Zhong-cheng Guo

Morphology of alpha-lead dioxide electrodeposited on aluminum substrate electrode

Abstract Alpha-lead dioxide was deposited by anodization of alkaline solution containing HPbO 2 − anions. Scanning electron microscopy (SEM) results show that the morphology is remarkably affected by the current density, concentration of HPbO 2 − anions, bath temperature and electroplating time. Compact and well adherent layers are possibly obtained under conditions of current densities ≤3 mA/cm 2 electrolyte containing 4 mol/L NaOH and 0.12–0.14 mol/L lead (II), bath temperature of 40 °C, and electroplating time of 2 h. EDS analyses show that the PbO 2 deposited in alkaline condition is highly non-stoichiometric at high current density.

Influence of nano-CeO2 on coating structure and properties of electrodeposited Al/α-PbO2/β-PbO2

Abstract Al/α-PbO 2 /β-PbO 2 composite electrodes doped with rare earth oxide (CeO 2 ) were prepared by anodic oxidation method investigate the influence of nano-CeO 2 dopants on the properties of Al/α-PbO 2 /β-PbO 2 -CeO 2 electrodes and the impact of α-PbO 2 as the intermediate layer. The results show that using α-PbO 2 as the intermediate layer will benefit the crystallization of β-PbO 2 and β-PbO 2 is more suitable as the surface layer than α-PbO 2 . CeO 2 dopants change the crystallite size and crystal structure, enhance the catalytic activity, and even change the deposition mechanism of PbO 2 . The doping of CeO 2 in the PbO 2 electrodes can enhance the electro-catalytic activity, which is helpful for oxygen evolution, and therefore reduce the cell voltage.

Effect of added cobalt ion on copper electrowinning from sulfate bath using doped polyaniline and Pb-Ag anodes

Abstract Effect of added Co2+(aq) on copper electrowinning was studied using doped polyaniline (Pani) and Pb-Ag(1%) anodes and a stainless steel cathode. The presence of added Co2+(aq) in the electrolyte solution was found to decrease the anode potentials. The optimum level of Co2+(aq) concentration in the electrolyte, with respect to the maximum saving of power consumption was established. Linear sweep voltammetry (LSV) was used to study the influence of added Co2+(aq) on the anodic processes in a copper sulfate-sulfuric acid electrolyte. The oxygen-evolution potential for Pani anode is depolarised at lower current densities (⩽0.01 A/cm2) and attains saturation at ρ(Co2+)o≈0.789 g/L; whilst the oxygen-evolution potential for Pb-Ag(1%) anode is depolarised at higher current densities (⩽0.02 A/cm2) and attains saturation at ρ(Co2+)o≈1.315 g/L. The preferred orientations of the copper deposits change from (220) to (111) with the addition of 0.394–0.789 g/L Co2+ but higher concentrations favor (220) orientation again.

High-temperature oxidation behavior of CeO2-SiO2/Ni-W-P composites

Abstract Ni-W-P matrix composites containing CeO 2 and SiO 2 nano-particles were prepared on common carbon steel surface by means of pulse electrodeposition, and the high-temperature oxidation behavior was investigated. The results show that when the oxidation time is controlled in 1 h, oxidation kinetics curve between oxidation mass gain rate and oxidation temperature of CeO 2 -SiO 2 /Ni-W-P composites accords with the index increasing law. When the oxidation temperature is controlled at 300 °C, the kinetics curve between oxidation mass gain rate and oxidation time accords with the linear increasing law. The composites as-deposited are in the amorphous state and turn into the crystal state at 400 °C. The microstructures of oxidation film on the composites will change from the compact state to the loose state with increasing oxidation temperature to 800 °C. They are still continuous and compact, and there are no crackle, strip and falling-out. CeO 2 and SiO 2 nano-particles co-deposited into Ni-W-P alloy can improve the high-temperature oxidation resistance.

Polyaniline anode for zinc electrowinning from sulfate electrolytes

Abstract Polyaniline (Pani) anode is tested to highlight the feasibility of reduction of both energy consumption and capital costs in zinc electrowinning from sulfate solution without any modification to the existing plant. Current density, electrolyte temperature, added gelatin, added Mn 2+ , oxygen-evolution potential, cell potential and long duration tests were investigated. The zinc deposits were also studied by means of scanning electron microscope (SEM) and X-ray diffraction (XRD). The results show that current density and added gelatin change the preferred crystal orientations of the zinc deposits. Compared with Pb-Ag(1%) anode used in industry, the cell voltage decreases by 0.15–0.30 V, energy consumption of Zn is 2.46–2.70 kW·h/kg which results in 20% energy savings. Long duration tests show that Pani anode can represent a good alterative ability for zinc electrowinning. Zinc deposits obtained have no Pb pollution. The additions of Mn 2+ ions and gelatin also change the surface morphology and deposit quality of the electrodeposited zinc, affecting the crystal orientation. These researches demonstrate that Pani anode has distinct advantages over acidic electrowinning process.

