Positive lead dioxide

The lead current collector in the positive lead—dioxide plate corrodes and the compounds which form are a function of the acid concentration and positive electrode voltage. Other reactions which take place at the positive electrode are shown. 

The recovered lead paste is a mixture of the positive (lead dioxide) and negative (lead sulfate) active materials, small metallic fractions from the grid and other materials that have been added to the battery paste such as carbon black, expanders, and reinforcing fibres. A typical range of components in recovered battery paste is given in Table 15.1. 

Hence sulphuric acid is used up and insoluble lead(II) sulphate deposited on both plates. This process maintains a potential difference between the two plates of about 2 V. If now a larger potential difference than this is applied externally to the cell (making the positive plate the anode) then the above overall reaction is reversed, so that lead dioxide is deposited on the anode, lead is deposited on the cathode, and sulphuric acid is re-formed. Hence in the electrolyte, we have ... 

Silver reduces the oxygen evolution potential at the anode, which reduces the rate of corrosion and decreases lead contamination of the cathode. Lead—antimony—silver alloy anodes are used for the production of thin copper foil for use in electronics. Lead—silver (2 wt %), lead—silver (1 wt %)—tin (1 wt %), and lead—antimony (6 wt %)—silver (1—2 wt %) alloys ate used as anodes in cathodic protection of steel pipes and stmctures in fresh, brackish, or seawater. The lead dioxide layer is not only conductive, but also resists decomposition in chloride environments. Silver-free alloys rapidly become passivated and scale badly in seawater. Silver is also added to the positive grids of lead—acid batteries in small amounts (0.005—0.05 wt %) to reduce the rate of corrosion. 

The excellent corrosion-resistant lead dioxide, Pb02, film formed on anodes and lead—acid battery positive grids in sulfuric acid has enabled lead insoluble anodes and lead—acid batteries to maintain the dominant positions in their respective fields. 

Lead dioxide is electrically conductive and is formed ia place as the active material of the positive plates of lead-acid storage batteries. Because it is a vigorous oxidizing agent when heated, it is used ia the manufacture of dyes, chemicals, matches (qv), pyrotechnics (qv), and Hquid polysulfide polymers (42) (see Polypous containing sulfur). 

At the cathode, or positive electrode, lead dioxide [1309-60-0] Pb02, reacts with sulfuric acid to form lead sulfate [7446-14-2] PbSO, and water in the discharging reaction... 

The mercurous sulfate [7783-36-OJ, Hg2S04, mercury reference electrode, (Pt)H2 H2S04(y ) Hg2S04(Hg), is used to accurately measure the half-ceU potentials of the lead—acid battery. The standard potential of the mercury reference electrode is 0.6125 V (14). The potentials of the lead dioxide, lead sulfate, and mercurous sulfate, mercury electrodes versus a hydrogen electrode have been measured (24,25). These data may be used to calculate accurate half-ceU potentials for the lead dioxide, lead sulfate positive electrode from temperatures of 0 to 55°C and acid concentrations of from 0.1 to Sm. 

The reaction of 1,2,4-triazine 4-oxides 8 bearing substituents at the 3, 5, and 6 positions with peroxyacetic acid proceeds as an N-oxidation process exclusively at the 1 position, resulting in 1,2,4-triazine 1,4-dioxides 14. Oxidation of 1,2,4-triazine 4-oxides 8 unsubstituted at the 5 position leads to 5-hydroxy-1,2,4-triazine 4-oxides 15 (76LA153). 

Lead dioxide (PbO,) forms the charged state of the active material in the positive electrode. 

Lead oxide (PbO) (also called litharge) is formed when the lead surface is exposed to oxygen. Furthermore, it is important as a primary product in the manufacturing process of the active material for the positive and negative electrodes. It is not stable in acidic solution but it is formed as an intermediate layer between lead and lead dioxide at the surface of the corroding grid in the positive electrode. It is also observed underneath lead sulfate layers at the surface of the positive active material. 

Figure 9. Conversion of grid material into lead dioxide (Pb02) by corrosion spine of a positive tubular plate. New plate 3mm diameter means 7.1 mm2 cross-section (nr2 with r = 1.5mm). Aged plate reduction of r by 0.03 x 15 = 0.45mm means nr2 = 3.5 mm2.

In Sec. 4.3.3 it has been shown that corrosion is one or the reactions that cause selfdischarge of the positive electrode. In connection with Fig. 8 it has been mentioned that an anodic current, the corrosion current, must flow continuously to stabilize the lead dioxide layer at the grid surface. Then the PbOA layer remains thin because PbOr is always converted into Pb02 by... 

Perchlorates are also produced electrochemicaUy. The oxidation of chlorate to perchlorate ions occurs at a higher positive potential (above 2.0 V vs. SHE) than chloride ion oxidation. The current yield of perchlorate is lower when chloride ions are present in the solution hence, in perchlorate production concentrated pure chlorate solutions free of chlorides are used. Materials stable in this potential range are used as the anodes primarily, these include smooth platinum, platinum on titanium, and lead dioxide. 

At the positive terminal, lead dioxide reacts with the electrons from the lead plate and the hydrogen and sulfate ions to form lead sulfate and water ... 

Pb02 Lead dioxide is an electrode material of relatively high electronic conductivity and high stability in acidic media, useful at high positive potentials. 

The lead-acid cell can be represented schematically as having a negative electrode of porous lead (lead sponge) and a positive electrode of lead dioxide, Pb02, both immersed in an aqueous solution of sulphuric acid ... 

An important feature of the positive electrode discharge concerns the nature of the PbS04 deposit since the formation of dense, coherent layers can lead to rapid electrode passivation. Lead dioxide exists in two crystalline forms, rhombic (a-) and tetragonal (/3-), both of which are present in freshly formed electrode structures. Since PbS04 and a-Pb02 are iso morphic, crystals of lead dioxide of this modification tend to become rapidly covered and isolated by lead sulphate, and their utilization is less... 

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