铅基合金阳极在锌电积过程中的成膜特性研究

【作者】 杨海涛；

【导师】 郭忠诚；

【作者基本信息】 昆明理工大学 ， 有色金属冶金， 2014， 博士

【摘要】 现代锌电积工业中Pb-Ag(0.5wt.%-1.0wt.%)和Pb-Ag(0.2wt%-0.3wt%)-Ca(0.06wt%-0.1wt%)合金阳极被大规模使用。阳极在使用过程中表面形成氧化层,而氧化层的物相、微观结构、导电性、孔隙率、附着力、析氧活性等与阳极的析氧过电位和耐腐蚀性紧密相关。为了探讨铅基合金阳极在锌电积过程中氧化膜的形成特性,本论文设计了评估阳极氧化层变化的实验体系。通过循环伏安曲线,阳极极化曲线,交流阻抗谱,扫描电子显微镜,X射线衍射,能谱分析等方法获得阳极氧化层实时状态数据。通过分析氧化还原反应的峰值电位、峰值电流、析氧过电位、表观交换电流密度、电荷传递电阻、表面粗糙度、微观形貌和腐蚀物相等参数评估阳极氧化层的变化特性。最终对阳极氧化层形成、变化和稳定,实现定量或半定量评估。论文选取锌电积工业中常用Pb-0.8%Ag和Pb-0.3%Ag-0.06%Ca轧制合金阳极,以及实验室研制的Pb-0.3%Ag-0.6%Sb新型轧制合金阳极作为研究对象,并将阳极电化学预镀膜处理,得到六种阳极实验试样(镀膜前后)。所得到的试样分别在四种不同的溶液体系内进行连续15天的极化。在不同的极化时间节点(0天,1天,2天,3天,6天,9天,12天,15天)取样测试了氧化层的电化学行为,微观结构和物相等方面的特性。纵向分析了阳极试样随极化时间的延长成膜特性的变化。横向对比了阳极类型和预镀膜处理对阳极成膜特性的影响。所得到的主要研究成果如下：(1)50g-L-1Zn2+;150g·L-1H2SO4溶液体系。不同的阳极试样成膜特性差异很大,阳极类型和镀膜处理均有明显的影响。随着极化时间的延长,析氧过电位整体呈现降低的趋势。未镀膜Pb-0.8%Ag合金在极化过程中,氧化膜微观颗粒尺寸先增大后减小,主体物相由α-PbO2向β-PbO2转变。极化结束后氧化膜均匀致密,由大量的呈四方晶系的细小颗粒组成,无孔洞。极化结束后析氧过电位780mV(500A·m-2)。镀膜Pb-0.8%Ag合金在极化过程中,氧化膜主体物相为α-PbO2,衍射峰强逐渐增强。极化结束后的氧化膜中既有锰的氧化物,也有裸露的铅的氧化物。锰的氧化物包裹在铅的氧化物外侧。极化结束时析氧过电位784mV(500A·m-2)。未镀膜Pb-0.3%Ag-0.06%Ca合金在极化过程中,氧化膜微观颗粒尺寸逐渐增大,腐蚀孔洞数量先增多后减少。极化结束后,微观形貌呈“菜花状”大颗粒。极化过程中氧化膜主体物相由PbSO4向α-PbO2转变。极化结束时析氧过电位771mV(500A·m-2)。镀膜Pb-0.3%Ag-0.06%Ca合金试样在极化过程中,氧化膜主体物相由α-PbO2向β-PbO2转变。极化结束时锰的氧化物包裹在铅的氧化物外侧。锰的氧化物呈片状,尺寸较大。铅的氧化物颗粒呈四方晶系,密集细小。极化结束时析氧过电位764mV(500A·m-2)。未镀膜Pb-0.3%Ag-0.6%Sb合金极化3天后氧化膜微观结构基本达到稳定状态。主要由“菜花状”大颗粒组成,布满腐蚀的孔洞,呈现了严重的腐蚀形貌。主体物相为α-PbO2,衍射峰随极化时间逐渐增强。极化结束时析氧过电位779mV(500A·m-2)。镀膜Pb-0.3%Ag-0.6%Sb合金试样在极化过程中,氧化膜主体物相变化趋势如下：PbSO→α-PbO2→β-PbO2。极化结束时氧化膜基本上没有锰氧化物的包裹。呈四方晶系的密集细小的铅的氧化物颗粒堆簇在一起。极化结束时析氧过电位768mV(500A·m-2)。(2)50g·L-1Zn2+;150g·L-1H2SO4;600mg·L-1Cl-溶液体系。六种阳极试样极化6天之后氧化膜形貌与物相基本达到稳定状态,主体物相均为α-PbO2。氧化膜微观形貌平整均匀,但是棱角清晰的颗粒均未出现。极化结束后析氧过电位差别很小,波动范围：712-730mV(500A·m-2)。在高浓度氯离子溶液体系内,溶液中的氯离子是合金阳极氧化膜形成过程的决定因素。阳极类型与镀膜处理对氧化膜性能的影响很小。(3)50g·L-1Zn2+;150g·L1H2SO4;5g·L-1Mn2+溶液体系。Pb-0.8%Ag合金阳极无论是否预镀膜处理,极化结束后氧化膜中既有锰的氧化物也有铅的氧化物,物相交错,颗粒粗大。未镀膜处理Pb-0.8%Ag主体物相为β-PbO2,析氧过电位653mV(500A·m-2)。镀膜处理后主体物相为α-PbO2,析氧过电位674mV(500A·m-2)。Pb-0.3%Ag-0.06%Ca和Pb-0.3%Ag-0.6%Sb合金阳极无论是否预镀膜,极化结束后氧化膜中既有锰的氧化物也有铅的氧化物,上下分布,界限清晰,锰的氧化物位于外层,尺寸大,结晶趋向不明显。铅的氧化物颗粒细碎位于内层,铅的氧化物中存在腐蚀腔和腐蚀孔洞。其中未镀膜Pb-0.3%Ag-0.06%Ca和镀膜Pb-0.3%Ag-0.6%Sb氧化膜主体物相为β-PbO2。极化结束后镀膜Pb-0.3%Ag-0.6%Sb合金析氧过电位最高701mV (500A·m-2)。未镀膜Pb-0.8%Ag和Pb-0.3%Ag-0.06%Ca合金析氧过电位最低653mV(500A·m-2)。(4)50g·L-1Zn2+;150g·L-1H2SO4;600mg·L-1Cl-;5g·L-1Mn2+溶液体系。三种阳极试样无论是否镀膜,极化结束时氧化膜结构相似,均匀平整、孔洞较少。物相差别较大,其中未镀膜Pb-0.8%Ag主体物相为PbSO4。镀膜Pb-0.8%Ag主体物相为α-Pb02。 Pb-0.3%Ag-0.06%Ca无论是否镀膜主体物相均为α-Pb02。镀膜Pb-0.3%Ag-0.6%Sb合金阳极主体物相为PbS04。未镀膜Pb-0.3%Ag-0.6%Sb合金阳极极主体物相为β-Pb02。极化结束后阳极试样析氧过电位差别较大,在50mV左右,其中镀膜Pb-0.3%Ag-0.06%Ca合金析氧过电位最低633mV(500A·m-2)。镀膜Pb-0.8%Ag合金析氧过680mV(500A·m-2)。总之,铅基合金阳极在锌电积过程中的成膜特性主要受三方面因素的支配：铅基合金类型,是否预镀膜处理,电积溶液组分。在纯酸性硫酸锌溶液中,不同的阳极试样成膜特性差异很大,阳极类型和镀膜处理均有明显的影响。在含高氯离子体系内,溶液中的氯离子是合金阳极氧化膜形成过程的决定因素。阳极类型与镀膜处理对氧化膜性能的影响很小。在含锰离子溶液体系内,阳极类型和镀膜处理均有明显的影响。在同含氯锰的溶液体系内,极化结束时阳极试样氧化膜结构相似,物相差别较大。体现了阳极类型,镀膜处理及溶液离子的多重影响。更多还原

