Understanding of Homogeneous Spontaneous Precipitation for Monodispersed TiO2 Ultrafine Powders with Rutile Phase around Room Temperature
✍ Scribed by Soon Dong Park; Young Hyun Cho; Whung Whoe Kim; Sun-Jae Kim
- Book ID
- 102974872
- Publisher
- Elsevier Science
- Year
- 1999
- Tongue
- English
- Weight
- 528 KB
- Volume
- 146
- Category
- Article
- ISSN
- 0022-4596
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✦ Synopsis
Monodispersed TiO 2 ultra5ne particles were obtained from aqueous TiOCl 2 solution with a 0.67 M Ti 4؉ concentration prepared by diluting TiCl 4 with the homogeneous precipitation process in the range 17}2303C. With the spontaneous hydrolysis of TiOCl 2 , which means the natural decrease of the pH value in the aqueous solution, all monodispersed precipitates were crystallized with the anatase or rutile TiO 2 phase during the reactions. The TiO 2 precipitate with the pure rutile phase was fully formed at temperatures below 653C, which did not involve the evaporation of H 2 O, and above 1553C, which were available by suppressing it. The TiO 2 precipitate with the rutile phase, including a small amount of the anatase phase, started to be formed at intermediate temperatures above 703C, showing the full formation of the anatase phase above 953C under the free evaporation of H 2 O. However, in the case of completely suppressing H 2 O evaporation at temperatures above 703C, the TiO 2 precipitate with the anatase phase that had already been formed by rapid reaction was fully transformed with the reaction time into the precipitate with the rutile phase by the vapor pressure of H 2 O. Therefore, the formation of TiO 2 precipitates with the rutile phase around room temperature would be caused by the existence of capillary pressure between the agglomerated needleshaped particles or the ultra5ne clusters, together with the slow reaction rate.