低银铅合金电极制备与性能研究

发布时间：2018-08-31 17:11

【摘要】：阳极材料的选用一直是湿法冶金过程的核心,其性质对于电沉积金属的品质和生产能耗都有很大影响。铅合金阳极材料因具有良好的耐蚀、催化活性、易加工及可回收利用等特点,一直是电化学工业的首选。因电解过程能耗巨大,而其阳极过电位的无功电耗可达1/3,因此铅合金阳极性能的改进可带来显著的节能效果并产生良好的经济效益。银对铅合金电极的催化性、耐蚀性、阳极压降等性能有助益但是成本高昂。一般工业常用铅银阳极的银含量约0.7-1%,约占电极成本的70%。相当多的研究都是尝试添加多种元素来减少银含量并保持或提高其性能,而对于铅合金微观组织结构对其电化学、力学性能的研究较少。本文选择含银0.5%的低银铅合金为研究对象,综合运用超声波干预凝固、等径通道转角挤压、室温轧制、低温冷轧及退火工艺这五种方法,成功获得了多种平均晶粒尺寸的样品；研究了样品的平均晶粒尺寸和组织分布,测试了其电阻率、极化曲线、槽电压、Tafel曲线、η-lgi图和显微硬度,探讨了工艺参数对其微观组织及性能的影响。测试与分析结果表明,采用超声波干预凝固+轧制方法获得了最佳电极综合性能。其优化工艺参数为：熔体温度643 K(370℃)、超声处理时间1 min、以及压下量20%的轧制工艺,在413 K(140℃)温度下退火1h。经此工艺处理的Pb-Ag合金电极,与铸造工艺相比导电性能、电化学性能和力学性能均得以显著提升。其中电导率提高44.86%,阳极极化过电位降低18.13%,槽电压降低4.82%,显微硬度提升2.23倍。Tafel曲线和η-lgi分析表明,采用该工艺利于获得较低的自腐蚀电流和析氧过电位,能提高阳极的耐腐蚀性及电导率,具备较佳的电化学性能。同时致密的微观结构使阳极表面的腐蚀形态有明显改变,由原来呈较集中的局部晶间腐蚀变为均匀腐蚀,这使得阳极使用寿命有较多的提升。金相显微观察表明,随合金平均晶粒尺寸的减小,合金的强度及电化学综合性能逐渐升高然后降低,其间存在晶粒尺寸10μm左右的最优值。1)当Pb合金阳极材料的平均晶粒尺寸进一步细化时,阳极材料的耐腐蚀性能变弱,电导率降低,原因是晶界密度及晶粒内部缺陷密度高,晶界面积大且界面能高,且内应力较强,其微观组织的热力学活性较高。(2)阳极材料的平均晶粒尺寸过大时,其耐腐蚀性能不强且电导率也不高,原因在于成分的非均匀分布。在与电解质相接触的电极表面的晶粒与晶界上,易诱生较大的电偶极势垒并构成超微电化学池,因此降低耐腐蚀性；同时,虽然此时银组元更可能分布于晶粒内部并以共晶组织的形式存在,晶界处的银较少,但因银含量低,晶界电子散射效应依然较强,故降低导电性。(3)对具有适中的平均晶粒尺寸的阳极材料而言,因电导率远高于Pb的Ag组元可能以单质的形式分布在晶界上,减弱晶界电子散射效应,从而提高了阳极电导率。由于晶粒尺寸适中(约10μm)且分布均匀致密,不易诱生局部的深入和快速腐蚀,因而阳极耐腐蚀性得以增强,合金阳极材料具有良好的综合性能。此外,晶粒大小适中时,内应力减小,结构的热稳定性较好,使其可在略高于再结晶温度的温度下稳定服役。采用超声波凝固技术,并结合大塑性变形、轧制及退火等加工方法,成功制备了0.5wt.%Ag的低银含量铅银合金电极,有效改善结构缺陷,提升了力学性能、催化活性及耐腐蚀性,使合金阳极综合性能提高。研究所获的处理方法简便而设备和工艺成本低,不仅对于电解领域节能降耗深具意义,还有利于电极材料的循环再利用,并能产生显著经济效益。进行了铅系难混溶合金固液界面能计算模型的研究,改进了可用于铅银二元合金固-液界面能热力学计算的Warren模型。建立的新模型可以对Pb-Ag、Pb-Cu、 Pb-Al及其他难混溶二元合金体系的固液界面能进行更为简捷和准确的估算,且计入了Warren模型未考虑到的温度对其摩尔体积的影响。
[Abstract]:The selection of anode materials has always been the core of hydrometallurgical process, and their properties have a great influence on the quality of electrodeposited metal and energy consumption. Lead alloy anode materials have been the first choice of electrochemical industry because of their good corrosion resistance, catalytic activity, easy processing and recyclability. The reactive power consumption of electrode overpotential can reach 1/3, so the improvement of lead alloy anode performance can bring remarkable energy-saving effect and produce good economic benefits. The catalytic performance, corrosion resistance and anode voltage drop of silver on lead alloy electrode are helpful but costly. The silver content of lead-silver anode commonly used in industry is about 0.7-1%, which accounts for the cost of electrode. A considerable number of studies have attempted to add a variety of elements to reduce the silver content and maintain or improve its properties, while less has been done on the electrochemical and mechanical properties of lead alloys. A variety of samples with average grain size were successfully obtained by the five methods of warm rolling, cold rolling and annealing. The average grain size and microstructure distribution of the samples were studied, and their resistivity, polarization curve, cell voltage, Tafel curve, _-lgi diagram and microhardness were measured. The results of test and analysis show that the optimum