解脱水与电解时间对溶盐电解TiO_2脱氧行为的影响

以无水氯化钙作为熔盐,采用熔盐电解法对TiO2阴极片进行脱氧,通过X射线衍射(XRD)和扫描电镜(SEM)对TiO2电解产物的相组成、电极表面形貌与元素组成进行观察与分析,研究熔盐的预电解脱水与熔盐电解时间对TiO2电解脱氧行为的影响。结果表明,熔盐未经预电解时,TiO2阴极片不发生脱氧反应,电解产物只有CaTiO3相;熔盐经预电解脱水后,TiO2电解产物部分或全部为低价钛氧化物,预电解时间达到15h即可有效去除熔盐中的水分,从而获得较佳的熔盐电解脱氧效果,电解产物为氧含量较低的Ti2O。TiO2电解脱氧是分步进行的,随电解进行,先后出现Ti2O3、TiO、Ti2O,由于钛的化合价逐渐降低,所需分解压升高,导致脱氧效率逐渐降低。TiO2阴极的脱氧反应是由表面到心部进行,电解后的阴极片明显分层,表层为氧含量较低的Ti2O,中间层为CaTiO3和钛的低价氧化物,心部为CaTiO3。     

NaCl-KCl-Na_2WO_4-CuO体系电解制备钨铜复合粉体研究

文中研究采用熔盐电解以由Na2WO4和CuO为活性物质电解获得钨铜合金复合前驱粉体.通过循环伏安法对电解质体系及电极过程进行定性分析认为Na2WO4减缓体系活性物质扩散速度,CuO与Na2WO4的电解非同步进行.通过改变活性物质的加入方式进行对比实验,结果表明：在温度750℃;以一定比例KCl-NaCl混合熔盐为电解质,在起始槽电压1 V,先加入CuO电解2 h;后加入Na2WO4,调整槽电压至2 V电解3 h,对产物进行X射线衍射（XRD）和扫描电镜（SEM）及能谱分析（EDS）表明,可以获得纯度达到98%的W-Cu合金粉体.     

Interfacial tension of aluminum in cryolite melts

The interfacial tension between aluminum and cryolite melts containing different salt additions has been measured based on a combination of the sessile drop and X-ray radiographie technique. A computer program was used to calculate the interfacial tension from approximately twenty randomly measured coordinate points of the drop profile. Aluminum and salt mixtures containing different amounts of Na₃AlF₆, A1F₃, NaF, A1₂O₃, CaF₂, KF, LiF, and NaCl were melted in a graphite or alumina crucible in a graphite resistor furnace under an argon atmosphere. The interfacial tension was found to be strongly dependent on the NaF/AlF₃ ratio. At the cryolite composition the interfacial tension was 481 mN/m at 1304 K, while it was 650 mN/m when the NaF/AlF₃ ratio was equal to 1.5. The change in interfacial tension with composition is explained by sodium enrichment of the Al/melt interface. Additions of A1₂O₃ increased the interfacial tension for a given NaF/AlF₃ ratio. KF was found to be surface active, while CaF₂, LiF, and NaCl slightly increased the interfacial tension by decreasing the sodium activity.     

The apparent solubility of aluminum in cryolite melts

The apparent solubility of aluminum in cryolite melts saturated with A1₂O₃ has been determined by titration with electrolytically generated O₂. The results may be expressed by wt pct Al = − 0.2877 + 0.0268 (NaF/AlF₃ wt ratio) + 2.992 × 10⁻⁴ (temp °C) − 0.00192 (% CaF₂) −0.00174 (% Li₃AlF₆) −0.00288 (% NaCl) with a standard deviation of ±0.017. Ranges covered were ratio 0.8 to 2.3, temperatures 969° to 1054°C, CaF₂ ≤ 14 pct, Li₃AlF₆ ≤ 20 pct, and NaCl ≤ 10 pct. There was no significant effect of adding 0 to 38. pct K₃A1F₆ or 0 to 10 pct MgF₂. It was found that solubility was approximately proportional to activity of aluminum when Al-Cu alloys were used. Possible mechanisms of solution are discussed. Monovalent aluminum is ruled out on the basis of the variation of solubility with NaF/AlF₃ ratio and a_Al. The favored, but not proven, mechanism involves formation of both sodium atoms and a colloidal dispersion of aluminum.     

