Abstract:Gibbsite crystals display large varieties of shapes and sizes when grown from sodium aluminate solution. The usage of gibbsite is partly determined by morphology, therefore, controlling the gibbsite morphology in accordance with usage arrests interests of both merchants and scientists. In present study, the effects of organic additives with various functional groups, oleic acid, 1-octadecanol and stearic acid on gibbsite morphology were investigated at the concentration of 0.1 g/L. Experiments were performed at the temperature of 65 ℃. Samples of gibbsite crystals were obtained from the decomposition of the unseeded synthetic sodium aluminate solution. The morphologies of these gibbsite crystals were examined with SEM, which shows that functional groups influence gibbsite morphology intensively. The morphologies of gibbsite nucleated from the pure solution and solution containing oleic acid, 1-octadecanol and stearic acid are as follows: mosaic gibbsite consisting of various shapes of crystals, radial agglomerate consisting of hexagonal pallets, mosaic and ball like agglomerate consisting of block crystals and loose, radial crystal consisting of irregular tiny nuclei. The facts indicate that it is possible to control gibbsite morphology at the presence of additives with various functional groups. The action mechanism of functional group to morphology was also proposed.

Key words: 1-octadecanol; stearic acid; oleic acid; Gibbsite morphology; functional group