Seeding technique for lowering temperature during synthesis of α-alumina

• This paper reports a method for producing α-Al2O3 at low temperature.
• A transparent alumina sol was prepared by hydrolyzing aluminum isopropoxide.
• The sol was converted to alumina gel by drying in air at room temperature.
• Seeding of α-Al2O3 crystallites promoted crystallization of alumina gel to α-Al2O3.
• Alumina gel seeded with 5% α-Al2O3 started to be crystallized to α-Al2O3 at 900 °C.

This paper reports a method for producing α-Al2O3 at low temperature using a seeding technique. A white product obtained by hydrolyzing aluminum isopropoxide in water at 80 °C was peptized using acetic acid at 80 °C, which transformed the white product to a transparent alumina sol. α-Al2O3 particles were added to the alumina sol as seed material; the sol containing α-Al2O3 particles was then transformed to an α-Al2O3-seeded alumina gel by drying the sol at room temperature. The non-seeded alumina gel remained boehmite after annealing at 300 °C and crystallized into γ-Al2O3 and α-Al2O3 at temperatures between 300 and 500 °C and between 900 and 1100 °C, respectively. The α-Al2O3 seeding promoted crystallization of the alumina gel into α-Al2O3. The promotion of crystallization was significant with an increase in α-Al2O3 particle content by weight in the final seeded alumina gel. With an α-Al2O3 particle content of 5%, the seeded alumina gel was partially crystallized into α-Al2O3 by annealing at a temperature as low as 900 °C.