Lead

Metallic lead is sometimes used in a pure or nearly pure form, usually because of its high density and ability to be bent and shaped. The metal is an efficient absorber of radiation and, for that reason, is commonly used as a shield for x rays, nuclear radiation, and other forms of radiation.

Far more commonly, however, lead is alloyed with one or more other elements to produce a product with special properties of interest for some specific application. More than half of all the lead used in the United States, for example, goes to the production of lead storage batteries. The positive plates, made of lead(IV) oxide, and the negative plates, made of spongy lead, are both made from an alloy containing 91% lead and 9% antimony. Over 80% of this lead is now recovered and recycled as a source of lead metal.

At one time, very large amounts of lead were used in the production of tetraethyl lead, a compound that reduces the amount of knocking in an internal combustion engine. The problem with tetraethyl lead, however, is that it tends to break down within an engine, releasing free lead to the environment. Because of the health hazards that lead poses for humans and other animals, tetraethyl lead has been banned for use as a gasoline additive.

Because of its chemical inertness, lead has also been popular as a covering for underground cables, such as buried cables that carry telephone messages, and for pipes through which liquids are transported. For many years, lead was the material of choice in the construction of water pipes since it was inert to most chemicals occurring in nature and easily shaped. With the recognition of lead's threat to humans, however, many of these applications have been discontinued.

Alloys of lead are also popular for the manufacture of solders. Ordinary plumber's solder, for example, contains about two parts of lead to one part of tin. This alloy has a melting point of about 527°F (275°C).

Lead compounds were once widely used also for paints. They were in great demand because they covered surfaces well and were available in a number of vivid colors. Among these were lead chromate (yellow), lead molybdate (reddish-orange), lead(II) oxide (canary yellow), red lead oxide (Pb₃O₄; red), and white lead, a complex lead carbonate/lead hydroxide mixture. As with other lead compounds, however, the potential health hazards of the element have greatly reduced the availability of lead-based paints.