铝基惰性复合阳极材料的脉冲电沉积制备及其电化学性能研究

【作者】 陈阵；

【导师】 郭忠诚；

【作者基本信息】 昆明理工大学 ， 冶金物理化学， 2013， 博士

【摘要】 在现代湿法冶金过程中,阳极材料对提高产品质量和节能降耗都起着关键作用。目前工业上电积锌等金属常用的铅合金阳极具有价廉、易成形、自我修复力强等优点,但也存在能耗高、机械强度低、耐蚀性和催化活性差、使用寿命短以及阴极产品等级低等难以根除的不足。论文针对铅合金阳极的固有缺点,采用脉冲复合电沉积法,在铝基体上制备了锌电积用Al/Pb-WC-CeO2和Al/Pb-WC-CeO2/β-PbO2-WC-CeO2节能惰性复合阳极材料,系统研究了电极微观结构变化与其析氧过电位、电催化活性、耐腐蚀性等电化学性能的关系及规律；并在实验室水平应用于锌电积工艺,探究电极在降低槽电压、提高电流效率和改善阴极产品质量方面的本质原因,探讨了复合电沉积机理及其影响因素。1、铝基体前处理为了增强铝基体与中间复合层(Pb-WC-CeO2)的结合力,对铝基体表面进行预处理的工序为：.喷砂→两步浸锌→镀镍,其中两步浸锌工艺是关键,Fe3+加入的目的是与锌形成Zn-Fe合金,减小晶粒尺寸,改善镀层结合力；镀镍层呈浅米黄色、表面光滑、结晶致密均匀,与基体结合良好,可满足后续电镀工艺的要求。2、Al/Pb-WC-CeO2的制备研究(1)采用双脉冲电沉积制备Al/Pb-WC-CeO2的最优工艺条件为：Pb(CH3CO O)2200～250g·L-1, HBF4160～200g·L-1, H3BO310～20g·L-1, C102H151O39N311-3g·L-1,阳离子活性剂0.5～1g·L-1, pH=0.5,正向占空比30%,负向占空比10%,正向电流120mA·cm-2,正向工作时间200ms,温度40℃。该电极在锌电积液中作阳极时属不可逆电极,能有效阻止溶液向镀层内部的渗透,有利于腐蚀性能的提高。(2)Ce02细化晶粒和整平镀层的作用明显,对镀层中WC含量有抑制作用；适宜的脉冲参数有利于致密晶核的形成,增大镀层比表面积,其中,增加正向工作时间和升高温度有利于基质金属与颗粒的共沉积,但温度过高会减弱固体颗粒在阴极表面的吸附。(3)与直流技术相比,脉冲电沉积的速率提高了约两倍,复合镀层表面更均匀平整,孔隙率低,析氧过电位明显降低,可有效降低槽电压。3、Al/Pb-WC-CeO2/PbO2-WC-CeO2复合电极的制备研究(1)采用单脉冲阳极氧化法制备Al/Pb-WC-CeO2/PbO2-WC-CeO2复合电极的最佳工艺条件为：Pb(NO3)2190g·L-1、Cu(NO3)2·3H2O15g·L-1、NaF0.5g·L-1、C eO230g·L-1、WC40g·L-1,温度60℃,正向平均电流密度75mA·cm-2,正向占空比30%。‘(2)微米WC使镀层晶粒变得粗大,纳米Ce02有填隙晶格和细化晶粒的作用,可有效降低孔隙率,减小镀层缺陷,对Pb02结晶时组织结构的影响起主导作用,并生成铅铈氧共渗化合物；两种颗粒的协同作用使Pb02在沉积过程中产生择优取向,但其物相仍以β-PbO2为主,电极表面形貌由纯Pb02的扁平八角状变成菱形结构。(3)与直流技术相比,采用脉冲技术制备的复合电极在表面形貌、耐蚀性、节能等方面都有着较为显著的改善。4、电极材料在电积锌中的性能比较(1)纳米Ce02和微米WC的协同作用使电极表面更为均匀、致密、整平,有较大的平均法拉第电流,局部微区尖峰电流分布均匀,具有稳定且良好的电催化活性。(2) Al/Pb-WC-CeO2/PbO2-WC-CeO2有最低的槽电压,且在耐腐蚀性、电流效率、使用寿命以及阴极锌中铅含量等方面均有较好的综合性能；失效的主要原因是沉积层逐渐脱落和使用过程中电极表面不可避免出现裂纹。(3)铅合金阳极的腐蚀行为受电极电位和疏松多孔的腐蚀产物的表面覆盖度0两个状态变量的影响；Al/Pb-WC-CeO2/PbO2和Al/Pb-WC-CeO2/PbO2-CeO2电极的腐蚀行为主要由电荷转移电阻控制,Al/Pb-WC-CeO2/PbO2-WC、Al/Pb-WC-CeO2/PbO2-CeO2-WC电极主要由扩散控制。5、复合电镀机理研究(1)脉冲电镀Al/Pb-WC-CeO2时,正、负向脉冲电流交替作用改变了电极表面的吸附、扩散和双电层结构；固体颗粒在阴极表面发生的吸附、脱附反应,影响了沉积过程和扩散过程。(2)在Al/Pb-WC-CeO2/PbO2-WC-CeO2的阳极氧化沉积过程中,F-的加入取代了Pb02晶格上的部分羟基,使Pb02晶体的(101)(200)(301)晶面的生长衍射峰强度增加,(110)(200)(301)(310)晶面的衍射峰减弱,晶粒生长产生了择优取向；两种颗粒的加入使Pb02的沉积过程由Pb(Ⅱ)离子直接向Pb(Ⅳ)的Pb02转化一步完成。更多还原

