Ti基Pb/Pb-WC-PANI复合阳极材料制备及其电化学性能研究

【作者】 曹梅；

【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】 目前,国内外湿法冶金行业用的阳极材料主要有铅银合金和钛基涂层阳极。铅基合金阳极是锌电积中使用最多的,但其重量大、强度低,易弯曲变形造成短路而使电能损失。钛基涂层阳极形状尺寸稳定,适于高电流密度(4.5～6.0kA/m2)和窄极间距(约5cm左右)的电积条件。但钛基贵金属及其氧化物涂层价格高昂；不含中间层的钛基电极中钛易钝化,导电性能降低；含中间层的钛基涂层电极,制造程序复杂；电沉积钛基二氧化铅的电化学活性提高,但其畸变大、易脆、机械加工困难、重量大、不易大型化、制备时间长,限制了其规模生产及使用。本文研制了一种Ti基新型惰性阳极,由钛基体、Pb底层及Pb-PANI-WC表面活性层组成。底层改善了表面层与钛基间的结合性能；表面层是铅和活性颗粒组成的复合镀层,反应过程中能降低析氧电位。且钛价格适中,导电性良好,质量轻,是阀型金属。该种电极材料在有色金属电积中有广阔应用前景。本文采用直流或脉冲电沉积法,在Ti基上制备铅基复合镀层；研究了镀液组成、固体颗粒及工艺条件对镀层性能的影响,从不同镀液中电沉积制备了Ti/Pb/Pb-PANI-WC复合镀层。采用阳极极化曲线、Tafel.EIS.循环伏安等手段在硫酸锌-硫酸溶液中测定了动力学参数,并以阳极析氧电位作为考核指标,优化了镀液组成和工艺条件。从酒石酸钾钠体系中直流电沉积制备了Pb-PANI和Pb-WC两种复合镀层的最佳制备工艺为：氧化铅100g/L,酒石酸钾钠170g/L,氢氧化钾55g/L,明胶1.5g/L,温度为室温,电镀时间90min,电流密度4A/dm2。Pb-PANI复合镀层镀液中PANI为15g/L, Pb-WC复合镀层WC为40g/L。从碱性(酒石酸钾钠-乙二胺四乙酸二钠体系)和酸性(氟硼酸体系)两种体系中直流电沉积制备Pb-PANI-WC复合镀层。优化得到碱性体系中最佳工艺条件为：电流密度1.5A/dm2,温度35℃,聚苯胺浓度15g/L,WC浓度为40g/L。酸性体系中的最佳工艺条件：电流密度是5A/dm2,温度35℃,聚苯胺浓度10g/L,WC浓度为40g/L。采用脉冲电沉积从碱性(酒石酸钾钠体系)和酸性(氟硼酸体系)两种体系中制备了Pb-WC-PANI复合镀层。优化得到碱性体系中最佳工艺条件为：氧化铅1OOg/L,酒石酸钾钠150g/L,氢氧化钾55g/L,明胶1.5g/L,聚苯胺浓度10g/L,碳化钨30g/L,周期1.5ms,脉冲导通时间0.3ms,平均电流密度3A/dm2,温度为室温。酸性体系中的最佳工艺条件：PANI:30g/L, WC:30g/L,脉冲导通时间：0.5ms,脉冲周期：1.5ms,平均电流密度：2A·dm-2,温度：25℃。利用SEM、XRD、EDS等现代测试手段对镀层的表面形貌、结构物相、成分进行了分析表征。用快速寿命实验方法考察了复合镀层在硫酸-硫酸锌溶液中1A/cm2下的预期使用寿命,并比较了镀层的电化学性能。脉冲电沉积获得的两种Pb-WC-PANI复合镀层表面明显比直流复合镀层结晶致密,没有明显晶界。XRD研究显示,复合镀层中出现了明显的Pb和WC的衍射峰,没有观察到PANI的衍射峰,且脉冲Pb-WC-PANI复合镀层的衍射峰强度弱于直流复合镀层。通过红外光谱分析,观察到复合镀层中有PANI的特征峰。EDS研究显示,直流复合镀层中WC含量明显低于脉冲复合镀层,酸性复合镀层中的颗粒含量明显低于碱性复合镀层。所有镀层中碱性脉冲Pb-WC-PANI复合镀层中WC含量最高,达到24.7%(wt%)。电化学性能比较,Ti基Pb-PANI复合镀层优于Pb-WC,同时优于纯铅镀层。说明PANI和WC的掺杂均有利于析氧催化活性的提高。两种体系中,脉冲电沉积Pb-WC-PANI复合镀层催化活性均优于直流复合镀层。比较两种体系中的脉冲复合镀层,得到,碱性条件下制备的复合镀层性能优于酸性复合镀层。比较了酸性、碱性脉冲复合镀层与Ti基贵金属涂层和两种铅银合金电化学性能,复合镀层析氧电位高于钛基贵金属涂层而低于铅银合金,耐蚀性均优于铅银合金阳极而比钛基贵金属阳极差,碱性镀液中所得复合镀层Ecorr=-0.323V, Icorr=7.10×10-6A/cm2。酸性脉冲复合镀层具有最大的伏安电荷(q*=0.4219C·cm-2),碱性复合镀层伏安电荷(q*=0.1907C·cm-2)大于铅银合金(含银0.6%的q*=0.0158C·cm-2)而低于钛基贵金属涂层(q*=0.2779C·cm-2)。阻抗谱显示Ti基贵金属涂层的电催化活性最好,两种脉冲复合镀层次之,其析氧催化活性均优于铅银合金阳极。复合镀层的强化寿命低于贵金属涂层电极和铅银合金电极。与铅银合金比较,复合镀层电流效率较高,而槽电压较低,作为阳极材料比铅银合金阳极更节能。新型Pb-WC-PANI复合镀层的重量不足铅银合金的20%,加之其催化活性优于铅银合金,槽电压低于铅银合金,因此是理想的阳极材料。论文得到了云南省教育厅青年科学基金(2011Y37324)、昆明理工大学分析测试基金等项目的联合资助。更多还原

【Abstract】 At present, lead-silver alloy and titanium based coating have been widely used as insoluble anodes in the hydrometallurgy industry at home and abroad. Although Lead-based alloy is the most commonly used anode material in zinc electrowinning, it is of heavy weight, low strength and is prone to warping, which can easily trigger short-circuit and then electric power may loss. Titanium based coating has stable shape and size, and can be applied in conditions such as high current density (4.5～6.0kA/m2) and narrow pole pitch (about5cm). However, the costs of the precious metal and its oxide are high. In addition, the titanium-based electrodes without the intermediate layer are passivated easily and have poor conductive properties. The manufacturing procedures of titanium-based electrodes with the intermediate layer are complicated. The lead dioxide be prepared by electrodeposition have good electrochemical activity, but its heavy weight, fragility and easy distortion result in its poor machinability, which finally limit its large-scale production and application.A new type of Ti-based inert anode made up of three layers is presented in this paper. Its bottom layer is made of titanium plate and is covered with lead undercoating. The surface Pb-PANI-WC layer is