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(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
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,
etc. Iron is a cheap, abundant, useful, and important metal.
Sources: CRC Handbook of Chemistry
and Physics and the American Chemical Society.
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