【Abstract】 In modern hydrometallurgy, the anode materials play a critical role in improving product quality and reducing energy consumption. The lead-based alloys known as cheap, easy to shape and self-healing are used as anode materials in zinc electrowinning. However, there are some inherent defects of lead-based alloys, including high energy consumption, low mechanical strength, poor corrosion resistance and catalytic activity, short service life and low level of cathode product. In the study, aluminum-based inert composite anode materials Al/Pb-WC-CeO2and Al/Pb-WC-CeO2/β-PbO2-WC-CeO2are prepared by pulse composite electrodeposition technology. The relationship between electrode microstructure and electrochemical properties like oxygen evolution overpotential, electrocatalytic activity and corrosion resistance are studied. The nature of electrode in reducing cell voltage, increasing current efficiency and improving cathode product quality are explored when the electrode was used in zinc electrowinning at laboratory level. Besides, the mechanism of composite electrodeposition and its influence factors are discussed.1. Pre-treatment of aluminum substrateIn order to enhance the bonding force of aluminum substrate and intermediate layer(Pb-WC-CeO2), some pre-treatment are applied in the surface of aluminum substrate by following processes:sandblast→two-step dip zinc(the key point)→nickelage. In two-step dip zinc process, Zn-Fe alloy formed by adding Fe3+which can refine grains and improve the bonding force of coating. The light beige nickelage layer with smooth, dense and uniform surface combined with the substrate well, which can meet the requirements of subsequent plating process.2. The study of Al/Pb-WC-CeO2electrode preparation(1) The optimum conditions for preparing Al/Pb-WC-CeO2electrode by double-pulse electrodeposition were:Pb(CH3COO)2200-250g·L-1, HBF4160-200g·L-1, H3BO310-20g·L-1, C102H151O39N311-3g·L-1, cationic surfactant0.5-1g·L-1, pH=0.5, WC40g·L-1,CeO240g·L-1, positive duty cycle30%, negative duty cycle10%, forward current density120mA·cm-2, forward working time200ms, temperature40℃. The composite electrode was irreversible electrode when it was used as anode in zinc electrowinning, which can prevent the solution infiltrating into coating effectively and improve the corrosion resistance significantly. (2) CeO2particles can refine grains, level off coating surface and restrain W content in the coating. Proper pulse parameters were favorable to forming dense crystal nucleus and increasing specific surface area of coating. It was conducive to co-deposition of Pb, WC and CeO2by increasing temperature and forward working time, but excess temperature will reduce the adsorption of solid particles on cathode surface.(3) Compared with DC technology, the electrodeposition rate of pulse technology increased about200%. The surface of composite coating was more uniform, lower porosity and decreased oxygen evolution overpotential significantly, which can reduce the cell voltage effectively.3. The study of Al/Pb-WC-CeO2/PbO2-WC-CeO2electrode preparation(1) The optimum conditions for preparing Al/Pb-WC-CeO2/PbO2-WC-CeO2composite electrode by single-pulse anodic oxidation method were:Pb(NO3)2190g·L-1, Cu(NO3)2·3H2O15g·L-1,NaF0.5g·L-1, CeO230g·L-1, WC40g·L-1, temperature60℃, forward average current density75mA·cm-2, positive duty cycle30%.(2) Micron WC increased coating grains, nanometer CeO2with interstitial lattice and grain refinement effect can reduce the porosity, lessen coating defects and played a key role in tissue and structure of PbO2crystallizing, forming lead-cerium-oxygen nitrocarburizing compound. For the synergistic effect of WC and CeO2, the PbO2grains produced preferred orientation, which resulted in the surface morphology of electrode turning into diamond structure from flat octagonal shape. But the main phase of electrode was still β-PbO2.(3) Compared with DC technology, the composite electrodes prepared by pulse technology had significant advantages in surface morphology, corrosion resistance, energy conservation.4. The comparison of electrode properties in zinc electrowinning(1) For the synergistic effect of CeO2and WC, the electrode surface was more uniform, compact and smooth, the average Faradic current was higher, current spikes of local area was uniform distribution and electrocatalytic activity was stable.(2) The Al/Pb-WC-CeO2/PbO2-WC-CeO2electrode with lowest cell voltage had better comprehensive properties in corrosion resistance, current efficiency, service life and lead contend of cathode zinc; the main reasons for failure were sedimentary shedded gradually and the electrode surface cracked inevitably, which leading to corrosion medium permeated into substrate. (3) The corrosion behavior of lead-based alloys were influenced by the electrode potential and the surface coverage(θ) of the porous corrosion production. That of Al/Pb-WC-CeO2/PbO2and Al/Pb-WC-CeO2/Pb02-Ce02electrodes were mainly controlled by charge transfer resistance, while the Al/Pb-WC-CeO2/PbO2-WC and Al/Pb-WC-CeO2/PbO2-CeO2-WC electrodes were mainly controlled by diffusion.5. The study of composite electroplating mechanism(1) During the pulse electroplating of Al/Pb-WC-CeO2electrode, the alternate effect of pulse current changed the adsorption, diffusion and double electrical layer of electrode surface; reaction of adsorption and desorption of solid particles on cathode surface affected the deposition and diffusion process.(2) During the anodic oxidation deposition of Al/Pb-WC-CeO2/PbO2-WC-CeO2electrode, adding F" replaced hydroxide radical of PbO2crystal lattice, which promoted the growth of (101)(200)(301) crystal plane of PbO2, decreased diffraction peak of (110)(200)(301)(310) crystal plane and produced preferred orientation in PbO2crystal. After doping CeO2and WC particles, the deposition of PbO2was changed into one step process:Pb(Ⅱ) ion was oxidated to Pb(Ⅳ) directly.更多还原