Alloys

Alloys

Lessons

In this lesson, we will learn:

  • The definition of an alloy and how alloys and metals are related.
  • To explain the benefits of using metal alloys over pure metal substances.
  • To explain how the structure of an alloy gives it unique properties to its constituent metals.

Notes:

  • As seen in our lesson on metallic bonding, the properties of metals are explained by the features of metallic bonding and the structure that it creates.
  • A lot of every day uses of 'metals' rely on their strength, which is the ability to withstand a force without breaking, and hardness, which is the resistance to being deformed (having its shape broken). However, many of these 'metals' we see are not pure metals.
    Many metals have quite low strength and hardness when pure because of the features of metallic bonding!
    • The malleable properties of pure metals (due to the metal ions not being stuck in place) actually mean that pure metals do not hold up to very high weight loads being applied to them. Under very heavy loads they will change shape and fail structurally.
      Practically this means that pure metals are normally not useful in the most physically demanding of structures, such as in buildings or bridges.
  • Alloys are a mixtures of two or more metals (or carbon) combined. Alloys still have the metallic structure but are harder compared to the pure metals they are made of. The changes to the metallic structure by adding a second metal element has a major effect on the metal ions' ability to move past each other:
    • Because the alloy, unlike the pure metal, is made of different types of atoms and therefore different-sized atoms in layers. The layers of atoms cannot slide over each other easily, so the structure is much harder and can take a larger weight load before the layers of atoms would be forced to move. See the diagram below:
  • There are many examples of alloys used in our everyday lives. Some examples include:
    • Steel which is an alloy of iron and carbon. Used in buildings and many other structures, there are a lot of different steel alloys depending on the ratio of iron to carbon used.
    • Amalgam which is an alloy of mercury, silver and other metals used in dental fillings.
    • Brass which is an alloy of copper and zinc used in locks, gears, and valves. It's also used in some musical instruments,
  • Smart alloys are alloys which are able to return to their original shape after being bent, by heating or electrifying it. This is a useful property for making glasses frames and other items that need to be 'a little bit' flexible.
  • Introduction
    What is an alloy?
    a)
    Recap on metallic bonding.

    b)
    Structure and properties of alloys.

    c)
    Examples of alloys and their uses.