Influence of lead dioxide surface films on anodic oxidation of a lead alloy under conditions typical of copper electrowinning

Cyclic voltammograms, current transients at constant potential and potential decay transients have been used to study the formation of lead dioxide surface films in the presence of cobalt ions and their role in decreasing the oxidation rate of a lead alloy under steady state conditions typical of copper electrowinning. The observations in the present work indicate, consistent with the surface film model, that the formation of a continuous PbSO₄ + α-PbO₂ film on the surface of the lead alloy in the presence of cobalt ions hinders further oxidation of the metal. The protectiveness of the film is dynamic in the steady state; the film is continuously forming and dissolving. Also studied was the potential of the oxygen evolution reaction on α-PbO₂ and β-PbO₂ in 170 g L⁻¹ H₂SO₄ with and without cobalt ions. The steady state potential for oxygen evolution on β-PbO₂ in 170 g L⁻¹ H₂SO₄ at 285 A m⁻² decreased in the presence of cobalt ions and the steady state potential of β-PbO₂ was essentially the same as that of (i) the Pb–Ca–Sn alloy and (ii) α-PbO₂. The implication is that the potential of the Pb–Ca–Sn alloy is determined by the α-PbO₂ and/or β-PbO₂ on its surface.     

Anodic oxidation of mecoprop herbicide at lead dioxide

The electrochemical oxidation of an aqueous solution containing mecoprop (2-(2-methyl-4-chlorophenoxy)propionic acid) has been studied at PbO₂ anodes by cyclic voltammetry and bulk electrolysis. The influence of current density, hydrodynamic conditions, temperature and pH on the degradation rate and current efficiency is reported. The results obtained show that the use of PbO₂ leads to total mineralization of mecoprop due to the production of oxidant hydroxyl radical electrogenerated from water discharge. The current efficiency for the electro-oxidation of mecoprop is enhanced by low current density, high recycle flow-rates and high temperature. In contrast, the pH effect was not significant. It has also been observed that mecoprop decay kinetics follows a pseudo-first-order reaction and the rate constant increases with rising current density.     

Energy storage capacity investigation of pulsed current formed nano-structured lead dioxide

An electro-deposition method was used for the preparation of nano-structured lead dioxide. The lead dioxide films prepared were used as positive electrodes of lead acid batteries. Different parameters such as pulse time (t_on), pulse height, and relaxation time (t_off) were optimized to obtain higher capacity. Depend on the pulse conditions, a range of different morphologies of various porosities and connectivity was obtained. The resulting batteries were discharged to a cut off voltage of 1.75 V by a pulsed current method. The energy storage ability of the prepared lead acid batteries shows a close relation with the morphology of cathode materials. Maximum capacity was observed when pulse and relaxation time was equal to 0.1 and 5 s, respectively, at a current density of 25 mA cm⁻². A change in morphology of lead dioxide from aggregated globular structure to nanofiber was occurred. It was found that the high surface area as well as high connectivity between particles resulted in increased discharge capacity. Analysis of electrochemical impedance spectroscopy (EIS) data revealed that the charge transfer resistance is decreased by a change in morphology from bulk globular to nanofiber as the energy storage test showed. The time dependence of impedance behavior of a sample prepared at t_on = 0.1 s and t_off = 5 s at 25 mA cm⁻² was investigated and the results are discussed.     

Special titanium dioxide layers and their electrochemical behaviour

This text describes the production of polycrystalline titanium dioxide layers by anodic spark deposition (ASD). These deposits show an interesting electrochemical and electrocatalytic behaviour. A reversible electrochemical transformation of the crystalline phases could be proved. Furthermore, the TiO₂-layers were used as electrode material for the cathodic reduction of molecular oxygen. In this process, cyclic voltammetry was employed, and the reduction of oxygen was successfully examined in dependence on surface-determining parameters such as layer thickness and pH value.     

Morphologic study of electrochemically formed lead dioxide

Various electrochemical methods with different conditions were used to prepare lead dioxide (PbO₂). The observation revealed that the morphology of deposited PbO₂ could be controlled by simply changing deposition parameters. Under the condition of oxygen evolution, which dominates the electrode process, uniformly distributed high porous structured PbO₂ was formed. The results indicated that large current density or high potential polarization should be one of the most important and necessary factors for forming high surface area PbO₂ deposit. Only β-PbO₂ was identified by X-ray diffraction measurement for the deposit prepared by present methods and solution. One potential application of this method is to prepare nanoscaled PbO₂ parallel lines.     

