Microstructural evolution of paramagnetic materials by magnetic freeze casting

External magnetic fields were applied during the process of directional solidification to control the microstructural patterning of ceramic scaffolds formed by freezing colloidal mixtures of magnetic and paramagnetic particles. Under low magnetic fields (<158mT), uniform and biphasic distributions of magnetite particles (Fe3O4) were observed. Uniform distributions of Fe3O4 formed under low field strengths (<40mT), while increasing the field strength/gradient (>70mT) led to the formation of biphasic patterns of iron-rich and iron-poor regions. Under shallow gradients of near-uniform fields, viscous forces dominate, causing the Fe3O4 particles to remain evenly distributed throughout the slurry. In contrast, larger field gradients exert forces on the Fe3O4 particles, attracting them toward the magnetic poles. Competition between the viscous and magnetic forces dictates the formation of uniform or biphasic patterning in magnetically aligned freeze cast scaffolds.