(Anglo-Saxon, iron; L. ferrum) Iron was used prehistorically:
Iron is a relatively abundant element in the universe. It is found in the sun and many types of stars in considerable quantity. Its nuclei are very stable. Iron is a principal component of a meteorite class known as siderites and is a minor constituent of the other two meteorite classes. The core of the earth -- 2150 miles in radius -- is thought to be largely composed of iron with about 10 percent occluded hydrogen. The metal is the fourth most abundant element, by weight that makes up the crust of the earth.
The most common ore is hematite, which is frequently seen as black sands along beaches and banks of streams.
Common irons is a mixture of four isotopes. Ten other isotopes are known to exist.
Iron is a vital constituent of plant and animal life and appears in hemoglobin.
Taconite is becoming increasingly important as a commercial ore. The pure metal is not often encountered in commerce, but is usually alloyed with carbon or other metals.
The pure metal is very reactive chemically and rapidly corrodes, especially in moist air or at elevated temperatures. It has four allotropic forms or ferrites, known as alpha, beta, gamma, and omega, with transition points at 700, 928, and 1530C. The alpha form is magnetic, but when transformed into the beta form, the magnetism disappears although the lattice remains unchanged. The relations of these forms are peculiar. Pig iron is an alloy containing about 3 percent carbon with varying amounts of Sulfur, Silicon, Manganese, and Phosphorus.
Iron is hard, brittle, fairly fusible, and is used to produce other alloys, including steel. Wrought iron contains only a few tenths of a percent of carbon, is tough, malleable, less fusible, and has usually a "fibrous" structure.
Carbon steel is an alloy of iron with small amounts of Mn, S, P, and Si. Alloy steels are carbon steels with other additives such as nickel, chromium, vanadium, etc. Iron is a cheap, abundant, useful, and important metal.
Sources: CRC Handbook of Chemistry and Physics and the American Chemical Society.
Last Updated: 12/19/97, CST Information Services Team