Reduction Of PbO Research Articles

Discovery of abundant shock-induced metallic lead nanograins in lunar zirconolite

The behaviors of radiogenic Pb in Zr-minerals are critical for reconstructing the chronological framework for the evolutionary history of our Earth and other planetary bodies. Previous investigations have revealed the presence of Pb nanograins in some terrestrial zircons and attributed it to radiation decay of U and mobilization and accumulation in zircon and a subsequent thermal metamorphic event. However, whether impact, a ubiquitous and fundamental process for the evolution of materials on planetary surfaces, can directly produce Pb nanograins in Zr-minerals remains unknown. Here, we report the discovery of abundant metallic Pb nanograins in zirconolite polycrystalline aggregates in the brecciated lunar meteorite Northwest Africa 8182. We propose that the metallic Pb nanograins and their host zirconolite polycrystalline aggregates formed during shock lithification of the host meteorite, which had a significant impact on micro-scale U-Pb isotopic chronology of shocked Zr-minerals. The formation of metallic Pb nanograins also indicates that a reduction of PbO took place during shock metamorphism.

Kinetics of Reduction of CaO-FeO x -MgO-PbO-SiO2 Slags by CO-CO2 Gas Mixtures

Kinetics of the reaction of lead slags (PbO-CaO-SiO2-FeO x -MgO) with CO-CO2 gas mixtures was studied by monitoring the changes in the slag composition when a stream of CO-CO2 gas mixture was blown on the surface of thin layers of slags (3 to 10 mm) at temperatures in the range of 1453 K to 1593 K (1180 °C to 1320 °C). These measurements were carried out under conditions where mass transfer in the gas phase was not the rate-limiting step and the reduction rates were insensitive to factors affecting mass transfer in the slag phase. The results show simultaneous reduction of PbO and Fe2O3 in the slag. The measured specific rate of oxygen removal from the melts varied from about 1 × 10−6 to 4 × 10−5 mol O cm−2 s−1 and was strongly dependent on the slag chemistry and its oxidation state, partial pressure of CO in the reaction gas mixture, and temperature. The deduced apparent first-order rate constant increased with increasing iron oxide content, oxidation state of the slag, and temperature. The results indicate that under the employed experimental conditions, the rate of formation of CO2 at the gas-slag interface is likely to be the rate-limiting step.

Modulation of Pb chemical state of epitaxial lead zirconate titanate thin films under high energy irradiation

The chemical states of epitaxial PbZrxTi1-xO3 films were investigated by an X-ray photoelectron spectroscopy as a function of the gamma-ray doses. An anomalous behaviour was observed in Pb4f states, and a core level of Pb4f shifts towards a higher binding energy at 50 kGy and towards a lower binding energy at 200 kGy. The behaviour can be explained by a radiation induced reduction of PbO to metallic Pb. The metal-insulator-metal electrodes were fabricated by lithography, and the current-voltage characteristics were measured. A negative differential resistance (NDR) was observed in the leakage currents at room temperature. A higher current and disappearance of NDR characteristics were found in the 200 kGy irradiated samples, which further confirms the presence of metallic Pb.

Sodium enrichment on glass surface during heating of heavy-metal-containing glasses under a reductive atmosphere

Sodium enrichment occurs on the surface of the glass that is in contact with the gas phase during the heat treatment of lead-containing glass under a reductive atmosphere. This technique was previously found to promote lead recovery in waste-glass treatment, and may be potentially applied to glasses containing other heavy metal oxides. Thus, the efficiencies of sodium enrichment were compared among glasses with different heavy metal species (PbO, CuO, and ZnO) in the heat-treatment under a CO-containing atmosphere. The sodium enrichment efficiencies in the treatment of the PbO- and CuO-containing glasses were higher than that in the treatment of the ZnO containing glass. This was because the efficiencies were related to the reduction of the heavy metal oxides. The mass ratio of Na to Si on the glass surface increased as the PbO concentration decreased via reduction of PbO. The sodium-rich phase was separated together with a copper-concentrated phase that was generated via the reduction of CuO. However, ZnO in the glass is thermodynamically more difficult to reduce in the CO-containing atmosphere used in the study, resulting in the lower efficiency of the sodium enrichment.