Corrosion resistance of electrodeposited RE-Ni-W-P-SiC-PTFE composite coating in phosphoric and ferric chloride

Abstract Corrosion rate and anode polarization curves of electrodeposited RE-Ni-W-P-SiC-PTFE composite coating in various concentrations of phosphoric and ferric chloride were researched. The results show that corrosion rate of the composite coatings increases with the increasing concentrations of phosphoric and ferric chloride, and reaches the maximum value when phosphoric concentration is 40% and ferric chloride concentration is 20% (mass fraction, the same below if not mentioned). Anode polarization curves of the composite coatings show that anode polarization current density of the composite coatings heat-treated at 200 °C or 500 °C is lower than that of other coatings heat-treated at 300 °C or 400 °C, which displays that the composite coatings heat-treated at 200 °C or 500 °C have better corrosion resistance. Besides, corrosion resistance of the composite coating heat-treated at 500 °C is better than that as deposited and RE-Ni-W-P-SiC composite coating heat-treated at 400 °C, and is also better than that of 316L stainless steel.

Effects of current density on preparation and performance of Al/conductive coating/a-PbO2-CeO2-TiO2/ß-PbO2-MnO2-WC-ZrO2 composite electrode materials

Abstract Al/conductive coating/ a -PbO 2 -CeO 2 -TiO 2 / β -PbO 2 -MnO 2 -WC-ZrO 2 composite electrode material was prepared on Al/conductive coating/ a -PbO 2 -CeO 2 -TiO 2 substrate by electrochemical oxidation co-deposition technique. The effects of current density on the chemical composition, electrocatalytic activity, and stability of the composite anode material were investigated by energy dispersive X-ray spectroscopy (EDXS), anode polarization curves, quasi-stationary polarization (Tafel) curves, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), and X-ray diffraction (XRD). Results reveal that the composite electrode obtained at 1 A/dm 2 possesses the lowest overpotential (0.610 V at 500 A/m 2 ) for oxygen evolution, the best electrocatalytic activity, the longest service life (360 h at 40 °C in 150 g/L H 2 SO 4 solution under 2 A/cm 2 ), and the lowest cell voltage (2.75 V at 500 A/m 2 ). Furthermore, with increasing current density, the coating exhibits grain growth and the decrease of content of MnO 2 . Only a slight effect on crystalline structure is observed.

Electrosynthesis and physicochemical properties of α–PbO2–CeO2–TiO2 composite electrodes

Abstract In order to investigate the effect of solid particles dopants on physicochemical properties of α-PbO2 electrodes, α-PbO2 composite electrodes doped with nano-TiO2 and nano-CeO2 particles were respectively prepared on Al/conductive coating electrodes in 4 mol/L NaOH solution with addition of PbO until saturation by anodic codeposition. The electrodeposition mechanism, morphology, composition and structure of the composite electrodes were characterized by cyclic voltammogram (CV), SEM, EDAX and XRD. Results show that the doping solid particles can not change reaction mechanism of α-PbO2 electrode in alkaline or acid plating bath, but can improve deposition rate and reduce oxygen evolution potential. The doping solid particles can inhibit the growth of α-PbO2 unit cell and improve specific surface area. The diffraction peak intensity of α-PbO2-CeO2-TiO2 composite electrode is lower than that of pure α-PbO2 electrode. The electrocatalytic activity of α-PbO2-2.12%CeO2-3.71%TiO2 composite electrode is the best. The Guglielmi model for CeO2 and TiO2 codeposition with α-PbO2 is also proposed.

Anodic behavior and microstructure of Al/Pb–Ag anode during zinc electrowinning

Abstract Anodic behaviors and oxygen evolution kinetics of Pb–0.8%Ag and Al/Pb–0.8%Ag anodes during the initial 24 h zinc electrowinning were investigated with cyclic voltammetry (CV) curves and electrochemical impedance spectroscopy (EIS). The results reveal that the anodic behaviors and reaction kinetics of the two anodes vary a lot during the anodic polarization which indicate the formation and stabilization of anodic layer. Compared with conventional Pb–0.8%Ag anode, Al/Pb–0.8%Ag anode has longer time of anodic polarization. At the very beginning of anodic polarization, the two anodes all exhibit higher potential of oxygen evolution reaction (OER) since the reaction is controlled by the transformation step of intermediates. Then, its OER potential is largely diminished and OER rate is deduced from the formation and adsorption of the first intermediate (S–OHads). In the prolonged anodic polarization, the anodic potential of Al/Pb–0.8%Ag gradually decreases and the final value is more stable than that of conventional Pb–0.8%Ag anode. On the anodic layer after 24 h of anodic polarization, the OER potential is controlled by the formation and adsorption of intermediate. The microstructures of Al/Pb–0.8%Ag and Pb–0.8%Ag anodes after 24 h of anodic polarization were analyzed by scanning electron microscope (SEM).

Effect of cooling ways on properties of Al/Pb-0.2%Ag rolled alloy for zinc electrowinning

Abstract In order to study the new anode materials for zinc electrowinning, Al/Pb-0.2%Ag rolled alloy was produced by composite casting and hot rolling. Then the effect of cooling ways on properties of Al/Pb-0.2%Ag rolled alloy was investigated. As the results of metallographic test indicated, with the increasing of cooling intensity, both Vickers hardness and yield strength of Al/Pb-0.2%Ag rolled alloy increase. Furthermore, the Al/Pb-0.2%Ag rolled alloy, cooled by ice salt, presents the finest grain size and shows the lowest oxygen evolution potential (1.5902 V), while that of alloy cooled by water and air are 1.6143 V and 1.6288 V, respectively. However, the corrosion current density and corrosion rate of the Al/Pb-0.2%Ag rolled alloy, cooled by ice salt, are the highest. This can be attributed to its largest specific surface area, which promotes the contact between the anode and electrolyte.