Although the precipitation of aluminium trihydroxide as gibbsite, via the Bayer process has been widely studied, the mechanism of crystal growth is poorly understood. This work focus on the morphology of gibbsite and the relative growth rates of individual crystal faces.Initial work was carried out to characterize aluminium trihydroxide and it was found that bayerite, another polymorph, precipitated at temperatures below 50 [degrees] C and its morphology depended on the method of precipitation. Gibbsite however, precipitated above this temperature and its morphology depended on the type of alkali aluminate solutions used. The method of precipitation does not affect the morphology, only the size of the precipitate formed. The morphology of gibbsite can be altered by the addition of organic compounds which are known to inhibit gibbsite precipitation. Some of these compounds were found to selectively inhibit the growth of individual crystal faces, thus altering the overall morphology of gibbsite. Boehmite, a polymorph of aluminium hydroxide, can be produced by partial dehydration of gibbsite at 300T. The morphology of boehmite consisted of diamond shaped crystals.The influence of cation incorporation on the morphology of gibbsite was studied experimentally and computationally (molecular modelling). These studies showed that there is a linear relationship between the amount of cation incorporated and atomic radii and between the amount of cation incorporated and the defect energy calculated. The equilibrium morphology of gibbsite predicted in the absence of media matched the morphology of gibbsite grown slowly from sodium aluminate, implying that the amount of sodium incorporation is low in these crystals.The growth rates of individual crystal faces were measured in situ, and found to be a function of supersaturation squared for the prismatic faces, possibly indicating ++ / that E growth occurs by spiral growth mechanism. The growth of the basal face was found to follow the spiral growth mechanism below a relative supersaturation of 0.815 and the birth and spread mechanism above this level. The activation energies and kinetic coefficients for the individual prismatic faces were also determined.Growth rate dispersion was observed in these microscopic studies, but the question of size dependency remains unanswered.The overall growth rates of gibbsite crystal, determined using rapid dynamic light scattering, was found to be an exponential function of supersaturation indicative of a birth and spread growth mechanism.

Thèse (M.Eng.) -- Université du Québec à Chicoutimi, 2003. / Bibliogr.: f. 130-134. Document électronique également accessible en format PDF. CaQCU

Thèse (M.Eng.) -- Université du Québec à Chicoutimi, 2003. / Bibliogr.: f. [184]-191. Document électronique également accessible en format PDF. CaQCU

Inaug.-diss.--München. / Lebenslauf. "Gottlieb Siegfried Bayers schriften": p.[72]-83.

The aim of this study was to determine the mechanism of Bayer residue flocculation. Hematite was chosen as the test substrate as it is a common Bayer residue mineral. Batch settling tests were used to gain an understanding of the aggregation mechanism and to compare the effect of different parameters on flocculation performance. Flocculant adsorption isotherm measurements were related to changes in flocculation performance. Infrared spectroscopy was used to ascertain the configuration of adsorbed flocculant on the hematite surface.Batch settling tests showed that under strong caustic conditions hematite is naturally coagulated and that flocculation occurs via a bridging mechanism. This was confirmed by results which showed that factors which affect the bridging efficiency of the flocculant had an impact on aggregation. In particular, temperature and caustic concentration were found to greatly influence flocculation performance. This is due mainly to changes in the viscosity of the liquor, but may also be linked to the kinetics of particle-particle and particle-flocculant collisions resulting in a less efficient aggregation process. Ionic strength did not impact on performance as the flocculant was at a limiting size for synthetic liquors containing TC >/= 50 and TA >/= 10.Increasing ionic strength did not increase the adsorption density of the flocculant on hematite nor did altering the salt cation species from Na(subscript)2+ to Ca(subscript)2+. It can be concluded, therefore, that the flocculant is chemisorbed through surface complexation, since if it were electrostatically bound an increase in flocculant adsorption should have been observed with increasing ionic strength or cation charge. The surface complexation mechanism was supported by infrared results which showed that the flocculant vibrational bands were shifted on adsorption. The magnitude and direction of ++ / the shift suggests a bridging bidentate structure at pHs >/+ 11, while a monodentate structure exists at pH 7. In the presence of calcium there is also some electrostatically adsorbed flocculant at pH 7, with the calcium being in a bidentate chelating structure, but this is not observed at much higher pHs.The flocculant had an adsorption isotherm best described by a Langmuir-Freundlich expression with a monolayer coverage of ~ 164 mu g m(subscript)-2 of hematite. The adsorption density was lowered by the presence of carbonate and silicate and the action of both is thought to be due to their adsorption on active sites blocking polymer adsorption. Carbonate has an impact on flocculant adsorption at concentrations > 10 mg g(subscript)-1 while in the case of silicate ~0.2 mg g(subscript)-1 is required for the adsorption density of the flocculant to be affected. While it has been confirmed that silicate does adsorb on hematite, it was not possible to determine whether this was adsorption of a silicate species or an aluminosilicate species.X-ray photoelectron spectroscopy (XPS) showed conclusively that sodium is not involved in the adsorption of the carboxylate to the hematite surface. The lower peak shift between the backbone carbon and the carboxylate carbon suggests that the carboxylate is bonded directly to iron which has a low effective charge.Flocculant adsorption was atomistically modelled using decanoate and decandioate molecules. Modelling supported the results from XPS and infrared analysis and showed the carboxylate oxygen atoms in both organic molecules bonded directly to the surface iron atoms. Adsorption was preferred on near unhydrated surfaces with the most stable adsorption configuration being a non-symmetrical bridging bidentate structure as inferred from the infrared results.

Thèse (M.Eng.) -- Université du Québec à Chicoutimi, 2005. / La p. de t. porte en outre: Mémoire présenté à l'Université du Québec à Chicoutimi comme exigence partielle de la maîtrise en ingénierie. CaQQUQ Bibliogr.: f. 128-131. Document électronique également accessible en format PDF. CaQQUQ

Sankt Gallen, Univ., Diss., 2003.

The thesis Application of Balanced Scorecard is focused on creation of strategic management system BSC for company Bayer, s. r. o. and its division Bayer MaterialScience. In theoretical part the system BSC and its four perspectives are introduced. In practical part the company Bayer, s. r. o., divisions, strategy and vision are introduced. There is a SWOT analysis of Bayer, s. r. o. and Bayer MaterialScience created and then the system Balanced Scorecard is applied. The thesis also includes system alignment of company and division. The system Balanced Scorecard is described by strategic maps that are included in annex.

Thesis (PhD)--University of South Australia, 1999

Thesis (PhD)--University of South Australia, 1999