Porous crystal structures obtained from directionally solidified eutectic precursors

Abstract

Interconnecting cage-like porous structures of several halide compounds were prepared by the selective leaching of one eutectic phase method. The binary eutectic precursors were prepared by directional solidification using the Bridgman crystal growth technique. Porous NaMgF3 (40% pore volume), CaF2 (57% pore volume) and BaF2 (43% pore volume) crystals were obtained after water leaching the NaF component of the directionally solidified NaF/NaMgF3, NaF/CaF2 and NaF/BaF2 eutectics with the appropriate entangled microstructure. The growth conditions for eutectic-coupled growth and the morphology of the eutectics have been determined. In the coupled growth regime, the size of the eutectic phases “λ” is fairly uniform and varies with the eutectic growth rate “v” as λ2v=constant, which allows us to control the pore size within the 0.5–10 μm range. The simplicity and versatility of the eutectic growth also allows us to fabricate highly aligned porous structures at relatively high production rates.