Ceramics Flashcards
General Properties of Ceramics
high compressive strength, relatively low tensile strength, brittle, low toughness, high hardness, good thermal + electrical insulator,
resistant to environmental conditions such as oxidation, relatively low cost.
Give examples of ceramic use (general uses)
clay products, whitewares (decorative), refractories, glass and abrasives (tough materials used for cutting grinding etc)
advantages of brick over stone
lower application costs and relatively low skill required
What ceramic products are made in a similar way to 2000 years ago
Pottery, porcelain, tiles, bricks and refractory bricks
what are the six categories of clay used in industry
brick, bentonite, common, fire, Fuller’s Earth, Kaolin
how does water make clay slippery
The polar water molecules come between layers of clay
What is sintering
the process of forming a solid mass of material through heat and pressure without melting to the point of liquefaction. Used to fuse the separate ceramic powder particles together.
What are typical sintering temperatures
850 for tiles to 1650 for engineering ceramics such as silicon nitride, silicon carbide, zirconium oxide
What form of sintering forms good high temperatures properties and conversely bad high temperature properties
liquid phase may cool to glass which has bad properties
liquid phase may crystallise which has good properties.
What phases do most ceramics consist of
glassy phases, crystalline phases and lots of holes
What does etching a ceramic mean
Polish the surface then proceed to heat in a furnace at a high temperature
What drives sintering
surface area. By heating up the particles, the surface area is reduced
what is liquid phase sintering
A technique of sintering that utilises a liquid to accelerate the process since transport through liquid is faster than through solid and capillary forces of liquids can rapidly rearrange particles and draw them together.
What can be a weakness in the microstructure of ceramic
Grain boundaries (the boundary or gap between two crystal grains)
What is a dislocation and what is special about them in ceramics
An extra plane of atoms which is an irregularity in the structure. They can generally move through the structure in metals (by breaking and reforming bonds) , allowing them to be malleable. This is only possible due to the nature of metallic bonding. Ceramics’ dislocations cannot move so there is no way to relieve stress. This means cracks will continue to propagate.
