Synthesis and Characterization of Aluminum Borate Ceramic Whiskers

Aluminum borates are synthesized via a precipitation process. Aluminum nitrate and calcium hexaboride (CaB ₆ ) as a source of B ₂ O ₃ were used. Various proportions of aluminum nitrate were mixed with CaB ₆ powder and to a solution of ammonium hydroxide. The resulting mixtures were evaporated and calcined up to 650°C. A porous ceramic with a framework structure of aluminum borate whiskers was synthesized in situ by firing the green compact bodies up to 1400°C under argon gas avoiding the oxidation of the CaB ₆ . The structure and morphology were investigated by XRD and SEM. The results indicate that whiskers exhibit a well‐crystallized structure with an average diameter distribution of about 500 nm and lengths ranging from 5 to 8 μm. Porous aluminum borate ceramic consisted of whiskers with a porosity of 9–21% for samples sintered up to 1400°C. Increasing the sintering temperature to 1500°C and CaB ₆ addition (15 wt%) deteriorated both the flexural strength and modulus of elasticity of the ceramic bodies.