About Iron

What is Iron

Iron is a chemical element with the symbol Fe (L.: Ferrum) and atomic number 26.

Iron is a group 8 and period 4 metal.

Iron is notable for being the final element produced by stellar nucleosynthesis, and thus the heaviest element which does not require a supernova or similarly cataclysmic event for its formation.

It is therefore the most abundant heavy metal in the universe.

History of Iron

The first signs of use of iron come from the Sumerians and the Egyptians, where around 4000 BCE, a few items, such as the tips of spears, daggers and ornaments, were being fashioned from iron recovered from meteorites. Because meteorites fall from the sky, some linguists have conjectured that the English word iron (OE ?sern), which has cognates in many northern and western European languages, derives from the Etruscan aisar which means "the gods". Even if this is not the case, the word is likely a loan into pre-Proto-Germanic from Celtic or Italic (Krahe IF 46:184f. compares Old Irish, Illyrian, Venetic and Messapic forms). The meteoric origin of Iron in its first use by humans is also alluded to in the Quran : "and We sent down Iron, in which is (material for) mighty war, as well as many benefits for mankind" (57:25).

Ancient Greeks considered Halybes to be "the inventors of iron". The people of the Caucasian Isthmus, Khaldi people (or Khalib/Halyb and Halisones by Strabo) were one of the oldest west-Georgian tribes (4th to 2nd millennia BC).

By 3500 BCE to 2000 BCE, increasing numbers of smelted iron objects (distinguishable from meteoric iron by the lack of nickel in the product) appear in Mesopotamia, Anatolia, and Egypt. However, their use appears to be ceremonial, and iron was an expensive metal, more expensive than gold. In the Iliad, weaponry is mostly bronze, but iron ingots are used for trade. Some resources (see the reference What Caused the Iron Age? below) suggest that iron was being created then as a by-product of copper refining, as sponge iron, and was not reducible by the metallurgy of the time. By 1600 BCE to 1200 BCE, iron was used increasingly in the Middle East, but did not supplant the dominant use of bronze.

Axe of iron from Swedish Iron Age, found at Gotland, Sweden.In the period from the 12th to 10th century BCE, there was a rapid transition in the Middle East from bronze to iron tools and weapons. The critical factor in this transition does not appear to be the sudden onset of a superior iron working technology, but instead the disruption of the supply of tin. This period of transition, which occurred at different times in different parts of the world, is the ushering in of an age of civilization called the Iron Age. Classical authors ascribe the first invention of ironsmithing to peoples of the Caucasus and eastern Anatolia, such as the Khaldi (Chaldei) and the Khalib (Chalybes).

The common alchemical symbol for iron, the metal of weapons, is that of Mars, the god of war.Concurrent with the transition from bronze to iron was the discovery of carburization, which was the process of adding carbon to the irons of the time. Iron was recovered as sponge iron, a mix of iron and slag with some carbon and/or carbide, which was then repeatedly hammered and folded over to free the mass of slag and oxidise out carbon content, so creating the product wrought iron. Wrought iron was very low in carbon content and was not easily hardened by quenching. The people of the Middle East found that a much harder product could be created by the long term heating of a wrought iron object in a bed of charcoal, which was then quenched in water or oil. The resulting product, which had a surface of steel, was harder and less brittle than the bronze it began to replace.

In China the first irons used were also meteoric iron, with archaeological evidence for items made of wrought iron appearing in the northwest, near Xinjiang, in the 8th century BCE. These items were made of wrought iron, created by the same processes used in the Middle East and Europe, and were thought to be imported by non-Chinese people.

In the later years of the Zhou Dynasty (ca 550 BCE), a new iron manufacturing capability began because of a highly developed kiln technology. Producing blast furnaces capable of temperatures exceeding 1300 K, the Chinese developed the manufacture of cast, or pig iron.

Iron was used in India as early as 250 BCE. The famous iron pillar in the Qutb complex in Delhi is made of very pure iron (98%) and has not rusted or eroded till this day.

This blast furnace in eastern Missouri consumed up to 11,000 tons of ore and 16,000 cords of wood annually from 1827 to 1891.If iron ores are heated with carbon to 1420–1470 K, a molten liquid is formed, an alloy of about 96.5% iron and 3.5% carbon. This product is strong, can be cast into intricate shapes, but is too brittle to be worked, unless the product is decarburized to remove most of the carbon. The vast majority of Chinese iron manufacture, from the Zhou dynasty onward, was of cast iron. Iron, however, remained a pedestrian product, used by farmers for hundreds of years, and did not really affect the nobility of China until the Qin dynasty (ca 221 BCE).

Cast iron development lagged in Europe, as the smelters could only achieve temperatures of about 1000 C; or perhaps they did not want hotter temperatures, as they were seeking to produce blooms as a precursor of wrought iron, not cast iron. Through a good portion of the Middle Ages, in Western Europe, iron was thus still being made by the working of iron blooms into wrought iron. Some of the earliest casting of iron in Europe occurred in Sweden, in two sites, Lapphyttan and Vinarhyttan, between 1150 and 1350 CE. Cast iron was then made into wrought iron by the osmond process. Some scholars have speculated the practice followed the Mongols across Russia to these sites, but there is no clear proof of this hypothesis. In any event, by the late fourteenth century, a market for cast iron goods began to form, as a demand developed for cast iron cannonballs.

Early iron smelting used charcoal as both the heat source and the reducing agent. In 18th century England, wood supplies became inadequate to enable the industry to expand and coke, a fossil fuel, began to be used an alternative. This innovation is associated with Abraham Darby at Coalbrookdale in 1709, but it was only later in the century that economically viable means of converting pig iron to bar iron were devised. The most successful such process was Henry Cort's puddling process, patented in 1784. Those processes permitted the great expansion in the production of iron that constitutes the Industrial Revolution for that industry.