PbSO4 Crystals Research Articles

A comparative kinetic study of Pb and Pb-Sb electrodes in sulfuric acid solutions

The electrochemical responses of Pb and Pb-3.4% Sb electrodes in 5 M H2SO4 were examined combining potential sweep and potential step techniques. The presence of antimony prevents the complete blockage of the electrode active surface by PbSO4 crystals during electro-oxidation, changing the composition and structure of the passive layer. The electro-oxidation of Sb was interpreted in terms of an adsorption-dissolution mechanism where in the rate-determining step one electron is transferred. The growth kinetics of the PbO inner layer was also studied. On the Pb-Sb electrode, the growth rate of PbO decreases because of a change in the transport mechanism of ions through the anodic layer.

Influence of antimony ions and PbSO4 content in the corrosion layer on the properties of the grid/active mass interface in positive lead–acid battery plates

Antimony in lead/antimony alloys is known to have a beneficial influence on the capacity and cycle life of lead–acid battery positive plates. The present work shows that Sb3O93− ions formed on oxidation of PbSb alloys improve the capacity of the Pb/PbO2 electrode, whilst SbOSO4− ions have an adverse effect and passivate this electrode. A mechanism of the influence of these ions is proposed based on the gel–crystal concept for the structure of PbO2. The paper also discusses the effect of PbSO4 formed at the grid/PAM interface on the capacity. It has been established that the major part of the PbSO4 crystals are oxidized to PbO2 within a few cycles. There still remain a certain number of PbSO4 crystals which border narrow pores and are oxidized at a very slow rate, thus preserving their influence even after 10 discharge–charge cycles. It has also been found that the higher the density of PAM the stronger the adverse effect of PbSO4 in the grid/PAM interface on the capacity. All these phenomena are related to the PCL effect and methods to suppress them are proposed.

Hydrothermal Growth of PbSO<sub>4</sub> (Anglesite) Single Crystal

Hydrothermal growth of single crystals of PbSO4, which is known as a natural mineral called anglesite, was investigated. Lead nitrate and nitric acid solutions were found to be useful for the growth of anglesite on the basis of the experimental results on the dissolution behavior. Relatively large euhedral single crystals bound by {210} and {101} planes were successfully grown in 1.5mol/kg Pb(NO3)2 at 400°C and 100MPa. Optical characterization revealed that the grown anglesite crystals can be useful for scintillators material.

The effect of nicotinamide on the charge/discharge behavior of PbO2 electrode in sulfuric acid solution

The effect of nicotinamide (NA) on the charge/discharge behavior of the positive electrode of a lead/acid battery was studied by cyclic voltammetry, charge/discharge cycling tests and scanning electron microscope observation. By adding NA into the sulfuric acid solution, the rate of capacity decrease of the PbO2 electrode was reduced and its cycle life was prolonged. This phenomenon was considered to be due to NA adsorption on PbO2, which causes a morphology change in the PbO2 and PbSO4 crystals to enlarge the electrode surface area.

Influence of the size of PbSO4 crystals on their solubility and the significance of this process in the lead-acid battery

When the PbO2 plate of the lead-acid battery is discharged, small PbSO4 crystals are initially formed which subsequently undergo recrystallization. In this paper the driving forces of the PbSO4 recrystallization process are established. The change in solubility of the small PbSO4 crystals with time in 1m and 0.1m H2SO4 is determined. Initially the solubility is high and decreases with time to reach a steady value, in agreement with that in the literature. SEM observations indicate that this process is associated with an increase in the volume of the PbSO4 crystals. The surface free energy of PbSO4 is estimated and a scheme for the recrystallization process at the PbO2 active mass is proposed.

?Breathing? of the lead-acid battery negative plate during cycling

By measuring the thickness of the negative plates with and without an expander, during cycling, it was established that the active mass volume pulsates, expanding during discharge and shrinking during charge. This phenomenon is due to the mechanical stress in the lead skeleton structure caused by the PbSO4 crystals. At each pulsation of the plate, slight changes in the structural parameters of the active mass are observed. These changes accumulate during cycling causing expansion or shrinking of the active mass. As a result of this the capacity of the plate decreases. These changes in the plate structure depend strongly on the expander.

Zur passivierung von blei in Schwefelsäure keimbildung und wachstum der PbSO 4-Deckschicht

The examination of the morphological structure (scanning electron microscopy), the crystal structure (X-ray-diffraction) and the electrochemical potential of the PbSO 4-film on lead, grown in sulfuric acid, leads to an hypothesis about the mechanism of the film nucleation and growth: A primary stage is the formation of a film, amorphous to X-rays and which is not in the range of the resolution of the scanning electron microscope. After this, in a second stage the well-known PbSO 4-crystals develop with linear dimensions of about 1 μm. Antimony solved in the electrolyte causes a more porous primary film and changes the equilibrium potential. Air-atmosphere accelerates the velocity of film growing and influences the equilibrium potential.

Mechanism of the Anodic Oxidation of Lead in Sulphuric Acid Solutions

AbstractThe processes of the anodic oxidation of lead in 1 n H2SO4 were studied by means of successive polarizations at constant potential and subsequent observation of the open‐circuit potential transients. The behaviour of the electrode was investigated at steps of 100 mV in the range lying between the equilibrium potentials of the Pb/PbSO4 and the PbSO4/PbO2 electrodes. Following each oxidation run the electrode was observed on the electron microscope. It was established that by oxidation up to — 450 mV (vs Hg/HgSO4 in 1 n H2SO4) crystals of PbSO4 are obtained. At potentials between — 450 and + 800 mV the pH of the solution in the intercrystalline spaces is raised and reaches values, where 5PbO · 2H2O and 4PbO · PbSO4 are formed. The composition of the layer changes along the depth of the layer according to the solubility product of the compounds obtained. At open circuit, the H2SO4 diffusion in the intercrystalline spaces causes a process of sulphatization of lead oxide and of the basic lead sulphates, which is reflected by the form of the open‐circuit potential transients. At potentials higher than + 800 mV, PbO2 is obtained in the intercrystalline spaces. At higher potentials the oxidation reactions of PbSO4, Pb and basic lead sulphates proceed with a high over‐voltage. At oxidation potentials above + 1000 mV the oxidation rate shows maximums.

Electrostatic Lattice Energy of PbSO4, BaSO4, SrSO4 and CaSO4

Abstract A plan for investigation of the physical chemistry of radical ions is stated with especial reference to the strict treatment of the lattice energy problem and the treatment of complex ionic crystals. First, the expressions suitable for the practical numerical calculation of Madelung’s coefficient of the general and the rectangular crystal lattice are derived from Ewald’s original general expressions. Next, they are verified in the two simple cases, NaCl and the rhombic CaCO3, by means of numerical application. Then, they are applied to the more complex cases, i. e., the rhombic crystals of PbSO4, BaSO4, SrSO4, and CaSO4, with SO4−− which is assumed to be a point charge. The degree of accuracy of the calculated values is further discussed; and, in connection with it, an attempt is made to estimate the extent of variability of Madelung’s “ coefficient” (or “constant,” as it is called). Finally, the electrostatic lattice energy is evaluated.