9.2 Uses of metals

2026 Syllabus Objectives

  1. Core: Describe the uses of metals in terms of their physical properties, including:
    • (a) aluminium in the manufacture of aircraft because of its low density
    • (b) aluminium in the manufacture of overhead electrical cables because of its low density and good electrical conductivity
    • (c) aluminium in food containers because of its resistance to corrosion
    • (d) copper in electrical wiring because of its good electrical conductivity and ductility

Historical Context of Metal Usage 🏛️

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The production and use of metals have been central to human technological development throughout history. The transition metals, particularly iron and copper, have proved most useful for construction and various purposes due to their unreactive or moderately reactive nature.

Key historical developments:

  • Iron production dates back to Middle Eastern cultures in the Middle Bronze Age, spreading through India and China
  • Traditional metalworking techniques, such as the forging of Samurai swords from Japanese steel, involved sophisticated processes of heat treatment and folding
  • The expertise of ancient smiths gave rise to numerous techniques and alloys suited for specific purposes
  • Modern understanding of metal structure has led to an even wider range of steels and alloys for demanding applications

Important: In addition to transition metals like iron and copper, aluminium has become increasingly important for a variety of modern applications.

Uses of Iron ⚙️

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The Iron Revolution

The Iron Bridge at Ironbridge in Shropshire, England, marks a historic milestone in the Industrial Revolution. Made from cast iron and opened in 1781, it was the first iron bridge in the world. Today, we use approximately nine times more iron than all other metals combined.

Properties and Limitations

Iron is a moderately reactive transition metal with the following characteristics:

  • Pure iron is quite soft and weak, making it unsuitable for construction on its own
  • Cast iron, obtained directly from the blast furnace, can be used for very large objects

Cast Iron Applications

Cast iron contains 2–4% carbon and was extensively used during the Industrial Revolution in:

  • Rails, boats, ships, and aqueducts
  • Buildings and bridge structures
  • Iron cylinders in steam engines
  • Cooking pots and pans (due to good heat conductivity)

Problems with Cast Iron

The high carbon content (2–4%) in cast iron creates significant limitations:

  • The carbon disrupts the lattice structure of iron
  • This makes the metal brittle and liable to shatter when excessive force is applied
  • Cast iron was too brittle for smaller or more sophisticated engineering applications

Corrosion Issues

Iron suffers from a major drawback: it rusts easily. When exposed to air and water, iron becomes coated with rust (hydrated iron(III) oxide):

Fe2O3⋅nH2O\text{Fe}_2\text{O}_3 \cdot n\text{H}_2\text{O}

This orange-red powder flakes off and weakens the structure, leading to:

  • Development of various anti-rusting methods
  • Creation of stainless steel alloys

Improvements to Iron

The strength of iron can be improved by:

  • Carefully controlling the amount of carbon present
  • Adding other metals to create different forms of steel matched to the intended use

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