Pb-Al层状复合节能阳极制备及其性能研究

【作者】 周生刚；

【导师】 孙勇； 竺培显；

【作者基本信息】 昆明理工大学 ， 材料学， 2011， 博士

【摘要】 当前湿法冶金工业中,铅合金阳极因其制备工艺简便、成本相对低廉仍被广泛应用于电积Zn、Cu、Ni等有色金属的生产中,但铅合金阳极析氧过电位高、无功损耗大以及其材料基体本身存在的内阻大、抗蠕变性差、易发生非均匀腐蚀、污染电解液及阴极产品等的诸多弊病一直制约着该领域的技术进步及经济效益。基于以上诸多问题,虽然目前已有涂层钛阳极可有效改善某些性能,但其昂贵的材料成本与制备工艺复杂性成为取代铅基合金阳极的瓶颈问题。本研究率先提出Pb-Al层状复合节能阳极的新材料构想,先后获得国家自然科学基金及国家"863"计划项目的资助,利用较为简便的工艺制备出了一种集轻质、高强、优良导电性、长寿命、低电耗、高电流效率及高阴极产品品位等优势于一体的节能阳极。论文通过引入第三组元过渡金属Sn,借助热压扩散复合工艺将Pb、Al两种非混溶材料过渡连接起来,所形成的薄层界面起到了固溶强化、良好的电传导性作用,通过实验验证了其物理化学性能的稳定可靠性,集Pb、Al各自的优势于一体得以同时发挥。系统研究了制备工艺对界面组织、力学协同变形能力、电阻率的影响关系,在此基础上,深入研究了Pb-Al层状复合阳极材料的电化学性能,以电积锌为例开展了模拟电解试验,并分析了Pb-Al层状复合阳极的节能机理。主要研究成果如下：(1)基于Pb-Al层状复合阳极材料制备工艺思想,分别对Pb-Al二元液固界面能及Pb-Sn-Al三元系热力学混合特性做了对比计算分析,在研究温度范围内,当温度上限达到753.15K,Al、Sn、Pb组分点含量(at.%)为：0.42%,73.55%,26.03%时,对应的最小混合吉布斯自由能约为-5.33×104J/mol,极大地改善了系统热力学难混溶性,为进一步制备Pb-Al层状复合材料提供了理论基础。(2)采用机械振动法制备出了界面结合良好的Al-Sn层状复合材料。Al和Sn两相中,(200)A1与(211)Sn成27.6°角形成界面时存在约25%的错配度,通过错配度计算,约每4个(211)Sn晶面间距与三个(200)Al晶面间距对应,即每4个(211)Sn就有一个点阵重合位置,这样的点阵匹配度是一种相对较低的界面能状态,形成了稳定的Al-Sn界面。Al-Sn层状复合材料时效150天的XRD分析结果显示,表层主要以β-Sn形式存在,仅有微量的SnO2生成。(3)在研究了Al、Sn可复合性的基础上,采用热压扩散焊接法制备了Pb-Al层状复合材料。通过EDS、SEM等分析了其界面形貌及相组织。研究发现,随着扩散温度和保温时间的增加,界面上最终形成了(α(主)+β(次))共晶体/(p(主)+a(次))共晶体/β(Sn-Pb)+Al多层连续过渡结构,且界面扩散宽度也在逐渐变大,由最初的2.5μm初相宽化到18.4μm。利用热动力学原理对界面扩散的原子迁移和相迁移规律进行分析,发现主相Pb-Sn共晶组织的生长采取分枝、搭桥的方式,α相通过分枝在β相上长大,β相分枝又在α相上长大,最终达到了两相交替的层状排列式组合,室温下保持了球团状相遇共晶组织,以使系统的能量处于最低状态,使界面具备了较好的热力学稳定性。(4)对不同工艺条件下制得的Pb-Al层状复合材料进行了力学性能及导电性能的测试与分析。Pb-Al层状复合材料与传统Pb-1%Ag合金相比较,同形状体积下其重量平均减轻32%,平均抗弯强度提高70.1%,界面平均维氏硬度提高205%。随着界面的合金化程度变大和界面宽化,在界面结合强度不断改善的同时也牺牲了一定的导电性,但由于界面层的厚度仅在单位微米数量级,其带来的界面电阻值仅在1.435×10-8-6.605×10-7Ω范围,从对材料的整体导电性的要求来讲,并不会给其应用为阳极材料带来明显的负面影响,能够将Al芯材的优良导电性能集中体现在层状基体结构中,使得阳极基体的内阻与同体积的铅合金阳极基体相比大幅降低。(5)极化曲线测试结果表明,Pb-Al层状复合阳极较Pb-1%Ag阳极极化电位平均降低18.2%,降低了自腐蚀溶解的可能性。表观电流密度为500A/m2电解时,无论Mn2+存在与否,Pb-Al层状复合阳极析氧电位均明显低于Pb-1%Ag合金板阳极的析氧电位,均缩短了且其达到相对稳定所需的时间。采用有效工作面积均为170mm×110mm×6mm的Pb-Al层状复合阳极与Pb-1%Ag合金阳极经过24天的现场模拟电解生产试验,各Pb-Al层状复合阳极在不同程度上均达到了降低槽电压、析氧电位及阳极实际电流密度的目的,Pb-Al层状复合阳极对应的电流效率均在92%左右,而Pb-1%Ag合金阳极对应的电流效率为89.74%。从能耗的角度计算,Pb-A1层状复合阳极对应的每吨锌产量的电耗平均较Pb-1%Ag合金阳极节省116kWh,节能效果意义明显。阳极腐蚀速率降低80%,阳极泥生成量减少90%左右,且阳极泥中的含铅总量仅为Pb-1%Ag合金阳极对应阳极泥的1/15；极大地改善了传统Pb-Ag合金阳极对应阴极锌产品易发生边缘枝晶的状况,说明Pb-Al层状复合阳极的结构设计及A1芯材的优良导电性起到了均化电极表面电流分布的作用：Pb-Al层状复合阳极的工程化模拟电解试验取得了良好的效果,达到了节能降耗、延长阳极使用寿命的效果。更多还原

