Fundamentals of lead-acid cells: Part XI. Phase formation at solid and porous lead electrodes

The development of lead sulphate on lead (charged) electrodes (massive and porous) has been examined by the potential-step technique. The behaviour of the solid electrode conforms to control by nucleation and growth processes. The exact form of the process is potential-dependent and becomes two-dimensional at more positive potentials. The behaviour of the porous electrode can be interpreted in terms of well-established theory for porous materials assuming that the same crystallisation processes are observed as for the case of solid electrodes.     

Fundamentals of lead acid cells: Part IV. The reduction of porous PbO2 electrodes in sulphuric acid

The reduction behaviour of porous lead dioxide electrodes is shown to be independent of rotation speed in a large excess of 5 M H₂SO₄. The reduction peak is broadened by the porosity. This porosity broadening is interpreted in terms of the reaction being driven more deeply into the pore structure as the front of the electrode becomes progressively more ressstive. The effect of different potential sweep rates on the current response and the effects of progressive redox cycles can be fully explained on this model.     

Fundamental studies of lead acid cells: Part III. Studies of the oxidation of lead sulphate

The kinetics of the nucleation and growth of lead dioxide on a lead based sulphate electrode have been re-examined. The processes involved and the subsequent redox cycle are reported and discussed. After the first cycle the current-time response under potentiostatic control changes and duplex lead dioxide layer formation appears to occur. The mechanism of growth of PbO₂ on a cycled Pb/PbSO₄/PbO₂ electrode can be interpreted in terms of an instantaneous nucleation and single layer growth followed by the conversion of the remaining lead sulphate in a second more extensive layer.     

Fundamentals of lead-acid cells: Part XIII. The influence of additives on the charge and discharge processes of the negative electrode

The effects of BaSO₄ and a lignosulphonate on the normal discharge and charge processes of a porous lead electrode have been examined by the potential-step technique. Here, BaSO₄ is shown to exert a major electrochemical effect on the discharge reaction while the lignosulphate is found to increase the available active surface area of the electrode.     

Transient processes in photogalvanic cells: Part I. Fundamentals

The theory of transient processes in photogalvanic cells is developed. The systems treated consist of a photoactive species B which can be oxidized (or reduced) to A in its excited state B^* by a one-electron acceptor Z which itzelf is reduced (oxidized) to Y. It is further assumed that both redox couples undergo one-electron transfer reactions at the metal electrodes. The electrode kinetics for both redox couples is taken into account. A computer program is described with which the following data can all be obtained as functions of time, after illumination has started: current, potential of the illuminated electrode, potential of the dark electrode, power, and the concentration profiles of A, B, Z and Y near the electrodes.     

Thermogravimetric study of the reduction of basic lead sulphate

In this paper, the results of the study of the reduction of basic lead sulphate with a gas (CO + CO₂) mixture are presented. This is a secondary reaction during the reduction of lead sulphate. The change in the both lead and PbS content in the reaction products, depending on the process temperature and the composition of the gaseous phase, was established. The comparison of the rate of the reduction reaction of lead sulphate and basic lead sulphate shows that the process proceeding with a higher output is the reduction of basic lead sulphate.     

Synthesis and characterisation of tribasic lead sulphate as the negative active material of lead-acid battery

Although tribasic lead sulphate (3BS) has been chemically prepared and found in the cured negative plates of lead-acid batteries (LABs), little was known about its behaviour if it is used directly as their negative active material (NAM). Here, we report a much more facile and energy-saving route to prepare phase pure 3BS powders: after β-PbO is reacted with PbSO₄ at 30 °C, elongated 3BS plates of 4~8 μm in length, 1~3 μm in width and 0.1~0.2 μm in thickness are obtained in 4 h. Compared with electrodes prepared from β-PbO, α-PbO and leady oxide, the as-prepared 3BS electrode shows much better performance, which discharges more than 90 at 120 mA g^?1 within 100 cycles of 100% DOD (depth of discharge) in a flooded cell. Therefore, 3BS can be used directly as NAM of LABs. It is also worth to notice that using 3BS can reduce the curing/drying time of the plates, thus save energy and produce uniformity in LAB production.     

Metal-betaine interactions. Part XII

Two copper(II) complexes of pyridine betaine (C₅H₅N⁺CH₂COO^–; pyBET) were prepared and characterized by X-ray crystallography. In [Cu(pyBET)(H₂O₂)₂(SO₄)]_n (1), each Cu (II) atom is in a distorted square-pyramidal environment surrounded by a carboxylato oxygen atom [1.944(5) Å], two oxygen atoms [1.921 (5) basal, 2.268(5) apical Å] from different sulfato groups, and two aqua ligands [1.944(4) Å]. The primary coordination sphere is extended into a zigzag chain through sulfato bridging linkages, and hydrogen bonding involving the aqua ligands generates a three-dimensional network. [Cu(pyBET)(H₂O)₂Cl₂]·H₂O (2) features a discrete metal complex with its distorted square-pyramidal coordination sites occupied by a carboxylato oxygen atom [2.000(2) Å], two aqua ligands [1.968(3) Å], and two chloro ligands [2.266(1), 2.469(1) Å] of which one is apical. The lattice water molecules form hydrogen bonds with the aqua and chloro ligands to yield a layer structure.     

A new design of lead amalgam/lead sulphate electrode for potentiometric measurement of sulphate

A new lead amalgam/lead sulphate electrode has been developed which is easy to handle and can be used in a simple measuring cell. Its electrochemical characteristics have been tested in two different cell systems. The potentials obtained were very stable, and reproducible within +/-0.04 mV. The electrode exhibited a Nernstian response to sulphate and its calculated standard potential (-350.68 +/- 0.13 mV) agreed very closely with that recorded in the literature.     

