Gibbsite Powder Research Articles

Managing Properties of Alumina Based Granules Prepared by Disk (Dished) Molding

Alumina-based spherical granules were prepared by disk granulation. Products of gibbsite thermoactivation in various reactors were used as the initial materials. In the course of molding, combustible additives (starch, carbon, wood meal) were added to the thermoactivated gibbsite powder, and NaOH (10 %), C2H5OH (15 %), Н3ВО3(6 %) to the wetting solution (H2O). With the product of centrifugal thermoactivation of hydrargillite, the prepared granules were stronger at the larger average size of pores; addition of NaOH, C2H5OH and H3BO3led to an increase in the specific surface area and micropore proportion but had different effects on the mechanical strength of the granules. Introduction of combustible additives (wood meal, activated carbon) affected only slightly the specific surface area, favored an increase in the total pore volume and mesopore volume, resulted in a decrease in bulk density and mechanical strength of the granules. Conditions were determined for preparation of a highly effective strong dessicant with large specific surface area (up to 340 m2/g) and average pore diameter up to 3.4 nm. Conditions were determined for preparation of strong ultramacroporous granules that are highly active to the Klaus process.

Calcination products of gibbsite studied by X-ray diffraction, XPS and solid-state NMR

The changes caused by heat treatment of gibbsite powder at 300–1473K were studied using the X-ray diffraction (XRD), X-ray photoemission (XPS) spectra and 27Al magic angle spinning nuclear magnetic resonance spectroscopy (27Al MAS NMR). XRD analysis indicates that the transformation sequence involves the formation of κ-Al2O3 as an intermediate phase between χ- and α-Al2O3. The crystallite size of χ-Al2O3 is as small as 10nm. XPS analysis indicates that the ratio of aluminium atoms to oxygen atoms in χ-Al2O3 and κ-Al2O3 increases, whereas the expected ratio is observed in α-Al2O3. The percentage of AlO4 units in the transition aluminas follows the same behaviour as the ratio of Al/O.

Microstructural Transformation with Heat-Treatment of Aluminum Hydroxide with Gibbsite Structure

Abstract Aluminum hydroxide with gibbsite structure was prepared, and the microstructural transformation of the sample heat-treated at various temperatures was investigated. The sample was characterized by field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), thermogravimetry and differential thermal analysis (TG-DTA), and BET surface area. The shape of the grains in the prepared sample was hexagonal prism-like morphology. The prepared sample kept a metastable state of alumina phase at higher temperatures than the commercially available gibbsite powders. The prepared gibbsite grains underwent characteristic structural change depending on the calcination temperature. The transformation of the surface morphology was initiated at 400 °C, leading to the formation of cracks with the direction parallel to the basal plane. After calcination at 1200 °C, a large number of grooves were formed on the surface of the lateral planes. The specific structural change of gibbsite induced by the heat treatment was strongly related to the topotactic dehydration from gibbsite and subsequent phase transition to aluminum oxides.

ＤＥＭシミュレーションによる遊星ミリングにおける消費電力の推算と粉砕速度定数との相関

Motion of balls during planetary ball milling was simulated with a DEM (Discrete Element Method) in order to predict the power consumption during the milling. Grinding experiment of gibbsite powder was conducted to assess the validity of the prediction method of the power consumption by DEM simulation and to investigate the correlation between the power consumption and the grinding rate constant. The calculated power consumption agreed well with the experimental one for various grinding conditions, such as various ball diameters, ball densities and ball filling ratios. The grinding rate constant is found to be correlated with the calculated power consumption.

Simulation of the movement of beads by the DEM with respect to the wet grinding process

AbstractThis work has shown a method for simulating the motion of beads in a bead mill based on the discrete element method (DEM) under wet grinding of a gibbsite powder, in correlation with the experimental work. The beads' motion was simulated under a wet condition and compared with the real motion observed and recorded by a video camera. At the base of the simulation the specific impact energy of beads was calculated. In the experiment, the gibbsite powder, suspended in water at 5.0 wt %, was subjected to grinding by the bead mill at different operating conditions. Particle‐size distribution of the product was measured and the grinding rate constant of the sample was determined as a change in the mean particle size of the ground product with time. Then, the specific impact energy was correlated with the grinding rate constant determined experimentally. It was found that good correlation between the two was achieved and by the proposed method the particle size reduction of the sample can be predicted. © 2006 American Institute of Chemical Engineers AIChE J, 2006

TSEFLAR™ – the centrifugal flash reactor for rapid thermal treatment of powdered materials

The concept of the centrifugal thermal activation (CTA) of powdered materials on a rotating solid heat carrier is developed. A compact centrifugal flash reactor has been manufactured and tested. The tested set-up provided: the heating of gibbsite powder to the temperature of 400–900 K with the rate more than 103 K/s; the duration of the powder thermal treatment less than 1.5 s; the regulation of the treatment duration by changing the speed of the plate rotation and the shape of the rotating heat carrier; the product output up to 40 dm3/h; the removal of the extracted steam containing gases and rapid quenching of the thermally activated solid products. The device tested has been used for the thermal activation of commercial aluminium hydroxide Al(OH)3 (gibbsite). The obtained thermally activated product possesses a high reactivity and can be used for the preparation of various alumina-based compounds.