【Abstract】 Because of the benefits of low cost and simple process, the lead-based alloy anodes have been widely used in the electro-deposition of nonferrous metals, such as Zn. Cu, Ni, etc. But the high anodic over potential for oxygen evolution, high reactive power loss as well as inherent problems like high internal resistance, low creep resistance, non-uniform corrosion and the contamination of the electrolyte and cathode products, has restricted the technological creativity and economic progress for the corresponding hydrometallurgical processes. To solve the problems above, although noble oxide coated Titanium anodes can efficiently improve certain properties, the complex process and high cost make it too hard to become a substitute for lead-base alloy anodes.In this paper, the concept of the Pb-Al laminated composite material as a new energy-saving anode is proposed for the first time. The present research, supported by the National High Technology Research and Development Program of China (national 863 plans projects) and the National Natural Science Foundation of China (NSFC), aims to obtain an energy-saving anode with light weight, high strength, good conductivity, long working period, low power consumption, high current efficiency and high quality cathodic product by a simplified process. By introducing the third element Sn, the immiscible materials Pb and Al are transitionally combined by the hot pressing diffusion technique, forming thin solid solution enhanced interfaces with good electrical conductivity so that the advantages of Pb and Al can be used simultaneously. Stability of physical chemistry of the interfaces is experimentally confirmed. Influence of preparation technology on the interfacial microstructure, the cooperative deformability and electrical resistivity are systematically studied. On this basis, further investigations are carried out on the electrochemical properties of Pb-Al laminated composite anode materials, simulated production of zinc electrowinning is performed, and the energy-saving mechanism of Pb-Al laminated composite anode materials are analyzed. The research results are as follows:(1) Based on the preparation principle of Pb-Al laminated composite anode materials, thermodynamic calculation is carried out to analyze the Pb-Al binary liquid-solid interfacial energy and characteristics of Pb-Sn-Al ternary system. When reaching the upper limit of temperature 753.15K, the minimum interfacial binding energy value is -5.33×104J/mol, with composition of the material is 0.42 at.%,73.55 at.% and 26.03 at.% for Al, Sn and Pb, respectively, and it provides theoretical basis for the preparation of Pb-Al laminated composite anode materials.(2) Al-Sn laminated composite with good bonding interface is obtained by hot dipping Sn on the surface of Al through the mechanical vibration method. when the (200)Al and (211)Sn crystal plane makes an angle of 27.6°between Al phase and Sn phase, there would be a mismatch of 25%. The results of mismatch calculation show that every four interplanar spacings of (211)Sn correspond with three interplanar spacings of (200)Al. That is, every four (211)Sn interplanar spacings have a coincidence lattice position, which makes a relatively low interfacial energy, leading to the stable Al-Sn interface. After the aging treatment of the Al-Sn layered composite material for 150 days, XRD analysis shows that besides small amounts of SnO2, the surface mainly in the form ofβ-Sn.