6 min readConcept sheetPart I (1 mark: match the alloy), Part II (2 marks: amalgam) and Part III (4 marks: alloys with composition and uses)

Alloys and their uses

An alloy is a homogeneous mixture of metals, or a metal and a non-metal. Alloying makes metals harder, stronger and more rust-proof.

AlloyA homogeneous mixture of two or more metals, or of a metal and a non-metal

AmalgamAn alloy of mercury with another metal, e.g. silver-tin amalgam for filling teeth

Brass vs bronzeBrass = copper + zinc; bronze = copper + tin

Stainless steelIron + carbon + nickel + chromium

Why we make alloys

To change the appearance and colour of a metal (brass looks golden).
To change its chemical activity, for example to resist corrosion (stainless steel).
To lower the melting point (solder and Wood's metal melt easily).
To increase hardness and tensile strength (strength when pulled).
To increase resistance to electricity, for heating wires.

Two ways to make an alloy

1
Fusion: melt the metals together, mix well and let the mixture cool.
Brass is made by melting copper and zinc together.
2
Compression: press finely powdered metals together under high pressure.
Wood's metal (lead, tin, bismuth and cadmium) can be made this way.

Common alloys and their uses

Alloy	Made of	Uses
Brass	Copper, zinc	Electrical fittings, medals, lamps and decorative items
Bronze	Copper, tin	Statues, coins, bells
Duralumin	Aluminium, copper, magnesium, manganese	Aircraft parts, pressure cookers, tools
Magnalium	Aluminium, magnesium	Aircraft body parts, light apparatus
Stainless steel	Iron, carbon, nickel, chromium	Utensils, cutlery, surgical instruments, vehicle parts
Nickel steel	Iron, carbon, nickel	Electric cables, aircraft parts, propellers
Silver-tin amalgam	Silver, tin, mercury	Dental fillings

Brass vs bronze

BrassCopper + zinc. Yellow and golden. Used for the kuthuvilakku (oil lamp), taps and electrical fittings.

BronzeCopper + tin. Reddish brown and hard. Used for temple bells, coins and statues.

Both are copper alloys. Students often swap them, so learn the second metal of each: zinc for brass, tin for bronze.

In real life

The Chola bronze statues of Tamil Nadu, such as the Nataraja, and the icons still cast at Swamimalai are copper alloys. Your stainless steel tumbler stays shiny because chromium and nickel protect the iron from rusting.

Exam angle

1 marks: “Duralumin is an alloy of: (a) Al, Cu, Mg, Mn (b) Cu, Zn (c) Fe, Cr, Ni, C (d) Cu, Sn” (a) Al, Cu, Mg, Mn.

2 marks: “What is an amalgam? Give one use.” An alloy of mercury with another metal. Silver-tin amalgam is used for filling teeth.

4 marks: “What are alloys? Give the composition and uses of brass, bronze, duralumin and stainless steel.” Definition, then each alloy with its metals and two uses: brass (Cu, Zn), bronze (Cu, Sn), duralumin (Al, Cu, Mg, Mn), stainless steel (Fe, C, Ni, Cr).

Remember it

Brass: Copper and Zinc. Bronze: Copper and Tin. Add Mercury and it becomes an amalgam.