The electrodeposition of lead dioxide on titanium

The initial stages of the potentiostatic deposition of lead dioxide from acidic lead nitrate solution, onto titanium wires, have been followed. The observed current transients and size distributions of the nuclei have been related to available theories of electrocrystallization by assuming a stochastic growth process. The inhibiting effects of fluoride ions are emphasized.     

Electrocrystallization of lead dioxide: Analysis of the early stages of nucleation and growth

The kinetics of the early stages of the electrocrystallization of lead dioxide onto a vitreous carbon electrode is studied via the analysis of the early rising portion of the current-time transients (CTT's). The CTT's are recorded when the rate of charge-transfer across the electrode/electrolyte interface is the sole controlling mechanism for crystal growth. Induction times for the nucleation of the 3D growth centres are determined as a function of the applied potential. A possible controlling mechanism for the onset of the nucleation of the 3D growth centres is thus considered to be the need for the formation of at least a monolayer of deposit and/or adsorbed layers.It has been shown that CTT's that are recorded during the charge-transfer controlled growth processes allows the possibility of observing the formation of two distinct phases of a deposit, a phenomenon that would not be observed if CTT's are recorded when diffusion is the controlling mechanism for growth. The electrocrystallization of lead dioxide is shown to proceed, at least initially, via the formation of two distinct phases of PbO₂.     

A novel flow battery: A lead acid battery based on an electrolyte with soluble lead(II): Part VII. Further studies of the lead dioxide positive electrode

Extensive cycling of the soluble lead flow battery has revealed unexpected problems with the reduction of lead dioxide at the positive electrode during discharge. This has led to a more detailed study of the PbO₂/Pb²⁺ couple in methanesulfonic acid. The variation of the phase composition (XRD) and deposit structure (SEM) have been defined as a function of current density, Pb²⁺ and H⁺ concentrations, deposition charge and temperature as well as the consequences of charge cycling. Pure α-PbO₂, pure β-PbO₂ and their mixtures can be deposited from methanesulfonic acid media. The α-phase deposits as a more compact, smoother layer, which is well suited to charge cycling. While the anodic deposition of thick layers of PbO₂ is straightforward, their reduction is not; the complexities are explained by an increase in pH within the pores of the deposit. The results suggest that operating the battery at lead(II) concentrations <0.3 M and elevated temperatures should be avoided.     

Interference colors of thin oxide layers on titanium

This work deals with the characterization of the color properties of different titanium oxide films, obtained by means of anodic oxidation. The color of these oxides varies with film thickness, since it is due to light interference phenomena taking place at the metal‐oxide‐air interfaces. Color measurements were carried out by using spectrophotometry techniques: the values obtained belong to the colorimetric space CIELAB, which is defined as standard colorimetric space. The results of these analyses were related to the oxide structure, analyzed with X‐ray diffraction techniques, which was determined to be either amorphous or semicrystalline. Also the oxide thickness was taken into account. This feature was derived both from ellipsometric data and from reflectance spectra: the two data are shown to be in good adherence. Both commercial purity titanium (grade 2 ASTM) and titanium alloy Ti‐6Al‐4V substrates were investigated. © 2008 Wiley Periodicals, Inc. Col Res Appl, 33, 221–228, 2008     

A comparison of electrochemical degradation of phenol on boron doped diamond and lead dioxide anodes

This work compares two electrode materials used to mineralize phenol contained in waste waters. Two disks covered with either boron doped diamond (BDD) or PbO₂ were used as anodes in a one compartment flow cell under the same hydrodynamic conditions. Efficiencies of galvanostatic electrolyses are compared on the basis of measurements of Total Organic Carbon (TOC) and Chemical Oxygen Demand (COD). Galvanostatic electrolyses were monitored by analysis of phenol and of its oxidation derivatives to evaluate the operating time needed for complete elimination of toxic aromatics. The experimental current efficiency is close to the theoretical value for the BDD electrode. Other parameters being equal, phenol species disappeared at the same rate using the two electrode materials but the BDD anode showed better efficiency to eliminate TOC and COD. Moreover, during the electrolysis less intermediates are formed with BDD compared to PbO₂ whatever the current density. A comparison of energy consumption is given based on the criterion of 99% removal of aromatic compounds.     

