Effects of Annealing on the Morphology and Porosity of Porous TiO2 Films Fabricated by Deposition of Aerosol Nanoparticles
Journal of Chemical Engineering of Japan
The present study investigates the impact of post annealing of TiO 2 nanoparticulate lms on their crystallinity, mechanical strength, and morphology. Non-agglomerated and amorphous TiO 2 nanoparticles of 46 nm diameter were synthesized in a plasma eld, and were subsequently deposited on substrates to form nanoparticulate lms. The lms were annealed at various temperatures in the range of 100-1,200°C. Phase transformations from amorphous-to-anatase and from anatase-to-rutile were observed at
... re observed at 400°C and at 1,000°C, respectively. The high rutile transformation temperature was considered to be due to a tensile eld induced by shrinkage of the lm. The as-deposited lm and the lms annealed at below 400°C had poor mechanical strength. Conversely, the lms annealed at over 500°C were strengthened by necking of the nanoparticles. The size of nanoparticles changed with increasing temperature. Annealing at 100-300°C caused the nanoparticles to shrink to approximately 30 nm. The nanoparticle diameters changed only slightly when annealed at 400-600°C because the annealing time was insu cient for changes to manifest. Annealing at 700-900°C caused the nanoparticle diameter to increase to approximately 50 nm because of sintering and coalescence of the nanoparticles. The diameter of the nanoparticles annealed at over 1,000°C became approximately 200 nm because of densi cation during the anatase-to-rutile transformation. The porosities of the lms annealed at below 900°C were over 80%. However, the porosities of the lms annealed at over 1,000°C decreased signi cantly due to densi cation.