10.3 Selected Alloy

An alloy is a mixture of metals made by mixing molten metals and cooling them. The development of alloys marked a significant turning point in history, particularly during the Copper Age (5000–3000 BC), when people started mixing molten copper with molten tin to create bronze. Bronze, an alloy of copper and tin, was harder than pure copper, making it ideal for creating durable tools and weapons. This era (3000 BC–1000 BC) is referred to as the Bronze Age.

Key Alloys and Their Composition:

• Bronze: Copper (90%) and Tin (10%)

• Uses: Used for making crockery and various tools.

• Steel: Iron (99%) and Carbon (1%)

• Uses: Commonly used in construction, machinery, railways, and vehicles. It is also used in weapons, knives, and scissors.

• Stainless Steel: Iron (74%), Chromium (18%), Nickel (8%)

• Uses: Rust-free steel used in making hospital tools, kitchen utensils, sinks, and more.

• Brass: Copper (65%) and Zinc (35%)

• Uses: Used in electric switches, utensils, and decorative items.

• Duralumin: Aluminium (95%), Copper (4%), Magnesium, Manganese, and Iron (1%)

• Uses: Used in the manufacturing of aircraft bodies and bicycle parts.

• Gold:

• 24-carat gold: Pure gold (100%)

• 22-carat gold: Gold (91.67%) and Copper (8.33%)

• 21-carat gold: Gold (87.5%) and Copper (12.5%)

• Uses: Jewellery, coins, and electronic connectors.

Alloy Composition and Naming:

In alloys, one metal is considered the representative metal, and its percentage is typically higher. The alloy is named after the representative metal. For example:

• Steel is primarily iron (99%) and is named after iron.

• Brass contains copper (65%) and zinc (35%) and is considered a copper alloy, although it contains both metals.

Summary of Alloys and Their Uses:

Alloy Composition Uses

Steel Iron (99%) + Carbon (1%) Rail and wheels, engines, vehicles, weapons

Stainless Steel Iron (74%) + Chromium (18%) + Nickel (8%) Knives, forks, kitchen sinks, chemical containers

Brass Copper (65%) + Zinc (35%) Electric switches, utensils, ornamental items

Bronze Copper (90%) + Tin (10%) Crockery, ornamental items, tools

Duralumin Aluminium (95%) + Copper (4%) + Magnesium, Manganese, Iron (1%) Airplane bodies, bicycle parts

Gold 24-carat (100% gold), 22-carat (91.67% gold, 8.33% copper) Jewellery, coins, electronics