The document discusses various ceramic shaping methods including:
1. Pressure fabrication and conventional pressing, extrusion, jiggering, and plastic forming for forming ceramics.
2. Slip casting techniques including conventional slip casting, pressure casting, and tape casting.
3. The document provides details on viscosity and rheology characteristics important for different ceramic forming processes.
1. Forming : Nomenclature
1. Pressure Fabrication Conventional pressing
Isostatic pressing
2. Plastic Forming Extrusion
Jiggering
Plastic forming
3. Slip Casting Conventional slip casting
Pressure casting
Tape casting
From D. J. Shanefield, “Organic Additives and Ceramic Processing,” Kluwer Academic Press
Advanced Electronic Ceramics I (2004)
Ceramic Shaping Methods
Shapes Viscosity Fluidization Solidification Compaction
Process
Yes
Dry Mostly- Very None Plastic Flow
Pressing uniform high of Binder
cross section
No
Injection Almost High Melted Cooling
molding any binder
Extrusion Uniform High Water Plastic Flow No
cross section
Roll Thin High Water Plastic Flow Yes
Compaction Sheets
No
Tape Thin Medium Organic Evaporation
Casting Sheets or water
Pressure Various Medium Water Wicking and/or No
Casting Plastic Flow
Slip Various Low Water Wicking No
Casting
From D. J. Shanefield, “Organic Additives and Ceramic Processing,” Kluwer Academic Press
Advanced Electronic Ceramics I (2004)
2. Schematic of Shaping 1
From D. J. Shanefield, “Organic Additives and Ceramic Processing,” Kluwer Academic Press
Advanced Electronic Ceramics I (2004)
Schematic of Shaping 2
porous
polymer
Slip casting of wet slip
From D. J. Shanefield, “Organic Additives and Ceramic Processing,” Kluwer Academic Press
Advanced Electronic Ceramics I (2004)
3. Viscosity: the door to the Rheology
y
A F
F dv
=η
A dy
v=0
Velocity gradient
x
(Shear rate)
z Shear Stress
Advanced Electronic Ceramics I (2004)
Pseudoplastic : Shear thinning
The shear rate increases
abruptly above certain
stress level
viscosity
- called as “shear thinning”
stress
- useful in paint industry
Pseudoplastic
: Thin film spread well along
the vertical wall
Apparent
while painting (thinned state)
viscosity
: do not drip or streak
Shear rate
during the drying period
- Useful for screen printing of
Another example?
thick film ink (many thick film
(mustard, catsup, salad dressing)
pastes wrongly described as
thixotropic)
From D. J. Shanefield, “Organic Additives and Ceramic Processing,” Kluwer Academic Press
Advanced Electronic Ceramics I (2004)
4. Plastic : Bingham
♦Desirable pattern for many ceramic
Yield
processes
Point
♦material flow(shear) while being
stress
molded at the high force(stress)
♦do not flow(shear) at the waiting
Plastic before firing(only gravity plays the
(Bingham) role of the force)
Shear rate
From D. J. Shanefield, “Organic Additives and Ceramic Processing,” Kluwer Academic Press
Advanced Electronic Ceramics I (2004)
Linear : Newtonian
♦ desirable for the slip casting
♦ the slurry for the slip casting should
easily fill the mold (like water) and
stress
prevent the trapping of air bubbles
♦ help prevent sudden slumping
caused by thixotropy during handling
Linear
and transport of the cast piece
(Newtonian)
♦ good for uniform casting rate
Shear rate
Advanced Electronic Ceramics I (2004)
5. Dilatant : Shear thicknening
♦ materials becomes too stiff to flow
smoothly at high shear rate
- called as ‘shear thickening’
♦can crack or even explode a die or mold
stress
during extrusion
♦occurs at very high solid loading
Dilatant - horizontal shear of closely packed
(Shear thickening) spheres requires the top layer to ride up
over the bottom one (dilating the
Shear rate
volume)
- lowering of solid loading, use of
dispersent can avoid or reduce the
dilatancy
From D. J. Shanefield, “Organic Additives and Ceramic Processing,” Kluwer Academic Press
Advanced Electronic Ceramics I (2004)
Yield Dilatant
♦ shear thinning at low shear
rate and shear thickening at
stress
high shear rate
♦ sometimes observed in clay
Yield slip
Dilatant
Shear rate
From D. J. Shanefield, “Organic Additives and Ceramic Processing,” Kluwer Academic Press
Advanced Electronic Ceramics I (2004)
6. Thixotropic
♦ hyteresis
♦ viscosity reduces with time
stress
Yield
Dilatant
Shear rate
From D. J. Shanefield, “Organic Additives and Ceramic Processing,” Kluwer Academic Press
Advanced Electronic Ceramics I (2004)
The viscosity ranges for the ceramic-forming processes
Approximate Viscosity's in Ceramic Processing
Shear rate
Process Viscosity
1/sec.
