Structure of ceramics Nur Asikin Binti Mohd Nazri Nor Syalmira Binti Amir Nur Afifah Binti Sarkhan Nur Afifah Binti Mohd Rafi Siti Sholihah Binti Che Ani Raudhah Binti Mohd Salleh

Ceramic crystal structures are often more complex since they are composed of at least two different elements bonding: Can be ionic and/or covalent in character The degree of ionic character depends on the electronegativity of the atoms

Degree of ionic character may be large or small SiC: small CaF 2 : large

Factors that determine crystal structure The crystal structure is influenced by: 1) relative sizes of the ions involved stable stable unstable

2) magnitude of the electrical charge of cation and anion. for most ceramics the bonding is predominantly ionic composed of electrically charged ions: “cations” and “anions”.

The crystal must be electronically neutral. The chemical formula reflects this charge balance. Anions are larger than cations, hence the <1. Each ion wants to have as many of the other ions as nearest neighbors. r cation r anion

The stability of the crystal structure is influenced by the ion contact The most common coordination numbers for ceramics are 4, 6, and 8.

Ceramic crystal structures A number of ceramic structures may be considered in terms of close-packed plane of ions, as well as unit cells. close-packed planes are composed of large anions. Two types of interstitials: 1) tetrahedral: coordination number 4 2) octahedral: coordination number 6

ceramic crystal structures depend on 1)the stacking of the close-packed anion layers (FCC and HCP arrangement possible). 2) way in which interstitial sites are filled with cations.

Magnetic ceramics (ferrites) have a spinel- like structure. Magnetic characteristics affected by the occupancy of the interstitial positions.

MECHANICAL PROPERTIES Very brittle in tension ( brittle fracture limited energy absorption) Limited load carrying capacity The strength of ceramic materials is strongly dependent on the processing (because of introduction of strength limiting flaws) Ceramics are usually much stronger in compression than in tension.

Hard (wear resistant) Resistant to plastic deformation Resistant to high temperatures Good corrosion resistance Low thermal conductivity Low electrical conductivity

APPLICATIONS Aerospace: space shuttle tiles, thermal barriers, high temperature glass windows, fuel cells

Industrial Applications: Aerospace Coating of metal heat engine parts ⇒ improved wear &/or high temperature damage. Their low densities ⇒ lighter turbine blades vs superalloys Materials considered: Si3N4, SiC and ZrO2 Draw back: disposition to brittle & catastrophic failure. helicopter gas turbine

Consumer Uses: glassware, windows, pottery, Corning¨ ware, magnets, dinnerware, ceramic tiles, lenses, home electronics, microwave transducers

Automotive: catalytic converters, ceramic filters, airbag sensors, ceramic rotors, valves, spark plugs, pressure sensors, thermistors, vibration sensors, oxygen sensors, safety glass windshields, piston rings

Industrial Applications: Automotive Spark plugs, water pump seals,catalytic converter. Heat engine: 1)Higher operating temperatures ⇒ Better fuel efficiency 2)Lower frictional forces & ability to operate with no cooling system 3) Excellent wear & corrosion resistance 4) Lower densities ⇒ Decreased engine weight

Medical (Bioceramics): orthopedic joint replacement, prosthesis, dental restoration, bone implants

Military: structural components for ground, air and naval vehicles, missiles, sensors

Computers: insulators, resistors, superconductors, capacitors, ferroelectric components, microelectronic packaging

Other Industries: bricks, cement, membranes and filters, lab equipment

Communications: fiber optic/laser communications, TV and radio components, microphones