Thermal Behavior and Phase Transformation of TiO 2 Nanocrystallites Prepared by a Coprecipitation Route
- PDF / 776,520 Bytes
- 8 Pages / 593.972 x 792 pts Page_size
- 63 Downloads / 191 Views
DUCTION
TiO2 is one of the important inorganic material, widely used in sunscreen,[1] photocatalyst,[2,3] and sensors.[4,5] TiO2 possesses three crystal structures: anatase, rutile, and brookite.[6] The anatase and rutile phases are Ti-O octahedral which formed a tetragonal structure, otherwise, the brookite phase formed an orthorhombic.[6] The common phases of TiO2 are anatase and rutile, where the rutile is the most stable one among the three phases. The phase transformation from anatase and brookite to rutile occurred when the anatase and brookite were calcined between 623 K to 1478 K (350 C to 1175 C),[7] and 773 K to 873 K (500 C to 600 C),[8] respectively. Recently, numerous techniques have been widely used for synthesizing the TiO2 nanopowders that have greater control properties, such as the coprecipitation,[9,10] hydrothermal,[11,12] and sol–gel method.[13,14] Among these, homogeneous precipitation is one of the most promising techniques because of the advantages of low cost, easy-to-acquire equipments, a simple synthesis process, and nanometric precursor particles. Using the coprecipitation route for synthesis, the amorphous TiO2 SHANG-WEI YEH, Graduate Student, YEN-LING CHEN, Assistant Professor, HORNG-HUEY KO, Associate Professor, and MOO-CHIN WANG, Professor, are with the Department of Fragrance and Cosmetic Science, Kaohsiung Medical University, 100 Shih-Chuan 1st Road, Kaohsiung 80782 Taiwan R.O.C. Contact e-mail: [email protected] CHI-SHIUNG HSI, Professor, is with the Department of Materials Science and Engineering, National United University, 1 Lein-Da, Kung-Ching Li, Miao-Li 36003, Taiwan R.O.C. Manuscript submitted March 14, 2013. Article published online August 30, 2013 METALLURGICAL AND MATERIALS TRANSACTIONS A
precursor powders were obtained for the precipitation through freeze-drying process. After calcinations, the crystalline TiO2 powders were obtained. Hsiang et al.[15,16] have pointed out that the activation energies of a-TiO2 and r-TiO2 crystallization were obtained, namely, 53 to 250 kJ/mol and 205 to 506 kJ/mol, respectively, and the values were dependent on aging process. The value of activation energy for TiO2 crystallization with aging treatment was higher than that without aging. In addition, Kumar et al.[17,18] also proposed that the activation energy of phase transformation from a-TiO2 transformed to r-TiO2 was 147 kJ/mol for the titania membranes prepared by sol–gel process. However, thermal behavior and phase transformation of TiO2 freezedried precursor powders prepared by a coprecipitation route have not been discussed in detail. In the present study, the TiO2 freeze-dried precursor powders synthesized using titanium tetrachloride as initial material prepared by a coprecipitation route were investigated. The thermal behavior and phase transformation of TiO2 freeze-dried precursor powders after calcination were investigated using differential scanning calorimetry/thermogravimetry (DSC/TG), X-ray diffractometer (XRD), transmission electron microscopy (TEM), selected area ele
Data Loading...
