Sangeetha Pulapaka

Do you play any musical instrument like say an electric guitar? (because you rock!)

Did you know that in musical instruments and the loudspeakers we use a mixture of metals to make them more effective and more sustainable. Like the magnets in a loudshpeaker and the pickups in a guitar use a mixture of metals such as iron, aluminium etc. This mixture is called an alloy.

Some alloys contain only one metal and it's mixed in with other substances that are nonmetals (cast iron, for example, is an alloy made of just one metal, iron, mixed with one nonmetal, carbon). The best way to think of an alloy is as a material that's made up of at least two different chemical elements, one of which is a metal. The most important metallic component of an alloy (often representing 90 percent or more of the material) is called the main metal, the parent metal, or the base metal. The other components of an alloy (which are called alloying agents) can be either metals or nonmetals and they're present in much smaller quantities (sometimes less than 1 percent of the total). Although an alloy can sometimes be a compound (the elements it's made from are chemically bonded together), it's usually a solid solution (atoms of the elements are simply intermixed, like salt mixed with water).

You might find the idea of an alloy as a "mixture of metals" quite confusing. How can you mix together two lumps of solid metal? The traditional way of making alloys was to heat and melt the components to make liquids, mix them together, and then allow them to cool into what's called a solid solution (the solid equivalent of a solution like salt in water). An alternative way of making an alloy is to turn the components into powders, mix them together, and then fuse them with a combination of high pressure and high temperature. This technique is called powder metallurgy. A third method of making alloys is to fire beams of ions (atoms with too few or too many electrons) into the surface layer of a piece of metal. Ion implantation, as this is known, is a very precise way of making an alloy. It's probably best known as a way of making the semiconductors used in electric circuits and computer chips.

Vivekanand Vellanki

For me, the interesting question is not the "what", but the "why". Why do we bother with alloys? or why are alloys interesting?

Alloys are interesting because they change the properties of the basic elements to make them more useful in daily life.

You might think of iron as a hard, strong metal tough enough to support bridges and buildings, but that's not pure iron.

Pure iron is a silvery-white metal that's easy to work and shape (malleable) and it's just soft enough to cut through (with quite a bit of difficulty) using a knife. You can hammer iron into sheets and draw it into wires (ductile). Also, pure iron reacts with moist air and corrodes (this is called rusting).

Clearly, pure iron is not a good material for construction. However, famous structures like the Qutb Minar in Delhi, or the Eiffel Tower in Paris are made of iron.

What's missing is that these structures are made from iron alloys. Different iron alloys exist that improve on the basic properties of iron to make iron more suitable as construction material.

Some iron alloys are described below. These are pure iron with varying degrees of carbon and other elements to change the properties of pure iron.

Pig iron: This is an alloy containing about 90–95 percent iron, 3–4 percent carbon, and traces of other elements such as silicon, manganese, and phosphorus, depending on the ore used. Pig iron is much harder than 100 percent pure iron, but still too weak for most everyday purposes.

Cast iron: One of the world's most famous iron buildings, the Capitol in Washington, DC has a dome made of 4,041,146kg (8,909,200 pounds) of cast iron. So, definitely suitable for construction. Cast iron has two big drawbacks: first, because it's hard and brittle, it's virtually impossible to shape, even when heated; second, it rusts relatively easily.

Steel: Steel is just another type of iron alloy, but it has a much lower carbon content than cast iron and other metals are often added to give it extra properties. Steel is such an amazingly useful material that we tend to talk about it as though it were a metal in its own right—a kind of sleeker, more modern "son of iron" that's taken over the family firm! Steel is used a lot in construction. Modern skyscrapers (e.g. the Burj Khalifa) are all built using some form of steel.

Stainless steel doesn't corrode easily and has a sleek look. Stainless steel has taken over our bathrooms and kitchens - our taps, kitchen sinks, etc are made out of stainless steel.