Influence of As2O3 added to PbO–CaO–SiO2 slag on the degradation mechanisms of stainless steel

The degradation of three stainless steel grades (23.8–25.0wt.% Cr and 3.8–19.0wt.% Ni) has been investigated after immersion in PbO–CaO–SiO2–As2O3 slag for 3h at 1200°C. The degradation mechanisms are related to the steel and slag composition. The effect of As2O3 is most pronounced in the slag with the highest PbO/SiO2 ratio, where dissolution of the steel in liquid Pb, coming from the reduction of PbO, is most severely present. The reduction of As2O3 to As causes alloying of the steel with As and subsequent liquid phase formation. The degradation degree increases with increasing Ni content of the steel.

Catalysis by Lead Oxide for Diethyl Carbonate Synthesis from Ethyl Carbamate and Ethanol

The catalysis by lead oxide in the reaction of ethyl carbamate (EC) with ethanol to form diethyl carbonate (DEC) was studied. The lead oxide catalyst exhibited an excellent stability, which could be reused five times without a significant loss in catalytic activity. X-Ray powder diffraction analysis showed that the recovered catalyst was a mixture of cubic metal Pb and orthorhombic PbO 2 , with the latter shown to be the real active component for the synthesis of DEC. Verification experiments showed that the reaction between DEC and PbO was the main reason for the reduction of PbO to metal Pb. 研究了氧化铅在氨基甲酸乙酯 (EC) 与乙醇反应合成碳酸二乙酯 (DEC) 中的催化作用. 结果表明, 氧化铅具有很好的稳定性, 重复使用 5 次, 其催化活性无明显下降. 回收的催化剂为立方晶相金属 Pb 和斜方晶相 PbO 2 的混合物, 结合反应结果可认为, 该混合物为反应的活性组分. 结果还发现, PbO 与 DEC 反应是 PbO 被还原为 Pb 的主要原因. The reaction between diethyl carbonate (DEC) and PbO is responsible for the reduction of PbO to metal Pb, and a mixture of cubic metal Pb and orthorhombic PbO 2 is the real active component for DEC synthesis.

Influence of Cr and Ni content in stainless steel on the degradation mechanisms in PbO–CaO–SiO2 slag

Degradation of stainless steel in contact with PbO–CaO–SiO2 slag at 1200°C is experimentally investigated. The contact between steel and slag leads to the reduction of PbO from the slag to liquid Pb, and concurrent oxidation of the steel. The degradation mechanisms can be divided into liquid slag and liquid metal corrosion and oxidation. High Cr content is beneficial as it promotes the formation of a Cr2O3 scale which shields the steel from the slag and liquid Pb. The high solubility of Ni in liquid Pb is responsible for the increasing dissolution rate with increasing Ni content of the steel.

Effect of coexisting inorganic chlorides on lead volatilization from CaO–SiO2–Al2O3 molten slag under municipal solid waste gasification and melting conditions

