Microstructure of Fe₂O₃ scaffolds created by freeze-casting and sintering

Fe₂O₃ scaffolds with an open porosity of ∼81% were fabricated by freeze casting of a suspension of hematite nano-particles in liquid camphene, sublimation of the camphene, and sintering of the interconnected walls of hematite particles concentrated in the interdendritic spaces. At high solidification velocity, the camphene dendrites created, after sublimation, equiaxed, interconnected macropores, whose size increases with decreasing velocity and which are surrounded by interconnected hematite walls. At the lowest solidification velocity, camphene dendrites grow radially into the sample along the temperature gradient, creating, after sublimation, aligned elongated macropores, 50-150 μm in diameter and 3-4 mm in length, surrounded by aligned hematite walls with low levels of microporosity after sintering. Hydrogen reduction of such a sample resulted in a metallic iron scaffold with the same elongated macropore and densified iron walls.