composite coating layer composed of lead and active particle. Generally the bottom layer can enhance the combination between the surface layer with the titanium substrates. When the chemical reaction on the surface layer happens, oxygen evolution potential correspondingly reduces. Meanwhile, Titanium, a kind of valve metal, is a good conductor of light weight. Ti/Pb-PANI-WC electrode prepared by electrodeposition can be used widely in the non-ferrous metal electrowinning filed.In this paper, lead based composite coatings are prepared by direct current or pulse electrodeposition on Ti substrate preparation. The effects of electrolyte compositions, solid particles concentration and process conditions on the properties of coating are investigated. The Ti/Pb/Pb-PANI-WC composite coatings are prepared respectively from different plating solution. The electrocatalytic properties of composite materials are studied by means of linear sweep voltammetry, Tafel plot, and A.C.Impedance and Cyclic voltammetry in ZnSO4-H2SO4solution. At the same time, the electrocatalytic activity of the composite materials in the oxygen evolution reaction is studied with aim of assessing the effect of electrolyte compositions and process conditions and gaining the better electrolyte compositions and process conditions.The Pb-PANI and Pb-WC composite coatings are prepared in sodium potassium tartrate electrolyte system by DC deposition. The better electrolyte compositions and process conditions can be obtained as follows:lead oxide100g/L, sodium potassium tartrate170g/L, potassium hydroxide55g/L, gelatin1.5g/L,T is room temperature, electroplating time90min and current density4A/dm2.。In the plating solutions of Pb-PANI composite coatings, PANI is15g/1, and WC is40g/L in those of Pb-WC composite coatings.The Pb-WC-PANI composite coatings are prepared in alkaline electrolyte system (including sodium potassium tartrate and disodium edetate) and acidic electrolyte system (fluoboric acid) respectively by DC electrodeposition. The better electrolyte compositions and process conditions can be obtained as follows:current density1.5A/dm2, temperature35℃, PANI15g/L, WC40g/L in alkaline electrolyte system. current density5A/dm2, temperature, PANI10g/L, WC40g/L in acidic electrolyte system.The Pb-WC-PANI composite coatings are prepared in alkaline electrolyte system (sodium potassium tartrate) and acidic electrolyte system (fluoboric acid) respectively by pulse electrodeposition. The better electrolyte compositions and process conditions can be obtained in alkaline electrolyte system as follows:lead oxide100g/L, sodium potassium tartrate150g/L, potassium hydroxide55g/L, gelatin1.5g/L, PANI10g/L, WC30g/L, pulse cycle1.5ms,pulse on-time0.3ms, pulse average current density3A/dm2, room temperature. The better electrolyte compositions and process conditions can be obtained in acidic electrolyte system as follows:PANI30g/L, WC30g/L, pulse cycle1.5ms,pulse on-time0.5ms, pulse average current density2A/dm2, temperature25℃.The surface appearance, phase structure and composition are characterized by means of SEM, XRD, EDS and other modern testing methods. The anticipated service lives of composite materials are measured by using accelerated life test in ZnSO4-H2SO4solution at a current density of1A/cm2. The electrochemical performances of composite materials are also compared. The surface of Pb-WC-PANI composite coating prepared by pulse electro-deposition is more compact than that