ABSTRACT
The attractive properties of lead and its alloys, as described in detail in Chapter 2 and the ease with which it can be processed as illustrated in Chapter 3, makes them invaluable in a wide range of modem applications. Contrary to the image in the general public that lead is a poisonous material that a society may be better off without, it is an invaluable material that one cannot do without in many areas of modem life. One cannot imagine a transportation industry today without lead acid batteries, a nuclear industry without lead shielding, electronic circuit boards without lead-based solders, or medical and industrial x-ray equipment without lead alloy collimators and shields. Like many other metals that are vital to high-technology industry, lead certainly poses environmental hazards, and this awareness has led to the minimization of the pathways of lead to humans and other biological species. This has led to the elimination of applications in which lead is dispersed in such a way that its recovery and recycling is difficult or human contact cannot be avoided. Such applications include use in paint, gasoline, water pipeline joints, and bearings. Whereas lead in gasoline is being eliminated, the gasoline tank itself is made of a teme-coated steel sheet, as illustrated in Chapter 3. Newer and modem applications of lead are continuously emerging and all these applications involve the use of lead in such a form that lead is almost completely recovered and recycled. In this chapter, we provide a brief discussion of a wide range of applications in which lead alloys are used. For more detailed treatments, readers are referred to sources listed in the References and the publications of various lead industry associations worldwide. Some of these applications such as its use as an acoustic barrier, handling of corrosive chemicals, nuclear radiation protection, and acoustic damping have been described to some extent in Chapter 2. By
in telegraphy [351]. Although there have been continued improvements in battery design, the basic electrochemistry of the lead-acid battery system has not changed since they were developed nearly 150 years ago [2,351354]. The lead-acid cell consists of a negative electrode of porous lead (lead sponge) and a positive electrode of lead dioxide, Pb02, both immersed in an aqueous solution of sulfuric acid:
Pb(s)/PbS04(s)!H2S04(aq)/PbS04(s)/PbQ (s)/Pb(s) (1)
In the concentration range used in the batteries, the sulfuric acid dissociates as H+ and HS04 -. The sum of the electrochemical reaction steps at the positive electrode is described as
Pb02(s) + 3H+(aq) + HSO;(aq) + 2e;::! PbS04(s) + 2H20(l) charge
The sum of the reaction steps at the negative electrode is given as
Pb(s) + HSO;(aq) ;::! H+(aq) + PbS04(s) + 2e charge
The overall electrochemical processes is represented by the equation
Pb(s) + Pb02(s) + 2H+(aq) + 2HSO;(aq) ~ 2PbS04(s) charge
The free-energy change of the reaction is - 372.6 kllmol and the standard equilibrium (Nemst) potential is 1.931 V [353,354]. More often, the reaction is written as follows:
which gives an equilibrium voltage of 1.941 V for a-Pb02 and 1.933 V for ~-Pb02' The dependence of this equilibrium on the activities of different reactant and product species is given by
