Abstract: The preparation process of nano-aluminum hydroxide sol by peptizing aluminum hydroxide precipitate produced via carbonation of sodium aluminate was investigated. The reaction, in which the sodium aluminate solution was dropwise added into abundant sodium bicarbonate solution, was analyzed. The XRD results indicated that the amorphous aluminum hydroxide precipitates transformed into pseudo-boehmite because the precipitates dissolved and recrystallized into pseudo-boehmite crystals during the sol preparation. Furthermore, the increase of absorption at 270 nm in the UV spectra indicated the presence of Al(OH)3-6 ion during the sodium aluminate solution with caustic ratio of 1.7 was neutralized to 1.3. Comparing with the absorption spectrum of the structure of six hydroxyl groups around Al atom, it could be concluded that the coordination numbers of Al atom with hydroxyl groups changed from four to six during the decomposition of sodium aluminate solution. Besides, the morphology of particles in the sol was also influenced by surfactants and acids used.

Key words: Nano-alumina, Sodium aluminate solution, Amorphous Al(OH)3, Pseudo-boehmite, Sol-gel process