The impact of twinning on the morphology of gamma-Al(OH)(3) crystals

Gibbsite, gamma-Al(OH)(3), is an important technical product, used mostly a s an intermediate in the production of aluminium. According to the literatu re, the morphology of natural and industrial gibbsite crystals is pseudohex agonal with {0 0 1} basal, and {1 0 0} and {1 1 0} side faces. Laboratory e xperiments on the growth of gamma-Al(OH)(3) crystals from unseeded sodium a luminate/sodium hydroxide solutions result in crystals land agglomerates) w ith various morphologies, such as lozenge-shaped or hexagonal plates as wel l as prisms. Optical polarisation microscopy shows many of the crystals to be twinned. Three kinds of reflection twin with both mirror and composition planes {1 1 0}, {0 0 1} and {1 0 0} were identified. In addition, [1 3 0] rotation twins with :0 0 1) as composition plane were found. The effect of various kinds of twinning on the growth morphology and growth kinetics of g amma-Al(OH)(3) crystals is studied. (C) 1999 Elsevier Science B.V. All righ ts reserved.