Today’s objectives-Powder and advanced
ceramics processing techniques
2. Powder processing
3. Other processing Techniques
b. Bio mimetic
c. Single crystals
d. Thermal oxidation
Know the basic concepts
e. Sputtering behind fabrication and use
f. PLD of three of these
• Prepare by mixing clay and lime (CaO)
• Calcinate at 1400C
• Grind into a fine powder.
– Higher surface area
– More reactive
• Add water=paste->sets and hardens->structural element
(especially in compression).
• With cements, the bonding process is a chemical hydration
reaction between the water that has been added and the
various cement constituents, not a drying event.
2Ca2 SiO4 5H 2O 3CaO * 2 SiO2 * 4 H 2O Ca OH 2 58 .7kJ
• The cement particles are bonded together by reactions that
occur at the particle surfaces. Smaller particles=more surface
• The reaction is complicated, is exothermic, and also
exhibits swings in ph as a function of time.
•During the original moon shots, NASA tested for and found
that it would be possible to make portland cement on the
moon using the particles there. Construction! But, where do
we get the water?
•If lime could be mined and refined, then it has a cementious
reaction that doesn’t require water, but rather CO2.
--grind to produce ceramic and/or glass particles
--inject into mold
--press to improve density by better packing (ideally close packed)
--sinter at elevated temperature to further densify by shrinking pores
• Sintering: useful for both clay and non-clay compositions.
• Compare powder processing to working with clay:
•Has to be dried
•No need to press
• Pressing minimizes pores
– Hydrostatic (all axes)
• Either can be at elevated temperatures
– “H Uniaxial P, HUP” or “HIsostaticP, HIP”
– Improve density without growing grain
– Usually only for high temperature materials
Stages of sintering
– Thus, if atoms are given enough energy to
move (i.e. during sintering), then grain
boundaries grow and pores shrink.
– Eventually, pores are pseudo spherical and
grain boundaries exist at every initial particle
junction. Why? Is this important?
– Process is atomic diffusion, not liquid flow.
– Introducing glass formers (TiO2, Bi2O3) will
improve pore reduction and boundary growth
as atomic diffusion is faster in the liquid, and
the liquid flows. Now we are combining
Y 2 o
t Somewhat like clays, but little if any glass.
Powder processing microstructure
• Some pores remain
• Many particles have fused.
• Pores are obvious crack propagation points (cracks)
• Ball bearings of SiN instead of steel
– Higher elastic modulus (320 instead of 200) so less deformation
– Better compressive strength (3000 MPa vs 900 MPa) so less wear
– Corrosion resistant
• Piezoelectrics (sonar, telephone vibration, inkjet printer
• Dielectrics (cell phones)
• Ceramic armor
• Used in:
– Electronics (cell phones)
– Suntan lotion
– Surge protectors
• 4 Million tons worldwide–11000 tons/day (=96% of total Ti use)
• 68% of worldwide TiO2 production capacity is in the hands of
five US-based companies: Dupont (1 million metric tons
annually), Millennium Chemicals, Huntsman Tioxide, Kerr-
McGee Chemical and Kronos Inc. http://www.roskill.com/reports/titaniummap
TiO2- from WikiPedia (!)
• As a pigment of high refringence Titanium dioxide is the most widely
used white pigment because of its brightness and very high refractive
index (n=2.4), in which it is surpassed only by a few other materials.
When deposited as a thin film, its refractive index and color make it an
excellent reflective optical coating for dielectric mirrors. TiO2 is also an
effective opacifier in powder form, where it is employed as a pigment to
provide whiteness and opacity to products such as paints, coatings,
plastics, papers, inks, foods, and most toothpastes. Used as a white
food coloring, it has E number E171. In cosmetic and skin care
products, titanium dioxide is used both as a pigment and a thickener. It
is also used as a tattoo pigment and styptic pencils.
• This pigment is used extensively in plastics and other applications for
its UV resistant properties where it acts as a UV reflector.
• In ceramic glazes titanium dioxide acts as an opacifier and seeds
crystal formation. In almost every sunblock with a physical blocker,
titanium dioxide is found both because of its refractive index and its
resistance to discoloration under ultraviolet light. This advantage
enhances its stability and ability to protect the skin from ultraviolet light.
• Want a high temperature before even
partial melting (liquid composition=0).
Need chemical insensitivity.
• Improve properties further by including
– less thermal expansion/contraction upon
– Resistance to thermal shock
– Increased insulation
• But, some disadvantages:
– Worse resistance to
– Weaker load bearing
capability (probably not a
problem since refractories
can be used to protect load-
– Some liquid is ok at max T.
• Prepare a liquid “sol” that is mostly colloidal
– Inorganic metal salts or metal
alkoxides (metal organics)
– Hydrolize and polymerize to form
a colloidal suspension (“sol”):
like glass, but not viscous & in solution
– Spray, dip coat, or spin coat
onto a substrate
– The cast sol now forms a “gel”
– Further drying converts to a loose ceramic
– Anneal to burn off the polymer
– Anneal at higher temperatures to densify
• This is a primary process for preparing small, pure
particles of most performance ceramics.
• If the sol is cast before the gel has set, then a porous,
low density material can be made (“aerogel”).
– Excellent thermal insulator
– Lousy mechanical strength
• Fibers can be drawn from the sol as well under
certain conditions. Thickness=C/speed½
• Annealing at lower temperatures allows porous
• Snails, seashells, krill, etc, have evolved methods for
fabricating phenomenally complicated ceramic structures
(mostly silica and calcia), usually at ambient conditions.
• Research continues into trying to understand how this is
done, and especially how we can mimic it.
– Proteins have been harvested, and even improved, for
low temperature fabrication of SiOx.
• The protein R5 is especially good at converting Si and O from
solution into crystalline SiOx.
• Applying the protein to a dental surface and exposing to a Si
rich solution offers the possibility of low temperature SiOx
deposition and thus simple tooth regeneration.
– Opposite halves of DNA base pairs are attached to a
substrate and a ceramic particle, respectively. The
particles can then be selectively bound to a surface in a
cost effective aqueous procedure, avoiding the
complexity of high energy and vacuum based deposition
techniques like CVD, PLD, and sputtering.
– Spiders are great at forming SiOx containing fibers.
Harvest these for mechanical or fiber-optic applications.
Single Crystal processing
• Czochralski growth
– Melt starting materials in a crucible
– Introduce a seed crystal
– Rotate and slowly extract the seed crystal
– Large diameter, dislocation free
Most common method for semiconductor substrates, but also optical materials.
Single crystal from polycrystalline bulk.
• Float zone
– Carrier concentration can be improved three orders of
magnitude over CZ methods.
Polycrystalline Ultra pure
raw materials single crystal
• Cements- strength and temperature vs time
• Powder processing-distinction between clays and
• Pressing-types and advantages
• Concepts and applications of three of the following
– Bio mimetic
– Single crystals Know the basic concepts
– Thermal oxidation behind fabrication and use
– Sputtering of three of these
Reading for next class
Optical Fiber processing
Chapter sections: Handout