The effect of inorganic chlorides on volatilization of lead compounds from CaO–SiO2–Al2O3 molten slag under simulating conditions of gasification and melting of municipal solid waste was studied.It was found from the experiments that the volatilization of lead compounds from CaO (30wt.%)–SiO2 (50wt.%)–Al2O3 (20wt.%) molten slag in a lab-scale electric furnace at 1773K in N2, N2–O2 or N2–CO–CO2 atmosphere was promoted by the addition of NaCl, KCl and CaCl2 to the slag containing PbO, in the order of CaCl2>NaCl>KCl. The rate of volatilization and the amount of volatilized lead compounds were the highest by employing CaCl2 in N2–CO–CO2 atmosphere, due to combined reduction of PbO to metallic lead (Pb) and chlorination of PbO to PbCl2. By heating the molten slag at 1773K for about 10min, almost 100% of PbO was removed by adding CaCl2 to the slag at a molar ratio of (Cl)/(Pb)=27. However, the heating of molten slag at 1773K for 10min was not sufficient for complete removal of PbO, even by adding an excessive amount of NaCl and KCl to the slag at a higher molar ratio of (Cl)/(Pb)=110.From the equilibrium calculations on the main elements involved in municipal solid waste in shaft-type gasification/melting furnace, almost 100% of lead compounds were predicted to volatilize as Pb, PbS and PbCl2. The ratio of PbCl2 increased with the increase in chlorine (Cl) content in the waste. It was considered by equilibrium calculations that increased volatilization of lead compounds was attributed to the pronounced formation of PbCl2 by the reaction of PbO with HCl which was released from NaCl, KCl and CaCl2.

Mechanism of formation of anodic excursion peaks on lead electrode in sulfuric acid

Potential step and linear sweep voltammetry are proposed in combination for the anodic excursion peaks (AEPs) measurement of lead in sulfuric acid during cathodic scanning in the positive potential range. The overall procedure of measurement is composed of three steps. The first one is to polarize the lead electrode with negative potential, which is necessary for passivated PbSO 4(O) formation. Then, the polarization potential is stepped to positive to make sure that pure Pb could be oxidized to produce PbO n intermediate. Finally, a low-rate cathodic linear sweep voltammetry measurement is conducted in a small potential range. Four AEPs have been observed without reduction of PbO 2 to PbSO 4, which is in confliction with the conventional understanding that AEPs would appear accompanying with a large reduction peak for PbO 2 discharge. A new mechanism is therefore proposed that AEPs corresponds to the oxidation of PbO n intermediate in the cathodic scanning, so AEPs can be used to indicate the difficulty for the oxidation of Pb to PbO 2, and could be applied to characterize the corrosion resistance of lead alloy grid in the positive plate of a lead-acid battery.

Transformation of inert PbSO 4 deposit on the negative electrode of a lead-acid battery into its active state

Different forms of lead sulfate (PbSO 4) are produced in both the cathode and anode in the course of discharging of a lead-acid battery. However, their difference in reaction activity has not been well recognized up to now. From this work, it is shown the cathode product PbSO 4(O) due to oxidation of Pb is rather inert and its accumulation could lead to decrease of the battery capacity and life; on the other hand, the anode product PbSO 4(R) due to reduction of PbO 2 has a much active property and is readily reversible in the charging–discharging recycles. To restore the battery capacity, it is critical to solve the deactivation of cathode by transforming PbSO 4(O) into PbSO 4(R). For such a purpose, inverse charging is performed, and a procedure from PbSO 4(O) to PbO 2 and to PbSO 4(R) is conducted under a series of measurements with cyclic voltammetry, electrochemical impedance spectroscopy, scanning electronic microscopy and X-ray diffraction spectroscopy. The results of inverse charging tests show that the new capacity of a sulfated battery is more than twice of the initial value, which proves the validity of the mechanism outlined.

Effects of tetrabutylammonium hydrogen sulfate as an electrolyte additive on the electrochemical behavior of lead acid battery

Tetrabutyl ammonium hydrogen sulfate is an ion-paring reagent that has similar properties with ionic liquid. Ionic liquids belong to new branch of salts with unique properties that have ever increasing applications in electrochemical systems especially lithium-ion batteries. For the first time, the effects of tetrabutylammonium hydrogen sulfate (TBAHS) as an electrolyte additive in battery’s electrolyte was studied on the hydrogen and oxygen evolution overpotential and anodic layer formation on lead–antimony–tin grid alloy of lead acid battery by using cyclic voltammetry and linear sweep voltammetry in aqueous sulfuric acid solution. The grid surface morphology after cyclic redox reaction was studied by using scanning electron microscopy. The results show that, by increasing TBAHS concentration in the electrolyte, hydrogen and oxygen overpotential were increased, and so the crystalline structure of PbSO4 layer changed. Also, cyclic voltammogram on carbon–PbO paste electrode shows that with presence of TBAHS in the electrolyte, oxidation and reduction peak current intensively increased and peak potential for oxidation and reduction of PbO were dependent on TBAHS concentration.

