From Atoms to Materials

In an alloy, the element that mixes with the metal may be a metal, or a non-metal (such as carbon in carbon steel). Corrosion of iron When iron is exposed to oxygen and water in air, it reacts quickly with them. The product is known as rust*. Rusted iron items usually lose their strength and need to be replaced. Snapshot Rusted iron rust 鏽 chromium 鉻 nickel 鎳 alloy 合金 Alloys We have learnt about many useful properties of pure metals. These properties make them suitable for many uses. However, some pure metals have weaknesses, e.g. not strong enough, or corrode easily. They may not be suitable for some uses. To improve certain properties of a pure metal, we can mix other elements with it. Such a uniform mixture of a metal with one or more other elements is called an alloy . An alloy usually has metallic properties. D Fig. 13.25 A bronze statue Fig. 13.26 Steel is used to make many tools. Bronze Copper is not strong enough for certain applications. By adding tin to it, we can make the alloy bronze, which is harder and stronger than pure copper. Steel Iron corrodes very easily. To deal with this problem, other elements, e.g. chromium*, nickel* or carbon, are added to iron. The alloy made this way is known as stainless steel. Stainless steel is much stronger and much more resistant to corrosion than iron. Nowadays, iron is mainly used to make various types of steel. Bronze and steel are two examples of alloys. 75 13 From Atoms to Materials © United Prime Educational Publishing (HK) Limited 2024 All rights reserved; no part of this publication may be reproduced, photocopied, recorded or otherwise, without the prior written permission of the Publisher. Sample