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3.11: Alloys

Difficulty Level: At Grade Created by: CK-12
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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&feature=related

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.

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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Vocabulary

alloy

Mixture of a metal with one or more other elements.

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Difficulty Level:
At Grade

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Grades:
7 , 8
Date Created:
Oct 31, 2012
Last Modified:
Sep 13, 2016
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