Reduction Of PbO Research Articles

Formation of Current Leakage Paths at the Interface between Dielectrics in Intense Electric Fields in a Gas Discharge Display Device

Electrically conducting paths were formed at the interface between a soda-lime glass substrate and a lead-glass overglaze in a gas discharge display panel under an electric field of 7 kV/cm. This resulted in the panel malfunctioning after 4000-h operation. The current leakage paths consisted of Pb atoms, produced by the reduction of PbO by Na ions. The rate of path formation was strongly sensitive to the electric field, substrate temperature, and also to the presence of ionized gases in the vicinity of the interface. Methods of avoiding insulation failure include using a Pb-free dielectric overglaze, sandwiching the electrodes between lead glasses, and reducing the intensity of the electric field.

Proposed mechanism for the action of palladium and nickel modifiers in electrothermal atomic absorption spectrometry

By the use of Fourier transform infrared spectrometry it was found that palladium chloride decreased the temperature of the reduction of PbO and Ga2O3 with graphite; nickel chloride only catalysed the reduction of Ga2O3. A hypothesis is proposed that nickel and palladium salts promote the reduction of compounds (in atomic absorption measurements) at relatively low ashing temperatures. The resultant free elements form intermetallic compounds or solid solutions with metallic Pd and Ni, thus reducing or almost eliminating loss of analyte due to sublimation of halides, oxides, dimers and other compounds. The high efficiency and universal action of Pd modifiers are because the Pd metal can be easily formed from its compounds and also by the unique catalytic properties of metallic Pd.

Radiation-induced dissolution of colloidal lead oxide

The reduction of Ludox-stabilized colloidal PbO{sub 2} using radiolytically generated viologen radicals (ZV{sup {minus}}) has been studied by using both steady-state {gamma}-radiolysis and pulse radiolysis techniques. The steady-state radiolysis results indicate that reduction of PbO{sub 2} is consistent with the overall reaction PbO{sub 2} + 4H{sup +} + 2ZV{sup {minus}} {yields} Pb{sup 2+} + 2ZV + 2H{sub 2}O. Temporal examination of the reduction process, monitored conductometrically and spectroscopically, reveals that two main steps are involved in the overall reduction process. The first step occurs rapidly and involves a one-electron reduction of a PbO{sub 2} colloid with virtually the simultaneous adsorption of a proton. Once the colloid possesses one electron, the second electron is more difficult to transfer and a slower electron-transfer step occurs consuming, again simultaneously, three protons to produce Pb{sup 2+}.

Surface processes observed by high-resolution electron microscopy: Beam-induced transformation and reduction in a modified β-PbO 2 crystal

Surface profile images of crystals of a modified β-PbO 2 produced by the leaching of Pb 3O 4 with dilute nitric acid have been examined at high resolution in the electron microscope. The sum of evidence is that hydrogen is present in the modified β-PbO 2 structure. The latter can easily transform to the rutile-type β-PbO 2. High-resolution surface profile imaging was used to study dynamic change in the surface of these crystals. In addition to apparent single-atom movement, cooperative movement of very large entities was observed. These mobile groups were invariably two lead atom layers thick corresponding to the repeat unit of the modified β-PbO 2. The cooperative motions involved scores to hundreds of atoms. In addition, small crystals about 10 nm across (containing a few hundred atoms) were observed to migrate on the surface until they became accreted to the substrate crystal. These small crystals changed their shape while in motion and even reflected the defects of the substrate when they were accreted. Finally, evidence was found for substantial electron-beam-induced reduction of PbO 2 to lower oxides with a gross modification of the crystal profile.

The suspension electrode technique for electrochemical analysis of lead dioxide

The suspension electrode technique was used to investigate the reduction behaviour of PbO 2 particles. The I-U curves obtained potentiodynamically can be divided into two ranges; 1. (a) the range of lower polarization, which is characterized by the reduction of PbO 2 adsorbed at the collector surface (film current); 2. (b) the range of higher polarization where only the redution of PbO 2 particles thrown towards the collector electrode takes place (suspension current). The I-U curve is affected by the electrolytic medium, the collector material, the stirring time before the reduction, the stirring rate, sweep rate, particle size and temperature. The film current can be largely increased by raising the temperature and extending the stirring time prior to reduction. Therefore, conditions of elevated temperature and increased stirring time should be preferred for quantitative analyses of the degree of discharge of PbO 2 active masses.

