【作者】 谢宏伟；

【导师】 翟玉春；

【作者基本信息】 东北大学 ， 冶金物理化学， 2010， 博士

【摘要】 FFC法是一种在氯化钙基熔盐体系中将固态金属氧化物直接电解制备固态金属或合金的方法,具有工艺简单,成本低等优点。如果采用惰性阳极则是一种绿色生产工艺。FFC法不要求固态金属氧化物溶解到熔盐中,避开了传统以氧化物为原料进行低温熔盐电解氧化物溶解度、溶解速度降低等问题。操作温度范围也可以根据需要,通过调整熔盐组成来控制。该法为低温熔盐电解制备金属提供了新思路。另外,氯化钙基氯化物熔盐的低熔点也为实现低温熔盐电解提供了条件。本论文以CaCl₂-NaCl熔盐为电解质,石墨为阳极,利用FFC法,施加3.1V恒电位,低温熔盐电解固态Al₂O₃、Al₂O₃-MgO、Dy₂O₃-Fe、Dy₂O₃-Fe₂O₃制备出了Al及Al-Mg、DyFe₂合金。采用直接阿基米德法、CVCC法结合阻抗测量技术测定了550℃～800℃,含CaCl₂质量百分数为71%～87%的铝电解用熔盐电解质体系密度和电导率。结果发现,在550℃～750℃范围,含CaCl₂质量百分数为71%～87%的CaCl₂-NaCl-Al₂O₃（饱和）熔盐体系的密度随着氯化钙含量的增加而增大,但不是线性关系;氧化铝的溶解降低了熔盐体系的电导率,增加了电导活化能。在550℃～800℃范围,含CaCl₂质量百分数为71%～82%的CaCl₂-NaCl-Al₂O₃（饱和）熔盐体系中组元是离子状态,电导率与温度呈线性关系,氯化钙的增加降低了熔盐体系的电导率和电导活化能。开发出新型石墨孔腔工作电极。其可靠、有效性通过对NiO和TiO₂两种具有代表性氧化物粉体循环伏安曲线和恒电位电解的检测进行了确认。应用新型石墨孔腔工作电极研究了固态Al₂O₃低温熔盐电解机理及阴极还原过程。研究表明Al₂O₃的还原机理是三价铝→铝一步完成,还原过程是部分氧化铝先电解生成金属铝和氧离子,氧离子和钙离子与未电解的氧化铝反应生成CaAl₂O₄和CaAl₄O₇,CaAl₂O₄和CaAl₄O₇进一步还原生成金属铝、CaAl₄O₇和Ca₃Al₂O₆,CaAl₄O₇进一步还原生成金属铝和Ca₃Al₂O₆,Ca₃Al₂O₆最终被还原成金属铝。对固体Al₂O₃的烧结、电解工艺进行了研究。确定颗粒粒径φ<38μm,烧结温度1400℃,烧结时间9h为氧化铝阴极片合适的烧结工艺条件;液态铝镁合金为导电体,熔盐温度800℃,烧结氧化铝为阴极,含氯化钙质量百分数82%的熔盐为合适的电解工艺条件。对Al₂O₃-MgO混合粉烧结片电解制备Al-Mg合金进行了研究。确定烧结温度1300℃,烧结时间8h是合适的阴极片烧结工艺条件;研究发现Al-Mg合金制备的阴极还原过程是部分Al₂O₃先被还原生成铝和中间产物CaAl₂O₄,CaAl₄O₇,中间产物和MgAl₂O₄电解生成金属镁和铝,电解出来的金属镁与金属铝合金化形成Al-Mg合金。对Fe-Dy₂O₃、Fe₂O₃-Dy₂O₃混合粉烧结片电解制备DyFe₂合金进行了研究。研究发现高的氯化钙含量和电解温度对合金制备有利;Fe-Dy₂O₃阴极片电解的阴极过程是氧化镝先电解出金属镝,金属镝扩散到铁粉中形成合金,合金化的过程是DyFe₅→DyFe₃→DyFe₂;烧结温度800℃,烧结时间4h为Fe₂O₃-Dy₂O₃阴极片的合适制备条件。DyFe₂合金电解制备阴极过程是Fe₂O₃先电解出Fe,DyFeO₃电解出Fe和Dy₂O₃,Dy₂O₃再电解出Dy原子,生成的Fe、Dy原子合金化过程是DyFe₅→DyFe₂。分析了阳极气体产生的顺序是先CO₂后CO。更多还原

