Lead oxides/dioxides

These equations are based on the thermodynamically stable species. Further research is needed to clarify the actual intermediate formed during overcharge. In reahty, the oxygen cycle can not be fully balanced because of other side reactions, that include gtid corrosion, formation of residual lead oxides in the positive electrode, and oxidation of organic materials in the cell. As a result, some gases, primarily hydrogen and carbon dioxide (53), are vented. 

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. 

Minium (Pb,04) represents a more highly oxidized form of lead oxide that enhances the electrochemical oxidation of lead oxide to lead dioxide. 

Lead forms two types of chemical compounds lead (II), and lead (IV) compounds based on Pb24 and Pb4 ions, where those based on Pb2 ions are the more stable. The metal is oxidized even at room temperature to lead oxide (PbO) and also by water that contains oxygen and forms lead hydroxide (Pb(OH),). In the lead-acid battery, the (less stable) lead (IV) oxide (lead dioxide, Pb02), is of greatest importance. Beside these two, a number of oxides are observed in the battery that are mostly mixtures. A brief survey will now be given of those compounds that are of interest for lead-acid batteries. 

The hrst working lead cell, manufactured in 1859 by a French scientist, Gaston Plante, consisted of two lead plates separated by a strip of cloth, coiled, and inserted into a jar with sulfuric acid. A surface layer of lead dioxide was produced by electrochemical reactions in the first charge cycle. Later developments led to electrodes made by pasting a mass of lead oxides and sulfuric oxide into grids of lead-antimony alloy. 

Methyldichlorosilane (CH3SiHCl2) combusts spontaneously in the presence of potassium permanganate, lead oxide and dioxide, copper (II) oxide and silver oxide, even when they are in an atmosphere of inert gas. 

Kato, Y., D. Saku, N. Harada, and Y. Yoshizawa, 1997. Utilization of high temperature heat using a calcium oxide/lead oxide/carbon dioxide chemical heat pump, J. Chem. Eng. Japan, 30 (6), 1013-1019. 

Newer secondary recovery plants use lead paste desulfurization to reduce sulfur dioxide emissions and waste sludge generation during smelting. Battery paste containing lead sulfate and lead oxide is desulfurized with soda ash to produce market-grade sodium sulfate solution. The desulfurized paste is processed in a reverberatory furnace. The lead carbonate product may then be treated in a short rotary furnace. The battery grids and posts are processed separately in a rotary smelter. 

When galena, a lead ore (composed of lead sulfide) is roasted in a well-ventilated, open furnace, part of the lead is oxidized by air oxygen to lead oxide and the sulfur to sulfur dioxide, which is released into the atmosphere (see Textbox 33) ... 

PbS + 02 = PbO + S02T galena lead oxide sulfur dioxide... 

The lead oxide thus formed then reacts with galena still in the furnace to yield molten lead, while more sulfur dioxide is evolved ... 

Freshly cast lead has a bright, silvery appearance. On exposure to the atmosphere, however, lead in the surface layer combines with atmospheric oxygen and carbon dioxide to form a dark, stable gray coating of mixed lead oxide and basic lead carbonate. This layer usually protects the metal from further oxidation and corrosion (see Fig. 38). Protected by a weathered surface layer, solid lead is stable to further corrosion. Lead is also very ductile and soft, being the softest metal known in antiquity. It is mainly because of these properties that lead was widely used for building, to make pipes and roofs, and in naval construction, for example. Solid lead flows, albeit very... 

Iron(III) oxide and chromium(III) oxide react exothermally, and lead oxide explosively. Copper oxide and manganese dioxide react at 350°C incandescently. 

Interaction of chlorine with methane is explosive at ambient temperature over yellow mercury oxide [1], and mixtures containing above 20 vol% of chlorine are explosive [2], Mixtures of acetylene and chlorine may explode on initiation by sunlight, other UV source, or high temperatures, sometimes very violently [3], Mixtures with ethylene explode on initiation by sunlight, etc., or over mercury, mercury oxide or silver oxide at ambient temperature, or over lead oxide at 100°C [1,4], Interaction with ethane over activated carbon at 350°C has caused explosions, but added carbon dioxide reduces the risk [5], Accidental introduction of gasoline into a cylinder of liquid chlorine caused a slow exothermic reaction which accelerated to detonation. This effect was verified [6], Injection of liquid chlorine into a naphtha-sodium hydroxide mixture (to generate hypochlorite in situ) caused a violent explosion. Several other incidents involving violent reactions of saturated hydrocarbons with chlorine were noted [7],... 

Red phosphorus reacts vigorously on heating with copper oxide or manganese dioxide and on grinding with lead oxide, mercury oxide or silver oxide, ignition may occur. Red phosphorus ignites in contact with lead peroxide, potassium peroxide or sodium peroxide, while white phosphorus explodes, and also in contact with molten chromium trioxide at 200°C. 

Hock and Kropf [253] studied cumene oxidation catalyzed by Pb02. They proposed that Pb02 decomposed cumyl hydroperoxide (ROOH) into free radicals (R0 , R02 ). The free radicals started the chain oxidation of cumene in the liquid phase. Lead dioxide introduced into cumene was found to be reduced to lead oxide. The reduction product lead oxide was found to possess catalytic activity. The following tentative mechanism was proposed. 

Bronsted theory See Bronsted-Lowry theory. bron-steth, the-3-re brown lead oxide See lead dioxide. braun led ak.sTd ... 

Lead is commonly obtained by roasting galena (PbS) with carbon in an oxygen-rich environment to convert sulfide ores to oxides and by then reducing the oxide to metallic lead. Sulfur dioxide gas is produced as a waste product. Large amounts of lead are also recovered by recycling lead products, such as automobile lead-acid electric storage batteries. About one-third of all lead used in the United States has been recycled. 

He continued his experiments and discovered even more new gases sulfur dioxide, silicon fluoride, ammonia gas, and nitrogen. However, his most important discovery was oxygen. In June 1774 Priestley got a burning lens with a diameter of 12 inches and immediately began to experiment with it. In one experiment he turned the lens on mercury calx (mercuric oxide) and obtained an air in which candles burned more brightly than they did in ordinary air. At first he did not know what to make of this result, so he continued experimenting. He soon found that he could get the same gas from certain other materials, such as lead oxide. 

The most important ingredient of a white paint used to be lead oxide. This was objectionable, as it could be swallowed by infants and lead to brain damage. Other white powders with strong covering properties were needed, and the current material of choice is titanium dioxide. Many painters still prefer lead oxide-based paint, as it has a more desirable warmer shade of white and it dries much faster than titanium oxide-based paint. When a mistaken stroke is made by a painter, lead paint that dries quickly can be covered up by another stroke, but titanium paint needs 3 days to dry before it can be covered up by another stroke. A solution is available in quick-drying additives to the titanium paint. 

When heated at 315°C, lead carbonate decomposes to lead oxide and carbon dioxide ... 

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