Ceramics- Synthesis of Powders Flashcards
Industrial minerals
85-98% purity. Mainly used for construction materials, refractories, whitewares, industrial chemicals.
Examples include, ball clay, kaolin, glass sand, bauxite
Benefication
Processes to improve the economic value (benefits) of the minerals suitable for usage
Methods of benefication
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
Industrial inorganic chemicals
98-99.9% purity. Used for electrical, magnetic, optical, mechanical, nuclear, chemical, biological applications.
Examples are alumina, magnesia, silicon carbide, ferrite, zirconia
Bayer process
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
Mechanical synthesis
Small particles produced by reducing the size of larger ones by mechanical force (comminution, crushing, grinding, milling)
How do ball mills work?
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
What happens as particles get finer?
Tendency for agglomeration. Less occurrence of comminution. Less probability of a flaw.
Particle size vs grinding hours for wet and dry milking
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
3 types of chemical synthesis
Gas phase reaction
Liquid phase reaction
Solid phase reaction
Types of gas phase reaction
Gas/gas, gas/liquid, gas/solid
Liquid phase reactions
Precipitation, evaporation, gel route
Solid phase reactions
Thermal decomposition, chemical reaction
Example gas phase reaction route
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
Gas phase reaction particle diameter formula
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
How can a liquid phase reaction work?
Homogeneous nucleation when solute concentration reaches a certain level. Followed by growth by diffusion
LaMer diagram
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
Solid phase reaction stages
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
Graph for general feature of decomposition
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
Avrami-Erofeyve equation for solid decomposition
α=1-exp(-kt^n)
Prout-Tompkikns equation for decomposition of solids
lnα/(1-α)=kt
Methods for measuring powder and their range (μm)
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
What do sedimentation and coulter counter methods do?
Detects change in electrical conductance of a fluid containing small particles
How does X-ray line broadening work and formula?
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
