Uses of Metals and Alloys
This topic explores the link between the specific physical and chemical properties of a metal and its practical applications. It also covers how these natural properties can be enhanced by creating alloys.
Part of the ESAT Chemistry syllabus — revision for the Engineering and Science Admissions Test (ESAT), the UAT-UK admissions test for Cambridge, Imperial, Oxford and UCL.
Key points
- A metal's use is determined by its properties. For example, conductivity (electrical and thermal), strength, density, malleability (can be shaped), ductility (can be drawn into wires), and chemical reactivity (e.g., corrosion resistance).
- Aluminium (Al) is used for aircraft and drink cans due to its low density and corrosion resistance from a protective oxide layer.
- Iron (Fe) is strong and cheap, making it ideal for construction (as steel), but it rusts easily if not protected.
- Copper (Cu) is an excellent electrical and thermal conductor and is ductile, making it perfect for electrical wiring and water pipes.
- Gold (Au) and Silver (Ag) are highly unreactive, malleable, and lustrous, leading to their use in jewellery and high-end electronics.
- Titanium (Ti) has a very high strength-to-weight ratio and is extremely corrosion resistant, making it essential for aerospace engineering and medical implants.
- Alloys are mixtures containing metals, designed with superior properties. For instance, steel (iron and carbon) is much harder and stronger than pure iron because the carbon atoms distort the regular iron lattice, preventing layers from sliding.
Definitions
- Alloy
- A material made by mixing a metal with at least one other element (metal or non-metal) to produce a substance with enhanced properties such as strength, hardness, or corrosion resistance.
- Malleable
- A property of a material, particularly metals, describing its ability to be hammered or pressed into a different shape without breaking or cracking.
- Ductile
- A property of a material that allows it to be stretched or drawn into a thin wire under tensile stress.
Worked example
The main component of an overhead power cable needs to be both a good electrical conductor and have a low density to minimise sagging and the need for support pylons. Which of the following metals is most suitable for this purpose? A) Copper B) Aluminium C) Steel D) Titanium
- 1
Analyse the requirements:
The material must have high electrical conductivity and low density.
- 2
Evaluate Copper (Cu):
It is an excellent electrical conductor, but it is relatively dense.
It is used in cables but often with a steel core for strength.
- 3
Evaluate Aluminium (Al):
It is a very good electrical conductor (though not as good as copper per unit volume) and has a very low density.
This combination makes it ideal for overhead cables.
- 4
Evaluate Steel (an alloy of Iron):
It is strong but a poor electrical conductor compared to Cu or Al, and is very dense.
It is used as a reinforcing core, not the main conductor.
- 5
Evaluate Titanium (Ti):
It has a low density and is very strong, but it is a much poorer electrical conductor than Al or Cu and is very expensive.
- 6
Conclusion:
Aluminium offers the best combination of low density and high electrical conductivity for this specific application.
Answer: B) Aluminium
Common mistakes
- ×Confusing strength with density. A material like steel is very strong, but for applications like aircraft or long cables, a high strength-to-weight ratio (as found in Al or Ti) is more important.
- ×Forgetting that corrosion resistance is a chemical property, not a physical one. Aluminium's resistance comes from a chemical reaction with oxygen to form a tough, unreactive oxide layer.
- ×Misunderstanding why alloys are stronger. It's not just a simple mix; the different-sized atoms in an alloy disrupt the regular crystal lattice, making it harder for layers of atoms to slip past each other.
No-calculator tips
- ✓For questions matching metals to uses, create a mental table. List the required properties (e.g., strong, light, conductive, unreactive) and check which metal fits the most criteria.
- ✓Use word association to remember key uses: Aluminium → Aeroplane; Copper → Conductor; Iron → Infrastructure.