comprehensive properties of the electrode are obtained by ultrasonic solidification and rolling. The optimum processing parameters are melt temperature 643 K (370 C), ultrasonic treatment time 1 min, and rolling process with 20% reduction, annealed at 413 K (140 C) for 1 h. Compared with the conductivity, the electrochemical and mechanical properties were improved significantly. The conductivity increased by 44.86%, the anodic polarization overpotential decreased by 18.13%, the cell voltage decreased by 4.82%, and the microhardness increased by 2.23 times. At the same time, the dense microstructure makes the corrosion morphology of the anode surface change obviously from concentrated local intergranular corrosion to uniform corrosion, which makes the service life of the anode increase a lot. The metallographic observation shows that with the decrease of the average grain size of the alloy. When the average grain size of Pb alloy is further refined, the corrosion resistance of the anode material becomes weaker and the conductivity decreases. The reason is that the grain boundary density and the defect density inside the grain are high, and the grain boundary area is low. (2) When the average grain size of anode material is too large, its corrosion resistance is not strong and its conductivity is not high, which is due to the non-uniform distribution of the composition. At the same time, although the silver component is more likely to be distributed in the grain interior and exist in the form of eutectic structure, there is less silver at the grain boundary, but because the silver content is low, the electron scattering effect at the grain boundary is still strong, so the conductivity is reduced. (3) For anodes with moderate average grain size. As far as the conductivity is concerned, the Ag component, which is much higher than Pb, may distribute on the grain boundary in the form of elementary substance, thus weakening the electron scattering effect at the grain boundary and thus improving the anodic conductivity. In addition, when the grain size is moderate, the internal stress decreases and the thermal stability of the structure is good, so that it can be used stably at a temperature slightly higher than the recrystallization temperature. The alloy electrode can effectively improve the structural defects, enhance the mechanical properties, catalytic activity and corrosion resistance, and improve the comprehensive performance of the alloy anode. Benefits. The calculation model of solid-liquid interface energy of lead-based hard-to-miscible alloys is studied. The Warren model which can be used to calculate the solid-liquid interface energy of lead-silver binary alloys is improved. The new model can be used to estimate the solid-liquid interface energy of Pb-Ag, Pb-Cu, Pb-Al and other hard-to-miscible binary alloys more simply and accurately. The influence of temperature on the molar volume of Warren model is not considered.
【学位授予单位】：昆明理工大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TF351;TG146.12

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