Iron
Iron is the fourth-most common element in Earth's crust, and the second-most common metal after aluminum. Its abundance is estimated to be about 5%. Sampling studies indicate that portions of Earth's core consist largely of iron, and the element is found commonly in the Sun, asteroids, and stars.
The chemical symbol for iron, Fe, comes from the Latin name for the element, ferrum. The most common ores of iron are hematite and limonite (both primarily ferric oxide; Fe2O3) and siderite iron carbonate (FeCO3). An increasingly important source of iron for commercial uses is taconite, a mixture of hematite and silica. Taconite contains about 25% iron. The largest iron resources in the world are found in China, Russia, Brazil, Canada, Australia, and India.
The traditional method for extracting pure iron from its ore is to heat the ore in a blast furnace with limestone and coke. The coke reacts with iron oxide to produce pure iron, while the limestone combines with impurities in the ore to form a slag that can then be removed from the furnace: 3C + 2Fe2O3 + heat → 3CO2 + 4Fe.
Iron produced by this method is about 90% pure and is known as pig iron. Pig iron is generally too brittle to be used for most products and is further treated to convert it to wrought iron, cast iron, or steel. Wrought iron is an alloy of iron and any one of many different elements, while cast iron is an alloy of iron, carbon, and silicon. Steel is a generic term that applies to a very wide variety of alloys.
Iron is one of a handful of elements that have been known and used since the earliest periods of human history. In the period beginning about 1200 B.C. iron was so widely used for tools, ornaments, weapons, and other objects that historians and archaeologists have now named the period the Iron Age.
Iron is a silvery white or grayish metal that is ductile and malleable. It is one of only three naturally occurring magnetic elements, the other two being its neighbors in the periodic table: cobalt and nickel. Iron has a very high tensile strength and is very workable, capable of being bent, rolled, hammered, cut, shaped, formed, and otherwise worked into some desirable shape or thickness. Iron's melting point is 2,797°F (1,536°C) and its boiling point is about 5,400°F (3,000°C). Its density is 7.87 grams per cubic centimeter.
Iron is an active metal that combines readily with oxygen in moist air to form iron oxide (Fe2O3), commonly known as rust. Iron also reacts with very hot water and steam to produce hydrogen gas and with most acids and a number of other elements.
The number of commercial products made of iron and steel is very large indeed. The uses of these two materials can generally be classified into about eight large groups, including (1) automotive; (2) construction; (3) containers, packaging, and shipping; (4) machinery and industrial equipment; (5) rail transportation; (6) oil and gas industries; (7) electrical equipment; and (8) appliances and utensils.
A relatively small amount of iron is used to make compounds that have a large variety of applications, including dyeing of cloth, blueprinting, insecticides, water purification and sewage treatment, photography, additive for animal feed, fertilizer, manufacture of glass and ceramics, and wood preservative.
Iron is of critical important to plants, humans, and other animals. It occurs in hemoglobin, the molecule that carries oxygen in the blood. The U.S. Recommended Daily Allowance (USRDA) for iron is 18 mg (with some differences depending on age and sex) and it can be obtained from meats, eggs, raisins, and many other foods. Iron deficiency disorders, known as anemias, are not uncommon and can result in fatigue, reduced resistance to disease, an increase in respiratory and circulatory problems, and even death.
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