Basic sulfates, lead oxides

Leaded Zinc Oxide. Oxides containing more than 5 wt % basic lead sulfate are classified as leaded and are made ia the American process from high lead materials, usually lead sulfide mineral, or by blending ziac oxide and basic lead sulfate. There is only one manufacturer ia the United States and the product contains 20—28 wt % basic lead sulfate. Leaded oxides are used only ia mbber ia the United States. 

Lander [1] has established that the paste is composed of basic lead sulfates, non-reacted lead oxides, hydrated lead oxides, free lead particles and basic lead carbonates. Some key thermodynamic data for basic lead sulfates, lead oxides and lead hydrates (hydroxides) are presented in Appendix 1 [2]. 

Basic sulfates are intermediate compounds that contain lead oxide and lead sulfate and to some extent also water (Table 1). They are stable only in alkaline environment. 

Table 1. Basic sulfates that are formed as intermediate compounds when lead oxide is mixed with sulfuric acid.

Unfortunately, the lead (II) compounds are not very conductive. Lead sulfate is an insulator and the lead oxides and basic lead sulfates are semiconductors. Before they are given the first charge, ealled formation , battery plates are composed of mixtures of these materials. Plate formation eannot proceed until a conductive pathway is formed. Pavlov and co-workers [10] have shown that in acid solutions, the materials next to the current-collector are first eonverted to conductive lead and lead dioxide. Formation then proeeeds inward towards the centre of the pellet (see Chapter 3). Lead sulfate is the last material to be eonverted in the formation process. The rate of formation is thus limited by the non-conductive nature of lead oxide, especially in the positive plate. 

The most widely used opaque white pigment was basic carbonate white lead, manufactured by a process little different from that known by the early Greeks in 400 B.C. Other commonly used pigments were zinc oxide, dating back to 1770 zinc sulfide, first produced in 1783 lithopone, developed in 1847 and basic sulfate white lead, which first appeared in 1855. 

Except for the electrochemical reaction (2.6), all other reactions depend on the pH of the solution. A number of electrochemical reactions proceed in this system, which form different electrode systems, depending on lead ion valency, solution composition and pH, and electrode potential. These reactions cover a potential range of 2.0 V. Table 2.4 summarises the electrochemical reactions involving Pb, lead oxides, PbS04 and basic lead sulfates, and the equilibrium potentials of the respective electrode systems. The reactions and the equilibrium potentials for the hydrogen and oxygen electrodes are also given in the table. Several chemical reactions in which basic lead sulfates take part are also included in Table 2.4. 

The actual pH of the solution in the pores on switching the current off is much higher, and hence the (pit curves are arrested at more negative potentials than those presented in Fig. 2.11 due to sulfation of the lead oxides and basic lead sulfates [17,23]. The potentials of these compounds are a function of pH and shift to more negative values with decrease of the solution pH (Table 2.4). 

The active mass obtained from pastes containing no H2SO4 (0%) has very low capacity, irrespective of the temperature of paste preparation. That is why battery manufacturers use basic lead sulfate pastes, and not lead oxide ones, for the production of positive plates. 

One of its major advantages is that it allows the reaction between lead oxide and H2SO4 to proceed in a semi-suspension state (i.e. at densities between 3.20 and 3.50 g cm ). This method has been developed in our laboratory [34,35]. On completion of the crystallization process of basic lead sulfate, the semi-suspension can be concentrated through removal of the excess water (by evaporation under vacuum) until a paste of a desired density is obtained. 

Since H2SO4 reacts with the lead oxides and basic sulfates in the paste, its concentration decreases. The lower acceptable limit of H2SO4 concentration is 1.025 rel. dens., so when selecting the number of plates to be loaded in the formation tank, the above parameter should be taken into account. Usually, 2.5—3 L of electrolyte with 1.06 rel. dens, are used per 1 kg of dry paste. 

Lead sulfate, blue basic Synonyms Blue lead Sublimed blue lead Definition Mixture of lead sulfate (45% min.), lead oxide (30% min.), lead sulfide (12% max.), lead sulfite (5% max.), zinc oxide (5%), carbon, etc. Properties Bluish gray insol. in water or alcohol dens. 6.2 noncombustible Toxicology Toxic material TLV (as Pb) 0.15 mg/m of air... 

Lead oxide, yellow Lead phthalate, basic Lead stearate Linoleyl alcohol Locust bean (Ceratonia siliqua) gum Lysolecithin Maleic anhydride Manganese oxide (ous) Manganese sulfate (ous) Methacrylic acid... 

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