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

Abstract

Please cite this article in press as: K. Yamamura, et al., Effect of hydrothermal process for inorganic alumina sol on crystal structure of alumina gel, J. Asian Ceram. Soc. (2016), http://dx. a b s t r a c tThis paper reports the effect of a hydrothermal process for alumina sol on the crystal structure of alumina gel derived from hydrothermally treated alumina sol to help push forward the development of low temperature synthesis of ␣-Al 2 O 3 . 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 the production of a transparent alumina sol. The alumina sol was treated with a hydrothermal process and transformed into an alumina gel film by drying at room temperature. Crystallization of the alumina gel to ␣-Al 2 O 3 with 900 • C annealing was dominant for a hydrothermal temperature of 100 • C and a hydrothermal time of 60 min, as production of diaspore-like species was promoted with the hydrothermal temperature and time. Excess treatments with hydrothermal processes at higher hydrothermal temperature for longer hydrothermal time prevented the alumina gel from being crystallized to ␣-Al 2 O 3 because the excess hydrothermal treatments promoted production of boehmite.

Evaluation of the modified reduction/expansion synthesis in the production of nanoparticulate alumina

“…The faceted structures are made of article that have an average particle sizes between 50 and 150 nm. Transferring the mixed paste of aluminum nitrate and urea from room temperature to a preheated oven involves an extremely fats heating of the mixture, leading to a thermal decomposition of the mixture in a temperature range between 160 to 250 o C, depending of the paste composition [7,12,13,15,16]. Aluminum nitrate decomposition has been reported to start at temperatures as low as 150 o C [15], meanwhile urea decomposes in a first stage between 180 -250 o C to form ammonium and isocianic acid followed by a further decomposition of the isocianic acid to a gaseous mixture of ammonium and carbon dioxide at temperatures above 350 o C [10,12].…”

“…Metal oxides nanoparticles synthesis have been widely investigated in recent years, mainly due to the large and important fields of application such materials could have (catalysts, semiconductors, sensors, medical science and devices, energy storage and batteries). Among the several studied methodologies alkoxides synthesis [1][2][3][4][5], sol-gel [6,7], plasma torch [8,9] are the most used. However many of these methodologies generally involve the use of multiple reaction/separation stages, often using expensive equipment and reagents that could be hazardous.…”

Structural and Optical Coefficients Investigation of γ-Al2O3 Nanoparticles using Kramers-Kronig Relations and Z–scan Technique

“…Except for stable α-Al 2 O 3 , the other metastable transitional phases of Al 2 O 3 can be employed as catalyst supports [7]. Due to the high stability of the γ-Al 2 O 3 and having a large specific surface area, it has more interested use in the most catalytic reactions as a catalyst or catalyst substrate in the automotive and petroleum industries [8,9]. Furthermore, the γ-Al 2 O 3 hybrid nanocomposite is very favorable for solar energy and solar collector heaters [10].…”