【Abstract】 In the modern zinc-electrowinning industry, the Pb-Ag(0.5wt%to1.0wt%) and Pb-Ag(0.2wt%to0.3wt%)-Ca(0.06wt%to0.1wt%) anode is widely used. The oxide layer will form on the surface of anode during polarization. The phase, microstructure, conductivity, porosity, adhesive force, and oxygen evolution activity of anodic oxide films are of considerable importance to the oxygen evolution overpotential and the work-durability of anodes during zinc electroextraction. To explore the formative characteristic of lead-base alloy anode during zinc electroextraction, the experimental systems for assessment of anodic oxidation layer were designed. The real time data of anodic oxide films is obtained by anodic polarization curves, quasi-stationary polarization (Tafel), electrochemical impedance spectroscopy techniques, SEM, XRD, and EDXS. The real-time status of anodic oxide films is evaluated using the parameters of peak potential, peak current, oxygen evolution overpotential, surface (exchange) current density, charge transfer resistance, roughness, phase and microstructure. The (semi-)quantitative evaluation of the formation, change and stability of anodic oxide films is achieved.Pb-0.8%Ag and Pb-0.3%Ag-0.06%Ca rolled aolly anode that is widely used in the zinc-electrowinning industry is selected for research subjects as well as Pb-0.3%Ag-0.6%Sb aolly that is developed in the laboratory room. Three kinds of the anode were deal with pre-film-plating. Then six experiments samples ware obtained. The six experiments samples is electrolyzed in four solution system for15days’continue polarization. The real time data of electrochemistry, phase and microstructure is tested upon reaching specific polarization time points (0,1,2,3,6,9,12, and15days). The formative characteristic of anodic oxide films with increasing polarization time is longitudinally analyzed. The impact of types and pre-film-plating on formative characteristic of anodic oxide films is transversely compared. The major research results are drawn as follows:(1)50g·L-1Zn2+;150g·L-1H2SO4. The formative characteristic of anodic oxide films changes with anode types and pre-film-plating. With increasing polarization time, the overpotential of oxygen evolution of six experiments samples mainly presented a declining trend.With increasing polarization time, the size of microscopic particles of Pb-0.8%Ag anodic oxide films first increased and then decreased. The main phase is transformed from α-PbO2to β-PbO2. After15days of polarization, the