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Single action pressing (from top)

Double action pressing with fixed die

Typical course of the pressure during pressing and ejection

Upper punch

Lower punch

Time

Pre

ssur

e

(Single action)

Green body formation

Powder conditioning

Granulation Slip casting Ceramic powder/polymerMixing

Agglomerates

Wet forming methods Plastic forming methods

Green body

Slips Plastic mass(Feedstock)

Dry forming methods

Wet forming methods

Powder

Suspension (Slip)

Solid-liquid separation

Slip casting Tape casting of slips

Mechanical separation of

liquid and powder(filtration)

Thermal separation of liquid and powder

(evaporation)

Surface charges of metal oxides in water

MeO

MeOH2O MeO

MeOH

OH

MeO

MeOH

OH

(1)

(2)

MeO

MeO+

OHMeO

MeO-

OH

H+ OH-

H

H

Low pH High pH

Wet forming

Potential

Distance

0

Powder particles in water

(Gouy-Chapman model)

Positive counter ions

Diffuse layer = “Cloud” made of counter ions

Negative surface potential(= Nernst potential)

Layer model for powder particles in electrolyte-containing water

(Stern model)

Diffuselayer

Electrolyte-containing system

Stern layerInner

OuterHelmholtz layer

Negativ, dehydratedNegativ, hydratedPositive, hydrated

Not fixed hydrated positive and negative ions

Fixed hydrated positive ions

Fixed dehydrated negative ions

Potential

Layer model for powder particles in electrolyte-containing water

Potential of the inner Helmholtz layer (i)

Potential of the outer Helmholtz layer= Stern potential (s, a)

Nernst potential0

Exponential decay in the diffuse layer

Decay to zerois simplified

Diffuse Layer

Zeta potential

Diffusing particleStern potential

Nernstpotential

Partial separation of the diffuse layer Potential difference

Potential at the shear plane S = Zeta potential (ZP)(= Potential difference)

Diffuse layer

Measurement of the zeta potential by electrophoresis

-- --

-

-

---

-

-+-

+

+

+Cathode Anode

+v

: Zeta potentialv: Particle velocity: Viscosity of the dispersion medium0: Dielectric constant in vacuum r: Relative dielectric constantE: Electrical field strengthv/E: Electrophoretic mobility

Er 0 v

Zeta potential

Particles in an electrical field

Stern potential

Diffuselayer

Nernstpotential

Dependancy of the zeta potential on the electrical field

ZP Stern potential

Zeta potential

Estimation of the physical stability by means of the zeta potential

Features of the stability Zeta potential (mV)

Maximum agglomeration and sedimentation +3 to 0

Distinct agglomeration and sedimentation -1 to -4

Barrier to agglomeration -5 to -10

Slight agglomeration -21 to -30

No agglomeration -31 to -40

Good stability -41 to -50

Very good stability -51 to -60

Excellent stability -61 to -80

Maximum stability -81 to -100

DLVO theory

Description of the interaction energy VT between two particles:

VT = VA + VR

VA: Contribution of the van der Waals attraction

VR: Contribution of the electrostatic repulsion

Van der Waals attraction

Repulsion

Attraction

xVA(x) = – A·r /(12x)

A: Hamaker constantr: Particle radiusx: Distance of the particle surfaces

Particles floccuate

VA

Electrostatic repulsion VR

VR(x)=2rr02 exp(–x)0: Dielectric constant in vacuumr: Relative dielectric constant: Surface potentialr: Particle radiusx: Distance of the particle surfaces: Debye-Hückel parameter

Particles dispersed

Contribution of the double layer to the interaction energy:

Attraction

Repulsion

x

VR

Thickness of the diffuse layer

21

2201

i

ii

r

zNekT

: Debye-Hückel parameter0: Dielectric constant in vacuumr: Relative dielectric constantk: Boltzmann constantT: Absolute temperaturee: Elementary chargeNi: Number of ions per volume unitzi: Charge number of ion species i

xx e

: Potential at the particle surface(Stern potential)

x: Potential at distance x from the surface

Stern potential

Nernstpotential Decay to 1/e

Decay to zero

Stern layer Thickness of the diffuse layer 1/

Thickness of the diffuse layer

Concentration dependence

1:1 electrolyte (e. g. NaCl)

Dependence on the ionic charge

2:1 electrolyte (e. g. CaCl2)3:1 electrolyte (e. g. AlCl3)

Total potential

x

RepulsionV

VR

VA

VT

Attraction

Total potentialSecondary minimum

Increasing salt concentration

Steric (Macromolecules)

Electrostatic(Surface charge)

Colloid stabilization mechanisms

HO C C CO

H

H

H

C C C H

7

H

H

7

H

HO C C CO

H

H

H

C C C H

7

H

H

7

H

HO C C CO

H

H

H

C C C H

7

H

H

7

H

Adsorption of oleic acid at oxide particles

Oxide particle

Steric repulsion

Small molecules

Macromolecules

Repulsion

Attraction

x

VS

Combined particle interaction

V

Van der Waals contribution

Steric contribution

Total potential

Steric stabilization by long-chained molecules (long range)

V Steric contribution

Van der Waals contribution

Steric stabilization by short-chained molecules (short range)

Mushroom Brush

Conformations

Interaction of organic additives with Al2O3

Adsorption of polyelectrolytes

Wet forming methods

Powder

Suspension

Solid-liquid separation

Slip casting Tape casting

Mechanical separation of

liquid and powder(filtration)

Thermal separation of liquid and powder

(evaporation)

Slip casting

Porous, water absorbing mold (gysum, CaSO42H2O

Cast copies the inner contour of the mold

Realization of small wall thicknesses:Increase of the cast thickness dx:

dtxcdx

c: constant (depending on the permeability and drain volume of the cast; solid yield and viscosity

of the suspensiont: time

Integration (x =0 at t=0):

ctx 2

x

t

ctx

2

Slip casting-Burner tubes (SiC)-

Processing additives

Additive

Solvent

Wetting agent

Deflocculant

Binder

Plasticizers (softener)

Antifoaming agents

Preservatives

Separating agents

Lubricants

Function

Suspending agent

Dispersing agent, reduction of the surface tension of the solvent

Inluence on particle interaction, control of surface charges and pH,

steric stabilizationGreen strength/machinability

FlexibilityModification of binder properties

Avoidance of bubbles

Attack by bacteria, fungi, algae

Mold release

Friction, punching properties

Examples

Water, alcohols, trichloroethylene, toluene

Stearates, dodecyl ammonium acetate

Citrates, polyacrylic acid

Polyvinylbutyral, polyacrylic acid

Phthalates, glycols, water

Octanol

Bactericides, fungicides, Cu salts

Fatty acids, fatty acid esters, wax

Glycerin

Slip

Doctor bladewith micro screw

Exhaust airDrying chamber

Preheated air

flexible green tape

Tape casting

Composition of a Al2O3 slip

Material Function wt%

Tape casting: Pin grid arrays

Al2O3