The cathodic reduction of PbO in the passive layer on lead in aqueous sulphuric acid

The cathodic reduction of the lead monoxide layer formed on lead in 30% aqueous H2SO4 under anodic oxidation at 0.6 V (vs. Hg/HgSO4 reference electrode) was investigated by linear sweep voltammetry, potential step and admittance measurements. The experimental data were analyzed respectively in terms of thin-layer electrochemistry, electrocrystallisation, and changes of resistance of the PbO layer under reduction. The results seem to be best interpreted from the theory of three-dimensional electrocrystallisation as PbO is reduced to Pb. At sub-zero temperatures the PbO peak observed on our voltammograms and potentiostatic current time transients reveals the splitting of the curves into two peaks, which may be a result of reduction of the same material but of different phases, namely, orthorhombic and tetragonal PbO.

Photoelectrochemistry in the lead-sulphuric acid system

In this paper we compare photoelectrochemical cyclic voltammograms with ordinary cyclic voltammograms. The two techniques are complementary in the sense that peaks are observed in one type of voltammogram at precisely those electrode potentials at which peaks are absent in the other. Our data allowed us to identify several peaks in the ordinary cyclic voltammograms. In particular, we located peaks corresponding to the reduction of PbO to Pb, and to the oxidation of PbO to α-PbO 2. In the photoelectrochemical cyclic voltammograms we observed two anodic photocurrent peaks and one cathodic photocurrent peak. We explain the two anodic photocurrent peaks in terms of a Schottky barrier in non-stoichiometric n-type PbO. The cathodic photocurrent peak is more mysterious, but is probably due to the photoreduction of non-stoichiometric p-type PbO, generated in the O 2-evolution region. The photocatalysis of O 2-evolution on the surface of β-PbO 2 was also observed.

Photocurrent spectroscopy of lead dioxide

Lead dioxide is a degenerate n-type semiconductor which behaves alrnost as a metal. When PbO 2 is reduced, however. the stoichiometry changes and a semiconducting phase with a much lower free electron density is formed. The deposition of PbO 2 on a platinum anode has been followed by interferometry, and the subsequent reduction of the film has been characterized by photocurrent spectroscopy. The latter technique has given information about the band gap and stoichiometry of the lower oxides of lead formed during the reduction of PbO 2. The mechanism of photocurrent generation and a simple model which takes account of the semiconducting properties of the lead oxides will be discussed.

X-ray photoelectron spectroscopic studies of PbO surfaces bombarded with He +, Ne +, Ar +, Xe + and Kr +

The surface composition of PbO has been studied with X-ray photoelectron spectroscopy after bombardment with several inert gas ions of 400 eV. The results show reduction of PbO to metallic Pb with the degree of damage following the order He + > Ne + >Ar +. Both Kr + and Xe + did not reduce the oxide. The depth of damage varied from ≈9 Å for He + to ≈1 Å for Ar + bombardment. The results were compared to a collisional and a thermal model of the sputtering process.

Auger analysis of thin oxide films on Pb–In alloys

The composition and stability of thin oxide films (?35 Å), thermally grown on Pb–In alloy substrates at room temperature and various oxygen pressures, were studied quantitatively by Auger electron spectroscopy. The results indicate that all oxide films are enriched in indium in varying amounts, depending on the alloy composition and oxygen pressure. For alloys contaning more than 10 at.% In, the surface layer of the oxide consists of pure In2O3 only; for alloys of lower In concentrations a mixture of PbO and In2O3 is formed. The mixed oxide appears to be unstable since the Auger data monitored during vacuum storage are indicative of the reduction of PbO with attendant formation of additional In2O3 occuring near the alloy–oxide interface.

