Low Temperature Synthesis of α -Alumina with a Seeding Technique

Abstract

This paper reports a method for producing α -Al 2 O 3 at low temperature, which uses a seeding technique. White precipitate of aluminum hydroxide, which was prepared with a homogeneous precipitation method using aluminum nitrate and urea in aqueous solution, was peptized by using acetic acid at room temperature and then transformed to a transparent alumina sol. To the alumina sol α -Al 2 O 3 particles were added as a seed, and then the sol containing α -Al 2 O 3 particles was transformed to an α -Al 2 O 3 -seeded alumina gel by drying the sol at room temperature. The nonseeded alumina gel was amorphous or fine crystallites even after being annealed at 600°C and was crystallized to γ -Al 2 O 3 at 700°C. The α -Al 2 O 3 seeding promoted crystallization of alumina gel to α -Al 2 O 3 . The promotion of crystallization was made remarkable with a decrease in α -Al 2 O 3 particle size and an increase in α -Al 2 O 3 particle content in weight for the final seeded alumina gel. With an α -Al 2 O 3 particle size of 150 nm and an α -Al 2 O 3 particle content of 5%, the seeded alumina gel was partially crystallized to α -Al 2 O 3 by annealing at a temperature as low as 700°C and mostly at 900°C.