| 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. |
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