Oxygen lead oxides

Lead is obtained from its ores by a method used with many metals. First, the ore is roasted (heated in air). Roasting, also called smelting, converts the ore to a compound of lead and oxygen, lead oxide (PbOi). Lead oxide is then heated with charcoal (pure carbon). The carbon takes oxygen away from the lead oxide. It leaves pure lead behind ... 

In the fumace/ketde batch process, a charge of drossed blast furnace buUion is treated in a reverberatory furnace or a kettie (see Fig. 12). Oxygen is supphed in the form of compressed air or as lead oxide blown into the bath through submerged pipes. The formation of lead oxide serves by mass action to assure the removal of the impurities to the desired low concentrations. The softening reactions are... 

Fig. 1. Schematic representation of a battery system also known as an electrochemical transducer where the anode, also known as electron state 1, may be comprised of lithium, magnesium, zinc, cadmium, lead, or hydrogen, and the cathode, or electron state 11, depending on the composition of the anode, may be lead dioxide, manganese dioxide, nickel oxide, iron disulfide, oxygen, silver oxide, or iodine.

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. 

The most important reactions of trichloroethylene are atmospheric oxidation and degradation by aluminum chloride. Atmospheric oxidation is cataly2ed by free radicals and accelerated with heat and with light, especially ultraviolet. The addition of oxygen leads to intermediates (1) and (2). 

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. 

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. 

Malinin et al. [634,647] have studied rates of decompositions of lead oxides. The reaction of Pb304 at 840 K yields some 15% atomic oxygen, obeys the Avrami—Erofe ev equation [eqn. (6), n = 2] and values of E are 320 and 190 kJ mole-1 at atmospheric pressure and in vacuum, respectively. 

The reaction between hydrogen and oxygen leads to the formation of water. This reaction has extended explosive regimes with respect to the p,T,c-parameters. A mechanistic analysis of the elementary reactions is available and the explosion mechanisms are imderstood in detail. Accordingly, this reaction serves well as a model for other dangerous processes in the explosive regime such as many oxidations with pure oxygen. 

The losses of lead as litharge (PbO) can be minimized if the impurity elements could be oxidized at an oxygen potential lower than that which causes the oxidation of lead. This can be achieved if the activities of the oxides of the impurity elements in the slag are decreased, for example, by the addition of an oxide which reacts very much more strongly with the oxides of the impurities than it does with lead oxide. Sodium hydroxide is a useful reagent for this purpose and sodium nitrate can be used as the source of oxygen. The reaction involved in this process, known as the Harris process, can be formally written as... 

Curing is the process of exposing plates pasted positive and negative to a regime of (a) controlled time (minimum 32h), (b) temperature (30-35°C), and (c) relative humidity (>90%). This process converts the free lead into lead oxide, using oxygen from the surrounding air. The plates are allowed to cure for a minimum of 32 h. Care is also taken to ensure that the maximum temperature of the plate does not exceed 60°C. The cured plates are then parted. 

In contrast, the present model is based on an experimental result, showing that the decomposition of RNO, in the presence of oxygen leads to oxygenates C,HvO, necessary for function 3 to turn over, with the release of NO and not N2 [5,28], (Let us note that the generalization of the present model to the oxidation of carbon particulates by N02 leads to the same result carbon partial oxidation and release of NO [31]). 

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) ... 

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... 

Melroy and co-workers88 recently reported on the EXAFS spectrum of Pb underpotentially deposited on silver (111). In this case, no Pb/Ag scattering was observed and this was ascribed to the large Debye-Waller factor for the lead as well as to the presence of an incommensurate layer. However, data analysis as well as comparison of the edge region of spectra for the underpotentially deposited lead, lead foil, lead acetate, and lead oxide indicated the presence of oxygen from either water or acetate (from electrolyte) as a backscatterer. 

Photolysis of PVC in the presence of oxygen causes oxidation of the polymer. However, under most (perhaps all) conditions, in both the presence and absence of oxygen, the photodegradation is complicated by scissions of carbon-chlorine bonds. Such scissions may lead to the formation of conjugated polyene sequences via sequential dehydrochlorination (Equation 1). The polyenes... 

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