Iron

Author: Robert Husted, Mollie Boorman

History

(Anglo-Saxon, iron; L. ferrum) Iron was used prehistorically:

• Genesis mentions that Tubal-Cain, seven generations from Adam, was "an instructor of every artificer in brass and iron."
• A remarkable iron pillar, dating to about A.D. 400, remains standing today in Delhi, India. This solid shaft of wrought iron is about 7 1/4 m high by 40 cm in diameter. Corrosion to the pillar has been minimal although it has been exposed to the weather since its creation.

Sources

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.

Isotopes

Common iron is a mixture of four isotopes. Ten other isotopes are known to exist.

Uses

Iron is a vital constituent of plant and animal life and works as an oxygen carrier 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.

Properties

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 usually has 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.