Single action pressing (from top)

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Kimberly Cameron
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1 Single action pressing (from top)

2 Double action pressing with fixed die

3 Typical course of the pressure during pressing and ejection (Single action) Upper punch Pressure Lower punch Time

4 Green body formation Powder conditioning Granulation Slip casting Ceramic powder/polymer Mixing Agglomerates Dry forming methods Slips Wet forming methods Plastic mass (Feedstock) Plastic forming methods Green body

5 Wet forming methods Powder Suspension (Slip) Solid-liquid separation Slip casting Mechanical separation of liquid and powder (filtration) Tape casting of slips Thermal separation of liquid and powder (evaporation)

6 Wet forming Surface charges of metal oxides in water (1) MeO MeO 2 O MeO Me O O (2) MeO Me O O + O - MeO Me O + O MeO Me O - O Low p igh p

7 Powder particles in water Diffuse layer = Cloud made of counter ions Positive counter ions Negative surface potential (= Nernst potential) Potential 0 Distance (Gouy-Chapman model)

8 Layer model for powder particles in electrolyte-containing water Electrolyte-containing system Inner Stern layer Outer elmholtz layer Negativ, dehydrated Negativ, hydrated Positive, hydrated Diffuse layer Not fixed hydrated positive and negative ions Fixed hydrated positive ions Fixed dehydrated negative ions (Stern model)

9 Layer model for powder particles in electrolyte-containing water Potential Potential of the inner elmholtz layer ( i ) Potential of the outer elmholtz layer = Stern potential ( s, a ) Nernst potential 0 Diffuse Layer Exponential decay in the diffuse layer Decay to zero is simplified

10 Zeta potential Diffusing particle Stern potential Nernst potential Diffuse layer Partial separation of the diffuse layer Potential difference Potential at the shear plane S = Zeta potential (ZP) (= Potential difference)

11 Measurement of the zeta potential by electrophoresis Cathode v + Anode v E r 0 : Zeta potential v: Particle velocity : Viscosity of the dispersion medium 0 : Dielectric constant in vacuum r : Relative dielectric constant E: Electrical field strength v/e: Electrophoretic mobility

12 Zeta potential Particles in an electrical field Stern potential Diffuse layer Nernst potential

13 Dependancy of the zeta potential on the electrical field ZP Stern potential

14 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

15 DLVO theory Description of the interaction energy V T between two particles: V T = V A + V R V A : Contribution of the van der Waals attraction V R : Contribution of the electrostatic repulsion

16 Van der Waals attraction V A Repulsion x V A (x) = A r /(12x) A: amaker constant r: Particle radius x: Distance of the particle surfaces Attraction Particles floccuate

17 Electrostatic repulsion V R V R Attraction Contribution of the double layer to the interaction energy: Repulsion x V R (x)=2r r 0 2 exp( x) 0 : Dielectric constant in vacuum r : Relative dielectric constant : Surface potential r: Particle radius x: Distance of the particle surfaces : Debye-ückel parameter Particles dispersed

18 Thickness of the diffuse layer Stern potential Nernst potential Decay to 1/e Decay to zero Stern layer Thickness of the diffuse layer 1/ x e x : Potential at the particle surface (Stern potential) x : Potential at distance x from the surface 1 r 0kT 2 e Niz i 2 i 1 2 : Debye-ückel parameter 0 : Dielectric constant in vacuum r : Relative dielectric constant k: Boltzmann constant T: Absolute temperature e: Elementary charge N i : Number of ions per volume unit z i : Charge number of ion species i

19 Thickness of the diffuse layer Concentration dependence Dependence on the ionic charge 1:1 electrolyte (e. g. NaCl) 3:1 electrolyte (e. g. AlCl 3 ) 2:1 electrolyte (e. g. CaCl 2 )

20 Total potential V Repulsion V T V R x V A Attraction

21 Total potential Secondary minimum Increasing salt concentration

22 Colloid stabilization mechanisms Electrostatic (Surface charge) Steric (Macromolecules)

23 O C C C O C C C 7 7 O C C C O C C C 7 7 O C C C O C C C 7 7 Adsorption of oleic acid at oxide particles Oxide particle

24 Steric repulsion V S Repulsion Small molecules Macromolecules x Attraction

25 Combined particle interaction Steric stabilization by long-chained molecules (long range) Steric stabilization by short-chained molecules (short range) V Steric contribution V Steric contribution Total potential Van der Waals contribution Van der Waals contribution

26 Conformations Mushroom Brush

27 Interaction of organic additives with Al2O3

28 Adsorption of polyelectrolytes

29 Wet forming methods Powder Suspension Solid-liquid separation Slip casting Mechanical separation of liquid and powder (filtration) Tape casting Thermal separation of liquid and powder (evaporation)

Slip casting Porous, water absorbing mold (gysum, CaSO 4 2 2 O Cast copies the inner contour of the mold Realization of small wall thicknesses: Increase of the cast thickness dx:

30 Slip casting Porous, water absorbing mold (gysum, CaSO O Cast copies the inner contour of the mold Realization of small wall thicknesses: Increase of the cast thickness dx: c dx dt x c: constant (depending on the permeability and drain volume of the cast; solid yield and viscosity of the suspension t: time Integration (x =0 at t=0): 2 x t c x x 2ct t

31 Slip casting -Burner tubes (SiC)-

32 Additive Processing additives Function Examples Solvent Wetting agent Deflocculant Binder Plasticizers (softener) Antifoaming agents Suspending agent Dispersing agent, reduction of the surface tension of the solvent Inluence on particle interaction, control of surface charges and p, steric stabilization Green strength/machinability Flexibility Modification of binder properties Avoidance of bubbles Water, alcohols, trichloroethylene, toluene Stearates, dodecyl ammonium acetate Citrates, polyacrylic acid Polyvinylbutyral, polyacrylic acid Phthalates, glycols, water Octanol Preservatives Separating agents Lubricants Attack by bacteria, fungi, algae Mold release Friction, punching properties Bactericides, fungicides, Cu salts Fatty acids, fatty acid esters, wax Glycerin

33 Tape casting Doctor blade with micro screw Slip Exhaust air Drying chamber Preheated air flexible green tape

34 Composition of a Al 2 O 3 slip Material Function wt%

35 Tape casting: Pin grid arrays Al 2 O 3

Colloid stability. Lyophobic sols. Stabilization of colloids.

Colloid stability. Lyophobic sols. Stabilization of colloids. Lyophilic and lyophobic sols Sols (lyosols) are dispersed colloidal size particles in a liquid medium (=solid/liquid dispersions) These sols