الفهرس | Only 14 pages are availabe for public view |
Abstract Pure (TiO2) titania and chromium (Cr) doped TiO2 nanocrystals were synthesized using hydrolysis method. The used molar ratios of chromium (III) acetate hydroxide: titanium tetra isopropoxide are 0, 5, 15, and 25 %. Synthesized nanopigments were classified to three categories first used assynthsized and others annealed at 500 ℃ and 700 ℃ respectively. X − ray diffraction analyses, FTIR and high-resolution transmission electron microscope (HRTEM) were utilized to investigate the microstructure and property of synthesized nanopigment. Also surface area of synthesized samples was estimated by BET method. Optical property of synthesized nanopigment was specified by UV/Vis/NIR spectroscopy. The combined influence of calcination temperature and chromium addition on the phase transformation, grain growth and near infrared (NIR) reflectivity of nanopigments has been investigated. Pure titania, annealed at 700 ℃ has shown the highest NIR solar reflectance (R ∗ ) up to 95% .The presence of Cr ion in annealed titania samples caused huge reduction in NIR reflectivity. While the NIR reflectivity of pure titania, used assynthesized was slightly reduced with increasing Cr ion content. Doped samples used as-synthesized have NIR solar reflectance higher than obtained for doped in other annealed series. S4 − 100 sample presented optimum reflectance behavior for both of cooling and aesthetic sides. The estimated optical energy gap (Eg), calculated from diffuse reflectance spectrum in sight of Kubelka– Munk assumptions, of the examined nanopigments were significant reduced in annealed nanopigments and slightly reduced in nanopigments the assynthesized. The variation in both dielectric constant (ε′), and ac conductivity (σac) as a function of applied frequency at different doping concentration of Cr were investigated. The measurements confirms that both ε′ and σac values of TiO2 were decreased with Cr doping in first series of samples and increased with Cr doping in second series of samples. |