Role of solvent composition and sintering time on the porosity of α‐alumina monoliths produced by freeze casting

Abstract

The present study reports the investigation of the influence of naphthalene–camphor binary solvent and the densification process on the pore structure formation of α‐alumina monoliths using the freeze‐casting technique with a freezing temperature control mechanism. Freeze‐casting technique allowed a controlled production of monoliths with high porosity (65%–70%) and distinct pore morphologies based on the adjustment of solvent composition (hypoeutectic, eutectic, and hypereutectic) and sintering time. In general, the longer the sintering time, the greater the average pore diameter (8–10 µm), the larger the grain size (∼319–596 nm), the higher the material density (∼1450–1650 kg/m3), the lower the open porosity (∼60%–49%), the higher the closed porosity (5%–18%), and the greater the compressive strength of the monoliths (hypoeutectic: 23.56 MPa; eutectic: 4.81 MPa; hypereutectic: 23.49 MPa). The study also reveals that the solvent composition directly influenced the alignment of the pore structure, as the pores of the final monolith resemble frozen solvent crystals. Hydraulic tortuosity varied from 1.30 to 1.53 for selected samples. Finally, solvent composition and sintering time proved to be important parameters that should be considered in the manufacturing process of porous ceramic structures via freeze casting.