Aem Lect13
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Transcript of Aem Lect13
Advanced Electronic Ceramics I (2004)From D. J. Shanefield, “Organic Additives and Ceramic Processing,” Kluwer Academic Press
Forming : Nomenclature
1. Pressure Fabrication
2. Plastic Forming
3. Slip Casting
Conventional pressingIsostatic pressing
ExtrusionJiggeringPlastic forming
Conventional slip castingPressure castingTape casting
Advanced Electronic Ceramics I (2004)From D. J. Shanefield, “Organic Additives and Ceramic Processing,” Kluwer Academic Press
Ceramic Shaping MethodsProcess
DryPressing
InjectionmoldingExtrusion
RollCompactionTapeCastingPressureCastingSlipCasting
Shapes
Mostly-uniformcross sectionAlmostanyUniformcross sectionThinSheetsThinSheetsVarious
Various
Viscosity
Veryhigh
High
High
High
Medium
Medium
Low
Fluidization
None
MeltedbinderWater
Water
Organicor waterWater
Water
Solidification
Plastic Flowof Binder
Cooling
Plastic Flow
Plastic Flow
Evaporation
Wicking and/orPlastic Flow
Wicking
Compaction
Yes
No
No
Yes
No
No
No
Advanced Electronic Ceramics I (2004)
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
From D. J. Shanefield, “Organic Additives and Ceramic Processing,” Kluwer Academic Press
Slip casting of wet slip
porouspolymer
Advanced Electronic Ceramics I (2004)
Viscosity: the door to the Rheology
x
y
z
v=0
A F
FA
dvdy
= η
Velocity gradient(Shear rate)
Shear Stress
Advanced Electronic Ceramics I (2004)
Pseudoplastic : Shear thinning
From D. J. Shanefield, “Organic Additives and Ceramic Processing,” Kluwer Academic Press
stress
Shear rate
viscosity
Apparent viscosity
Pseudoplastic
The shear rate increasesabruptly above certainstress level- called as “shear thinning”
- useful in paint industry: Thin film spread well along the vertical wall while painting (thinned state)
: do not drip or streakduring the drying period
- Useful for screen printing ofthick film ink (many thick film pastes wrongly described as thixotropic)
Another example?(mustard, catsup, salad dressing)
Advanced Electronic Ceramics I (2004)
Plastic : Bingham
From D. J. Shanefield, “Organic Additives and Ceramic Processing,” Kluwer Academic Press
stress
Shear rate
YieldPoint
Plastic(Bingham)
♦Desirable pattern for many ceramic processes
♦material flow(shear) while being molded at the high force(stress)
♦do not flow(shear) at the waiting before firing(only gravity plays the role of the force)
Advanced Electronic Ceramics I (2004)
Linear : Newtonian
stress
Shear rate
Linear(Newtonian)
♦ desirable for the slip casting♦ the slurry for the slip casting should
easily fill the mold (like water) and prevent the trapping of air bubbles
♦ help prevent sudden slumping caused by thixotropy during handling and transport of the cast piece
♦ good for uniform casting rate
Advanced Electronic Ceramics I (2004)
Dilatant : Shear thicknening
stress
Shear rate
Dilatant(Shear thickening)
♦ materials becomes too stiff to flow smoothly at high shear rate- called as ‘shear thickening’
♦can crack or even explode a die or mold during extrusion
♦occurs at very high solid loading- horizontal shear of closely packed spheres requires the top layer to ride up over the bottom one (dilating the 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)
stress
Shear rate
YieldDilatant
♦ shear thinning at low shear rate and shear thickening at high shear rate
♦ sometimes observed in clay slip
Yield Dilatant
From D. J. Shanefield, “Organic Additives and Ceramic Processing,” Kluwer Academic Press
Advanced Electronic Ceramics I (2004)
stress
Shear rate
YieldDilatant
♦ hyteresis♦ viscosity reduces with time
Thixotropic
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
Process
Injection Molding and ExtrusionScreen Printing of Decorative InkDoctor Blade Tape CastingSlip Casting into Porous Molds
ViscosityCentipoise100,00040,0007,000
700
Shear rate1/sec.1000400 to 1000700 to 10007
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)
Preparation of a Homogeneous Slurry
From D. J. Shanefield, “Organic Additives and Ceramic Processing,” Kluwer Academic Press
Inorganic ContentCeramic Powder
+
Organic Contents1. Binder2. Plasticizer3. Solvent4. Dispersent
Design of Slurry1. Viscosity2. Stress-Shear- method of shaping
3. Homogeneity(Solubility Parameter)
4. Drying Parameter5. Organic Content
(Solid Loading)
Advanced Electronic Ceramics I (2004)
Cohesive energy density (c)∆H - RT
c = Vm
c: cohesive energy (cal/cm3)∆H : Heat of vaporization (cal/mol)R : gas constant (1.987 cal/degree•mole)T : temperature (degree)Vm : molar volume (cm3/mol)
Heat of vaporization & solubility
Reflect van der Waals forces holding the molecules of the liquid together
Amount of energy required to separate the liquid into gas
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)
Hildebrand Solubility Parameter
In 1936, Joel H. Jildebrand proposed the following solubility parameter
∆H - RT 1/2
δ = c 1/2 = Vm
Unitδ /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)
Hildebrand Solubility Parameter: Plasticizer
Plasticizer δTCP 9.1DMP 8.4DBP 8.4DOP 8.3BBP 8.8Citroflex 4 7.4Citroflex A-4 7.5DBM 8.15DOA 8.15TOP 7.9
Advanced Electronic Ceramics I (2004)
Solubility Parameter of Mixtureratio wt% vol% SP γ
n-Heptane 4 57.15 60.51 7.4 2.2isopropylalcohol 2 28.56 27.02 11.5 8.9n-butylacetate 1 14.29 12.47 8.5 5.4
SP= 0.6051x7.4 + 0.2702x11.5 + 0.1247x8.5 = 8.64γ= 0.6051x2.2 + 0.2702x8.9 + 0.1247x5.4 = 4.4
Hydrogen Bonding Index
51
17
10
51
17
10
γ
δ
γ
δ
Soluble Soluble
Binder A Binder B
Advanced Electronic Ceramics I (2004)
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 slip4. Good casting rate5. Easy mold release6. Good drainage7. Adequate green strength8. Low drying shrinkage9. 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)
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)