Nanocrystalline Functional Alumina and Boehmite Materials: Synthesis, Characterizations and Applications

Abstract

In this dissertation, synthesis, characterization and applications of nanocrystalline functional alumina (Al2O3) and boehmite (-AlOOH) materials have been systematically studied. The processing method was focused on sol-gel method. The purpose was to synthesize, characterize and then find suitable applications such as superhydrophobic and antireflective applications to the as-prepared nanocrystalline alumina and boehmite materials.

Based on a modified sol-gel process, nanocrystalline flaky boehmite powder was synthesized, and transition alumina powders with morphologies of nanoparticles and nanorods with high surface areas were prepared from the flaky boehmite powder.

Furthermore, nanocrystalline -alumina powder with novel morphology was also obtained from the flaky boehmite powder at a relatively low temperature of 1000 °C without using seed. The -alumina crystallites of 5 nm in size were observed for the first time, and more interestingly such nanocrystallites existed on the surface of the nanorods with widths of about 15 nm and lengths of 50-300 nm. The detailed processing parameters of such nanocrystalline -alumina powder were studied and the formation scheme of the novel morphology of such nanocrystalline -alumina powder was illustrated, while the phase transformation from - to -alumina was tentatively discussed.

More work was done to synthesize nanocrystalline -alumina powder with nearly spherical morphology from gel powder, as compared to the nanocrystalline -alumina powder obtained from the flaky boehmite powder.

On the other hand, flaky boehmite film was produced by spin coating from the same sol suspension as in the alumina powder processing. By modifying the surface chemistry, the boehmite film became superhydrophobic and antireflective. The formation process and thermal stability of such superhydrophobic antireflective boehmite film were studied and discussed. A set of roughness parameters was related to the superhydrophobic and the antireflective properties.