Design of Unidirectional Freeze-Casting Device Members: John Simmonds Joe Hastings Michael Harty Michael Beachy Michael Cook (MET Department) Department of Mechanical and Aerospace Engineering Old Dominion University, Norfolk, VA 23529

Gantt Chart

Actual Freeze-casting device Equipment Design Freeze-casting device Schematic Actual Freeze-casting device

Initial Cold finger design Cold finger design stage 2 Equipment Design Initial Cold finger design Cold finger design stage 2 Teflon mounting block added to reduce thermal conduction to freeze- casting device Cold finger design stage 1 More uniform temperature dispersal Sample shelves Enables the ability to put more than one sample in the freeze drier at one time

Thermal gradients with initial design Equipment Design Thermal gradients with initial design Thermal gradients after introduction of dewar insulation sleeve and sample mold insulation sleeve Thermal gradients after introduction of dewar insulation sleeve

Dewar insulation sleeve Equipment Design Dewar insulation sleeve Dewar insulation sleeve installed Dewar and sample mold insulation sleeves installed Sample Mold insulation sleeve

Equipment Design Initial sample mold with 12 mm sample diameter fabricated from polydimethylsiloxane. New sample mold with 19 mm sample diameter as well as an increased height. Teflon was used to fabrication the new mold the simple fact that it is less costly and easier to handle.

Thermocouple The K type thermocouple is the current sensor used to understand freeze front velocities within our experiment. Our Current Data Logger and data logging software are a LabQuest Mini by Vernier and LoggerLite, respectively.

Problems: Thermocouple K type thermocouples do not have a high enough degree of accuracy for our experimental system. (Standard: +/- 2.2C or +/- .75%) Due to this issue, a different thermal measuring system has to be installed to more accurately and precisely detect the temperature gradients during ceramic slurry trials.

Freeze-casting device Schematic Freezing Front Velocity The main control of the fabrication of the ceramics is the ability to speed up or slow down the freezing front velocity of the samples. Through experimentation with the changing of several variables it has been found that the best way to do this is via changing the height of the cold finger above the liquid nitrogen. The main criteria for determining if the freeze front velocity control is successful is the concept of repeatability. Many dry runs were completed using just straight water and no sign of repeatability was accomplished. Freeze-casting device Schematic

Present Freeze-casting device Configuration Freezing Front Velocity Success was achieved after the addition of the insulating sleeve. The sleeve, as previously discussed reduced the convective effects of the surrounding nitrogen gas on the sides of the sample. This allowed the sample to be frozen from the bottom upwards only. Once the water samples were found to have a repeatability at 30mm above liquid level the process was deemed repeatable and slurry production was continued. Present Freeze-casting device Configuration

Freezing Front Velocity During Slurry processing the freeze-front velocities were again analyzed. It was found that the freeze-front velocity sped up greatly compared to just pure distilled water samples. This problem was dealt with through the now proven ability to adjust the freeze front velocity by varying the height. Currently, samples have been produced at the following heights above liquid level: 20mm, 25mm, 30mm, 35mm, 40mm, 45mm, 50mm, 55mm, 60mm and 65mm.

Freezing Front Velocity Using these samples we have been able to determine freeze-front velocities that are linear in nature from 22μm/s to 6 μm/s, with the fastest being at heights of 20mm above and progressively working upwards in height and down in freeze-front velocity.

Freeze-casting Machine Slurry Preparation Vacuum Chamber Ball Milling Machine Freeze-casting Machine Sintering Furnace Oven Freeze Drier