(3) Pb-Al laminated composites are prepared by means of hot pressing diffusion, on the basis of the study of the Al-Sn solder ability. EDS and SEM are carried out to analyze the interface topography and phase structure under varied preparing conditions. The results show that with increasing diffusion temperature and holding time, an alternately distributing continuous multilayered transition structure with a principal phase ofα(Sn-Pb)+β(Sn-Pb) solid solution is ultimately generated on the interface. The fraction of new generated phase increase with temperature and holding time, and the diffusion breadth also changes from a 2.5μm wide primary phase to a 18.4μm multiphase continuous transition diffusion layer. Thermodynamic principles are used to analyze the atom/phase transformation of interfacial diffusion. The results indicate that the Pb-Sn eutectic structure of the principal phase grows through branching and bridging. The a phase grows on theβphase through branching, and simultaneously theβphase grows on the a phase, leading to an ultimate staggered layered structure. Cores of the two phases grow radically since formed, and a final spherical meeting eutectic structure is formed, so that the total system energy remains minimum, and the interfaces possess good thermodynamic stability.(4) Interfacial microhardness analysis, conductivity and integral bending property test are carried out on Pb-Al laminated composite materials obtained under different preparing conditions. The results show that compared with Pb-1% Ag alloy material, the weight of the Pb-Al laminated composite materials is reduced by 32% on average with the same shape and volume, the average bending strength is increased by 70.1%, the average interfacial Vickers hardness is enhanced by 205%. With the alloying extent and interface broadening, the interfacial bond strength is increased but it decreases the conductivity on the other hand. However, thanks to the unit microns level thickness of the interfacial layer, the interface resistance value is from 1.435×10-8Ωto 6.605×10-7Ω. However, it will not have a significant negative impact when the Pb-Al laminated composite materials used as anode to meet the overall conductivity requirements, and it makes Al as the core material can present an excellent electric conductivity for the layered structure anode material matrix. Thus, the internal resistance of the Pb-Al laminated materials is lower than that of the lead alloy anode substrates in the same volume.(5) The results of polarization curves show that compared with the Pb-1% Ag anodes, the anodic polarization potential of the Pb-Al laminated anodes is decreased by 18.2%, it reduces the possibility of self-corrosion. When the apparent current density is 500A/m2, regardless of the existence of Mn2+, the anodic oxygen evolution potential of Pb-Al laminated anodes is lower than Pb-1% Ag alloy anodes, so as to speed up the electrode polarizing process. The Pb-Al laminated composite anodes with dimension of 170mm×110mm×6mm are tested in pilot scale experiment for 24 days and the anodes are found to perform well in industrial electrolysis conditions. The corresponding average current efficiency of Pb-Al laminated composite anodes is about 92%, while the corresponding average current efficiency of Pb-1% Ag alloy anodes is only about 89.74%. The calculating results of energy consumption (per tonne of zinc produced) show that, compared with Pb-1% Ag alloy anodes, Pb-Al laminated composite anodes have reduced energy consumption by 116kWh, energy-saving effects are very obvious, and at the same time, the quantity of anode mud and the anodic corrosion rate is reduced by 90%,80%, respectively. The edge dendrite phenomenon of cathode zinc products has been greatly improved due to the fact that the optimized layered structure design of the composite anodes, and the good conductivity of Al core material. Finally, the aim of saving energy and lowering anodic corrosion has been obtained according to the production practice of Zinc electrolysis.更多还原