High porosity hafnia ceramics by freeze casting

Abstract

Highly porous hafnia ceramics are prepared by freeze casting. The major challenge resides in the high density of the hafnia particles typically leading to settling in the slurry. To address this, we optimized the suspension formulation to achieve structures with porosities of 68–74 %. Our approach includes a reduction in additive quantities and an adjustment of the pH value for suspension stabilization and prevention of particle settling. The use of PVA and PEG ensures a green body strength during the process yielding in cellular microstructure with pore channels aligned in the freezing direction throughout the sample. With increasing solid loading, the scaffolds become denser and the pore wall thickness increases. Compressive strength tests confirm the enhanced stiffness of the samples with 15 vol% hafnia. Samples with 10 vol% hafnia show a buckling-dominated failure behavior. Our results provide valuable insights to the preparation of suspensions containing high density materials.

Keywords

• Hafnia
• Porous ceramics
• Freeze casting
• Anisotropy