Preparation and properties of porous Al₅BO₉ for high‐temperature wave‐transparent and thermal insulating applications

Abstract

Porous Al 5 BO 9 is a promising high-temperature wave-transparent material. However, method for the preparation of this material is not readily available.Herein, porous Al 5 BO 9 ceramics with controlled porosity and small volume shrinkage are successfully prepared by using Al 2 O 3 and B 2 O 3 as starting materials without pore formers. The SEM and pore size distribution studies show that the as-prepared porous Al 5 BO 9 ceramics exhibit a uniform pore structure and a narrow pore size distribution. Intriguingly, simply adjusting the densities of the green bodies, the density and porosity of the porous Al 5 BO 9 ceramics can be controlled. The pore-forming mechanism is presumed to be a combination of boron oxide volatilization during the high-temperature synthesis and lap of elongated grains. Porous Al 5 BO 9 ceramics have good high-temperature stability, which can maintain dimensional and composition stability up to 1673 K. The compressive strength can reach 211 MPa at 32.4% porosity and the dielectric constant can be as low as 3.02 at 43.2% porosity. In addition, the dielectric constant and loss tangent keep almost unchanged with temperature.