Freeze-cast alumina pore networks: Effects of freezing conditions and dispersion medium
Alumina ceramics were freeze-cast from water- and camphene-based slurries under varying freezing conditions and examined using X-ray computed tomography (XCT). Pore network characteristics, i.e., porosity, pore size, geometric surface area, and tortuosity, were measured from XCT reconstructions and the data were used to develop a model to predict feature size from processing conditions. Classical solidification theory was used to examine relationships between pore size, temperature gradients, and freezing front velocity. Freezing front velocity was subsequently predicted from casting conditions via the two-phase Stefan problem. Resulting models for water-based samples agreed with solidification-based theories predicting lamellar spacing of binary eutectic alloys, and models for camphene-based samples concurred with those for dendritic growth. Relationships between freezing conditions and geometric surface area were also modeled by considering the inverse relationship between pore size and surface area. Tortuosity was determined to be dependent primarily on the type of dispersion medium.
© 2015 Elsevier. Received 24 March 2015; received in revised form 8 May 2015; accepted 11 May 2015. Available online 1 June 2015. This work was supported by a NASA Office of the Chief Technologist's Space Technology Research Fellowship and used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. This work also made use of the OMM Facility which receives support from the MRSEC Program (NSF DMR-1121262) of the Materials Research Center at Northwestern University and the EPIC facility (NUANCE Center-Northwestern University), which has received support from the MRSEC program (NSF DMR-1121262) at the Materials Research Center; the International Institute for Nanotechnology (IIN); and the State of Illinois, through the IIN. The authors would like to thank Dr. Fabian Stolzenburg for the suggestion to use a thermoelectric cooler as a cold plate.