The PTA sol was prepared using titanyl sulfate(TiOSO4), peroxide (H2O2) and ammonia (NH3·H2O) as raw materials. The semitransparent, light yellow AS(autoclaved sol) with ultra-fine needle-like anatase crystals was synthesized by autoclaving the PTA sol at 80-100℃ for different times. The anatase crystals were needle-like and 80 nm in length, 20-30 nm in diameter. The FTIR, XRD, SEM were used to analyse the chemical structure,properties of the AS and influencing factors during the sol preparation. The mechanism model of the AS formation was established based on the inorganic and crystal structural chemistry. The PTA molecules were decomposed to form Ti4+ under hydrothermal conditions and the Ti4+ were hydrated with water to get [Ti(OH)4(OH2)2]0, a growing units of the anatase crystals. The appearance of the needle-like anatase crystals and the anatase precipitate are also explained in this paper.
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