【Abstract】 The method of direct electrochemical reduction solid oxides to prepare solid metals or alloys in molten CaCl₂ base chloride salts is named FFC Cambridge Process, which is simple and low cost, and is a green process using the inert anode.The problems that include oxide required dissolving into molten salt and oxide’s low solubility and low dissolved rate in traditional low temperature molten salt can be avoided through FFC method. It is a new method to apply the FFC for preparing metals or alloys in low temperature molten salts. Addition to, CaCl₂-NaCl has the low melt point and it assures the feasibility of application of FFC in low temperature molten salt.In the paper, the FFC Cambridge Process method was used to prepare Al and Al-Mg, DyFe₂ in molten CaCl₂-NaCl. A graphite rod was employed as the anode and Al₂O₃, Al₂O₃-MgO, Dy₂O₃-Fe, Dy₂O₃-Fe₂O₃ were served as cathode respectively. The voltage between the cathode and the anode was 3.1 V. Preparation of Al and Al-Mg, DyFe₂ alloys in low temperature molten salt by FFC was studied and Al, Al-Mg, DyFe₂ alloys were obtained.The electrical conductivity and density of molten salts for Al electrolysis was measured by direct Archimedes method and CVCC technology from 550℃to 800℃respectively. The density of molten CaCl₂-NaCl-Al₂O₃ （w（CaCl₂）= 71%-87% corresponding to NaCl, saturated Al₂O₃） systems was increased with the incressing CaCl₂ content, however, the relation of density and CaCl₂ content was not linear from 550℃to 750℃. The additive Al₂O₃ decreased the electrical conductivity, and increased the activation energy of conductance in CaCl₂-NaCl system. The relation of the electrical conductivity of molten CaCl₂-NaCl-Al₂O₃ （w（CaCl₂）= 71%-82%corresponding to NaCl, saturated Al₂O₃） and temperature was linear from 550℃to 800℃. With the CaCl₂ content incresed, the electrical conductivity of systems was decreased, and the activation energy of conductance was also decreased.The new graphite cavity working electrode is developed and applied. Dependability and validity of the new graphite cavity working electrode was affirmed through testing cycle voltage curves and constant potential electrolysis of the NiO and TiO₂ typical powders. The electrochemical reduction mechanism of solid Al₂O₃ was obtained by the cycle voltage method with the graphite working electrode and the reduction process were known by the constant potential electrolysis at different times. The reduction mechanism of solid Al₂O₃ was one step from Al³⁺→Al. The reduction process was as follows. Firstly, Al₂O₃ was partially electrolyzed to form Al and O^2-, then CaAl₂O₄ and CaAl₄O₇ was formed by the O^2- and Ca²⁺ in the molten salts compound with Al₂O₃, CaAl₂O₄ was electrolyze to form Al and CaAl₄O₇, and CaAl₄O₇ was electrolyzed to form Al and Ca₃Al₂O₆, finally the Ca₃Al₂O₆ was electrolyzed to form Al.To prepare the suitable electrolysis cathode Al₂O₃ pellet, the Al₂O₃ particle size, molding pressure, sinter temperature and sinter time were investigated. The optimal conditions of Al₂O₃ cathode pellet preparation were that the particle size was 38μm, the sinter temperature was 1400℃and the sinter time was 9h. The effect of the different cathode materials, such as the commercial Al₂O₃ powder, the Al₂O₃ sintered pellets, corundum powder, corundum tubes and the sintered Al₂O₃ tubes on the electrolysis were studied by using different conductors including metallic wire, melted Al and Al-Mg alloy. The result showed that the melted Al-Mg alloy as the conductor, the sintered Al₂O₃ rods as cathode, at 800℃and in molten salts with w（CaCl₂）= 82% were optimal electrolysis conditions.The effects of Al₂O₃-MgO mixture’s sinter temperature and time on the electrolysis were investigated. The appropriate sintered conditions were at 1300℃and 8h sinter. The electrochemical reduction process of the cathode were as follows. First, Al₂O₃ was electrolyzed to form Al, CaAl₂O₄ and CaAl₄O₇, then MgAl₂O₄ was electrolyzed to form Al and Mg during the Al-Ca compound oxides were electrolyzed, finally the Mg and Al atoms obtained was alloyed.The effects of the temperature and CaCl₂ content in molten salt on electrolysis were studied when Fe-Dy₂O₃ was used as the cathode. The result indicated that high electrolysis temperature and high CaCl₂ content was advantage to prepare pure DyFe₂. The electrochemical reduction process of Fe-Dy₂O₃ was that as follows. First Dy₂O₃ was electrolyzed to form Dy, then Dy atoms diffused into Fe body, the formation sequence of alloy was DyFe₅→DyFe₃→DyFe₂. The effects of the sinter temperature and time of Fe₂O₃-Dy₂O₃ mixture on electrolysis were investigated. The appropriate sinter conditions were at 800℃and 4h sinter. The effect of the molten salt temperature and CaCl₂ content on the electrolysis was studied. The result indicated that high electrolysis temperature and high CaCl₂ content was advantage to prepare pure DyFe₂. Temperature was key factor to form DyFe₂. The electrochemical reduction process of Fe₂O₃-Dy₂O₃ were that first Fe₂O₃ was electrolyzed to form Fe, then DyFeO₃ was electrolyzed to form Fe and Dy₂O₃, and Dy₂O₃ was electrolyzed to form Dy, finally Fe and Dy were alloyed to form DyFe₅→DyFe₂. The anode gases were CO₂ and CO.更多还原