Centipoise
1000
Injection Molding and Extrusion 100,000
400 to 1000
Screen Printing of Decorative Ink 40,000
700 to 1000
Doctor Blade Tape Casting 7,000
7
Slip Casting into Porous Molds 700
1000 cp (centipoise) = 1 Pa•sec = 1N/m2
From D. J. Shanefield, “Organic Additives and Ceramic Processing,” Kluwer Academic Press
Advanced Electronic Ceramics I (2004)
7. Preparation of a Homogeneous Slurry
Inorganic Content Design of Slurry
Ceramic Powder 1. Viscosity
2. Stress-Shear
+ - method of shaping
3. Homogeneity
Organic Contents (Solubility Parameter)
1. Binder 4. Drying Parameter
2. Plasticizer 5. Organic Content
3. Solvent (Solid Loading)
4. Dispersent
From D. J. Shanefield, “Organic Additives and Ceramic Processing,” Kluwer Academic Press
Advanced Electronic Ceramics I (2004)
Heat of vaporization & solubility
Cohesive energy density (c) Reflect van der Waals
forces holding the molecules
∆H - RT of the liquid together
c=
Vm
Amount of energy
c: cohesive energy (cal/cm3) required to separate the
∆H : Heat of vaporization (cal/mol) liquid into gas
R : gas constant (1.987 cal/degree•mole)
T : temperature (degree)
Vm : molar volume (cm3/mol)
For a solution to occur, the solvent molecules must overcome this
intermolecular stickiness in the solute and find their way between and
around the solute molecules. This is accomplished best when the
attractions between the molecules of both components are similar.
http://sul-server-2.stanford.edu/byauth/burke/solpar/
Advanced Electronic Ceramics I (2004)
8. Hildebrand Solubility Parameter
In 1936, Joel H. Jildebrand proposed the following
solubility parameter
∆H - RT 1/2
δ = c 1/2 =
Vm
Unit
δ /cal1/2cm-3/2 = 0.48888 x δ /MPa1/2
δ /MPa1/2 = 2.0455 x δ /cal1/2cm-3/2
(cal/cm3)1/2=(4.184x106J/m3)1/2 =(4.184MPa)1/2=2.0455MPa1/2
Advanced Electronic Ceramics I (2004)
Hildebrand Solubility Parameter for solvents
http://sul-server-2.stanford.edu/byauth/burke/solpar/
Advanced Electronic Ceramics I (2004)
10. The properties for the casting slip
1. Low viscosity
2. High specific gravity (shorten casting time, increase green
density, and lower drying shrinkage)
3. Deflocculated slip
4. Good casting rate
5. Easy mold release
6. Good drainage
7. Adequate green strength
8. Low drying shrinkage
9. Newtonian flow
Advanced Electronic Ceramics I (2004)
slip casting
♦ Porous mold absorb the water from the slip. After the body
becomes dry enough to have self-supporting strength, the mold
halves are separated for removal.
(ex.) slip casting of clay in plaster of Paris molds
- plaster of Paris is calcium sulfate
- some divalent calcium ions from the mold dissolve the in the slip,
slightly collapsing the double layer
- the slip then agglomerates to some degree, causing the deposited
clay body becomes more porous
- Water can easily diffuse through the highly porous first-deposited
clay, allowing more clay to also deposit quickly and build up to a
practical thickness
From D. J. Shanefield, “Organic Additives and Ceramic Processing,” Kluwer Academic Press
Advanced Electronic Ceramics I (2004)
11. slip casting
http://www.algonet.se/~keram/pdf/Slip%20Casting.pdf
Advanced Electronic Ceramics I (2004)
slip casting
U. P. Schönholzer et al., Am.Ceram. Soc. Bull., 79(12), 45 (2000)
Advanced Electronic Ceramics I (2004)