Low-temperature synthesis of α-alumina based on sol-gel processes

ABSTRACT

Typically, synthesis of α-alumina (α-Al₂O₃) has been performed by annealing the aluminium hydroxide (AH) at temperatures higher than 1000°C, which leads to a high energy consumption. Accordingly, α-Al₂O₃ is desired to be synthesised by low-temperature processes for reducing energy consumption. This review describes our studies on the low-temperature synthesis of α-Al₂O₃ based on a sol-gel reaction. AHs were prepared by the hydrolysis of aluminium alkoxide and homogeneous precipitation from aluminium inorganic salt (alkoxide AH and inorganic AH, respectively). Alumina sols (ASs) were prepared by peptising the alkoxide AH and the inorganic AH with acids (alkoxide AS and inorganic AS, respectively). The ASs were converted to alumina gels (AGs) by dehydration in air at room temperature (alkoxide AG and inorganic AG, respectively). The ASs were seeded with α-Al₂O₃ nanoparticles and/or treated hydrothermally. Inorganic AS and AG were suitable to produce α-Al₂O₃ compared to alkoxide AS and AG. The use of formic acid as peptiser promoted crystallisation of AG to α-Al₂O₃. The seeding and the hydrothermal treatment also promoted the crystallisation. The alumina started to be crystallised to α-Al₂O₃ at a temperature as low as 400°C with the above three conditions.

KEYWORDS:

• Sol-gel
• alumina
• homogeneous precipitation
• hydrothermal process
• seeding technique
• crystallisation

Disclosure statement

The α-Al₂O₃ particles and the other chemicals were supplied by Ionic Liquids Technologies and Kanto Chemical, respectively. No financial support was provided by the two companies.

Additional information

Funding

This work was partially supported by Hitachi, Ltd.