Improvement of alumina-based porous body fabricated by freeze casting route via alpha alumina/colloidal silica sol precursors

Abstract

In this paper, alumina-based porous bodies were fabricated by the freeze casting method, and the effects of solid content and freezing conditions on mechanical properties, water permeability, and microstructure of samples were thoroughly investigated. Microstructural evaluation revealed highly porous microstructures with unidirectionally aligned porosities in the samples. SEM micrographs exhibited uniform pores with an average size of 5 μ m. Additionally, EDS analysis and SEM mapping showed a comprehensive interconnected porous framework among alumina particles fabricated by amorphous colloidal silica during the freezing step. Mullite phase was observed in the XRD patterns of the samples after sintering at 1400 °C for 2 h. Maximum compressive strength reached 145 MPa, and this significant mechanical strength was owing to the particle densification caused by the mullitazation reaction between alumina and silica during sintering. Physical properties measurements illustrated the minimum open porosity of 41 vol.% and the maximum bulk density of 2.1 g cm ^−3 . Permeability assessment as an important factor to evaluate filtration efficiency showed at least 0.22 (g. cm ^−2 . s ^−1 .bar ^−1 ) water flow rate, which was approximately twice greater than that of other recent works.

Keywords

• freeze casting
• porous ceramics
• aligned porosity
• alumina
• permeability