SEM images of xz
cross-sections perpendicular to the cold finger show that in conventional
freeze-casting
(A&D), nucleation produces a disordered layer of ceramic particles. Under
bidirectional
freeze-casting
(C&F), with dual temperature gradients, ice crystals grow both vertically
and
horizontally into
a well-aligned lamellar structure.
Berkeley Lab Researchers Develop Nature-Mimicking
Freeze-casting Technique for Fabricating Advanced Porous Materials
(December 11, 2015) It
has often been said that nature is history’s greatest innovator and if that is
true then scientists with the U.S. Department of Energy (DOE)’s Lawrence
Berkeley National Laboratory (Berkeley Lab) are learning from the best. Berkeley
Lab researchers have developed a freeze-casting technique that enables them to
design and create strong, tough and lightweight materials comparable to bones,
teeth, shells and wood.
“Our bidirectional freeze-casting technique could provide an
effective way of manufacturing novel structural materials, in particular
advanced materials such as composites, where a high level of control over the
structure is required,” says Robert Ritchie, an internationally recognized
authority on the mechanical behavior of materials with Berkeley Lab’s Materials
Sciences Division who led this study along with Antoni Tomsia, who is also with
Berkeley Lab’s Materials Sciences Division. “We were inspired by the
sophisticated hierarchical architectures ranging from the nano/microscopic to
macroscopic scales in certain natural materials that result in outstanding
properties despite being porous and made from weak constituents.”
Tony Tomsia
(left), Hao Bai (seated) and Rob Ritchie led the development of a bidirectional
freezing technique
that induces ceramic particles to assemble into scaffolds with centimeter-scale
aligned, porous
lamellar structures. (Photo by Roy Kaltschmidt)
Using their bidirectional freezing technique, the Berkeley
researchers were able to successfully induce ceramic particles to assemble into
scaffolds with centimeter-scale aligned, porous lamellar (alternating layered)
structures, similar to that of nacre (mother-of-pearl). This ordered
hierarchical structure was achieved by covering a laboratory “cold finger” with
a polydimethylsiloxane wedge that featured different slopes. The result was
controlled nucleation and growth of ice crystals during the freezing process
under dual temperature gradients.