Ceramics

What are ceramics in the context of materials science?

Inorganic, non-metallic compounds formed between metallic and non-metallic elements, typically with ionic or ionic-covalent bonds.

What are common examples of ceramics?

Aluminium oxide (alumina), zirconium oxide (zirconia), silicon dioxide (quartz).

What is the crystal structure requirement for ceramics?

Must be electrically neutral, with arrangement depending on ionic radii and charges of cations/anions.

What are typical crystal structure positions in ceramics?

Tetrahedral or octahedral positions.

What are silicate ceramics primarily composed of?

Silicon and oxygen, the two most abundant elements in Earth's crust.

What is the structure of silica and its melting temperature?

Silica has atoms not closely packed (low density) but strong Si-O bonds; melting temperature ~1710°C.

What are layered silicates?

Sheet structures with net negative charge balanced by cation layers; found in clays and minerals.

What are examples of carbon ceramics?

Amorphous carbon (carbon black), diamond, graphite, carbon nanotubes, graphene.

What is meant by polymorphic forms in ceramics?

Different crystal structures of the same element/material that result in different properties.

What is an anion vacancy?

A missing negatively charged ion in the ceramic lattice.

What is a cation vacancy?

A missing positively charged ion in the ceramic lattice.

What is a Frenkel defect?

A cation displaced to an interstitial site, maintaining charge balance.

What is a Schottky defect?

A paired absence of a cation and anion to maintain neutrality.

Do ceramics undergo plastic deformation before fracture?

Almost never; they fracture before significant plastic deformation under tensile load.

Why are tensile tests difficult for ceramics?

Difficult to prepare required geometry, grip without fracturing, and they fail at ~0.1% strain.

What test is used instead of tensile tests for ceramics?

Three-point bending test to measure flexural strength (modulus of rupture).

Why can three-point bending measure tensile properties of ceramics?

Ceramic compressive strength is much greater than tensile strength, so tensile failure occurs first.

How does porosity affect ceramics' properties?

Increased porosity decreases both elastic modulus and flexural strength.

Why are ceramics widely used in orthopaedics?

They have high strength, wear resistance, and biocompatibility for bone-contact applications.

What is calcium phosphate (hydroxyapatite) and its role in bone?

Main mineral in bone, osteoconductive, osteointegrative, and osteoinductive, promoting bone growth and integration.

What is alumina and why is it used in implants?

Aluminium oxide; high strength, fatigue resistance, inert under physiological conditions, and high surface wettability.

What is stress shielding in orthopaedic implants?

Loss of bone density when an implant takes most of the load, reducing mechanical stimulus to bone cells.

Why might ceramic-on-ceramic hip implants squeak?

Surface interaction between two hard ceramic components during movement can generate noise.