Improved strength and control over surface-magnetized titania porous structures freeze cast under oscillating magnetic fields

Abstract

Fabrication processes that produce porous structures with a high strength-to-weight ratio are sought after in many industries. The process of freeze casting is a way to achieve these porous structures with high strength-to-weight ratios, but only in a single direction (the direction of the templating-ice growth). Application of a magnetic field to these structures allows for an increase of mechanical strength in an additional orthogonal direction, therefore allowing them to be applied in more complex loading scenarios. Using a Helmholtz coils setup, it is possible to apply weak, uniform fields (<10 mT) in a variety of directions, magnitudes, or frequencies. Previous research has shown that the application of these weak uniform fields, in particular, oscillating fields from a Helmholtz coils setup, has led to increased mechanical strength through microstructural alignment, but only when using iron oxide structures. To mitigate this, a surface magnetization process was used to increase the magnetic response from non-ferrimagnetic materials, specifically titania, along with a higher magnetic strength (20 mT) Helmholtz coils setup. These surface-magnetized materials and oscillating fields led to an increase of strength of 10x when compared to non-surface-magnetized materials and 2x when compared to surface-magnetized materials under no field due to decreased porosity and increased alignment of mineral bridges. This demonstrates that increased material response for non-ferrimagnetic titania can be induced through the application of an oscillating field in conjunction with the surface-magnetization process.