Transgranular SCC mechanism of thermally treated alloy 600 in alkaline water containing lead

This work aims to understand a SCC failure mode of thermally treated steam generator tubing materials in high temperature water containing lead. The effect of lead contents on the anodic polarization curves of alloy 600 (UNS NO6600) and alloy 690 (UNS NO6900) has been studied in a solution of pH 10 at 200 °C and 315 °C. Lead increased the active peaks of alloy 600 and alloy 690 in mild alkaline water at high temperatures. A reduction of PbO to a metallic lead in alloy 690 is easier than that of alloy 600. When lead was added into the solution, a relative ratio of Cr from among the main metallic elements (Cr, Fe, and Ni) of alloy 600 and alloy 690 decreased in the outer corrosion film. Alloy 690 TT showed a transgranular stress corrosion cracking (TGSCC) in a 10 M NaOH solution with 5000 ppm of lead. Intergranular stress corrosion racking (IGSCC) was observed in the 100 ppm lead condition, and some TGSCC was detected on the fracture surface of the alloy 600 MA cracked in the 10,000 ppm lead solution. IGSCC seemed to be retarded by a crack blunting around the grain boundaries, and the TG cracking mode of the thermally treated alloy 600 and 690 seemed to be related to a crack blunting at the grain boundary carbide and a film dissolution by lead in an alkaline solution.

Kinetics of reduction of lead smelting slags with solid carbon

Research techniques and a methodology have been developed that enable the reduction kinetics of molten lead smelting slags with solid carbon to be studied. The rates of reduction of PbO–FeO–Fe2O3–CaO–SiO2 slags with carbon have been measured for a range of slag compositions for PbO concentrations between 3 and 100 weight percent, and temperatures between 1423 and 1573 K. The reduction rates were determined for both graphite and coke. Within the range of process conditions examined, it has been shown that the reaction rates are almost independent of carbon reactivity, SiO2/CaO and SiO2/Fe ratio in the range of compositions investigated and are not influenced by the presence of sulphur in the slag.The apparent first order rate constants for oxygen removal increase with increasing PbO concentration and oxygen activity in the slag. The data indicate that the rate limiting reaction step for the reduction of lead slags with solid carbon is the chemical reaction at the gas/slag interface.

Influence of pH of the H 2SO 4 solution on the phase composition of the PbO 2 active mass and of the PbO 2 anodic layer formed during cycling of lead electrodes

