This document summarizes an investigation into the ice crystal growth mechanism during two-dimensional freeze casting with clathrate hydrates. Freeze casting of zirconia slurries was conducted with varying concentrations of isopropanol (IPA) as an additive. Preliminary results found similar freezing front velocities across concentrations, indicating freezing rate may not explain previously observed enlarged pore structures. Initial freezing temperatures remained constant with IPA content, contrary to an expected decreasing trend. Microscope images revealed potentially larger ice crystals with IPA, though more study is needed to better understand the crystal growth mechanism. Future work involves time-lapse video and trials with other alcohols to further elucidate the source of enlarged porosity in freeze casted

1. Investigation of Ice Crystal Growth through 2D
Freeze Casting with Clathrate Hydrates
Ivan Torres & Khalid Niles-Rodney
Department of Mechanical and Aerospace Engineering
Materials Science and Engineering Program
Professor Joanna McKittrick
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2. Outline
1. Bioinspired Design
2. Freeze Casting Process
3. Motivation
4. Clathrate Hydrates
5. 2D Freeze Casting Observation
6. Conclusion
2

3. Bioinspired Design
3

4. Bioinspired Design
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[1] Clark, R. Boxfish. Retrieved from http://ngm.nationalgeographic.com/2008/04/biomimetics/clark-photography
[2] Frank, M.B. Mars urchin: A bioinspired sediment sampler based on the mouthpiece of a sea urchin
Biological
Systems
Engineering
Applications

5. Bioinspiration in Freeze Casting
5
Biology
Layered
Fish Scales
[3] Porter, M.M. Mckittrick, J. Meyers, M.A. Biomimetic Materials by Freeze Casting.JOM. 2013.65.720-727
[4] Naleway S.E., Yu C.F., Porter M.M., Sengupta A., Iovine P.M., Meyers M.A., McKittrick J. Bioinspired composites from freeze casting using
clathrate hydrates. Materials & Design 2015;71:62-7.
Bioinspired Freeze
Casted Layered
Structures
Natural Bone

6. Freeze Casting Process
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7. Freeze Casting
● Simple, physical process
— No chemical reactions involved
● Controlling the microstructure of ceramics material
— Lamellar, porous structures obtained
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PVC BOX

8. Freeze Casting
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[5] Deville, S. Freeze-Casting of Porous Ceramics: A Review of Current Achievements and Issues. Adv. Eng. Mater. 2008. 10:
155–169.
Slurry
● Ceramic particles: Zirconia (ZrO2)
● Liquid (Solvent): Water
● Additive: Isopropanol (IPA)
● Small traces of other polymers to aid
process

9. Freeze Casting
9
[5] Deville, S. Freeze-Casting of Porous Ceramics: A Review of Current Achievements and Issues. Adv. Eng. Mater. 2008. 10:
155–169.

10. Previous Results
● Studies indicate enlarged pores
when ~5-7 vol. % IPA was
added to ZrO2
o Began to decrease with
additional concentration of
IPA
● TiO2 showed same decrease in
pore size after 7% IPA
o Pore size influenced by ice
formation, not solid loading
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[4] Naleway S.E., Yu C.F., Porter M.M., Sengupta A., Iovine P.M., Meyers M.A., McKittrick J. Bioinspired composites from freeze casting using clathrate
hydrates. Materials & Design 2015;71:62-7.

11. Motivation
11

12. Motivation
How are these enlarged pores actually
being formed?
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13. Motivation
● Objective: To observe ice crystal growth and determine what
physical mechanism is responsible for enlarged porous structures in
final scaffolds
● Potential Mechanism 1: Larger unit cell structures
● Potential Mechanism 2: Slower freezing rates
o Allow for more appropriate control over pore size in scaffolds for
biomedical applications
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14. Clathrate Hydrates
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15. Example (Methane Hydrate)
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“Burning Ice”Structure of
Gas Hydrate

16. Clathrate Hydrates
● Non-stoichiometric structures
● Guest molecule (IPA) encapsulated
within a lattice of water molecules
● Dependent on stacking & guest
molecule cavity size
o Structure I (h1)
o Structure II (h2)
● Both unit cell sizes are larger than
pure ice structures
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[4] Naleway S.E., Yu C.F., Porter M.M., Sengupta A., Iovine P.M., Meyers M.A., McKittrick J. Bioinspired composites from freeze casting using
clathrate hydrates. Materials & Design 2015;71:62-7.

