Ceramics

Question 1

Stone

Answer 1

Typically, there are three categories of rock; sedimentary rock which form by the build up of sediment over millions of years, igneous rocks which form by the cooling of lava from volcanic activity, and metamorphic rock, which was either metamorphic or sedimentary rock that has been metamorphosed into another form because of heat and pressure. Sedimentary rocks are typically ‘grainy’ in appearance, whereas igneous and metamorphic rocks are more cohesive and dense.

All stone exhibits similar properties; it is weak in tension, strong in compression and low in toughness. This brittleness makes it easy to chisel stone, but also necessitates the use of structures loaded in compression rather than tension.

Question 2

Glass

Answer 2

Glass is an amorphous solid; that is, it does not have a regular crystalline pattern like metals. In essence, it is a very viscous liquid. This structural feature is what makes glass transparent, however it is also what makes glass extremely brittle as the planes of atoms cannot slip past one another (i.e bend). Glass has low toughness and is weak in tension.

Common window glass is a mixture of silica, soda and lime. The soda inhibits crystallisation and the lime makes the glass non-water soluble. These glasses soften at above 850C and are relatively cheap to make.

Toughened glass, the successor to the former material, is a heat treated material where the outer surfaces are cooled quicker than the insides, so that as the interior cools, it pulls the exterior into a state of tension. This effectively acts as a barrier which shock loading must first overcome before the glass can shatter.

Question 3

Cement

Answer 3

Cement is a ceramic material produced when alumina, soda and lime are reacted at high temperatures. Like other ceramics it is strong in compression but weak in tension, exhibiting low toughness. It is often used in composites such as concrete and asphalt (not to be confused with bitumen).

Question 4

Bricks

Answer 4

Bricks are traditionally made of clay, but nowadays may be made from concrete. Very early construction in Sydney originally used sandstone blocks cut from quarries, but it is much more cost effective to manufacture bricks from clay. Bricks may be pressed or extruded to shape, recognised by being solid of having small holes in them respectively. Bricks are still used commonly in construction, with many large bricks walls now employing use of “besser” blocks, which are large concrete blocks with two hollow channels in them.