Fabrication of porous magnesium spinel with directional pores by unidirectional solidification

A porous magnesium spinel (MgAl2O4) with directional pores was fabricated by unidirectional solidification in pressurized argon and hydrogen mixed gases. Two different kinds of pores with large directional and small facet shape were formed in the solidified samples. The former pores were dominant in the porous structure. A small amount of free corundum phase was formed in the solidified porous spinel as a secondary phase by vaporization of MgO component during the solidification process. With increasing total gas pressure, the pore size of the solidified samples decreased while no change in the porosity. The porosity and pore size of the samples increased with increasing hydrogen partial pressure. The porosities of the samples fabricated under 10%H2–90%Ar and 1%H2–99%Ar mixed gases were 30 and 10%, respectively, and that under Ar atmosphere was very low, non-porous.