Fabrication of transparent self-supporting alumina films by homogeneous precipitation process

Abstract

This paper reports fabrication of transparent self-supporting alumina films by using homogeneous precipitation and peptization processes. White precipitate of aluminum hydroxide was prepared with a homogeneous precipitation method using aluminum nitrate and urea in aqueous solution. The obtained aluminum hydroxide precipitate was peptized by using acetic acid at room temperature, which resulted in production of a transparent alumina sol. The alumina sol was transformed to an alumina gel film by drying the sol at room temperature. The alumina film was amorphous or fine crystallites even after annealed at a temperature as high as 500°C, and was crystallized to £-Al 2 O 3 at 900°C.

Effect of hydrothermal process for inorganic alumina sol on crystal structure of alumina gel

“…The inorganic alumina sol was prepared in accordance with our previous work [22]. The homogeneous precipitation method was then used for producing precipitate of aluminum hydroxide, as follows.…”

“…Another difficulty is that alcohol produced with the hydrolysis of the alkoxide remains in the final materials, which also deteriorates the function. Bearing mind, our group proposed a method for producing alumina with the use of aluminum salt [22], which is much less expensive than alkoxide. Aluminum hydroxide was prepared with a homogeneous precipitation method using aluminum nitrate and urea in aqueous solution, and alumina sol was obtained by peptizing with acetic acid at room temperature (inorganic alumina sol).…”

Effect of peptiser species on crystallisation of alumina gel produced by sol–gel process

“…Aluminium hydroxide is peptised with acid to transform it into alumina sol; then, the sol is gelated under evaporation of the solvent. Our research group has studied the preparation of alumina sol, using a homogeneous precipitation method and fabrication of alumina gel [18]. In this study, acetic acid was used as a peptiser for aluminium hydroxide produced via the homogeneous precipitation method to obtain alumina sol.…”

Seeding technique for lowering temperature during synthesis of α-alumina

“…The author's previous work proposed methods for preparing alumina sol from inorganic aluminum salt using a homogeneous precipitation method and for fabricating alumina [13]. The obtained alumina consisted of amorphous or fine crystallites even after annealing at temperatures as high as 500 • C and was crystallized to ␥-Al 2 O 3 at 900 • C, which implied that the alumina must be annealed at even higher temperatures to produce transformations to ␣-Al 2 O 3 .…”