During charge and discharge of lead-acid batteries the concentration of the H 2SO 4 solution in the pores of the active material and in the interface grid/active mass varies widely. In this investigation, the influence of pH of the H 2SO 4 solution on the phase composition of the positive active mass (PAM) and of the interface PAM/grid is studied. The influence of pH on the phase composition of the interface is determined indirectly by cycling Pb electrodes between 0.70 and 1.60 V (versus Hg/Hg 2SO 4) in H 2SO 4 solutions of various concentrations and determining the phase composition and the structure of the anodic layer formed. The influence of pH on the phase composition of the PAM is investigated by immersing fully charged PAM samples into H 2SO 4 solutions of various concentrations and determining the phase composition of the PAM and the size of the α-PbO 2, β-PbO 2 and PbSO 4 crystals. It has been found that the outer sub-layer of the anodic layer participates in the cycling processes and its phase composition depends on the pH of the solution and on the potential scan rate. The reduction rate of PbO 2 in this sub-layer depends on the solution pH. If the reduction of PbO 2 proceeds in solutions with pH between −1.0 and −0.50, the rate of the processes is high. When it proceeds at pH>−0.50 the reduction rate is lower. This behaviour of the PbO 2/PbSO 4 electrode influences the power performance of the lead-acid battery when the positive plates are the power limiting component. The rate of oxidation of PbSO 4 to PbO 2 is determined by the pH of the solution because the solubility of PbSO 4 depends on pH. In concentrated solutions the solubility of PbSO 4 is low, the charge process is slow and some unoxidised PbSO 4 may remain in the charged plate. In diluted H 2SO 4 solutions, the solubility of PbSO 4 is high and PbSO 4 crystals are oxidised fully during charge. It has been found that the phase composition of the PAM depends on the pH of the solution since the hydrated part of the PbO 2 particles interacts with the ions in the solution as a result of which the crystal zones/hydrated zones and hydrated zones/solution equilibria are changed. The content of α- and β-PbO 2 crystal zones in the PAM depends on the pH of the solution. In the pH region between −0.75 and 0, SO 4 2− ions which have penetrated into the hydrated gel zones react with Pb 2+ ions from the nonstoichiometric part of the PAM (PbO 2− δ ) forming PbSO 4 molecules, which leave the hydrated zones and enter the solution forming PbSO 4 crystals there. When the PAM is immersed in solutions with pH between 0 and −1.0, the content of the crystal phases of α- and β-PbO 2 decreases. In this pH region the average size of the β-PbO 2 crystals decreases while that of α-PbO 2 remains constant or increases slightly. The results of this investigation evidence that the PAM is a dynamic system, which interacts with the ions in the solution, and hence the phase composition of the PAM depends on the concentration of the H 2SO 4 solution.

Cyclic voltammetric behavior of the lead electrode in sodium sulfate solutions

Cyclic voltammograms (CVs) of the Pb electrode were obtained in Na 2SO 4 solutions as a function of starting potential, electrolyte concentration, voltage range and voltage scanning rate. The shape of the voltammograms was found to depend on the starting potential as well on the sweep number. This is probably due to changes in the activation state of the electrode surface. In the first sweep, the anodic portion of the voltammograms is characterized by a shoulder and three peaks as a result of the formation of PbSO 4, PbO, PbO 2 and transformation of PbSO 4 to PbO 2, respectively, on the electrode surface before the evolution of oxygen. On the other hand, in the second and later sweeps, an additional anodic peak appeared which may be due to the formation of intermediate oxides. The cathodic portion shows the occurrence of three peaks corresponding to the reduction of PbO 2 to PbSO 4, PbO 2 to PbO and the latter with PbSO 4 to spongy lead, respectively, followed by the formation of PbH 2 before evolution of hydrogen. A correlation was made between the anodic peaks and their corresponding cathodic ones. Increasing the sulfate anion concentration increased the highest of the peak currents and shifted the anodic peak potentials towards more negative values. A linear relationship was obtained between the logarithm of the anodic peak current densities and the logarithm of SO 4 2− anion concentration. An increase in the scan rate enhanced the current density of both the anodic and cathodic branches. Also, the anodic potentials are shifted towards more positive values, whereas the cathodic peaks are shifted in the negative direction, indicating irreversible formation of the passive film on the electrode surface.

High-Temperature Oxidation of Methane by Supported Lead Oxide

The kinetics of the reduction of PbO supported on Al2O3by methane is studied in the temperature range 760–927°C. The reaction order with respect to methane is equal to unity and the apparent activation energy is ∼40 kcal/mol. When the extent of PbO reduction is 0.5–0.6, the selectivity of methane conversion changes drastically: only CO2is formed at lower extents of reduction, whereas CO is the main product at higher extents.