of Pb-WC-PANI composite coating prepared by DC electrodeposition and it doesn’t have obvious grain boundary. XRD of composite coating shows that there is obvious diffraction peak of Pb and WC, but diffraction peak of PANI hasn’t been observed, and the intensity of diffraction peak Pb-WC-PANI pulse composite coating is weaker than that of direct current composite coating. The infrared spectrum analysis shows that there are characteristic peaks of PANI in the composite coating. Composition analysis shows that the WC content in direct current composite coating is much lower than that in the pulse composite coating, and the WC content in composite coating prepared in acidic electrolyte is much lower than that in the composite coating prepared in alkaline electrolyte. Among all of the composite coatings, the WC content in Pb-WC-PANI pulse composite coating prepared in alkaline electrolyte is the highest, up to24.7%(wt%).As for the electrochemical performance, the electrochemical performance of the Pb-PANI composite coating is superior to that of Pb-WC composite coating and the pure lead coating, which proves that with other substances added in PANI and WC, their oxygen catalytic activity can be improved. In these two kinds of system, the catalytic activity of pulse electrodeposition Pb-WC-PANI composite coating is better than that of direct current composite coating. With the pulse composite coating of these two kinds of system being compared, the property of the composite coating prepared in alkaline electrolyte is better than that of the acid composite coating.With the electrochemical performance of the acidic and alkaline pulse composite coatings and that of Ti-based precious metal coating and two kinds of of lead silver alloy being compared, the oxygen evolution potential of the acidic and alkaline pulse composite coatings is higher than that of the Ti-based precious metal coating but lower than that of the lead silver alloy. The corrosion resistance of the acidic and alkaline pulse composite coatings is superior to that of lead silver alloy anodes but worse than that of Ti-based precious metal coating. The voltammetric charge of the acidic pulse composite coating(q*=0.4219C·cm-2) is the largest. The voltammetric charge of the alkaline pulse composite coating (q*=0.1907C·cm-2) is larger than that of the lead silver alloy but lower than that of Ti-based precious metal coating (q*=0.2779C·cm-2). The impedance spectrum shows that the catalytic activity of Ti-based precious metal coating is the best, followed by the two kinds of pulse composite coating, whose oxygen catalytic activity are superior to that of the lead silver alloy anodes. The anticipated service lives of the composite coating is shorter than that of the precious metal coating electrode and lead silver alloy electrode. Compared with the lead silver alloy, the current of composite coating is of higher-efficiency, but the cell voltage is the opposite. Consequently, using the composite coating as the anode material is much more efficient than using lead silver alloy anodes.The new type of Pb-WC-PANI composite coating is lighter than lead silver alloy, even less than the20%of it. Combined with its better catalytic activity and lower slot voltage, it may be an ideal anode material.The projects are supported by Scientific Research Fund of Yunnan Provincial Education Department (2011Y37324), Analysis Measurement Research Fund of Kunming University of Science and Technology.更多还原