Synthesis of Cubic Alpha-Alumina Using a Blocking Reagent of Tetraethyl Ammonium Hydroxide

This study was an attempt to obtain a stable and reproducible cubic primary alumina by a hydrothermal method using various aluminum precursors, AIP, AlO(OH), and Al(OH)3. Tetraethyl ammonium hydroxide was introduced as a blocking reagent to control the shape of alumina. The synthesized primary alumina powders from Al precursors showed a boehmite structure after hydrothermal treatment at 200 °C for 1 h. The primary alumina powders synthesized using the precursors of AIP and AlO(OH) had irregular shapes, however the cubic-shape of approximately 300 nm was observed in the primary alumina powder synthesized using Al(OH)3 precursor. The cubic primary alumina samples were transformed to different solid phases like gamma-, delta-, theta-, and alpha-phases according to the calcined temperatures. The theta-phase alumina formed at 1100 °C continually kept the cubic shape, but the shape was collapsed at 1200 °C. However the cubic alpha-alumina alpha-alumina was stably remained by thermal treatment at 1100 °C under the fierce oxygen atmosphere.