Electrochemical behavior of lead in sulfuric acid solutions

The electrochemical behavior of the lead electrode has been studied by cyclic voltammetry (CV) in sulfuric acid solutions, with concentrations ranged from 0.05 to 5 M. Also, the effect of a sweep rate, the range of potential polarisation and temperature has been examined. Special attention has been paid to unusual anodic processes, i.e., “anodic excursion” peaks that accompany the main reduction peak. The presence of a small, and previously unrecognized cathodic peak, preceding “anodic excursion” peaks, has been documented. Since all these peaks appear on the CVs only when the electrode potential is cycled in a wide potential range, limited by hydrogen and oxygen evolution, it has been proposed that they are related to the reduction of the lead dioxide to the bare metal, occurring at high negative potentials. The presence of a small reduction peak preceding “anodic excursion” peaks, as well as the presence of the main reduction peak of the lead dioxide has also been related to the exposure of the bare metal. When the lead dioxide, formed at high positive potentials, is reduced (PbO 2→PbSO 4), a large increase of the molar volume is expected and, as a result, the surface cracks, exposing the bare metal. These parts of the surface are then oxidized in “anodic excursion” peaks. To repeat these redox processes, the electrode has to be reduced again at high negative potentials, i.e., at the conditions when reduction to the metal occurs. The CVs performed only in a positive potential range confirmed that the reduction of PbO 2 to PbSO 4, which follows the formation of PbO 2, is not related to the “anodic excursion” peaks and it also means that no cracks of the surface occur, as long as the potential cycling of the electrode to high negative potentials, and the resulting reduction to the metal, are avoided. Therefore, when the lead electrode is used as a positive electrode in a battery, no corrosion due to the exposure of the bare metal is expected.

Effect of polarisation mode, time and potential on the properties of the passive layer on lead-tin alloys

Taking into account the dynamic behaviour of the passive layer formed on lead and lead-tin alloys, this work emphasises the effect of the polarisation potential and the polarisation time on the electronic conductivity of the passivation layer. When the lead electrode was polarised in the passivity region (700 mV versus Hg/Hg 2SSO 4 electrode), the polarisation resistance increased but decreased when tin was alloyed. This behaviour is interpreted by the increasing formation of semi-conducting PbO and conducting tin oxide. With a potential incursion in the PbO 2 region (1500–2000 mV), semi-conducting lead oxide, PbO x, was formed. The decrease in polarisation resistance is explained by the electronic properties of PbO x which is assumed to be less resistive than PbO, and, subsequently, the increase in polarisation resistance versus time is interpreted by the reduction of PbO x at 700 mV.

Electrochemical behaviour of lead electrode in sulfuric acid solution containing citric acid

The electrochemical behaviour of a lead electrode as the positive electrode (in PbO 2 form) and the negative electrode of a lead/acid battery in sulfuric acid solution containing different concentrations of citric acid has been studied by cyclic voltammetry. For the behaviour of lead as a positive electrode, a new layer of PbO 2 is formed in the presence of citric acid. It is difficult for this layer to be reduced and, therefore, the conductivity between the positive grid and the positive active material will be greater than that in pure sulfuric acid solution. The peak currents attributed to the formation and reduction of PbO 2, and to the evolution of oxygen, increase with the concentration of citric acid. The limits of the effects are reached at about 2 g/1 citric acid in 4.5 M H 2SO 4. For the behaviour of lead as a negative electrode, the peak currents attributed to the oxidation of lead to PbSO 4 and to the evolution of hydrogen gas also increase with the concentration of citric acid. In 4.5 M H 2SO 4, the limits of these effects are reached at a citric acid concentration of 2 and 3 g/1, respectively. The observed behaviour is caused by the adsorption of citric acid on the PbO 2, lead and PbSO 4 surfaces.

Ring-disk electrode studies of soluble intermediates formed during the polarization of Pb in H 2SO 4

The use of a rotating ring-disk electrode to detect soluble Pb(1V) and Pb(11) species released into H 2SO 4 has made it possible to give complementary interpretations for the processes occuring during the anodization and successive reduction of Pb electrodes. It has been shown that soluble Pb(1V) species act as intermediates during the formation tetravalent oxides of Pb, and that the generation of tetravalent products is always preceded by the information of divalent products even at high positive potentials. During the reduction of PbO 2, species are released. Part of the tetravalent products formed at Pb are reduced only at high negative potentials.