Chemistry - Alloys

Metals are one of the materials we see all around us in everyday life, but did you realize that they are nearly all in the form of alloys? An alloy is a substance composed of two or more metals, or of a metal or metals with a nonmetal. Alloys are used to alter the properties of a metal, for example, magnesium. This is a light, soft and highly reactive metal. When alloyed with aluminum it is light, strong and corrosion resistant and can be used in the making of aircraft and cars.

Alloys are not a new discovery. Humans have been using metals since the end of the stone age - first during the bronze age and then during the iron age. During the bronze age, only the low reactivity metals like gold, silver, copper and tin were available. These were too soft for many uses but we discovered that certain combinations of these metals mixed together made materials hard enough for everyday use.

Alloying can also make dense metals lighter and expensive metals cheaper. Remember the story of Archimedes? This illustrates both ideas. According to legend, the king had given a lump of gold to a goldsmith to make a crown. When he received the crown, he suspected that the goldsmith had alloyed the gold with silver, which was cheaper and less dense. Archimedes was given the task of finding out if the gold had been alloyed. He couldn't damage the crown and needed a way of measuring the volume of the crown to check it's density. Apparently, when he noticed that the water in his bath rose when he got in, he realized that he could use the idea to get the volume of the crown and then work out the density.

Eventually, ancient humans discovered how to smelt more reactive metals like iron. Straight out of the smelter, iron is very brittle because of the impurities. But when it is purified and alloyed with carbon, it becomes more malleable and ductile. Weapons and tools made from iron superseded those made from bronze as they had better properties - the iron age had begun.