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Alloys

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Metals such as iron are useful for many purposes because of their unique properties. For example, they can conduct electricity and bend without breaking. However, pure metals may be less useful than mixtures of metals with other elements. For example, adding a little carbon to iron makes it much stronger. This mixture is called steel. Steel is so strong that it can hold up huge bridges, like the one pictured above. Steel is also used to make skyscrapers, cargo ships, cars, and trains. Steel is an example of an alloy.

What Are Alloys?

An alloy is a mixture of a metal with one or more other elements. The other elements may be metals, nonmetals, or both. An alloy is formed by melting a metal and dissolving the other elements in it. The molten solution is then allowed to cool and harden. Alloys generally have more useful properties than pure metals. Several examples of alloys are described and pictured below. You can learn about another alloy—the amazing alloy called memory wire—at the following URL. If you have braces on your teeth, you might even have this alloy in your mouth!

http://www.youtube.com/watch?v=LSNRwtTMH6w

Examples of Alloys

Most metal objects are made of alloys rather than pure metals. Objects made of four different alloys are shown in the Figure below .

Brass saxophones, stainless steel sinks, gold bracelets, and bronze statues are all made from alloys

Brass saxophone: Brass is an alloy of copper and zinc. It is softer than bronze and easier to shape. It's also very shiny. Notice the curved pieces in this shiny brass saxophone. Brass is used for shaping many other curved objects, such as doorknobs and plumbing fixtures. Stainless steel sink: Stainless steel is a type of steel that contains nickel and chromium in addition to carbon and iron. It is shiny, strong, and resistant to rusting. This makes it useful for sinks, eating utensils, and other objects that are exposed to water. "Gold" bracelet: Pure gold is relatively soft, so it is rarely used for jewelry. Most "gold" jewelry is actually made of an alloy of gold, copper and silver. Bronze statue: Bronze was the first alloy ever made. The earliest bronze dates back many thousands of years. Bronze is a mixture of copper and tin. Both copper and tin are relatively soft metals, but mixed together in bronze they are much harder. Bronze has been used for statues, coins, and other objects.

Q: Sterling silver is an alloy that is used to make fine jewelry. What elements do you think sterling silver contains? What properties might sterling silver have that make it more useful than pure silver?

A: Most sterling silver is about 93 percent silver and about 7 percent copper. Sterling silver is harder and stronger than pure silver, while retaining the malleability and luster of pure silver.

Summary

  • An alloy is a mixture of a metal with one or more other elements. An alloy generally has properties that make it more useful than the pure metal.
  • Examples of alloys include steel, bronze, and brass.

Vocabulary

  • alloy : Mixture of a metal with one or more other elements.

Practice

Choose an alloy from the list at the following URL, and then do a Web quest to learn about its composition, properties, and uses. Create a poster or brochure to share what you learn.

http://en.wikipedia.org/wiki/List_of_alloys

Review

  1. What is an alloy? Describe an example.
  2. What are some useful ways alloys may differ from pure metals?

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