1. Ceramics, Glass and Carbon.
CHE 333 Class 24
Ceramics, Glass and Carbon.

2. Glass Silica Tetrehedra
Tetrahedral Structure SiO44-
Si – O ionic ratio is 0.29 tetra CN
Unit cell of silicates.
High Crystobalite 1470 to 1710C

3. Soda Glass Another structure using silica tetrahedron
as a basic building block. However there is
no three dimensional regularity to the
structure, so it is regarded as “Amorphous”
It is the structure associated with glass.

4. Silicates Kaolinite clay structure. Secondary (Si2O5)2- silicate
van der Waals bonds hold sheets
together unless water is present.
(Si2O5)2- silicate

5. Ceramic Phase Diagrams
Applications of “White ware” as
a function of composition.

6. Powder Processing First step is milling the ceramic to form a
particular size range, followed by sizing.
Second stage may involve adding a lubricant
and binders to permit particles to flow and
bond together during later processing.
Third stage involves compacting the powders
in a mold which is the final shape of the
part. It is usually oversize.
A “green” compact is formed after these
operations.

7. Particle Sintering The green compact has little structural strength
and is “Sintered” to increase the density of the
part and increase its strength. Sintering is
conducted at temperatures above 0.66Tm, as
diffusion is a major part of the process.
A “neck” is formed between adjacent
particles by surface diffusion. This is a new
chemical bond. The porosity in the part
decreases, so the external dimensions of
the part decrease. The higher the sintering
temperature and the longer the time, the
denser the part and the smaller the voids.

8. Pore Density V Sintering Time

9. Ceramic Properties Strength depends upon pore volume
Refractoreis because of low thermal
conductivities and high melting points

10. Ceramic Slip Casting

11. Glass Residual Stress

12. Carbon Diamond structure drills, Rare, expensive Graphite structure
Lubricants, pencils, copiers, tyres.
Common, cheap, good conductor

13. “New” Carbon Structures
Fullerenes consist of hexagonal and pentagonal
arrangements of carbon atoms.
Carbon nanotubes can be produced more expensive
than diamond, very strong “ Nano”.
Rope to moon possible, filters, fuel cell electrodes