A flexible route to high strength α-alumina and aluminate spheres

Abstract

The formation of hollow alumina spheres is accomplished by coating polystyrene beads of 3 μm and 50–80 μm diameter with carboxylic acid functionalized alumina nanoparticles (alumoxanes) from aqueous solution 2–8 wt%. The resulting coated beads were heated to 220°C to calcine the alumoxane to porous amorphous alumina before washing with toluene to remove the polystyrene from inside the ceramic coating. The resulting hollow spheres were sintered at 1000°C to form α-alumina. The α-alumina spheres have been characterized, by SEM (scanning electron microscopy), BET, and hardness measurements, that show the hardness of the hollow alumina sphere (1900 ± 100 Kg.mm−2) approaches that of corundum (ca. 2000 Kg.mm−2). Multilayered bi-phasic spheres may be prepared by subsequent coating the α-alumina spheres with a solution of a metal-doped alumoxane. After calcining, the mixed metal oxide phase (CaAl12O19, Er6Al10O24, MgAl2O4, Al2TiO5, and Y3Al5O12) forms outside of the alumina sphere resulting in a composite like ceramic bi-layer sphere. Pre-formed hollow alumina spheres were incorporated into a resin and ceramic thin film formed from a 1 wt% A-alumoxane aqueous solution. The hardness of the composites is compared to the matrix materials themselves.