What materials are used for static structures?

The first materials used were made of stone, especially stones like flint that could be chipped to make sharp edges and points. Ancient peoples discovered metals, either in pure form, or in ore, that is mixed with non-metals. Copper, tin, gold, and iron were known before 2000 B.C.E. Copper, tin, and gold are very soft and not very useful as tools or weapons.

A method of hardening metals is to mix two or more different metals forming what is called an alloy. Bronze is made by adding tin to copper and was known by about 4000 B.C.E. in what is now Iran and Iraq. The tin came from southern England. Bronze is a hard metal that can be melted and cast in various shapes, including statues. Today bronze is used for bells and cymbals.

Not much later methods were found to convert iron ore, which is iron mixed with either oxygen or sulfur, to pure iron using a charcoal fire. Iron replaced bronze as a material for tools and weapons because it was cheaper and didn’t require long trade routes to obtain the tin. To keep iron from being brittle the carbon must be removed. If the iron is heated to red-heat and then hammered the carbon is forced to the surface where it can be removed. The result is steel that contains less than about 1% carbon.

Steel is a versatile alloy of iron and carbon because additional materials can be added to change its properties. Very hard steel, called tool steel, contains tungsten, molybdenum, and chromium, among other minor additions. Its hardness can be changed by heating it and then cooling it very quickly by quenching it in water or other liquids. Stainless steel used in knives, forks, and spoons has 18% chromium and 10% nickel. Other stainless steels use different amounts of these two metals as well as molybdenum and magnesium. Stainless steel does not rust, but isn’t as hard as tool steel.

Pewter is a tin alloy that was developed in England for plates and cups. It adds copper, bismuth, and antimony to tin. Originally lead was used, but because it is poisonous, it is no longer found in pewter.

Brass is typically 80% to 90% copper with zinc added. Actually, brass was made before metallic zinc was isolated! The zinc ore calamine was melted with copper. Brass is used as a decorative metal as well as in bullet casings. If aluminum and tin are added it is resistant to corrosion by sea water.

Gold is another very soft metal. It can be made harder by adding copper and silver in equal quantities. Gold alloys are measured in karets. 24-karat gold is pure gold while 18-karet gold has 18 parts gold and 6 parts other metals. 10-karet gold has 10 parts gold and 14 parts other metals.

Titanium is used in many alloys today because it is lightweight and corrosion resistant. Many alloys of both metals and non-metals are used in electronics. Some LED lamps contain the metals gallium and aluminum and the non-metal arsenic.


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