Abstract: Nano-sized TiO2 was prepared by Sol-gel technique. The phase and size of the as-derived powders were analyzed by XRD. The effect of electron beam on the microstructures and phase transformation of TiO2 heat treated at various temperatures for different times was studied by in-situ TEM and SED. It is shown that below 250℃ amorphous phase TiO2 is presented. Upon heating the amorphous phase can be transformed to anatase and rutile and 70%(volume fraction) rutile can be detected after being calcined at 750℃ for 1h. The rest was anatase. Given the electron beam, anatase and rutile can be obtained from powders processed at 250℃ and 360℃. With increasing sizes, the effect of electron beam on the process of phase transformation is delayed. Rutile phase can not be observed by beam heating for short time in the sample heat treated at 600℃ for 1h. However, if the two phases of anatase and rutile coexist, the electron beam can facilitate the transformation to the final stable rutile. These changes may be due to the reactive vacuum atmosphere. In addition, a new phase is identified as TiC after beam heating for some seconds in the sample with amorphous phase.
Effect of electron beam on microstructures and phase transformation of TiO2 prepared by Sol-gel technique
Abstract:
Nano-sized TiO2 was prepared by Sol-gel technique. The phase and size of the as-derived powders were analyzed by XRD. The effect of electron beam on the microstructures and phase transformation of TiO2 heat treated at various temperatures for different times was studied by in-situ TEM and SED. It is shown that below 250 ℃ amorphous phase TiO2 is presented. Upon heating the amorphous phase can be transformed to anatase and rutile and 70% (volume fraction) rutile can be detected after being calcined at 750 ℃ for 1h. The rest was anatase. Given the electron beam, anatase and rutile can be obtained from powders processed at 250 ℃ and 360 ℃. With increasing sizes, the effect of electron beam on the process of phase transformation is delayed. Rutile phase can not be observed by beam heating for short time in the sample heat treated at 600 ℃ for 1h. However, if the two phases of anatase and rutile coexist, the electron beam can facilitate the transformation to the final stable rutile. These changes may be due to the reactive vacuum atmosphere. In addition, a new phase is identified as TiC after beam heating for some seconds in the sample with amorphous phase.
Fig.2 TEM images of powders dried at 110 ℃ for 24 h (a) and (b) —Original powder; (c) —After 30 s beam heating; (d) —After 2 min beam heating
图3 250 ℃干燥的粉末在电子束照射后的TEM和SED像
Fig.3 TEM and SED images of powders dried at 250 ℃after electron beam heating for different time (a) —Original powder; (b) —After 30 s beam heating; (c) —After 1 min beam heating; (d) —SED corresponding to (a) ; (e) —SED corresponding to (b) ; (f) —SED corresponding to (c)
Fig.4 TEM and SED images of rutile powders (a) —Heat treated at 360 ℃ for 15 h; (b) —Heat treated at 600 ℃ for 3 h; (c) —SED corresponding to (a) ; (d) —SED corresponding to (b) after 30 s beam heating
图5 两相共存时的TEM照片
Fig.5 TEM images of two phases coexisted in sample afterheat-treatment at 750 ℃ for 3 h (a) and 7 h (b)