8/2/2019 Freeze Casting 2012
http://slidepdf.com/reader/full/freeze-casting-2012 1/16
Freeze Casting of Porous Ceramics
Dr. xxxxxxxxxx
31.01.2012
8/2/2019 Freeze Casting 2012
http://slidepdf.com/reader/full/freeze-casting-2012 2/16
Colloidal Near-Net-Shaping Techniques
8/2/2019 Freeze Casting 2012
http://slidepdf.com/reader/full/freeze-casting-2012 3/16
Colloidal Near-Net-Shaping Techniques
8/2/2019 Freeze Casting 2012
http://slidepdf.com/reader/full/freeze-casting-2012 4/16
Prozessschritte von Freeze CastingÜberblick
J.Ceram.Soc.Jpn. 2011, 119, 147-160
8/2/2019 Freeze Casting 2012
http://slidepdf.com/reader/full/freeze-casting-2012 5/16
Kristallwachstum
8/2/2019 Freeze Casting 2012
http://slidepdf.com/reader/full/freeze-casting-2012 6/16
Einfluss der Einfriergeschwindigkeit
Phil. Trans. R. Soc. A 2010 368, 2099-2121
8/2/2019 Freeze Casting 2012
http://slidepdf.com/reader/full/freeze-casting-2012 7/16
Einfluss der Gefriereinrichtung
8/2/2019 Freeze Casting 2012
http://slidepdf.com/reader/full/freeze-casting-2012 8/16
Einfluss des Lösungsmittels (LöMi)
Flüssiges Wasser Wasser als Eis
Temperaturausdehnung (TAD) beim Einfrieren
+9% !!!
8/2/2019 Freeze Casting 2012
http://slidepdf.com/reader/full/freeze-casting-2012 9/16
Bildung von Eiskristallen
Adv.Eng.Mater. 2008, 10, 3, 155-169
H2O:Water (m.p.= 0°C)
TAD= +9%
8/2/2019 Freeze Casting 2012
http://slidepdf.com/reader/full/freeze-casting-2012 10/16
Anderes LöMi – Andere Struktur
Camphene
(m.p.= 45-46°C)TAD= -3,1%
Solidified camphene dendrites
tert-Butanol
(m.p.= 26°C)
TAD= +2%
Prismatic Channels
8/2/2019 Freeze Casting 2012
http://slidepdf.com/reader/full/freeze-casting-2012 11/16
Einfluss der Partikelgröße anPorenmorphologie
8/2/2019 Freeze Casting 2012
http://slidepdf.com/reader/full/freeze-casting-2012 12/16
Freeze Casting: Vorteile
• Low shrinkage• Independent on material• Easy control through sintering step• Porosity design• Relatively high mechanical properties in the green state• Environmentally friendly
8/2/2019 Freeze Casting 2012
http://slidepdf.com/reader/full/freeze-casting-2012 13/16
Freeze Casting: BestimmendeParameter
•
Solid content of the suspension (10÷50 vol% = 20÷85wt%)• Particle size (20nm ÷6.5 μm)
• Solvent (pure solvents and eutectic mixtures; aqueous and non-aqueous
techniques: viscosity, thermal conductivity, surface tension, melting point,
volume change, vapor pressure, crystal structure)
•Freezing direction, rate and temperature (velocity of freezing
front, temperature gradient)
• Freezing device and cryoprotector additions(isotropic/anisotropic cooling = homogeneous/direction solidification)
• Pressure and temperature of freeze-dryer (sublimation step)
8/2/2019 Freeze Casting 2012
http://slidepdf.com/reader/full/freeze-casting-2012 14/16
Freeze Casting: Probleme und Grenzen
• During the whole process the slurry must be absolutely stable againstsedimentation
• Solid load is limited (breakthrough concentration)• Most investigations reported – 1÷3 cm (lab scale). Homogeneity of the temperature
filed and the freezing kinetics will become problematic for larger bodies
(wärmeleitfähigkeit und viscosität des LöMi, temperaturgradient) – möglicheLosung -> Einfrieren unterm Druck
• Temperaturausdehnung may become critical during freezing and lead to cracks
and flaws
• Flaws during sublimation of the solvent – has been never optimized – terra
incognita
• Larger particles will lower the critical velocity (cv – the particles become
encapsulated by solid)
8/2/2019 Freeze Casting 2012
http://slidepdf.com/reader/full/freeze-casting-2012 15/16
Beispiele aus Literatur
Materials Powder
Particle Size Solvent Cooling Conditions Pore Size
Sintering
Temperature
Alumina 700 nm Silica Sol Cold Plate, -30°C 80 μm No sintering
Alumina 700 nm Silica Sol Metallic Mould, -40°C 50 μm 1100-1500
Alumina 400 nm CampheneMould, from 55 to
22°C5-20 μm 1600°C
Alumina 400 nm Water From 22 to -100°C 2-200 μm 1500°C
Alumina 200 nm t-BuOH From 0 to -15 50 μm 1500°C
Glass 6.5 μm Water Mould, -55°C 100-150 μm 620°C
Bioglass - Camphene Mould, from 60 to20°C
20-40 μm 700-1100°C
SiC 16 μm Water Mould, -40°C 300 μm No sintering
TiO2 150 nm Water Cold support, -18°C 15 μm 1000°C
8/2/2019 Freeze Casting 2012
http://slidepdf.com/reader/full/freeze-casting-2012 16/16