| A novel electrochemical synthesis process including process parameters, phase changes and microstructure, of nanosized single phase and composite titanium dioxide powders in aqueous solutions using the intermediate product-titanium tetrachloride from TiO2 powder industry has been investigated, which is closely related to update the present TiO2 powder production processes.As a kind of raw chemical material in common use, the conventional titanium dioxide has being widely used as pigment, additives of printing ink, and additives in paper for improving its whiteness. It is also an important material of functional ceramics, semiconductor and activator. In particular, with the diameter of titanium dioxide nanosized, titanium dioxide behaves in some unique properties such as good ultraviolet absorptivity, transparence and harmless, special color effects, and photocatalytic activity. These excellent properties make it widely used in the automobile industry, cosmetic for sun-burn prevention, high-grade pigments, waster water treatment, environmental protection, bacterium killing, adsorbent, and functional ceramics. The further research and development of novel n-Ti02 preparation routes are meaningful for both academic and technological advances.The process parameters of preparing nanosized titanium dioxide powders were systematically studied by electrochemical synthesis experiments at room temperature. The rutile phase and anatase phase powders were obtained in the sizes of 9. 7nm and 9. 2nm respectively, and the complete crystal powders were formed after calcined at 400 ℃ for two hours. In the process of experiments it was observed thatthe low current density resulted in rutile phase powders, while the addition of little amount of ions of sulfate promoted the formation of anatase phase powders. With some proper conditions, the mixture of rutile and anatase phase powders could be obtained. The sizes of the powders increased in a relatively slowrate when the temperature was below 400℃, but the size of the powders increased faster when the temperature is higher than 400℃.Electrochemical syntheses for nanosized single- and multi-component alumina, zirconia powders were experimentally studied. Two kinds of r-Al2O3 and t-ZrO2 powders in the sizes of 15nm and 7. 6nm respectively without any heat treatment were obtained at room temperatures. The r-Al2O3 powders, calcined at 500℃ for two hours, can be obtained in the size of 20nm, and at 950℃, a-Al2O3 with a size of 60nm was received. While t-ZrO2 calcined at 400℃, m- ZrO2 calcined at 800℃ for two hours were received in near-complete crystallized forms .The TiO2/Al2O3, TiO2/ZrO2 composite powders as well as Al2TiO5 ZrTiO4, were investigated experimentally with electrochemical synthesis method. The well crystallized R-TiO2/ r-Al2O3 , R-TiO2/t-ZrO2 were obtained at 500℃. When heated at 950℃, the R-TiO2/r-Al2O3 phase other than R-TiO2/r-Al2O3 phase was obtained. As for composite powders of R-TiO2/ r -Al2O3, alumina is mainly distributed on the surface of titanium dioxide. Furthermore, the Al2Ti05 powders were obtained after heated at 1200℃ for 3 hours. In similarity, R-TiOs/t-ZrO2 powders in well-crystallized forms were obtained after heat-treated at 400癈 for two hours while ZrTiO, pow'ders were successfully obtained after heat-treated at 1200℃.Surface modification of nanosized rutile phase powders coatedby organic and inorganic reagents were studied. The coating effects of these modifiers are evaluated in the order of (NaPOa)6>C2HsOH>Na2SiO3>H2O>NaOH. The organic modification reagent such as sodium stearate and polyethylene glycol can modify the nanosized powders, sodium stearate has good effect when its adding amount to nano-TiO2 is 8%, the concentration is about 0.1 mol/L, the value of pH is 5, and the reaction period is up 30 minutes. To modify the powders with polyethylene glycol, the amount must be limited from 1% to 2%, the value of pH is between 3 and 5, and the reaction period should be up to 2 hours, the effect will be mo...
|
PDF Full Text Request