Lead dioxide transformation

In electrolytes containing both sulphate and chloride ions, the sulphate ion favours the formation of lead sulphate which is rapidly transformed to lead dioxide. The continuing satisfactory operation of the anode depends upon the initial conditions of polarisation. The lead dioxide is of better quality and more adherent when formed below 108 Am in solutions containing higher sulphate concentrations or when the water is agitated" . 

To a certain extent, the formation of the tetrabasic variant is desired, because 4PbO PbS04 forms fairly large crystals when transformed into lead dioxide (PbO,). This results in a mechanically stable active material, but there are disadvantages, because it is more difficult to transform this material into lead dioxide, i.e., the formation process (see below) is more expensive (and takes longer) and the initial capacity is slightly reduced (cf., e.g., Ref. [19]. For "long-life batteries" (Bell systems cell), a special process has been developed to produce pure tetrabasic material [20]. 

When dry material or a slurry has been filled, "pickling" is required, which means that the plate is stored in sulfuric acid for a short time. The material is soaked by the acid and transformed, at least partly, into lead sulfate (PbS04), as in the pastemixing process (Section 4.4.2.1). When minium is used, during the "pickling" process lead dioxide is also formed according to Eq. (4). 

CH2)2L0) were prepared. - " Such compounds can be oxidized with lead dioxide to N-picryl-9-aminocarbazyls (133). These black species are dehydrogenating agents though stable in dry chloroform the transformation of violet-black color into orange in benzene solution suggests that they... 

Dimethylcarbodihydrazide (280) reacts with aldehydes to afford 1,5-dimethyltetrahydro-l,2,4,5-tetrazin-6-ones (281), which can be oxidized by silver oxide, potassium ferricyanide or lead dioxide to yield radicals (282) related to the verdazyls these can be transformed into tetrahydro-l,2,4,5-tetrazines (283) by hydrogenation over palladium (80AG766). 

Active mass — The portions of a -> battery or -> accumulator which are participating in electrode reactions, i.e., in the transformation of chemical into electrical -> energy or vice versa. In a -> lead-acid battery active masses are lead dioxide and lead, with the lead or lead alloy grid serving as -> current collector and mechanical holder and all other components are not active masses. For maximum -> energy density the fraction of active mass in the overall cell weight should be as large as possible. 

The oxidation of the pyrroleamine (77) gives 78 with lead tetraacetate,78, 79 while the ether (79) in benzene with lead dioxide is transformed into the dimeric product (80).17... 

Graebe and Kraft showed that the methyl group of a methylated phenol can be transformed into carboxyl by a process describable as an oxidative alkali fusion, the oxidant being lead dioxide. They applied the method successfully to the three cresols, the three toluic acids, 2,4-dimethylphenol, and o-cresotinic acid (1, available from Eastman). A preparative procedure for the conversion of (1) into 2-hydroxyiso-phthalic acid (2) is as follows. A mush of 240 g. of potassium hydroxide pellets and... 

Water is the active medium of PEFCs. From a chemical point of view, water is the main product of the fuel cell reaction. It is the only product in hydrogen fuel cells. Cells supplied with direct methanol or ethanol as the fuel produce water and carbon dioxide in stoichiometric amounts. The low operating temperature implies that water is present in liquid form. It mediates direct electrostatic as well as colloidal interactions in solutions or ink mixtures containing ionomeric, electronic, and electrocatalytic materials. These interactions control phase separation and structural relaxation phenomena that lead to the formation of PEMs and CLs. Variations in water content and distribution, thus, lead to transformations in stable structures of these media, which incur modifications in their physicochemical properties. It is evident that many of the issues of understanding the structure and function of fuel cell components under operation are intimately linked to water fluxes and distribution. 

Alloying constituents are released when the grid material is transformed into lead dioxide. If not absorbed by the active material, they are leached out of the positive plate and can reach the negative electrode by diffusion. 

Reaction 3.3 is an equilibrium between lead hydroxide and lead dioxide in the presence of water. Then this water can transform the Pb02 particle into an open system. This open Pb02 particle allows for the transfer of ions between the solution outside the particles and the hydrated zones of the particle. Actually, the hydrated zones occupy about 30% of the PAM. Besides the equilibrium between the hydrated and crystal zones, hydrated zones are also in equilibrium with ions in the solution. In this way, the hydrated linear polymer chains containing Pb, O, and OH can be formed, which plays a critical role in both electron and proton conductions. Both high electron and proton conductivities of these polymer-like chains are necessary conditions for the reaction of discharge of Pb02 to proceed. 

Requirements for Lead Dioxide Variant Formation and Transformation... 

The changes in structure and kinetics during charge of the porous Pb02 electrode were studied by Ekdunge and Simonsson in 1985 [57]. It is conunonly believed that the transformations between lead sulfate and lead dioxide occur via a dissolution precipitation mechanism involving dissolved Pb + ions. According to this mechanism, the oxidation reaction can be formally written as... 

To a certain extent, the formation of the tetrabasic variant is desired, because 4Pb0 PbS04 forms fairly large crystals when transformed into lead dioxide (Pb02). 

The transformation of 303 into narwedine (304) proved troublesome. Various oxidizing reagents were evaluated but all attempts resulted in the polymerization of the starting material and only minute amounts of narwedine (304) could be detected in the reaction mixtures. Manganese dioxide, lead dioxide, and silver oxide did not allow the isolation of appreciable amounts of coupUng product. When a solution of Kj[Fe(CN) ] was employed in the oxidative cycUzation, 1.4% of narwedine was obtained. 

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