Preparation and Characterization of Aluminum Borate

Aluminum borate, 9Al 2 O 3 ·2B 2 O 3 or Al 18 B 4 O 33 , was synthesized by the reaction of stoichiometric amounts of α‐Al 2 O 3 and B 2 O 3 . The Al 18 B 4 O 33 material was formed into a dense ceramic by pressureless sintering with CaO, MgO, or CaAl 2 B 2 O 7 additives. The material was characterized by low bulk density, moderate coefficient of thermal expansion (3 × 10 −6 /°C to 5 × 10 −6 /°C), moderate strength (210 to 324 MPa), and low dielectric constant.