【作者】 杨少华；

【导师】 邱竹贤； 张廷安；

【作者基本信息】 东北大学 ， 有色金属冶金， 2008， 博士

【摘要】 以氧化镁为原料熔盐电解法制备铝镁合金有其独特的环境效益和经济优势。同时,该研究成果可以进一步发展为一种新的镁电解工艺,为镁工业提供新的研究发展思路。试图在Na3AlF6-AlF3体系中以氧化镁为原料制备Al-Mg合金。镁在Al-Mg合金中的含量均很低,最高为0.08w%。从两种制备Al-Mg合金的还原机理上都否定了在Na3AlF6-AlF3体系中可以制备Al-Mg合金的可能性。以RECl3-KCl-MgCl2为电解质合金中Mg含量可以达到4.76%。但合金中同时由Al还原出了电解质中的RE元素形成了Al-Mg-RE三元合金。通过Al直接还原实验,证实了Al-Mg合金中RE元素是由Al直接还原而来,合金中的RE元素含量比较稳定,质量百分比为0.8-1.2%。MgF2-LiF-KCl为电解质体系研究了KCl对电解质临界电流密度的影响,结果表明KCl加入到电解质中,可以增加电解质对MgO的溶解性能。Al-Mg合金中镁含量随电解时间的延长而逐渐增加,最高达到9.2%。而电流效率随电解时间的延长也有所升高,最高达到了79.4%。进行200A实验室扩大实验中发现槽电压比较平稳,基本上没有发生太大的变化,变化的幅度在0.6V之内,电流效率为82.6%。BaF2-LiF-MgF2电解质体系电流效率都比较高,最高可以达到89.4%,最低也有81.7%。电解质中KCl含量增加并没有使电解的电流效率提高。但同不加KCl相比较,加了KCl的电解质的电流效率还是比不加KCl的电解质的电流效率高。45%BaF2-13%LiF-33%MgF2-9%KCl电解质体系的电流效率在其它条件相同的情况下比45%BaF2-13%LiF-42%MgF2电解质体系的电流效率提高了11%。当电解时间在60min时,电流效率最大,达到了87.7%。之后电流效率有下降的趋势,但最小的电流效率还是保证在82%以上。随着电解时间的延长,合金中镁含量逐渐增高,在3h内,合金中镁含量达到了18.6%,在保证电解质中维持2%的氧化镁浓度,可以使电解在电流密度为0.7A/cm2的情况下正常进行。电化学实验证明电解质中有最正的析出电位的K+离子的析出电位为-2.25V,而镁在BaF2-MgF2-LiF-KCl体系中相对于铂电极在钨电极上的析出电位-1.42V。说明镁离子有比电解质体系中其它离子更正约830mV的析出电位。不同电流下电流时间的常数基本上没有发生改变,说明镁离子的沉积过程由镁离子在熔体中的扩散控制。由计时电流曲线中上升部分的电流I和t1/2的关系图可知电流I和t1/2呈良好的线性关系,说明镁离子在钨电极上的成核过程是瞬时成核起主导作用。电解质的密度随温度的升高而减小,同时KCl含量的增加和MgF2的含量减少共同作用可以使电解质的密度减小。电解质的初晶温度随KCl含量的增加和MgF2的含量减少共同作用而降低。用CVCC技术测定熔盐电解质的电导率,结果表明：随温度的升高,熔盐电解质的电导率上升,电解质成分中KCl含量的增加和MgF2的含量减少可以使电解质的电导率升高。透明槽实验研究发现氧化镁在电解质中的溶解过程可分为四个连续的过程。阳极侧面的气体生长是个动态的连续过程,小气泡可以汇合成大气泡溢出电解质,而阳极底部的气体是一个小气泡慢慢的长大,变成一个大气泡,甚至气体可以生长到直径和阳极的直径(Φ=5mm)一样大时才从阳极的侧面上很快的溢出电解质。阳极气体的析出行为和阴极有很大的关系,底部生成的阳极气体均是从靠近阴极的阳极侧面溢出电解质。同时,靠近阴极的阳极侧面气体直径比另一侧阳极侧面的气体直径小。在低电流密度下,阳极气体的气泡直径比较小,在高电流密度下,阳极气体的气泡直径比低电流密度下生成的气泡直径大。更多还原

