Ceramics- Synthesis of Powders

Question 1

Industrial minerals

Answer 1

85-98% purity. Mainly used for construction materials, refractories, whitewares, industrial chemicals.
Examples include, ball clay, kaolin, glass sand, bauxite

Question 2

Benefication

Answer 2

Processes to improve the economic value (benefits) of the minerals suitable for usage

Question 3

Methods of benefication

Answer 3

Crushing, grinding.
Settling, floatation, segregation.
Separation of magnetic minerals.
Filtration of soluble impurities.
Centrifugation.
Drying.
Sometimes have to go back and forth between mechanisms in this order

Question 4

Industrial inorganic chemicals

Answer 4

98-99.9% purity. Used for electrical, magnetic, optical, mechanical, nuclear, chemical, biological applications.
Examples are alumina, magnesia, silicon carbide, ferrite, zirconia

Question 5

Bayer process

Answer 5

Process to refine alumina from natural mineral bauxite.
Crushing, grinding
Pressure vessel at 180°C and add NaOH
Makes Na[Al(OH)4] solution (red mud)
Crystallisation adding water and Al(OH)3
Rotary kiln to Al2O3

Question 6

Mechanical synthesis

Answer 6

Small particles produced by reducing the size of larger ones by mechanical force (comminution, crushing, grinding, milling)

Question 7

How do ball mills work?

Answer 7

Smaller balls in the mill (rotating cylinder) have higher speed and KE than larger balls which have lower speed and more potential energy. They hit and break each other

Question 8

What happens as particles get finer?

Answer 8

Tendency for agglomeration. Less occurrence of comminution. Less probability of a flaw.

Question 9

Particle size vs grinding hours for wet and dry milking

Answer 9

Dry has strep initial decrease then curves to level off more. Wet milking has less steep decrease initially but delayed curve and levelling off so crosses dry line. Scale of graph up to about 80hrs

Question 10

3 types of chemical synthesis

Answer 10

Gas phase reaction
Liquid phase reaction
Solid phase reaction

Question 11

Types of gas phase reaction

Answer 11

Gas/gas, gas/liquid, gas/solid

Question 12

Liquid phase reactions

Answer 12

Precipitation, evaporation, gel route

Question 13

Solid phase reactions

Answer 13

Thermal decomposition, chemical reaction

Question 14

Example gas phase reaction route

Answer 14

Gas species forms nuclei which grow into particles or can create bulk crystals. Easy to obtain very fine powder and less agglomeration due to less concentration in gas

Question 15

Gas phase reaction particle diameter formula

Answer 15

D=(6C0M/πNρ)^1/3
C0 is element concentration in gas
M is molecular weight of product
N is number of particles
ρ is density of product

Question 16

How can a liquid phase reaction work?

Answer 16

Homogeneous nucleation when solute concentration reaches a certain level. Followed by growth by diffusion

Question 17

LaMer diagram

Answer 17

Solute concentration vs time. Steep incline to peak just after concentration where homogeneous nucleation starts. Curve back down below this concentration into growth by diffusion region and levels off at solubility concentration

Question 18

Solid phase reaction stages

Answer 18

Initial powder. Nucleation. Grain growth. Either sintering into joined grains or further grain growth. Smaller initial powder and homogeneous mixing may lead to reduction of heating time and temperature needed

Question 19

Graph for general feature of decomposition

Answer 19

α vs time. Slow increase from origin, then fast increase between nucleation and grain growth stages, then slower increase for sintering and further growth.
α=ΔW/ΔWmax goes 0 to 1

Question 20

Avrami-Erofeyve equation for solid decomposition

Answer 20

α=1-exp(-kt^n)

Question 21

Prout-Tompkikns equation for decomposition of solids

Answer 21

lnα/(1-α)=kt

Question 22

Methods for measuring powder and their range (μm)

Answer 22

Sieving: 20-10000
Sedimentation: 0.1-100
Coulter counter: 0.5-400
Optical microscopy: >1
SEM: >0.1
TEM: >0.001
X-ray line broadening: <0.1

Question 23

What do sedimentation and coulter counter methods do?

Answer 23

Detects change in electrical conductance of a fluid containing small particles

Question 24

How does X-ray line broadening work and formula?

Answer 24

As crystal size decreases, the width of the diffraction peak increases.
D=Kλ/βcosθ
D is crystal size
K is constant
λ is x-ray wavelength
β is broadening as a full width at half maximum
θ is diffraction angle for the peak