Iron

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.

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.

Common oxidation states of iron include:

• the Iron (II) state, Fe⁺², previously ferrous
• the Iron (III) state, Fe⁺³, previously ferric
• the Iron (IV) state, Fe⁺⁴, previously ferryl, stabilized in some enzymes
• Iron (VI) is also known, if rare. In the form of potassium-ferrate (K₂FeO₄) it is a selective oxidizer for primary alcohols. The solid is only stable under vacuum and dark purple in both (caustic) solution and as a solid.
• iron carbide Fe₃C is known as cementite.

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.

Uses

Iron is the most used of all the metals, comprising 95 percent of all the metal tonnage produced worldwide. Its combination of low cost and high strength make it indispensable, especially in applications like automobiles, the hulls of large ships, and structural components for buildings. Steel is the best known alloy of iron. 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.

Iron is a vital constituent of plant and animal life and works as an oxygen carrier in hemoglobin. Animals incorporate iron into the heme complex, an essential component of proteins involved in redox reactions, including respiration. Inorganic iron is also found in the iron-sulfur clusters of many enzymes, such as nitrogenase and hydogenase. A class of non-heme-iron enzymes is responsible for a wide range of functions within several life forms, such as methane monooxygenase, ribonucleotide reductase, hemerythrins and purple acid phosphatase.

Iron distribution is heavily regulated in mammals. For example, when the body is fighting a bacterial infection, the body "hides" iron so it cannot be used by the bacteria.

Isotopes

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

Hazards

Excessive dietary iron is toxic, because excess ferrous iron reacts with peroxides in the body, producing free readicals. When iron is in normal quantity, the body's own antioxidant mechanisms can control this process. In excess, uncontrollable quantities of free radicals are produced.

The lethal dose of iron in a 2 year old is about 3 grams of iron. One gram can induce severe poisoning. There are reported cases of children being poisoned by consuming between 10-50 tablets of ferrous sulfate over a few hour period. Overconsumption of iron is the single highest cause of death in children by unintentional ingestion of pharmaceuticals.

If iron intake is uncontrollably high, a disease results, called hemochromatosis. The iron excess accumulates in the liver, with siderosis and organ damage as a result. For this reason, people shouldn't take iron supplements unless they suffer from iron deficiency and have consulted a doctor. Blood donors are at special risk of low iron levels and are often recommended to supplement their iron intake.