Iron - the second most unusual substance on earth.

written by Michael Harwood

Iron is the second most abundant element in the earth's crust (after aluminum) and it is the element that has had the greatest influence on the earth's history (so far). Unlike aluminum it is really easy to extract from iron ore (just heat it with charcoal and limestone). When pure it is soft and malleable, yet it forms many alloys with all sorts of useful properties. Iron is quite reactive chemically and rapidly corrodes (rusts) in moist air and warm temperatures. [There is probably a benefit to this feature, but the author cannot think of one at present.] Iron has a higher melting point than copper (about 1,535º C compared to 1,083º C) which is why the bronze age occurred before the iron age. Apart from its greater abundance, iron provided a harder and stronger material than the earlier metals.

Because iron is so easy to work with, it can be made into almost any shape. Iron has been used from prehistoric times (before 3000 BC) to make ornaments, weapons and tools. As recorded in Genesis (4:22), Tubal-Cain, the eighth descendant from Adam, was a forger of bronze and iron instruments. In Europe and the Middle East the iron age began around 1200 BC. Where would civilization be today without the plough, axe and saw? History would be quite different without our heritage of iron weapons: swords, cannons, portcullises, rifles, barbed wire, tanks, aircraft carriers. Steel making reached its zenith in the 16th-17th century with Damascus steel used to make the sharpest and most flexible sword blades. Their manufacture is now a lost art.

Nowadays, we use 20 times more iron (mostly in various forms of steel) than all the other metals put together. Iron is also the cheapest metal. Iron has been crucial in almost every part of the transportation industry: from horseshoes, and iron rimmed wagon wheels, to bridges, trains (iron horses), railroads, cars and ocean liners.

One of the most unusual properties of steel is that it expands at the same rate as concrete. Is this accident or design? This allows us to use steel bars in reinforced concrete to build large and multistory buildings. Concrete is strong in compression but weak in tension. Reinforcement allows for less concrete to be used because the steel carries all the tension; also, the concrete protects the steel from corrosion. Without iron all big structures would need a large number of pillars - like Greek temples or the Roman aqueduct at Nîmes.

Aside from construction and tools, the most important use of iron depends on its very unusual magnetic properties. Each iron atom acts like a small magnet, yet instead of cancelling each other out, there is a long range ordering effect that cannot be explained by normal physics, only by quantum physics. The fact that iron is magnetic was essential to the exploration and mapping of the world. Not only are compasses useful for orienteering in Algonquin park, but their invention allowed transoceanic trade routes with the consequent economic growth and foundation of our country. The most important use of magnets today is in electric motors and generators. Much of our heavy industry is dependant on these things. If iron were not ferromagnetic, you would have no alternator to recharge your car battery, no iron to make electromagnets in buzzers, doorbells, scrapyards, no magnets in loudspeakers, no power tools. Without the magnetic properties of iron, we would only have electricity from batteries!

We also need iron to survive. The 4.5 g in our bodies is essential for haemoglobin to transport oxygen to our cells.

I will end this article by looking at a more technical aspect yet still amazing property of iron: some of its many useful and unique alloys. Iron forms literally thousands of alloys. (See ) Solid metal can be hammered, rolled, heated, chilled, given acid or electrochemical baths. Each of these leads to a slight change in the crystalline structure.

Pure iron is a soft, ductile, gray-white metal of high tensile strength that has few uses. Cast iron (containing up to 5% carbon) was the first alloy to be used widely. It is poured from a smelter into moulds made in damp sand or other materials. Because cast iron expands slightly when cooling(!) it keeps it shape well and can be economically cast into complex shapes where strength is not the primary concern. It is hard, but brittle and used for large heavy objects like engine blocks, crankshafts, wood stoves. Wrought iron has less than 0.2% carbon, but about 2% slag . It is as strong in compression as cast iron, but it has much greater tensile strength. It is used for ornaments and tools made by blacksmiths.

Steel is an even further refinement of iron containing less than 1% carbon, and small amounts of various other elements to create special properties. Stainless steel (containing 11% chromium) doesn't rust and is used for items like surgical instruments. Nichrome steel has a high resistance to electricity and is used in toasters and electric heaters. Tool steel is extremely hard and is used for cutting tools and drill bits. Spring steel is very flexible and has a 'memory' which causes it to return to its original shape when released.

After over 5000 years we still depend on the tried and true properties of this unusual material while continually researching new alloys and compounds.  A true miracle material!! Who could have designed something with all of these properties?!

P.S. Can you figure out why there are no steel coins?