부산대학교 도서관

The precipitation of nanoscale alumina particles from sodium aluminate solutions by dilution and neutralization with water and oxalic acid in the presence of a surface-active polymers polyvinylpyrrolidone (PVP) and polyvinyl alcohol (PVA) is investigated. This study is exploratory as to the use of Bayer liquors as a source of nanoscale alumina and provides some fundamental insights necessary for an understanding of the overall kinetics and mechanisms involved in the precipitation process. The particle sizes are determined by dynamic light scattering (DLS). Scanning electron microscopy is used to image the particles and to determine composition by energy dispersive analysis by X-rays (EDAX). Transmission electron microscopy (TEM) is used to determine primary particle sizes. The alumina particles precipitated in the presence of PVP had diameters of 80 to 300 nm. The alumina precipitated in the presence of PVA had diameters of 200 nm to 1.2μm. The sizes obtained from DLS experiments do not correlate with increasing supersaturation. DLS of sols prepared using oxalic acid alone without polymer surfactant additive yielded particles with average diameters of 200 to 300 nm. The TEM image of the sols trapped between nitrocellulose membranes shows the particles as nearly spherical, of diameter 176nm, and not pure alumina as originally expected. These particles have a gel like structure and deform under stress. Dehydration of these particles leads to aggregation of amorphous fibrous particles of aluminum trihydroxides contaminated with sodium. [ABSTRACT FROM AUTHOR]