The Synthesis And Characterization Of Aluminiun Oxyhydroxide Nanometer Colloids

In this dissertation, aluminum oxydroxide (AlOOH) nanometer colloids refer extensively to the nanometer-scaled colloids of Al(OH)3, AlOOH, and their multilevel dehydration products. Depending on the various contents of Al, O and OH, these nanometer-scaled colloids exhibit multiform structures and multipurpose properties. Since the microscopic morphologies of AlOOH nanometer colloids may be controllable, they can be applied extensively in structural ceramics, catalysts, absorbents, and microelectronic functional materials, and have attracted considerable research efforts in the fields of modern materials science and technology.In the preparation techniques in existence, surfactants, precipitants, degelatants, etc., are generally employed in the syntheses of AlOOH nanometer colloids. The syntheses procedures are often complicated and time-consuming, and the pH values usually need to be regulated. Thus it is of vital importance to explore a simple and straightforward synthesizing method. In this dissertation, we try to demonstrate a successful solvothermal alcoholysis route to prepare AlOOH nanometer colloids with various morphologies. The main results are listed below.(1) By using the alcoholysis reactions between anhydrous AlCl3and methanol, ethanol, and n-propanol, under various conditions, we have prepared nanometer-scaled flakes of AlOOH nanometer colloids. The lower critical temperature of the alcoholysis reactions to produce AlOOH nanometer colloids is determined to be160℃.(2) XRD, SEM, and TEM techniques have been employed to characterize the prepared samples. The samples mainly consist of nanoflakes of various sizes and multilevel degrees of conglomeration. The crystallinity of the samples increases with the raising of reaction temperature and prolonging of reaction time.(3) When methanol is used as the precursor, the product mainly consists of Al(OH)3-like species. Otherwise, the multilevel dehydration products of Al(0H)3may be acquired. With the elevation of temperature and prolongation of time, AlOOH-like ones are ultimately obtained.(4) Through systematically analyzing the obtained characterization results, we can deduce the reaction and growth mechanism. It can be postulated that the reactions occur via the following routes: AlCl3+3ROHâ†'Al(OR)3+3HC1Al(OR)3+3ROHâ†'Al(OH)3+3ROR Al(OH)3â†'AlOOH+H2OAs to the formation of the nanoflakes, it can be postulated that bulk Al(OH)3are first formed when the temperature is low and the time is short. The multilevel dehydration of the bulk Al(OH)3colloids occur with the elevation of temperature and prolongation of time. Since AlOOH, the ultimate dehydration product, has a layered structure, the samples obtained tend to exhibit the nanoflake morphology. In the formation of nanoflakes, the OH groups at the surfaces also play an important role. The higher is the temperature and the longer is the reaction time, the thinner is the thickness of the nanoflakes. Under the effects of the surface OH groups and the van der Waals forces among them, the nanoflakes tend to curve and even envelop into nanoballs.