【Abstract】 Preparation of Al-Mg alloy by molten salt electrolysis method from magnesium oxide has special advantages of environment and economy. At the same time, the method can be further developed to a new electrolytic technology on magnesium industry, and to come forth a new thought for studying on magnesium metallurgy.Preparation of Al-Mg alloy was tried in Na3AlF6-AlF3 electrolyte from magnesium oxide, and the results could not match with satisfaction of experimental goal. Content of magnesium in alloy was very low, the highest was 0.08%(w). The method, which Al-Mg alloy was prepared in Na3AlF6-AlF3 electrolyte from magnesium oxide, was denied on two reduction mechanisms.Content of magnesium in alloy, which its electrolyte was RECl3-KCl-MgCl2, could reach 4.76%(w). However, element of alloy consisted of Rare Earth, and Al-Mg-RE ternary alloy was prepared in this electrolyte. RE element in alloy was proved that it was reduced directly by aluminum by experiment of aluminum reduction. Content of RE in alloy was stable, it was between 0.8-1.2%.Critical current density of electrolyte was studied in MgF2-LiF-KCl electrolyte. The results could show critical current density of electrolyte was affected by content of KCl in electrolyte, and KCl as additive could promote solubility of magnesium oxide in electrolyte. Content of Mg in alloy increased gradually with electrolytic time, the highest was 9.2%(w). Current efficiency increased with electrolytic time, the highest was 79.4%.200A experiment was carried out in laboratory, the results showed that voltage of cell was stable, the range of variation was small, it was about 0.6v, and current efficiency was about 82.6%.Current efficiency was high for BaF2-LiF-MgF2 electrolyte, the highest was 89.4%. Results of research showed that current efficiency was not increased with content of KCl in electrolyte. Compared with no additive of KCl in electrolyte, however, the current efficiency which the electrolyte consisted of amount KCl was higher than that of no KCl in electrolyte. Take 45%BaF2-13%LiF-33%MgF2-9%KCl and 45%BaF2-13%LiF-42%MgF2 for example, the current of former increased about 11% more than that of the latter. The current efficiency was the highest when the electrolytic time was 60 minutes, its value was 87.8%. After that time, the current efficiency decreased slowly, the lowest, however, was higher than 82%. Content of magnesium in alloy increased gradually with electrolytic time. During 3 hours, the content of magnesium reached 18.6%. To guarantee content of magnesium oxide in electrolyte over 2%, the electrolysis could maintain normally with 0.7A/cm2 current density.It was proved by electrochemistry experiment that decomposed voltage of K+, which was the most positive ion in electrolyte, was-2.25V. Mg2+, however, its decomposed voltage relative platinum electrode on tungsten in BaF2-MgF2-LiF-KCl electrolyte was-1.42V. This could show that decomposed voltage of Mg2+was more positive about 830mV than that of other ions in electrolyte. The constant of current and time hardly changed under different current, conclusion could be drawn that process of Mg2+ decomposition was controlled by diffusion of Mg2+ in electrolyte. The rising part of current, which was studied in chronoamperometry experiment, was a good line relationship with time rooting, this could prove that key action of nucleation process was instant nucleation for magnesium ion on tungsten.Density of electrolyte decreased with rising of temperature, common action with increasing content of KCl and decreasing content of MgF2 could lead to reduce density of electrolyte. Liquidus of electrolyte decreased because of common action that content of KCl increased and content of MgF2 decreased in electrolyte. Conductivity of electrolyte was measured by method of continuously vary cell constant, the results showed that conductivity of electrolyte increased with rising of temperature, and the same results with content of KCl increased and content of MgF2 decreased in electrolyte.Process of solubility about magnesium oxide in electrolyte was measured in transparent cell. The results could show the process was four continuous steps. Growth of bubble on anode side was a dynamic continuous process. The big bubbles, which were merged by small bubbles, could overflow electrolyte. On the contrary, bubble at anode bottom was slowly grown up by a small bubble, the big bubble could overflow electrolyte when its diameter was big enough, even the diameter could grow up to 5mm which was the diameter of anode in the experiment. Overflowing speed of bubble on anode side was very fast. Behavior of bubble on anode was in close relationship with cathode. The bubbles grown at bottom of anode were all overflowed on anode side which was near the cathode, and the bubbles grown on side of anode, which was near the cathode, were all smaller than that of opposite side. Diameter of bubble was smaller in low current density than that of high current density.更多还原