Aluminum Trihydroxide Research Articles

Dispersion viscosity of aluminum trihydroxide of various particle size distributions in an unsaturated polyester resin

AbstractThe effect of filler particle size distribution on the viscosity of an aluminum trihydroxide/unsaturated polyester resin dispersion was studied. Four basic aluminum trihydroxides with distinctively different particle sizes were combined to generate various particle size distributions systematically. The particle size distribution producing the minimum viscosity was determined by employing a modified extreme vertices experiment design for mixtures to establish a quadratic model which was then optimized. The predicted viscosities in general as well as the particle size distribution corresponding to the minimum viscosity agreed well with the observed data.

Phase composition of skeletal ruthenium catalyst

1. An x-ray and thermogravimetric study was made of the phase composition of a skeletal ruthenium that was obtained by the decomposition of a Ru−Al alloy (30% Ru) with caustic alkalis. It was found that, besides highly dispersed metallic ruthenium, the catalyst contains bayerite. 2. Skeletal ruthenium catalyst when heated to 600° decomposes in stages due to dehydration of the bayerite. 3. The same as in the case of the Ni−Al alloy, complex aluminum salts are formed during the leaching of the aluminum from a Ru−Al alloy, which then decompose with the formation of aluminum trihydroxide.

Alumina trihydrate crystallization. Part 2. A model of agglomeration

AbstractIn the second part of this paper on the kinetics of crystallization of aluminum trihydroxide from caustic aluminate solutions, interest is specially focused on the analysis of crystal size distribution as a function of time, in an isothermal batch crystallizer.Breakdown and agglomeration are shown to affect these curves simultaneously. While only qualitative information on breakdown was obtained, agglomeration could be isolated experimentally. Its rate was measured and fitted to a kinetic model which pictures agglomeration as the result of binary collisions between particles.

A quantitative study of new crystal formation in seeded caustic aluminate solutions

A quantitative study of secondary nucleation of aluminium trihydroxide Al(OH) 3 in pure caustic aluminate solutions of Bayer process composition shows that when crystallization is preceded by an induction period (or time lag before crystallization gets underway at the expected rate) a saturation number of nuclei becomes established in a time which is often short compared to the overall growth cycle. Thereafter, the numbers do not increase although the nuclei become larger with growth time. Saturation number N, is correlated with initial supersaturation, S, and the length of the induction period, τ, by the relationship N= K n S τ , where K n is a constant. Values of K n calculated at different temperatures cannot be correlated by an Arrhenius type relation. The induction period is correlated with the initial supersaturation by the relation τ= aS b , where a and b are constants for a given temperature and seed surface area. In general, the indiction period decreases with increases in initial supersaturation, temperature and seed surface area. At sufficiently high surface areas there is no measurable induction period and little or no secondary nucleation.

Polycrystallization of aluminium trihydroxide

Polycrystals of aluminium trihydroxide have been examined by means of optical and scanning electron microscopy. It is shown that all of the common growth flaws (twinning, dislocations, internal boundaries, sub-structures, branching) which can lead to polycrystal formation are present in crystals of aluminium trihydroxide.

Secondary nucleation of aluminium trihydroxide in seeded caustic aluminate solutions

Scanning electron microscopy shows that secondary nucleation of aluminium trihydroxide in seeded caustic aluminate solutions of industrial composition is closely associated with the crystal growth process via surface nucleation mechanism. When crystallization is preceded by an induction period, the seed crystals develop and give birth to large numbers of secondary nuclei. The role played by impurities normally present in Bayer process solutions is examined and a qualitative mechanism for the secondary nucleation process discussed. Under certain experimental conditions (high supersaturation, absence of impurities), the initial crop of secondary nuclei can grow dendritically. These dendrites can then break away from crystal surfaces to form an additional crop of secondary nuclei.

Anodic Oxide Hydration Measured by Ion Probe Mass Spectrometry

The water content of barrier layer anodic alumina films was measured using the ion probe mass spectrometer: a method of sputtered ion mass analysis. Film thicknesses ranged from 100 to 2000Aå, with the oxides left intact on the basis metal during the analysis. The analytical procedure was first calibrated against standard samples of aluminum trihydroxides and monohydroxides. Then data were obtained for different thicknesses of boric‐acid‐anodized barrier layer oxides. The various aspects of the fragmentation patterns that were obtained are suggestive of a trihydroxide composition. Representative spectra are included, to illustrate the use of this method of surface analysis.

Crystal growth and nucleation of aluminium trihydroxide from seeded caustic aluminate solutions

The scanning electron microscope has been used to follow changes in surface topography of crystal surfaces of aluminium trihydroxide during crystallization. By relating topographical features to known theories of crystal growth and nucleation, it has been possible to infer the mechanisms of aluminium trihydroxide crystallization from seeded caustic aluminate solutions of industrial composition.

Crystallisation of bayer aluminium trihydroxide

Observations on the nucleation, growth and agglomeration of crystalline aluminium trihydroxide in caustic aluminate solutions under Bayer process conditions are described.