Ceramics

Question 1

What is a ceramic?

Answer 1

Defined as an inorganic solid with ionic and/or covalent bonding.

Question 2

What are AX compounds?

Answer 2

A material that has a 1:1 ratio of cations and anions. Different AX compounds can have different crystal structures (geometry is determined by the radii of the atoms/ions involved).

Question 3

What is one type of AX structure?

Answer 3

Cesium chloride, is similar to a BCC structure except that the centre ion is a Cesium (draw it).

Question 4

What are silicates mainly composed of?

Answer 4

Composed of Si and O.

Question 5

What do we use to characterise the structures of different silicates?

Answer 5

We use various arrangements of SiO4^4- tetrahedra.

Question 6

What are the different crystallographic forms of crystalline silica?

Answer 6

Quartz, Cristobalite and Tridymite.

Question 7

How is silica glass formed?

Answer 7

One way is when silica isn’t given enough time for the tetrahedra to arrange itself into a regular repeating pattern.

Question 8

What are the general types of silicates?

Answer 8

Silica, Simple and layered

Question 9

What is a simple silicate?

Answer 9

When there is a single tetrahedron in isolation.

Question 10

Why do ionic crystalline ceramics show brittle fracture?

Answer 10

The main reason is electrostatic repulsion, if we were to somehow get plastic deformation we would get like charges next to each other and since like charges repel there is too much energy causing it to fracture. Also, slip is less likely to occur because ceramics have very few close-packed planes

Question 11

Why do covalent bonded crystalline ceramics show brittle fracture?

Answer 11

The main reason is that covalent bonds are directional, so when trying to deform these structure the bonds may not have their preferred bond angles lined up. Also, slip is less likely to occur because ceramics have very few close-packed planes

Question 12

What is the main structural difference between ceramic and metal crystal structures?

Answer 12

For ceramic crystal structures, we have 2 or more atoms or ions represented in the structure meanwhile for metallic crystal structures we only ever represent one type of atom even if it’s an alloy.

Question 13

What are the main benefits of glass?

Answer 13

It’s optical transparency and the relative ease of fabrication

Question 14

What are some types of glass and their main properties?

Answer 14

Vitreous glass - High silica purity, surface temperature and chemical durability
Soda-lime glass - Low melting/working points, cheap, easy to add additives
Pyrex/borosilicate glass - higher thermal shock, chemical durability, low coefficient of thermal expansion.

Question 15

What is the difference in the solidification of crystalline material and non-crystalline materials?

Answer 15

When a crystalline material cools there is a specific point where the material melts. But for a non-crystalline material, there is a point where the curve slope changes which is the glass transition temperature.

Question 16

What are the sections on a temperature viscosity graph and their general characteristics?

Answer 16

1) Strain point, the material will break if an attempt is made to break it.
2) Annealing point, sufficiently rapid atomic diffusion to remove residual stresses
3) Softening point, max temp a glass can be handled without distortion
4) Working point, easy to deform/ work
5) Melting point, Material considered a liquid

Question 17

What are the shape-forming techniques?

Answer 17

1) Pressing, glass goes into the female mould and then a male mould is pressed into it to form the glass to the desired shape.
2) Blowing, a gob of glass is formed into a temporary shape, and then compressed air is forced into the shape that conforms the glass to the mould.
3) Drawing, Used to form constant cross sections such as sheets and rods

Question 18

What are some heat treatments of glass?

Answer 18

1) Annealing reduces residual stress by heating up to the annealing point and then slowly cooling it.
2) Tempering increases the strength of glass by inducing compressive residual surface stresses by heating above tg and then accelerated cooling

Question 19

What happens when water is added to clay?

Answer 19

The water molecules form a thin film around the clay particles and fit between the layered sheets.

Question 19

What is hydroplasticity

Answer 19

The ease of forming is due to clay (when mixed with an appropriate amount of water) forming a plastic mass.

Question 20

What happens to an item once it has been shaped via hydroplasticity?

Answer 20

The item will be dried which will shrink the item because of the evaporation of water and then fired which will also shrink the item due to the particles being drawn together.

Question 21

Why can’t the formed item be fired straight away?

Answer 21

Because the water particles will evaporate into steam inside the item causing internal pressure causing it to explode.

Question 22

Why do surface cracks form when the item is dried too fast?

Answer 22

The water leaves the surface first, causing the surface to contract, but on the inside of the item, the water hasn’t left yet, causing strain on the item.

Question 23

What is Vitrification?

Answer 23

One part of the clay becomes liquid and flows around the solid parts acting like glue keeping them all together.

Question 24

What is bisqueware?

Answer 24

After the item is first fired it tends to be reasonably strong and durable but not waterproof, the item at this state is termed bisqueware.

Question 25

What is glazing?

Answer 25

The purpose of glazing is to make the item waterproof then the item is fired again to form a continuous layer on the item.