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

Porous Al5BO9 is a promising high‐temperature wave‐transparent material. However, method for the preparation of this material is not readily available. Herein, porous Al5BO9 ceramics with controlled porosity and small volume shrinkage are successfully prepared by using Al2O3 and B2O3 as starting materials without pore formers. The SEM and pore size distribution studies show that the as‐prepared porous Al5BO9 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 Al5BO9 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 Al5BO9 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. [ABSTRACT FROM AUTHOR]