Active mass, lead dioxide

The standard potential for the anodic reaction is 1.19 V, close to that of 1.228 V for water oxidation. In order to minimize the oxygen production from water oxidation, the cell is operated at a high potential that requires either platinum-coated or lead dioxide anodes. Various mechanisms have been proposed for the formation of perchlorates at the anode, including the discharge of chlorate ion to chlorate radical (87—89), the formation of active oxygen and subsequent formation of perchlorate (90), and the mass-transfer-controUed reaction of chlorate with adsorbed oxygen at the anode (91—93). Sodium dichromate is added to the electrolyte ia platinum anode cells to inhibit the reduction of perchlorates at the cathode. Sodium fluoride is used in the lead dioxide anode cells to improve current efficiency. 

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. 

Oxalic acid is readily oxidized in watery solution it is converted into COa and HaO, slowly by simple exposure to air, more rapidly in the presence of platinum-black or of the salts of platinum and gold under the infiuence of sunlight or when heated with HNOa, manganese dioxid, chromic acid, Br, Cl, or hypo-chlorous acid. Its oxidation, when it is triturated dry with lead dioxid, is sufficiently active to heat the mass to redness. HaSO<, HbPOi, and other dehydrating agents decompose it into HaO, CO, and COa. 

Gel—Crystal Structure of the Lead Dioxide Active Mass... 

This lead compound forms prismatic crystals with a length of 1—4 pm and 0.2—08 pm in cross section. Its density is 6.5 g cm. It is poorly soluble in water, 0.0262 g L. 3BS is obtained when leady oxide is mixed with sulfuric acid solution (up to 8 wt % H2S04/Pb0) and constitutes the basic component of the battery paste when the latter is prepared at temperatures below 70 °C. Tribasic lead sulfate exerts an influence on the structure of the lead dioxide active mass and thus on some of the performance characteristics of the battery. 

The two lead dioxide modifications can also be prepared by formation of battery plates in appropriate electrolytes. For example, battery plates have been formed in alkaline Na2Pb02 solutions [82], or in 3.5 M H2SO4 solution [57]. In the latter case, the active mass which... 

The TEM pictures in Fig. 2.33 evidence that the lead dioxide active mass comprises particles with crystal (a- or p-Pb02) or amorphous zones and hydrated (gel) zones. Figure 2.33c features Pb02 particles with predominantly crystal structure. Only single surface zones are hydrated. 

This highly heterogeneous structure of the Pb02 particles obtained during the electrochemical formation of the lead dioxide active mass evidences that the processes of Pb02 formation proceed through hydration and dehydration stages ... 

The above-described structure of the lead dioxide particles is likely to exert an influence on the electrochemical and chemical processes that proceed in the positive active mass on charge and discharge, as well as on the behaviour of the positive plates in sulfuric acid solution. 

Influence of Sb, As and Bi on the Reversibility of the Lead Dioxide Active Mass Structure... 

The type of basic lead sulfate in the paste affects the structure of the active materials formed, especially of the lead dioxide active mass. And the active mass structure in turn determines the charge/discharge cycling performance of the battery. Thus, control of the a-PbO p-PbO ratio... 

The lead dioxide active mass has a fairly complex structure, sensitive to foreign substances, which may degrade or get passivated under the action of even small amounts of additives to the positive paste, respectively to PAM. That is why the number of additives to the positive paste is limited and their effect is not always unambiguous. 

Model for the structure of lead dioxide active mass... 

As evident from Fig. 2.21 in Chapter 2 of this book, oxides with stoichiometric coefficients <1.4 have high ohmic resistance. Thus, a high-resistance interface layer forms between the active mass and the grid, which reduces the energy and power output of the battery during discharge. However, this layer does not affect the total amount of lead dioxide contained in the formed positive active mass. Hence, the discharge time of passivated and unpassivated plates... 

Deterioration of the Performance of Lead Dioxide Active Mass.107... 

FIGURE 3.3 Structure of the lead dioxide active mass. (FromD. Pavlov, andE. Bashtavelova, J. Electrochem. Soc., 131,1468, 1984 D. Pavlov, and E. Bashtavelova, J. Electrochem. Soc., 133, 241, 1986 D. Pavlov et al., Structure of the Lead-Acid Battery Active Masses, in Proc. Int. Symp. Advances in Lead-Acid Batteries, Vol. 84-14, p. 16, Electrochemical Society, Pennington, NJ, 1984.)... 

DETERIORATION OF THE PERFORMANCE OF LEAD DIOXIDE ACTIVE MASS... 

Certain chemicals such as silicon dioxide have a cytotoxic effect on the alveolar macrophage, which results in the accumulation of particles in a given area. As the macrophages lose their activity, these particles become less subject to removal, leading to the development of masses containing dead cells and particles. 

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