Properties of Boehmite AlO(OH) Nanoparticles as the Coatings and Fillers

Boehmite nanoparticles with different shapes and lengths were used in the preparation of the boehmite films and coatings, and as the fillers for an organic polymer. Then, it was investigated how the shapes and lengths of the particles reflected the characteristics of the films, coatings and fillers. The films were prepared by casting an aqueous sol of the nanoparticles on a Teflon-lined plate, drying and peeling. The coatings were fabricated on porous alumina tubes or graphite sheets by dipping the substrates into a sol of the nanoparticles. The boehmite-polyvinyl alcohol (PVA) composite films, in which the nanoparticles are fillers, were prepared by casting a mixture of a boehmite nanoparticle sol and PVA. The films, coatings and composites were characterized by TEM, TG-DTA, gas permeability, pore size distribution and thermal expansion measurements. In the films, fibrous particles with aspect ratios over 50 aggregated in parallel to each other to form slit-like micropores, on the other hand, plate- and rod-like particles with aspect ratios below 10 randomly aggregated to form meso pores. Corresponding to this, for the coatings on porous alumina tubes and graphite sheets, the fibrous particles gave much low gas permeability and high thermostability, respectively, compared with the plate-like and rod-like particles. For the boehmite-PVA composite films, the fibrous particles gave lower thermal expansion than the plate-like and rod-like particles.