The dissolution of aluminum oxide in cryolite melts

Several modifications of Al₂O₃ were prepared. Al₂O₃ samples pressed to tablets were dissolved in cryolite melts at temperatures between 975 and 1090°C. The dissolution rates obtained are consistent with the consecutive occurrence of two rate laws. The dissolution rate changes at an Al₂O₃ content of 5 to 6 pct in the cryolite melts. The results are discussed with consideration of other experimental and theoretical work. It is concluded that the alteration of the rate law may be explained by structural changes in the melts.     

熔盐电解生产Al-Sr合金的新工艺及其加料周期

研究了以SrCO3为原料熔盐电解法生产Al-Sr合金新工艺,采用连续脉冲-示波器法测定电解过程的反电动势.结果发现:(1)延长电解时间,合金中锶的质量分数逐渐增加,最高可达18.54%;(2)增加电流密度,反电动势亦随之增加,而升高温度反电动势则有所降低;(3)在电解过程中,反电动势逐渐增加,但向熔体中加入SrCO3后,反电动势明显降低.因此确定在正常电解时是SrCO3在分解.以此规律制定了正常生产的加料周期和加料量,保证了生产的稳定进行.以SrCO3为原料生产Al-Sr合金,不但减少了环境污染,也降低了Al-Sr合金的生产成本.     

铝电解惰性阳极近十年的发展状况

概述了近十年来4种铝电解惰性阳极的最新进展,评述了各自的优点和存在的问题,以及面临的挑战和应用前景。其中金属陶瓷、金属合金和梯度材料是当前研究的重点。它们的原理都是利用金属改善阳极的导电导热性、抗热震性和可加工性;陶瓷或在阳极表面形成陶瓷以抵抗熔融冰晶石的腐蚀。     

Preparing different phases of Mg-Li-Sm alloys by molten salt electrolysis in LiCl-KCl-MgCl2-SmCl3 melts

Different phases of Mg-Li-Sm alloys were prepared by galvanostatic electrolysis in LiCl-KCl-MgCl2-SmCl3 melts at 670 °C.The electrolysis process and phase control of Mg-Li-Sm alloys were studied.The microstructures of α,α+β,β phases of Mg-Li-Sm alloys were characterized by X-ray diffraction(XRD) and optical microscope(OM).Analysis of scanning electron microscopy(SEM) and EDS mapping analysis showed that Mg distributed homogeneously in Mg-Li-Sm alloys.EDS result showed that the distribution of Sm was more at...     

超声对熔盐电解法制备Al--7Si--Sc合金组织的影响

Al-Si系合金在现代工业、交通等领域广泛应用,合金元素钪可进一步改善其加工和使用性能.采用超声协同熔盐电解法制备Al-7S-Sc三元合金,研究探索超声作用对合金组织及强化相分布的影响.发现超声协同熔盐电解制得合金中Sc含量提高,团簇共晶硅组织和AlSi_2Sc_2相显著细化,共晶硅团簇尺寸由约500降低至200μm,减小约60%,细化后AlSi_2Sc_2相分布均匀.超声协同电解法可显著优化Al-7Si-Sc合金组织,有助于控制改善现行工艺中合金元素偏聚、组织不均匀现象.     

熔盐电解制备铝锂合金中阳极过程动力学参数的分析与计算

680℃下,在LiCl-LiF-KF体系中分别以LiCl和Li2CO3为原料电解制备铝锂合金,采用连续脉冲-计算机法测量阳极过电压并研究极化曲线的变化,根据电极过程动力学的理论计算并分析了CO2-3放电机理和反应速度控制步骤.研究表明：在电流密度为0.1-0.3 A·cm-2的Tafel区内,LiCl电解电极反应受电化学极化控制,Li2CO3电解电极反应受化学极化控制;电解Li2CO3时整个电极反应速率是由炭阳极上配合氧离子的缓慢放电引起的电化学控制步骤决定的.