钛白粉生产中操作条件对水解过程的影响

水解过程是硫酸法钛白粉生产至关重要的一步。为了进一步探究水解过程的机理，选用工业中浓缩后的钛液为原料，通过响应面试验考察了4个操作条件，即搅拌速率、加料速率、加热时间、底水量对二氧化钛水解过程中水合二氧化钛粒子的粒径、过滤时间和水解率的影响，给出了各响应与4个操作条件的回归关系模型，并给出了最优的操作条件。该结果将用于指导工业生产。     

TiO2-PDVB Janus particles enhanced compatibility of titanium dioxide and recycled waste styrofoam

People are always puzzled by “white pollution” in recent decade. Recycling of waste styrofoam as a coating is a good sustainable solution to resolve this problem. However, the poor compatibility between inorganic additives and polymer hinders the application of recycled polystyrene. In this article, anisotropic Janus particles were used to increase the compatibility of titanium dioxide/waste styrofoam coatings. SEM results show that Janus particles can be anchored at the interface between styrofoam and titanium dioxide, increasing the dispersion of titanium dioxide, and improving the compatibility of inorganic particles and organic polymer. The glass-transition temperature of styrofoam coating increases from 77 °C to 89 °C in titanium dioxide/styrofoam contained 1 wt % of Janus particles, which certified that Janus particles have compatibilization on titanium dioxide/styrofoam coating. Attributing to this compatibilization, the tensile strength of titanium dioxide/styrofoam with 1 wt % of Janus particles rises about 45% compared with titanium dioxide/styrofoam. The yield stress, storage modulus, and viscosity of titanium dioxide/styrofoam contained 1 wt % of Janus particles are the smallest and the closest to Newtonian fluid. Janus particles used in the recycled styrofoam coating is benefit to expand the application of waste styrofoam and the new anisotropic Janus compatibilizer. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 137, 48691.     

深还原钛渣硫酸法制取钛白实验研究

以含钛铁精矿直接还原冶炼的含钛物料（深还原钛渣）为原料,对硫酸法制取颜料级钛白粉的工艺进行了研究。实验结果表明,深还原钛渣具有良好的酸解性能,酸解率可达97%;酸解后得到的钛液过滤性能好;但酸解钛液中氧化镁和氧化铝浓度过高,所以直接以该钛液为原料制得的钛白颜料性能差。采用深还原钛渣和钛精矿按一定比例混合酸解,可以避免钛液杂质含量过高对最终钛白产品质量造成的影响。深还原钛渣较佳用量为不高于钛原料总质量的20%。     

Electrochemical oxidation of 1,3,5-trimethoxybenzene in aqueous solutions at gold oxide and lead dioxide electrodes

A kinetic study of the electrochemical oxidation of 1,3,5-trimethoxybenzene (TMB) by direct electron transfer at treated gold disk was combined with results of electrolysis in order to produce total degradation into CO₂ and H₂O at Ta/PbO₂ anode. The oxidation of TMB at gold electrode was studied by cyclic voltammetry. The cyclic voltammogram shows one irreversible anodic peak (I) corresponding to the oxidation of adsorbed TMB molecules. The proposed mechanism is based on the hypothesis of two-electron oxidation of TMB molecule leading, via intermediate of a radical cation, to the formation of the 2,4,6-trimethoxyphenol (TMP) and an adsorbed polymeric film. The TMP molecule undergoes a rapid oxidation leading to the formation of 2,6-dimethoxy-p-benzoquinone (DMBQ) as a major product. Degradation of TMB was studied by galvanostatic electrolysis using Ta/PbO₂ anode. The influence of initial TMB concentration and applied current density was investigated. Measurement of total organic carbon (TOC) and analysis by HPLC were used to follow this degradation. The experimental data indicated that the removal of TMB follows a pseudo first-order kinetic. The efficiency of the electrochemical process increases at lower current density and higher TMB initial concentration while it decreases with the TOC removal progress.     

