Simultaneous control of mechanical strength and hierarchical structure in freeze-casted porous alumina by two-step sintering

Abstract

To increase mechanical strength of porous ceramics, here, an effective two-step sintering (TSS) technique capable of producing highly porous alumina with enhanced mechanical strength is suggested. Based on the sintering theories, here, a significantly lower activation energy for densification at low temperature region allowed a beneficial temperature range for the TSS to be deduced. With a specific TSS regime (T1 = 1550°C and T2 = 1400°C), significantly higher compressive strength levels (8.00–15.24 MPa) were measured with an apparent porosity of 56.49% compared to conventional sintering (1.03–1.86 MPa) with similar apparent porosity of 57.84%. Specifically, another TSS regime (T1 = 1550°C and T2 = 1380°C) left submicron-sized open pores within the lamellar walls, providing a hierarchical porous structure with enhanced mechanical strength. An evaluation of the mechanical stability by a finite element analysis indicated outstanding compressive strength even with small pores in the lamella walls. © 2023 The American Ceramic Society.