Macroporous Alumina Ceramics with Aligned Microporous Walls by Unidirectionally Freezing Foamed Aqueous Ceramic Suspensions

Abstract

This paper reports a novel way of producing macroporous ceramics with aligned microporous walls by unidirectionally freezing foamed aqueous ceramic suspensions. The stability of the air bubbles introduced by magnetic stirring was improved remarkably using polyvinyl alcohol (PVA) as both a binder and emulsifying agent. Furthermore, the unidirectional freeze casting method could not only trap the air bubbles in the solidified sample successively but also induce the preferential growth of ice dendrites. This endowed the samples with uniform macropores surrounded by aligned microporous alumina walls after freeze drying and sintering. The sample produced with a PVA content of 8 wt% showed a high compressive strength of 4.6 ± 1.6 MPa at a high porosity of 91 vol%.

Controlled freezing and freeze drying: a versatile route for porous and micro-/nano-structured materials

“…In this process, PVA was used as a binder and emulsifying agent to stabilize air bubbles generated in aqueous alumina suspensions. 54 The freeze dried and subsequently calcined porous alumina could be further annealed and bridged at high temperatures to improve its mechanical strength. Inspired by the hierarchical complexity present in nature (e.g.…”

Control of pore channel size during freeze casting of porous YSZ ceramics with unidirectionally aligned channels using different freezing temperatures

“…For example, Han et al 15 adopted a camphene-based freeze casting method to fabricate ceramics with aligned, equiaxed pores, in which the pore volume fraction, channel size and pore shape were controlled by varying freezing temperature, solid content and sintering condition. Yoon et al 16 speed during the foaming process. Hong et al 17 produced highly porous zirconia ceramic bodies with interconnected pores by freeze casting technique using camphene-based slurries.…”

Strength enhancement of ultralight alumina‐dried foams from particle‐stabilized foams with assistance of agar and PVA

“…After treated by freezing-thawing, the cell wall of sintered foams is tortuous (see Figure 8 (C) and (D)), which is in accordance with the un-smooth particle wall of dried foams (see Figure 4 (B)). In Young-Hag Koh's work, 37 there are preferentially oriented aligned micropores formed in the alumina walls, aligning toward the center of the macropores, which is caused by the preferential growth of ice dendrites since heat would dissipate through the air bubbles during freezing. 38 However, in this present wok, the cellular wall exhibits a single-grain layer without aligned micropores as shown in Figure 8 (E) and (F).…”