ABSTRACT
Metals are by far the most reactive of these three groups. That is why metals are found in nature in the form of compounds. Metals are extracted from their ores where nature put them. The metal compounds in the ores, oxides, sulfides, nitrides, and the like are very stable compounds. When the metal is removed from these other elements, they want to go back to where they came from. We take metals from their ores and refine them so that they are formable and easily fabricated into many desirable shapes. Metals are very useful materials, as evidenced in Figure 1.1. But we pay a price for this convenience. On their way back to their natural habitat, they may react with many elements that exist in whatever environments to which they may become exposed, including those that are not normally found in ambient atmospheres. These metal attackers include the acids; caustic bases; the gaseous hydrogen, oxygen, and nitrogen atmospheres; and many of the halides, chlorine, and fluorine in particular. The metals industry spends billions of dollars extracting metals from their compounds as found in nature, and then billions more to protect them from reactions that occur in their new environments. Estimates of losses in U.S. industries due to corrosion of steels fall in the range $70 billion
to $80 billion per year. But some metals are not very reactive. These are the expensive precious metals. Gold does not have to be extracted from oxides and sulfides because it does not form such compounds. It is usually found (but not easily located) in nature as a pure elemental metal.
