A KINETIC STUDY ON THE PHASE TRANSITION OF TIO2 AND PARTICLE GROWTH MECHANISM AT NON-AMBIENT CONDITION

TiO2 is a kind of materials with many technological and geological applications, such as pigment, china, photocatalysis, electronic, catalysis, pressure standard etc. TiO₂ possesses six polymorphs; however the most common ones are anatase and rutile.

By using in situ high temperature X-Ray diffraction, the phase transition from anatase to rutile at temperatures 850, 863, 875, 888 and 900ºC were investigated. The results of transition percentage versus time show that the phase transition from anatase to rutile is a first-order reaction, and is characterized by an activation energy of 432.788±25.657 KJ/mol. The rate constants “A” in the Arrhenius equation is determined at 4.847454×1015 sec^-1.

Environmental scanning microscopy was employed to find out the influence of temperature and time on particle growth. Two group experiments were performed. One is time fixed for 10 hours with sintering temperatures at 888, 900, 930, 960 and 1000ºC. The other is sintering at 1000 ºC for 0, 5, 10, 15 and 20h. Environmental scanning microscopy images show that below 1000ºC, the influence of temperature on particle growth is not observable, and fine crystal form does not occur in rutile. At 1000ºC, particles grow up with increasing time. Fine crystal form occurs in rutile after sintering for 10 hours. The relationship between lnD_t (D_t is the average particle size in time t) and time shows that particles have experienced two different growth periods.