microstructure was mainly composed of tetragonal crystalline grains with very few cavities. The uniform, well-defined crystal grains and regularity is obtained. The overpotential of oxygen evolution is780mV(500A·m-2).With increasing polarization time, the main phase of coating Pb-0.8%Ag is α-PbO2. The intensity of diffraction peak gradually increased. Both manganese oxide and leady oxide are observed on the anodic oxide films after15days polarization. The leady oxide was wrapped in manganese oxide. The overpotential of oxygen evolution is784mV(500A-m-2).With increasing polarization time, the size of microscopic particles of Pb-0.3%Ag-0.06%Ca anodic oxide films increased. The quantity of corrosion holes first increased and then decreased. The main phase is transformed from PbSO4to α-PbO2. The anodic oxide consisted mainly of a large cauliflower-like crystal grains. The overpotential of oxygen evolution is771mV(500A·m-2).With increasing polarization time, the main phase of coating Pb-0.3%Ag-0.06%Ca anode is transformed from α-PbO2to β-PbO2. Both manganese oxide and leady oxide are observed on the anodic oxide films after15days polarization. The leady oxide was wrapped in manganese oxide. The manganese oxide is plate shaped with large size. The leady oxide was mainly composed of fine tetragonal crystalline grains. The overpotential of oxygen evolution is764mV(500A·m-2).The composition of Pb-0.3%Ag-0.6%Sb anodic oxide layer reaches a stable state after3d of polarization. The anodic oxide consisted mainly of a large cauliflower-like crystal grains with many deeper holes.The main phase is α-PbO2. The intensity of diffraction peak gradually increased. The overpotential of oxygen evolution is779mV(500A·m-2).With increasing polarization time, the main phase of coating Pb-0.3%Ag-0.6%Sb anode is changed as PbSO4→α-PbO2→β-PbO2. The manganese oxide is disappeared after15days polarization. The leady oxide was mainly composed of fine tetragonal crystalline grains. The overpotential of oxygen evolution is768mV(500A·m-2).(2)50g·L-1Zn2+;150g·L-1H2SO4;600mg·L-1Cl-。The composition of six anode sample reaches a stable state after6d of polarization. The major phase of the oxide layer is α-PbO2no matter type of lead-based alloy and pre-film-plating. The oxide film is uniform. The uniform, well-defined crystal grains are disappeared. The oxygen evolution overpotential sway a little (712-730mV). It is demonstrated that high content Cl-decides the formation of anodic oxide films in acid zinc sulfate electrolyte system.(3)50g·L-1Zn2+;150g·L-1H2SO4;5g·L-1Mn2+。