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Ceramics & glasses - Coggle Diagram
Ceramics & glasses
Properties & Bonding
brittle
glassy
non-conducting (insulator)
elastic
ionic bonding
high moduli (typically)
brittle fracture strength when in tension
brittle crushing strength when in compression, 10x larger
low tolerance for stress concentrations or high contact stresses
abrasion resistant
high temperature capabilities
corrosion resistant
inorganic and non-metallic
Material groups
structural
high temperature applications
Si3N4
SiAlON
Al2O3
ZrO2
Electrical
magnetic and electronic applications
PZT
BaTiO3
Bioceramics
medical applciations
Al2O3
Hydroxyapatite
Glass
Processing
Milling
raw powders milled in distilled water
Drying and granulation
dry the slurry, crush any agglomerates and sieve powder
Compaction
press the materials
Sintering
heat the compact to cause densification
to be effective want a very high surface area for high surface energy
pore removed by growth together with strong bonding between adjacent particles
Needs:
mechanism of transport, energy source to activate and sustain material transport process
Mechanisms:
vapour phase
movement from positive radius of curvature to negative radius with lower vapour pressure
no shrinkage or densification
smaller particles = faster sintering
solid state
driven by reduction of free energy in a system
delta
L/L_o = ((K x
gamma
x
alpha
^3 x D x T) / (k x T x d^n))^m
gamma
= surface energy,
alpha
^3 = atomic volume of the difusing vacancy, D = self diffusion coefficient, k = boltzmann constant, T = temperature, d = particle diameter, t = time, K = geometric constant, n(~3) & m(~0.4) = power relationships
liquid phase
reactive liquid
Injection moulding
ceramic powder mixed with organic binder
mixture injected using a standard injection moulding machine
Binder removed by thermal baking or through solvents
can then be sintered
Additives
selection depends on a number of varaiable
green strength required
ease of machining
compatibility with ceramic powder
nature of consolidation process
Some are not soluble in water and don't provide benefit for slip casting. But are excellent for warm mixing to prepare powder for injection moulding
gums
waxes
thermoplastic resin
thermosetting resin
Organic binders
can be burned off at low temperature and result in minimal contamination
Inorganic binders
become part of the composition
lesson E-ceramics for list of types of addatives and what they are used for
Raw material selection
dependant on the properties required in the finished component
alloying makes ceramics weaker so avoid
dependant properties
purity
influences:
strength, stress, rupture life and oxidation resistance
Effect:
dependant on chemistry of ceramic and impurity, its distribution and the service conditions of the component
Key for:
electrical, magnetic and optical properties
particle size distribution
uniform particle size does not produce good packing, still results in over 30% void spaces
for maximum packing multiple particle sizes need to be included
adding particles of size equivalent to largest voids reduces pore volume to 26%, a 3rd smaller particle size can reduce to 23%
low porosity and fine grain size:
High strength
large particle or high porosity:
low thermal conductivity and high thermal shock resistance
reactivity
densification of compact powder at high temp is driven by change in surface free energy
small particles with high surface area have high surface area free energy and thus have string thermodynamic drive to decrease surface area by bonding
determines:
temperature and time at temperature necessary for sintering
objective of consolidation step is to achieve maximum particle packing and uniformity