Synthesis and Characterization of Aluminum Borate Ceramic Whiskers

Aluminum borates are synthesized via a precipitation process. Aluminum nitrate and calcium hexaboride (CaB6) as a source of B2O3 were used. Various proportions of aluminum nitrate were mixed with CaB6 powder and to a solution of ammonium hydroxide. The resulting mixtures were evaporated and calcined up to 650 degrees 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 degrees C under argon gas avoiding the oxidation of the CaB6. 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 mm. Porous aluminum borate ceramic consisted of whiskers with a porosity of 9-21% for samples sintered up to 1400 degrees C. Increasing the sintering temperature to 1500 degrees C and CaB6 addition (15 wt%) deteriorated both the flexural strength and modulus of elasticity of the ceramic bodies.