Photodegradation of benzothiazole ionic liquids catalyzed by titanium dioxide and silver-loaded titanium dioxide

In recent years, ionic liquids(ILs) have been widely used in extraction, synthesis, electrochemistry and other fields.Meanwhile, the environmental impact of ILs has been attracting a lot of attention, and eco-friendly treatment for ILs is becoming a necessary subject. In this study, photocatalytic degradations of benzothiazole ILs catalyzed by titanium dioxide(TiO_2) and silver-loaded titanium dioxide(Ag/TiO_2) were studied for the first time. The degradation of benzothiazole hexafluorophosphate([C4 Bth]PF6) could reach more than 99% within 240 min with the catalysis of TiO_2. To improve catalytic efficiency, Ag/TiO_2 was synthesized and characterized by UV–Vis diffuse reflectance absorption spectra(DRS) and X-ray photoelectron spectroscopy(XPS). The degradation of [C4 Bth]PF6 could reach more than 99% within 120 min in the degradation catalyzed by Ag/TiO_2. The photodegradation products of benzothiazole ILs are composed of inorganic substances or organic substances with simpler structures, which are easier to decompose and less toxic. The degradation system proposed by this study could provide a simple, green,safe, and economical method for the efficient treatment of benzothiazole ILs.     

钛白废水处理研究

以造纸白泥和石灰为中和剂,采用两段中和+曝气沉淀工艺处理钛白废水,考察了中和过程中的时间、温度、中和剂投加量及曝气时间对水质的影响。较佳工艺条件为第一阶段投料比m(废水)∶m(造纸白泥)=1 000∶13.6,常温中和15 min,此时废水pH为5.61,第二阶段m(废水)∶m(石灰)=1 000∶1.4,常温中和5 min,曝气30 min后静置5 min,废水pH为7.25,Fe2+质量分数<0.1%,出水达到《国家污水综合排放标准》GB 8978—2002的二级排放要求。     

The effect of drying on dispersions of nano-particulate titanium dioxide in ethylene glycol

This paper first demonstrates that the UV attenuation of a well-milled aqueous dispersion of nano-particulate rutile TiO₂ is 200 times greater than the attenuation of visible 550 nm light. The corresponding UV attenuation of rutile dispersions in ethylene glycol is however only ∼ 50% of that of the aqueous dispersion. It is shown that the different behaviour of suspensions in water and in ethylene glycol depends on the way in which the TiO₂ was dried. If the rutile is pre-treated, by washing in ethanol before conventional oven drying, the differences between the optical properties of the aqueous and non-aqueous suspensions can be eliminated. Possible reasons for the beneficial effects of the ethanol pre-treatment are proposed.     

Paramagnetic properties of carbon-doped titanium dioxide

ABSTRACT: This paper reports the experimental results on paramagnetic properties of carbon-doped titanium dioxide. The electron paramagnetic resonance study of the samples has been carried out both in dark and under illumination. The nature of defects and their dynamics under illumination of carbon-doped TiO_2 samples are discussed.     

The influence of adsorbed layers on the rheological behavior of titanium dioxide dispersions

The aim of this study is to relate the influence of stearic acid on the rheological behaviour of titanium dioxide dispersions in alkyd resin solutions to the composition of the adsorbed layer on the dispersed particles.The adsorption of alkyd resin was studied using gel permeation chromatography. From the differences occurring in the molecular size distributions of the initial resin and the residual resin after adsorption, it followed that the adsorbed molecules extended throughout the whole molecular size distribution with a maximum at an equivalent chain length of 2800 Å.Stearic acid adsorption — determined using a radioactive tracer technique — was reduced by the presence of alkyd resin in the system.Titanium dioxide dispersions in alkyd resin solutions exhibited Newtonian rheological behaviour, showing that the adsorbed resin molecules protected the dispersed particles very well against flocculation. By counteracting the alkyd resin adsorption, the presence of stearic acid in the systems induced flocculation, leading to Bingham rheological behaviour. A direct relationship was shown to exist between the obtained Bingham yield values and the stearic acid adsorption.