Properties of Materials: Glass and Ceramic – JSS1 Basic Technology Lesson Note (First Term)

Ceramics are hard, brittle materials made by shaping clay and chemicals and firing them at high temperatures, and glass is a special type of ceramic.

Behavioural objectives

By the end of the lesson, students should be able to:

1. define ceramic and give examples of ceramic products;
2. list the properties of ceramic materials;
3. state the raw materials used for making glass;
4. describe the stages of making glass;
5. list the properties and examples of glass products.

What are ceramic materials?

Ceramic is a hard, brittle, heat-resistant material made by firing a mixture of clay and chemicals at high temperatures.

• Ceramic products: objects made from clay and chemical materials.
• Firing: heating a shaped object in a kiln or furnace until it becomes hard.
• Kiln: a special oven used for firing clay products.

Examples of ceramic products

• Clay pots: used for cooking, storing water and planting flowers.
• Tiles: used to cover floors and walls.
• Basins: used in bathrooms and toilets, such as wash-hand basins.
• Bricks: fired clay blocks used in building.
• Plates and cups: household items made of fired clay.
• Glass: a type of ceramic made from sand and other chemicals.

What are the properties of ceramic materials?

The properties of ceramics are the qualities that describe how they behave and what they can be used for.

1. Resistant to corrosion: they do not rust or rot easily.
2. Heat resistant: they withstand very high temperatures, so they are used in furnaces and ovens.
3. Electrically resistant: they do not allow electricity to pass, so they are insulators.
4. Hard and strong: they resist scratching and wear.
5. Compressive strength: they can carry heavy loads that press on them without crushing.
6. Easily moulded when wet: wet clay can be shaped before firing.
7. Brittle: they break easily when dropped on the ground.

What is glass?

Glass is a hard, usually transparent ceramic material made by melting sand, lime, potash, soda and lead oxide together.

• Transparent: light passes through it, so we can see clearly through it.
• Molten glass: glass that has melted into a hot liquid in a furnace.
• Forming: shaping the molten glass into the desired object.

What are the raw materials for making glass?

There are five raw materials for making glass: sand, lime, potash, soda and lead oxide.

How is glass made?

Glass is made in four stages: mixing, heating, cooling and annealing.

1. Mixing: the raw materials are measured and mixed together.
2. Heating (firing): the mixture is placed in a furnace and heated until it becomes molten glass.
3. Cooling: the molten glass is formed into objects and cooled to become rigid glass.
4. Annealing: the glass is heated again and allowed to cool slowly.

Why is glass annealed?

• Removes stress: slow cooling takes out the strain left inside the glass.
• Reduces breakage: annealed glass is less likely to crack or shatter easily.

What are the properties of glass?

Glass is brittle, transparent and resistant to corrosion.

1. Brittle: it breaks easily when dropped or hit.
2. Transparent: it allows light to pass through.
3. Resistant to corrosion: it does not rust and is not easily attacked by chemicals.
4. Hard: it is not easily scratched.
5. Electrical insulator: it does not conduct electricity.
6. Can be shaped when molten: hot glass can be formed into many shapes.

Examples of glass products

• Cups and bottles: used for drinks and food storage.
• Mirrors: glass with a shiny coating at the back.
• Glass tubes: used in laboratories.
• Electric bulbs: glass covers that protect the lighting part.
• Glass windows and doors: let light into buildings.
• Eyeglasses and lenses: help people see clearly.

Evaluation

1. What is a ceramic?
2. List five properties of ceramics.
3. What are the raw materials for making glass?
4. List three properties of glass.
5. Why is glass annealed?

Assignment

In your notebook, list the four stages of making glass in order and give five examples of glass products.