Low temperature synthesis of α-alumina through a hydrothermal process combined with a seeding technique

Abstract

This paper reports a method for producing α-Al₂O₃ at low temperatures by using a hydrothermal process and a seeding technique. White aluminum hydroxide precipitate prepared through a homogeneous precipitation method using aluminum nitrate and urea was peptized by using formic acid at room temperature to transform it into a transparent alumina sol. After the sol was hydrothermally treated, α-Al₂O₃ nanoparticle seeds were added to the sol. The sol containing the α-Al₂O₃ nanoparticles was transformed into an α-Al₂O₃-seeded alumina gel by drying at room temperature. The non-seeded alumina gel began to crystallize into α-Al₂O₃ at 500 °C. The α-Al₂O₃-seeding promoted the crystallization of the alumina gel to α-Al₂O₃. A remarkable α-Al₂O₃ crystallinity was achieved with an increase in α-Al₂O₃ content by weight in the final seeded alumina gel. Even with a content as low as 1%, the seeded alumina gel was partially crystallized to α-Al₂O₃ at a temperature as low as 400 °C.

Keywords:

• Sol-gel
• alumina
• homogeneous precipitation
• peptization
• formic acid
• hydrothermal process
• seeding technique, crystallization

Acknowledgments

This work was partially supported by Hitachi, Ltd.