17. Clathrate Hydrates & Freeze Casting
● Differential Scanning Calorimetry
o Measures decomposition of
sample to a reference during
change in heat flow
o Verifies phase
transformation during freeze
casting, correlating with h1
clathrate hydrates
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[4] Naleway S.E., Yu C.F., Porter M.M., Sengupta A., Iovine P.M., Meyers M.A., McKittrick J. Bioinspired composites from freeze casting using
clathrate hydrates. Materials & Design 2015;71:62-7.

18. Mechanism of Enlarged Porosity - 1
● Enlarged crystal structure of the
clathrate hydrates is directly
related to enlarged ice crystals
within the scaffold
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[4] Naleway S.E., Yu C.F., Porter M.M., Sengupta A., Iovine P.M., Meyers M.A., McKittrick J. Bioinspired composites from freeze casting using
clathrate hydrates. Materials & Design 2015;71:62-7.

19. Mechanism of Enlarged Porosity - 2
● λ = ice lamellae wavelength
● v = freezing front velocity
● A, n = material constants
● Assumption: V = V(C,t)
o C = Concentration of IPA
o t = time
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λ = Av-n
[6] Wegst, U.G.K. Bai, H. Saiz, E. Tomsia, A.P. Ritchie, R.O. Bioinspired structural materials. Nat Mater. 2015/01//print.

20. Slurries & IPA
● The freezing point of a pure solvent is lowered by the addition of a solute
which is insoluble in the solid solvent.
● Antifreeze properties
● In the liquid solution, the solvent is diluted by the addition of a solute, so
that fewer molecules are available to freeze.
● In this case,
20Amount of Solute (%)
FreezingPoint(°C)

21. 21
Antifreeze Properties
Slurries & IPA

22. Hypothesis
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0 1 3 5 7 10 15
IPA %
PoreSize
InitialFreezing
Temperature
Possible Initial Freezing Temp. (Anti Freeze)
Pore Size
Possible Initial Freezing Temp. (Expected)

23. 2D Freeze Casting
Observation
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24. Freeze Casting Setup
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25. Implemented Design
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● Clear acrylic box
o Microscope slide
o Moving back slider for
variable thickness
o Optimal thickness for ice
growth observation will be
determined
● Assembled box fits onto a 2”
Copper/Aluminum Rod System

26. 26
Experimental Methodology
● Prepare slurries of ZrO2
varying in IPA concentration:
0,1,3,5,7,10,15%
● Carry out freeze casting
process as previously
mentioned
● Determine freezing front growth
rate by measuring
displacement & temperature at
2 min intervals

27. Results
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Calipers ImageJ
• Similar velocity profiles
• Indicate freezing rate may not be physical mechanism
responsible for enlarged pores

28. Results
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• Does not concretely support either hypothesis
• Yet it does show that there is no linearly decreasing trend
• Demonstrates that the initial freezing point may remain constant with
varying IPA %
Avg. Initial
Freezing
Temp. (°C)
Standard
Deviation
(°C)
-17.76 3.91

29. Preliminary Microscope Images
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3% IPA
1 mm

30. Conclusion
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31. Conclusion
● Freezing rate may not be the source of enlarged pores due to similar
velocity profiles
● Initial freezing temperature displays a constant trend for varying IPA
concentrations
Future Work
● Implement time-lapse video for closer inspection of freezing front
● Continue trials with other alcohols (n-propanol, ethanol, n-butanol)
o Attempt to show that these other monofunctional alcohols may also
induce relatively larger final porosities
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32. Acknowledgements
● Professor Joanna McKittrick, Ph.D.
● Ph.D. Graduate Research Assistants Steven E. Naleway & Michael B. Frank
● Undergraduate Research Assistants Kerry Chou & Yajur Maker
● We would like to thank our respective programs: CAMP, STARS
● This work is supported by a Multi-University Research Initiative through the Air Force Office of
Scientific Research of the United States (AFOSR-FA9550-15-1-0009).
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33. Questions?
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