Growth rates of gibbsite single crystals determined using in situ optical microscopy

Growth of nordstrandite: effect of carboxylates on surface morphology

“…Although observations indicating two-dimensional nucleation on the surfaces of gibbsite crystals have been reported in the literature [10,14,18,20,21], our higher resolution AFM images show extensive monolayer growth steps on the nordstrandite basal surfaces. These images clearly indicate growth from two-dimensional nucleation, and in many cases show that monolayer nuclei formed on existing nuclei to produce concentric steps.…”

“…Using electron microscopy, Kodama and Schnitzer [12] observed ''contour-like patterns'' on bayerite surfaces and Van Straten and De Bruyn [13] reported a ''hill-and-valley'' structure on bayerite surfaces. Lee and Parkinson [14] used in situ optical microscopy to observe the formation of nuclei on the basal faces of gibbsite precipitating in a sodium aluminate-sodium hydroxide solution. Using electron microscopy, Wefers [15] observed features suggestive of spiral growth on the basal faces of synthetic gibbsite crystals, and Aldcroft and Bye [16] observed screw dislocation edges and linear growth steps on the basal faces of synthetic nordstrandite crystals.…”

Organic compounds in the processing of lateritic bauxites to alumina Part 2: Effects of organics in the Bayer process

“…At higher supersaturation levels, precipitation by a birth-and-spread mechanism becomes dominant (Brown, 1972a(Brown, , 1972bLee and Parkinson, 1999;Li et al, 2003). This process accelerates the rate of crystallization by secondary nucleation at the gibbsite surface and the consequent production of new growth sites.…”

“…These results are consistent with the theoretical model developed by Fleming et al (2000), who showed that the dominance of the basal (001) plane may be explained by the lower surface energy afforded by its 6-fold coordination of Al in comparison to 5-fold coordination in the other faces. The growth rate dispersion between crystal facets is a key determining factor in the final shape of each crystal, but for gibbsite precipitation the very mechanism of crystallisation may also be different for different facets: Lee and Parkinson (1999) showed that, with supersaturation above 0.81, birth and spread becomes the dominant mechanism on the basal face whereas spiral growth remains dominant on the prismatic faces.…”

Growth of nordstrandite: effect of chloride on surface morphology

“…Studies reporting observations of Al(OH) 3 mineral surfaces include scanning electron microscopy and transmission electron microscopy observations of various step structures on the surfaces of gibbsite and bayerite [8][9][10][11], in situ observations of the formation of nuclei on the basal faces of gibbsite using optical microscopy [12], and transmission electron microscopy observations of screw dislocation edges and linear growth steps on the basal faces of nordstrandite crystals [13]. In addition, atomic force microscopy (AFM) has allowed the observation of some monolayer steps (0.5 nm in height) as well as higher features such as growth hillocks on gibbsite surfaces [14][15][16][17], and Watling [18] reported that the basal faces of gibbsite were rougher when the crystals were grown in the presence of alditols and hydrocarboxylates.…”