Study On Preparation Of ITO Nanomaterial And Its Mesoporous Assembly System By Chemie Douce

ITO (Indium Tin Oxide) is a category of important material bearing indium, which accounts for over 60% of the total indium product yield. ITO is a highly simplified N-type semiconductor. Because of its excellent photoelectric performance, it is extensively used in the fields such as electric industry, automobiles, construction industry, solar energy, space navigation and military affairs, luminescent materials and devices, as well as microwave shield and laser radioprotection. The present work on preparation of ITO powder and suspension for the application of coating with wet method and on the synthesise of ITO mesoporous assembly system, is supported by the National High Tech Research and Development Program of China (863 Program) under Grant No. 2002AA302606, namely, "Preparation and Development of Multi-Functional Nanometer Size Oxide Composite Suspension with Electric Conductivity". The work done here are very important to develop new type nanocomposite materials of ITO for their application in new fields.ITO powder was prepared by precursor-pyrolysis method, one of chemie douce, in this dissertation. The relations between pH value and the metallic ion concentration in the reaction solution were studied to prepare a suitable ITO precursor with "two-drop" method at first. And the process of ITO precursor-pyrolysis was then investigated via through thermogravimetric analysis. ITO powder with different surface shapes were gained through the pyrolysis of ITO precursor at the suitable calcinations temperature depending on the effects on the crystal structure of ITO powder. The results show that the clubbed nanometer ITO powder has been prepared when choosing the 25% ammonia solution to add dropwise, with the ratio of diameter to lengthï¿ of 30nm～40nm x 140nm～300nm, while the near-spherical nanometer ITO powder has been prepared when choosing the 5% ammonia solution to add dropwise with the diameter ofï¿ of 20nm～30nm, under the other same conditions. The optimal reaction conditions for synthesis of ITO powder with the cubic iron manganese ore crystal structure, perfect crystallization, monodispersity, uniform size, good electrical conductivity, as well as the resistance ratio of 1.92×10^-3Ω·mm are: the added dispersant is MC, the reaction temperature is 70℃, the concentration of [In³⁺] in the reaction solution is 0.10M, and the ratio of Sn-doped is 9:1, and the pH value is 7～8 in the reaction solution, the temperature of heat treatment is 700℃and the time of heat treatment is 2h.To improve the crystal structure, distribution of crystallite size and dispersion of ITO powder, the effects of dispersants added in the reaction of preparing ITO precursor on the properties of ITO powder was discussed. No effects on ITO crystallite size are found when non-ion surfactant PP and PG were added, but the enhanced effect on the crystal intensity of ITO powder when PG was added. Moreover, PP and PG are helpful for dispersity of ITO powder. However ITO crystallite size is reduced when polymer MC is added. The effects of the influence factors on the surface shape, crystal structure, crystallite size and electrical conductivity of the prepared nanometer ITO powder was discussed with the nucleation and growth mechanism of LaMer theory and semi-conductivity and electrical conductivity mechanism of ITO. ITO nanopowder prepared by chemic douce is ready for the preparing ITO suspension.The stabilized ITO ethanol absolute suspension and ITO aqueous suspension were prepared by ball milling and ultrasonic cavitations dispersion method through dispersing ITO powder into ethanol absolute and distilled water separately, and the effects of ball milling time and dispersants on the stabilization of ITO suspension were studied. The results showed that under ball mill dispersing period of 24h, TC and BA optimalÎ¥value of such dispersing agents is 5% separately, while for the dispersing agent PP, itsÎ¥value is between 5% and 10%, its dispersible effect is better than that of the first two dispersing agents. It is also discovered that, when the dispersing agent relative ITO powder quality fraction is 5%, ball mill dispersing time of 48h is the optimal ball milling dispersion time, and within 15d, PP, TC and BA can enable the RSH to maintain within 10%. In the ball milling dispersion time period between 24h and 96h, the descending order of ITO suspension stability is PP＞BA＞TC. It is seen that through the research on the stability of suspension in aqueous phase, dispersing agent MC has good dispersing effects in the ITO suspension process during the ball milling. When the MC amount used accounts for relative ITO powder quality fraction is constant, with MC amount used , ITO powder amount used and ball milling dispersion time increase, ITO suspension stability enhances; When the MC amount used is 15%, the ball milling dispersion time is 48h, the ITO suspension stability becomes best, and its RSH is within 1.8% during 120d.Based on DL VO stabilization theory and space steric hindrance theory, the functional mechanisms of four agents on the stability of ITO suspension can be explained as follows: PP is of steric hindrance, TC and BA are of electrostatic hindrance and MC is of electrostatic and steric hindrance. ITO thin film was prepared by the spin coating process of spreading membrane on the ITO ethanol absolute suspension uniformlue. The block resistance of the film is 196Ω/â–¡, the transmittance of the visible light is equal to or more than 87.8%, and the reflectance of the infrared light is about 70%.Based on the sol-gel of chemie douce, IO/SiO₂ and ITO/SiO₂ mesoporous nanocomposite were synthesized by immersion- pyrolysis. The results showed that the mesoporous composite ITO/SiO₂ has the better photoluminescence enhancement effect than IO/SiO₂ with the peak intensity value of 504, when excited wave length is 275nm, the emitted wave length in the position of 360nm. Based also on the sol-gel of chemie douce, SiO₂ aero gel and IYO/SiO₂ aero gel were prepared by gel- mixing drying method. The results showed that ITO/SiO₂ aero gel has the better photoluminescence enhancement effect than SiO₂ aero gel with the peak intensity value of 1647, when excited wave length is 220nm, the emitted wave length in the position of 398nm, and at this moment, its PL spectrum has had the right offset, which is 15nm. Thus from the results mentioned above, ITO/SiO₂ aero gel has the best photoluminescence properties among the mesoporous nanocomposites prepared here.Review of the preparation, performance and application of ITO nanomaterials in China and abroad was given in this dissertation. The preparation principle, dispersion stability theory and mechanism of semiconducting of ITO nanomaterials were analyzed. ITO nanopowder was prepared by precursor-pyrolysis method, ITO suspension was prepared by ball milling and ultrasonic cavitations dispersion method, ITO/SiO₂ mesoporous composite was synthesized by gel- mixing drying method and immersion- pyrolysis. A useful exploratory experiments of ITO nonmaterial in its preparation technology, forming mechanism, physical performance and influence factors lay the basis of development and application of heat insulation or photoluminescence composites, and new type functional composites of ITO.