We continue to review some of the most important materials in heat treatment and metallurgy. What could be more important to metallurgy than iron?

Iron (Chemical symbol: Fe)

Iron is an Anglo-Saxon word. The chemical symbol for iron (Fe) comes from the Latin word ferrum. Archaeological evidence suggests that people have known about and have been using iron for at least 5,000 years. Ancient Egyptian iron objects have been dated to around 3500 B.C. These objects also contain approximately 8% nickel, indicating the iron may have originally been found in a meteorite, as smelting technology had not yet been developed. The Iron Age began around 1500 B.C. when the Hittites of Asia Minor began to smelt iron ore and make iron tools.  

Iron is a lustrous metallic element with a grayish tinge. It is ductile and a solid at room temperature. Iron is found in the stars and is the fifth-most-plentiful element (oxygen, silicon, aluminum, iron) in the Earth's crust, comprising approximately 5.6% (5.63 x 104 milligrams per kilogram). Its abundance in rocky planets like Earth is due to its original production by fusion in high-mass stars. Iron is the most inexpensive and commonly used metal.

Iron and its alloys account for 95% of worldwide metal production, and it is used in virtually all machines, buildings, roads, bridges, vehicles, weapons, household items and tools. The majority of iron is used in steel. There are many different types of steels. Each is made with iron alloyed with different elements, such as carbon, silicon and nickel. Steel has greatly enhanced properties, including strength, formability and weldability.

Iron is combined with other elements and used in many products. For example, iron chloride is an important compound used in sewage-treatment systems. It is also used as fabric dye and a coloring agent for paints. It is an additive to animal feed. Iron chloride is also used in printed circuit boards. Iron sulfate is used to treat anemia or iron deficiency. It is also used in treating sewage particles in water tanks. Iron hydroxide is a compound used in home water-purification systems. Iron arsenate can be found in insecticides because it prevents a variety of pest attacks in plants.

Iron is also essential to animal life, transporting oxygen in blood via the hemoglobin molecule. The blood cells are red because of the interaction between iron and oxygen, specifically because of the way the chemical bonds between the iron and the oxygen reflect light.

Here are a few important facts about iron.

  • Atomic number: 26
  • Atomic weight: 55.845
  • Density @ 300K (g/cm2): 7.874
  • Atomic mass (amu): 55.847
  • Melting point (K): 1811 (1538°C/2800°F)
  • Boiling point (K): 3134 (2861°C/5182°F)
  • Heat of vaporization (kJ/mol): 340.2
  • Ionization potential (V): 5.786
  • Ionization energy (eV): 7.902
  • Heat of fusion (kJ/mol): 14.9
  • Number of stable isotopes: 3
  • Oxidation states: +3, +2
  • Electron configuration: [Ar]4s23d6