Iron
Iron is the fourth most common metal element in the earth's crust and forms the basis for much modern industry. Iron is also a common element among the bodies of the solar system, including the Sun, planets and meteors. The atomic weight of iron is 55.847, and its atomic number is 26. Its atomic symbol is Fe, from the Latin word ferrum. It has a melting point of 2800.4°F (1538°C) and a boiling point of 5181.8°F (2861°C).
Iron occurs naturally in combination with oxygen in the ores hematite, limonite and magnetite. These have about a fifty percent iron content. Since high-grade ores such as these have slowly been depleted, the use of lower-grade ores like taconite, (with twenty to forty percent iron content) has increased. In addition, recycled iron and steel has become essential in steel production.
As a metal, iron has been in use since before recorded history. Early man learned of iron either by fire or while fashioning stone implements. Forges were created to reduce the metal from ore and to eliminate the carbon and other impurities before working it into the desired shapes. One source of iron for many early cultures was meteorites, many of which are composed of an iron- nickel substance resembling stainless steel. Over time, more sophisticated iron production methods were invented. Iron production began in earnest with Abraham Darby's (1678-1717) coke-burning furnaces that yielded iron in commercial quantities and made it affordable for industry. Because of this innovation, Darby is considered the father of the Industrial Revolution.
Pig iron is extracted from iron ore in blast furnaces. It contains about five percent impurities, mostly carbon. Most pig iron is sent into steelmaking. It was formerly used to make cast iron, but now cast iron accounts for only about eight percent of pig iron used.
Cast iron is noted for its strength and its ability to be easily formed, or cast, into shapes. Cast iron was one of the most popular building materials during the 1800s. It is used today for engine blocks, sewer lids and fire hydrants.
Wrought iron contains slag, the dross from the reduction process. It is stronger than cast iron, but must be worked to be formed. In the past, it has been used for fences, railings and farm implements, but it is rarely used today.
When iron is alloyed with varying amounts of carbon and other metals a wide range of grades and types of steels are the result. The conversion process invented by Henry Bessemer (1813-1898) in 1856 made steel affordable and marked the end of the Iron Age.
Iron is associated with oxygen in the blood of vertebrates, including human beings. Iron oxide forms the substance which gives red blood cells their color and which carries oxygen to the tissues of the body. (In invertebrate species, iron is only one of many possible minerals to serve this function. Many arthropods, for instance, have green blood which contains copper.) Iron is also an essential agent in the transporting of oxygen in respiratory enzymes. Primary sources of dietary iron are meats, especially liver, nuts and legumes. Discovery of the role of iron in metabolism was first made by American pathologist George Whipple in 1925 during his research on the human liver.
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