Both manganese oxide and leady oxide are observed no matter if pre-film-plating for Pb-0.8%Ag anode after15days polarization. Coarse grains and alternating phase are also observed. For Pb-0.8%Ag anode, the major phase of the oxide layer is β-PbO2and oxygen evolution overpotential is653mV (500A-m-2). For coating Pb-0.8%Ag anode, the major phase of the oxide layer is α-PbO2and oxygen evolution overpotential is674mV (500A·m-2).Both manganese oxide and leady oxide are observed no matter if pre-film-plating for Pb-0.3%Ag-0.06%Ca and Pb-0.3%Ag-0.6%Sb anode after15days polarization. The manganese oxide is outside. The leady oxide is inside. The distribution with clear layers is observed with many corrosion holes. For Pb-0.3%Ag-0.06%Ca and coating Pb-0.3%Ag-0.6%Sb anode, the major phase of the oxide layer is β-PbO2and oxygen evolution overpotential is674mV (500A·m-2). The oxygen evolution overpotential of coating Pb-0.3%Ag-0.6%Sb is highest (0.701V at500A·m-2). The oxygen evolution overpotential of Pb-0.8%Ag and Pb-0.3%Ag-0.06%Ca anode is lowest (0.653V at500A·m-2).(4)50g·L-1Zn2+;150g·L-1H2SO4;600mg·L-1Cl-;5g·L-1Mn2+.The oxide layers are almost the same with uniform microstructure and less corrosion holes for three anode sample no matter if pre-film-plating. But the major phase of the oxide layer is different. The major phase are PbSO4for Pb-0.8%Ag and coating Pb-0.3%Ag-0.6%Sb. The major phase is α-PbO2for Pb-0.3%Ag-0.06%Ca and coating Pb-0.8%Ag. The major phase are β-PbO2for Pb-0.3%Ag-0.6%Sb.The oxygen evolution overpotential of Pb-0.3%Ag-0.6%Sb is lowest (633mV at500A·m-2). The oxygen evolution overpotential of Pb-0.8%Ag anode is highest (0.680V at500A·m-2).In summary, the formative characteristic of lead-base alloy anode during zinc electroextraction is controlled by the following three aspects:type of lead-based alloy; pre-film-plating process; the composition of electrolyte. The formative characteristic of anodic oxide films changes with anode types and pre-film-plating in pure acid zinc sulfate electrolyte system. The formative characteristic of anodic oxide films is decided by high content Cl-in acid zinc sulfate electrolyte system containing high Cl-. The effect of anode types and pre-film-plating is poor. The formative characteristic of anodic oxide films changes with anode types and pre-film-plating in acid zinc sulfate electrolyte system containing Mn2+. The oxide layers are almost the same with uniform microstructure and less corrosion holes for three anode sample no matter if pre-film-plating in acid zinc sulfate electrolyte system containing Cl-and Mn2+. But the major phase of the oxide layer is different. The formative characteristic is controlled by the three aspects:type of lead-based alloy, pre-film-plating process, the composition of electrolyte.更多还原