Polarography of some sulphur-containing compounds : Part XII.Anodic waves of dialkyldithiocarbamates

Dialkyldithiocarbamates give only a one-electron anodic wave. The various adsorption phenomena are probably caused by varying orientation of the mercury compounds on the electrode surface; the irregular i-t curves recorded at —0.04 V and the anomalous behaviour of the anodic current between +0.2 V and —0.4 V can be interpreted as the behaviour of an adsorbed film at the electrode. Analytical measurements are best made in 60% ethanolic 0.1 M sodium hydroxide media at concentrations of about 10^-5 M dialkyldithiocarbamate; a method is given for the analysis of the monoalkyl and dialkyl compounds in mixtures.     

Survey on mass determination systems: Part I. Fundamentals and history

The influence of mass and force on the frequency of vibrating bodies today is widely applied. In Part I of the survey the historical roots are reviewed and the physical principles of the several arrangements modes of operation explained.This revised version was published online in November 2005 with corrections to the Cover Date.     

Heterocyclo-Substituted Sulfa Drugs: Part XII. Mercapto-S-Azo-Benzothiazol Dyes and Their Metal Complexes

New azo sulfadrugs of 2-mercapto-S-azo ( p '-heterocyclo-substituted benzene-sulfonyl) benzothiazole derivatives (L 1 and L 2 ) were synthesized by coupling of p '-heterocyclo-substituted-benzene-sulphonyl diazonium salts with 2-mercapto-benzothiazole in acid medium. The corresponding iron(III), cobalt(II), nickel(II), copper(II), and mercury(II) chelates were prepared in a 1:1 metal to ligand molar ratio. The ligands and their chelates were characterized on the basis of microanalysis, UV, IR, and H 1 -NMR spectrometry. Thermal decomposition of the complexes was studied in static air. On the basis of the thermogravimetric curves some decomposition steps could be correlated with the proper decomposition products. The photochemical behavior of the ligands and their complexes were investigated. The photosensitivity shown by the complexes was attributed to the photoreactivity of their free ligands. The ligands and their chelates were screened in vitro for their antimicrobial activities (antibacterial and antifungal). The complexes induce a remarkable increase in the antimicrobial activity compared to the corresponding ligands.     

Photogalvanic cells: Part XI. The thionine-coated electrode

Studies using ring-disc electrodes, cyclic voltammetry, optical absorption and X-ray photoelectron spectroscopy show that up to twenty monolayers of thionine can be irreversibly coated on to platinum or tin oxide electrodes. On such electrodes the electrode kinetics of the thionine-leucothionine couple are still reversible or quasi reversible. In contrast the reduction of Fe(III) is much slower on a coated electrode compared to a clean electrode. Koutecky-Levich plots show that there is a second potential-independent rate-limiting step. This blocking of the Fe(III) reduction means that the thionine coated electrode is the ideal electrode for a photogalvanic cell using the iron thionine system.     

铅及铅锑合金阳极膜中硫酸铅的氧化过程

应用电位阶跃和交流阻抗法分别研究铅和Pb-5wt% Sb合金在4.5mol·dm^-^3H~2SO~4(30℃)中于1.3V(vs. Hg/Hg~2SO~4, 下同)生长20min后的阳极膜在0.9V还原5min后再在1.4V将膜中硫酸铅氧化的过程。实验结果表明在0.9V还原二氧化铅而得到的硫酸铅能在1.4V于1min内氧化为二氧化铅。这是由于此种硫酸铅处于硫酸铅颗粒表层的缘故。至于颗粒内部由铅直接生成的硫酸铅的氧化为二氧化铅就要缓慢得多。合金中的锑能使二氧化铅晶核形成和生长速率显著降低。     

Electrodimerization: Part XII. Coupling mechanism of activated olefins at preparative scale concentrations

Previous studies have shown that the electrohydrodimerization mechanism of activated olefins is of the radical-radical coupling type in the millimolar range. The present work attempts to determine the mechanism up to the decimolar range on the particular example of p-methyl-benzylidene-malononitrile (MBM) in DMF. The kinetics of the system are studied using chronopotentiometry. The corrections of ohmic drop and double-layer charging and the conditions in which sphericity and migration of the reactants may be neglected are discussed first and experimentally tested on the fluorenone/fluorenone anion system. It is concluded from the kinetic analysis of the MBM reduction that the radical-radical nature of the coupling step does not change when passing from the millimolar to the decimolar level. The residual water is shown to play an important role in the overall reaction, the formation of an anion radical-water adduct being an essential step.     

Precipitation of lead as lead sulphate by destructive oxidation of EDTA

Gravimetric determination of lead (5–100 mg) by homogeneous precipitation of lead sulphate from a solution containing lead(II), EDTA and sulphate by destructive oxidation of EDTA with hydrogen peroxide or sodium bromate is described. Aluminium(III), iron(III), zinc(II), manganese(II), copper(II), nickel(II), tin(II) and antimony(III) do not interfere in the method. The method can successfully be applied to the analysis of type metal.     

The chemistry of pentavalent organobismuth reagents : Part XII. Synthesis of isoflavanones and 3-aryl-4-hydroxycoumarins

The arylation of chroman-4-one and 4-hydroxycoumarin derivatives by pentavalent arylbismuth reagents has been carried out. Chroman-4-one gives the 3-diphenyl derivative, whereas 3-formyl and 3-oxalyl derivatives are phenylated to isoflavanones in moderate to high yields. Arylation of 4-hydroxycoumarins by various Bi(V) reagents gives rise to functionally substituted 3-aryl-4-hydroxycoumarins in high yields.