Unidirectional Freeze Casting Group Status Report

Unidirectional Freeze Casting Team Members Faculty Advisor:Dr. Dipankar Ghosh Graduate Student:Nikhil Dhavale Team Manager:John Simmonds Joe Hastings Michael Harty Michael Beachy Michael Cook (MET Department)

Freezing Device Development Previous experimentation utilized convection as a primary effect for freeze casting the samples. During sample formation significant thermal gradients were noted at the sides of the sample molds. This created a negative impact for maintaining unidirectional freezing action of the sample. Two modifications to the freezing device have been made to negate these effects.

Freezing Device Development An insulating sleeve constructed of dense foam was created to direct the cooling forces to only the bottom of the sample, which in turn promotes freezing of the sample in unidirectional fashion. A steel rod was suspended in the LN 2 and the freezing device cooling plate was placed in contact with the rod. This method replaced the previous freezing techniques that were driven by convection with a more controllable conduction freezing force.

Formation of the Sample Column formation, indicated be vertical lines, in this sample of water can clearly be seen.

Slurry Production The slurry being used is comprised of nano-sized particles of aluminum oxide, distilled water, a dispersant and a binding agent. Various ratios of alumina, binding agents, and dispersant are being assessed to determine the optimal ratio for the greatest material strength of the finished sample. Once all of the ingredients are mixed, the slurry is ball milled for 24 hours. An initial sample of unfrozen slurry was placed in the furnace to determine if the mixing ratios are correct. After 24 hours in the furnace, the consistency of the dried sample contained small clumps that required force to break apart. This cohesion shows promise for the samples produced from freeze casting from this batch.

Samples of Frozen Slurry In these pictures, unfrozen slurry samples Are being subjected to sublimation in a freeze drier prior to being placed into a furnace for sintering

Current News Control of the freezing velocity is showing significant improvement over previous efforts. This is plainly seen in the water sample that demonstrates the columnar formation. Material composition of the slurry mixture continues as different combinations of alumina, binding agent and dispersants are assessed.

Future Work Initial production of ceramic material from unidirectionally frozen slurry mixture. Analysis of ceramic material using Scanning Electron Microscopy as well as compression, ballistic and static testing.