ENGI1002 - Topic 5

What is a ceramic?

Ceramics are inorganic and non-metallic, usually a mixture of a metal and a non-metal element.

What do ionic crystals need?

• Charge neutrality

• Physical stability

What are some ceramic properties?

• Hard

• Insulating

• Stable at high temperatures

• Chemically inert

When do ceramics perform best?

Ceramics perform best in compression as the cracks get pushed back together.

What are the ceramic point defects?

• Frenkel

• Schottky

What are Frenkel defects?

A cation leaves its site to an interstitial.

What is a Schottky defect?

A cation and anion vacancy pair.

How are crystalline ceramics bonded?

Crystalline ceramics are ionically or covalently bonded.

What hardens ceramics?

Strong bonding makes ceramics hard.

Why do ceramics fracture before any plastic deformation?

Ceramics are brittle and have little plastic deformation before fracture.

Why are ceramics brittle?

Ceramics are brittle because slip is blocked due to electrostatic repulsion.

How are mechanical properties of ceramics measured?

Mechanical properties in ceramics are usually measured in bending.

What is concrete?

Concrete = cement + aggregate. Cement hydrates to form C-S-H which binds it.

What is glass?

Glass is a network former. Network modifiers break bridges, lowering melting point and viscosity.

What is graphite?

Graphite is a hexagonal close packed structure.

Graphite layer structure?

• Covalent bonds within sheets.

• Weak Van der Waals forces between layers.

What is graphene?

• Single sheet

• Very stiff and strong

• High carrier mobility