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)