Use of Metals

9.2 Uses of Metals

Overview

Metals are widely used in industries, transport, construction, electronics, and household applications because of their distinct physical properties such as conductivity, malleability, ductility, strength, and resistance to corrosion. In this section, we focus on specific uses of aluminium and copper and link these uses directly to their physical properties.

1. Aluminium

Aluminium is a lightweight, silvery-white metal with the chemical symbol Al. It has a low density, good electrical conductivity, malleability, and excellent corrosion resistance due to the formation of a protective oxide layer.

1(a) Aluminium in the Manufacture of Aircraft – Low Density

• Low Density:
  • Aluminium has a density of 2.7 g/cm³, which is about one-third the density of steel.
  • Low density means the material is lightweight, which is crucial in the aerospace industry to reduce the mass of aircraft.
  • Lighter aircraft require less fuel, increasing fuel efficiency and reducing operational costs.
• Strength-to-Weight Ratio:
  • Although aluminium is lighter, it can be alloyed with other metals such as copper, magnesium, and zinc to improve its strength without significantly increasing its weight.
  • This high strength-to-weight ratio makes it ideal for constructing aircraft frames, wings, and fuselage.
• Resistance to Fatigue and Corrosion:
  • Aluminium’s resistance to corrosion (due to the oxide layer Al₂O₃) ensures that the metal can withstand harsh atmospheric conditions during flight.

Application Example:

• The body of modern passenger aircraft (e.g., Airbus A320, Boeing 737) is made from aluminium alloys such as duralumin (aluminium + copper + magnesium + manganese).

1(b) Aluminium in Overhead Electrical Cables – Low Density and Good Electrical Conductivity

• Low Density Advantage:
  • Aluminium is about 70% less dense than copper, so cables made from aluminium weigh less.
  • This makes it easier to install overhead power lines over long distances because less structural support is needed.
• Good Electrical Conductivity:
  • Although aluminium is less conductive than copper, its low density means that a thicker aluminium cable can carry the same current as a thinner copper cable while still weighing less.
  • Conductivity of aluminium ≈ 60% that of copper, but weight per unit length is much lower.
• Cost Efficiency:
  • Aluminium is less expensive than copper, making it a cost-effective choice for large-scale electrical power distribution.
• Corrosion Resistance:
  • Aluminium resists corrosion due to its oxide layer, making it suitable for outdoor environments.

Application Example:

• Overhead power transmission lines often use aluminium conductors reinforced with steel (ACSR – Aluminium Conductor Steel-Reinforced) for added strength.

1(c) Aluminium in Food Containers – Resistance to Corrosion

• Corrosion Resistance:
  • When exposed to oxygen, aluminium forms a thin, stable layer of aluminium oxide (Al₂O₃).
  • This layer acts as a barrier against further oxidation and protects against acidic or basic substances found in some foods.
• Non-Toxic and Safe:
  • Aluminium is non-toxic and does not react significantly with most foods, making it safe for packaging.
• Lightweight and Malleable:
  • Can be easily rolled into thin sheets (aluminium foil) and shaped into cans, trays, and containers.
  • This makes packaging, storage, and transportation more efficient.
• Thermal Conductivity:
  • Aluminium quickly transfers heat, allowing even cooking or baking when used in food trays and containers.

Application Examples:

• Aluminium foil for wrapping food to prevent contamination and preserve freshness.
• Aluminium beverage cans (often coated internally to prevent reaction with acidic drinks).
• Ready-meal trays for oven and microwave use.

2. Copper

Copper is a reddish-brown metal with the chemical symbol Cu. It is known for its excellent electrical conductivity, thermal conductivity, ductility, and corrosion resistance.

2(a) Copper in Electrical Wiring – Good Electrical Conductivity and Ductility

• Electrical Conductivity:
  • Copper is one of the best conductors of electricity, second only to silver.
  • Its high conductivity allows efficient transmission of electricity with minimal energy loss.
  • Conductivity of copper ≈ 5.8 × 10⁷ S/m.
• Ductility:
  • Ductility means copper can be drawn into thin wires without breaking.
  • This property allows copper to be manufactured into long, continuous wires for use in electrical circuits.
• Corrosion Resistance:
  • Copper does not rust like iron; it forms a protective green patina (copper carbonate) in moist air.
  • This ensures durability in wiring systems over many years.
• Thermal Conductivity:
  • Good heat conduction prevents wires from overheating, increasing safety.

Application Examples:

• Household wiring: Copper wires are standard for internal wiring in homes and appliances.
• Power cables: Used in underground and marine power transmission cables.
• Electronic devices: Copper is used in circuit boards, connectors, and microchips.

Summary Table – Uses of Aluminium and Copper Linked to Physical Properties