by Chris Woodford. Last updated: October 12, 2020.
Almost every material we could ever want is lurking somewhere in the planet beneath our feet. From the gold we wear as jewelry to the oil that powers our cars, Earth's storehouse of amazing materials can supply virtually every need. Chemical elements are the basic building blocks from which all the materials inside Earth are made. There are 90 or so naturally occurring elements and the majority of them are metals. But, useful though metals are, they're sometimes less than perfect for the jobs we need them to do. Take iron, for example. It's amazingly strong, but it can be quite brittle and it also rusts easily in damp air. Or what about aluminum. It's very light but, in its pure form, it's too soft and weak to be of much use. That's why most of the "metals" we use are not actually metals at all but alloys: metals combined with other substances to make them stronger, harder, lighter, or better in some other way. Alloys are everywhere around us—from the fillings in our teeth and the alloy wheels on our cars to the space satellites whizzing over our heads. Let's take a closer look at what they are and why they're so useful!
Photo: This fuel tank from the Space Shuttle was made from a super-light aluminum-lithium alloy, so it's a whopping 3400 kg (7500 lb) lighter than the tank it replaced. Cutting weight from the basic structure of the Shuttle meant it could carry heavier payloads (cargo). Photo by courtesy of NASA Kennedy Space Center (NASA-KSC).
What is an alloy?
Photo: This sample of a titanium-zirconium-nickel alloy is being made to levitate (float in mid air) using electricity. It's one of many remarkable new materials being developed for possible use in space. Photo by courtesy of NASA Marshall Space Flight Center (NASA-MSFC).
You might see the word alloy described as a "mixture of metals", but that's a little bit misleading because 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).