STRUCTURAL AND MORPHOLOGICAL MODIFICATIONS OF SINTERING MICROCRYSTALLINE TIO2 - AN XRD, HRTEM AND FTIR STUDY

Degussa P25 (mostly anatase) activated at T less-than-or-equal-to 873 K exhibits fairly regular Particles and mainly one family of strong coordinatively unsaturated Ti4+ sites, active towards CO at 77 K. After firing at T greater-than-or-equal-to 1000 K, the phase becomes rutile, the crystallites become larger, and their morphology becomes more irregular, while less and less uncoordinated Ti4+ sites are produced on activation, yielding CO bands absorbing at lower nu. The modifications of crystal morphology and of surface activity towards CO are not due to the anatase-rutile phase transition, as a similar behaviour with firing temperature is exhibited by pure rutile.