Precipitation of nanoscale aluminum hydroxide particles

The precipitation of nanoscale alumina particles from sodium aluminate solu tions by dilution and neutralization with water and oxalic acid in the pres ence of a surface-active polymers polyvinylpyrrolidone (PVP) and polyvinyl alcohol (PVA) is investigated. This study is exploratory as to the use of B ayer liquors as a source of nanoscale alumina and provides some fundamental insights necessary for an understanding of the overall kinetics and mechan isms involved in the precipitation process. The particle sizes are determin ed by dynamic light scattering (DLS). Scanning electron microscopy is used to image the particles and to determine composition by energy dispersive an alysis 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 1.2 mum. The sizes obtained from DLS experiments do not correlate with increasing supersaturation. DLS of sols prepared using oxalic acid alone without polymer surfactant additi ve yielded particles with average diameters of 200 to 300 nm. The TEM image of the sols trapped between nitrocellulose membranes shows the particles a s nearly spherical, of diameter 176 nm, 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.