Lead electrocrystallization during reduction of solid oxides

On the basis of data concerning the dependence of the value of the limiting current of the reduction of PbO 2 to PbO 1·34 on alkali concentration, the change of active component of impedance, R s in course of PbO 2 reduction and the dependence of R s on ω − 1 2 , it is concluded that the process starts at the PbO 2/electrolyte interface and proceeds in the solid oxide phase. The suggestion is made that the localization of the reduction process depends on the distribution of defects of different type in the crystal lattice. A system of lead dendrites arises when PbO 2 is reduced.

Die änderung der stromverteilung in porösen positiven elektroden von akkumulatoren und galvanischen primärzellen während ladung und entladung

In the porous thick electrodes of primary and secondary galvaniv cells, the distribution of current undergoes characteristic changes during charge and discharge. In general, the current distribution may become more and more even, if the electrode reaction takes place in a homogeneous phase, and if the neccessary voltage profile can be developed within the electrode. This is the case with the manganese dioxide electrodes of dry cells. In these electrodes, the current distribution is already evened out after a period representing not more than about 15% of the total cell capacity. However, the reduction of PbO 2 and NiOOH in lead—acid and in alkaline secondary cells respectively, and of the HgO electrode in alkaline primary cells, proceeds in a heterogeneous phase system. Consequently, the initial distribution of current in these electrodes is maintained over a prolonged period. Instead of the evening out of current, here a reaction layer may be observed, moving inwards from the solution electrode interface. The electrodes discussed are examined by means of electrical analogues. Special attention is paid to the influence of diffusion.

Temperatures and rates of reduction of PbO 2, Pb 3O 4, and PbO by hydrogen and carbon monoxide

Liquid metals have been proposed in the past as high temperature heat transfer media in concentrating solar power (CSP) systems. Until the mid 80s test facilities were operated with liquid sodium-cooled central receivers. After a period of reduced interest in that approach, several new efforts have been reported recently, particularly from the US, South Africa and Australia. In addition, several recent publications have highlighted the attractive properties of liquid metals for CSP applications. A new contribution to this topic has been launched by Karlsruhe Institute of Technology (KIT) and the Solar Institute of the German Aerospace Center (DLR), combining their experience in CSP and liquid metal technology. The overall goals of this project are planning, design, construction and operation of a small concentrating solar power system in the 10 kW thermal range (named SOMMER) using liquid metal as heat transfer fluid for re-gaining operation experience and validating design methodology and providing a complete design concept for a large pilot CSP plant based on liquid metal technology, up to evaluation of O&M cost and levelized cost of electricity. This paper describes the current status of the work on the design and setup of SOMMER, the research goals of this facility, first results of numerical activities in view of the liquid metal cooled receiver design and the connection to the design activities for the pilot plant.

The Kinetics of the Reduction of Lead Monoxide by Hydrogen

The rate of reduction of fused lead monoxide particles in a differential reactor with H2-N2 and H2-H2O mixtures has been measured by absorbing the H2O of reaction or chemically analysing the product, Pb-PbO. After falling from a high initial value, the reduction rate remains virtually constant until 40-50% of the PbO has been reduced, and then slowly declines. The rate of reduction is independent of the gas flow rate from 5-151. S.T.P./min and not markedly influenced by variations in particle size from -36+52 to -7+10 mesh B.S.S. With H2-N2 mixtures the rate of reduction of PbO at 575 and 675 �C is proportional to pH2, and with H2-H2O mixtures at 575 �C it is proportional to pH2/(1+0.5pH2O), where pH2, and pH2O are the partial pressures of H2 and H2O, respectively. The activation energy for reduction with H2-N2 and H2-H2O mixtures over the temperature range 475-775 �C is 39 kcal/g-mole. Chemisorption of H2 on the PbO appears the most likely rate controlling step at the Pb-PbO interface. Rates of reduction over the steady rate period, k0, are correlated by the expression k0=f(R)[pH2/(1+0 5 pH2O)] exp(-39 000/RT), where f(R) is a parameter related to particle shape and size.