Optimum revolution and rotational directions and their speeds in planetary ball milling

A grinding rate of a gibbsite powder sample was examined by using a planetary ball mill and it was well correlated with the specific impact energy, which was calculated by Discrete Element Method (DEM). This implies a fact showing the confidence of the simulation result. Based on this result, an optimum rotation-to-revolution speed ratio and rotational direction of the pot to the revolution disk were investigated by the simulation work. A significant large specific impact energy is obtained when the mill pot is rotated at around the critical speed ratio in the counter direction to the disk revolution at around the critical speed ratio.

Scale-up method of planetary ball mill

The objective of this paper is to investigate the scale-up method of the planetary ball mill by the computational simulation based on Discrete Element Method. Firstly, the dry grinding of a gibbsite powder by using four different scales of planetary mill was developed to compare the grinding rate with the specific impact energy of balls calculated from computational simulation. The grinding rate is well correlated with the specific impact energy in all mills; and its relationship is expressed by a linear correlation. It points out that the specific impact energy is very useful for estimation of the grinding rate and optimization for the operational conditions. Secondly, the scale-up method for the planetary mill was established by evaluating the impact energy. The impact energy is proportional to the cube of the diameter of the pot, the depth of the pot and the revolution radius of the disk, respectively. When the planetary mill is scaled-up in geometrical similarity, the impact energy of the balls is proportional to 4.87 power of the scale-up ratio.

Adsorption of Carboxylic Acids on Submicrocrystalline Aluminum Hydroxides in Aqueous Solution. Part I: Qualitative Study by Infrared and Raman Spectroscopy

Adsorption of acetic, oleic, benzoic, and salicylic acids on submicrocrystalline aluminum hydroxide samples is investigated in aqueous solutions. Experimental infrared and Raman spectroscopic data are analyzed to determine the reactivity of the monocoordinated hydroxyl groups located on the edge faces of bayerite or gibbsite crystals. Two key parameters were (1) the effect of concentration of aqueous solutions of the acids, and (2) the variation in specific surface areas of different samples of bayerite and gibbsite powders. Strong preferential adsorption to bayerite was observed over the whole pH range. No adsorption to gibbsite was detected. Data from the literature indicate that acetate, oleate, and benzoate form bidentate complexes on bayerite while salicylate forms a monodentate complex. The infrared spectra show that only monocoordinated hydroxyl groups are reactive, in the bayerite samples, and the band at 1020 cm−1 corresponds to the deformation mode of the monocoordinated hydroxyl groups whose stretching vibration was at 3465 cm−1. It is suggested that the specific surface areas given by the adsorption isotherms is a condition necessary for adsorption, but not sufficient in itself. Adsorption requires the presence of Al-OH2+1/2 species as well as the presence of steps or of a packaging sequence ABABABA rather than a packaging sequence ABBAABBA of the hydroxyl planes. The gibbsite impurity present in the bayerite sample reacted completely, while the lateral OH in the gibbsite sample did not, reflecting the lower reactivity in gibbsite relative to extended domains of bayerite.

Correlation of grinding rate of gibbsite with impact energy in tumbling mill with mono-size balls

Dry grinding of a gibbsite powder was conducted in air using a tumbling ball mill with mono-size of media (balls) ranging from 4.8 to 31.7 mm diameter to investigate ball size effect on grinding rate. The impact energy of balls during grinding was calculated by the method proposed previously in order to correlate with the grinding rate. The grinding rate increases with an increase in the rotational speed of the mill, subsequently, it falls around the critical speed. The maximum grinding rate shifts toward higher rotational speed range as the ball size becomes large. In the range of rotational speed before the grinding rate falls, the grinding rate is improved when grinding with balls of 12.7 mm or less, while it is reduced when larger balls over 15.9 mm are used. A similar trend can be seen in the relation between the specific impact energy of balls and the rotational speed of the mill. The grinding rate is proportional to the specific impact energy of balls regardless of the ball size. Therefore, the specific impact energy of balls plays a significant role in governing the grinding rate in tumbling ball milling of the sample powder.

Correlation of grinding rate of gibbsite with impact energy of balls

This article discusses the effects of the ball-filling ratio and mill scale on the correlation of grinding rate of a gibbsite powder with the ball impact energy simulated by the particle element method (PEM).

Simultaneous calcination and spheroidization of gibbsite powders in an RF thermal plasma

Thermal treatment of gibbsite (Al(OH) 3) powders of different particle size was studied in inductively coupled thermal plasma operating at normal pressure. Calcination and spheroidization took place simultaneously although spheroidization did not occur with coarse feed particles. Microsized or nanosized Al 2O 3 particles of different phase composition were produced depending on the size of injected grains. The microsized powders were mainly formed by melt solidification. In the formation of nanopowders, however, evaporation of small grains followed by homogeneous nucleation from the vapor phase and grain growth seem to be the dominant processes.

内外筒相互回転型ミルにより粉砕された水酸化アルミニウム粉末の特性

Gibbsite powder was ground in air by a double rotating cylinders mill under three different conditions in order to investigate the effect of grinding condition on the characteristics of ground products. Case-1 in which two cylinders are rotated in reverse directions gave higher impact energy of balls than the other cases (Case-2: batch operation and Case-3: continuous operation) in which only the inner cylinder is rotated to attain the same amorphization of the material. The powders produced in Cases-2 and 3 had a larger specific surface area than that by Case-1. Heat generation rate during the dissolution in water of the powder produced by Cases-2 and 3 was much faster than that by Case-1. The reactivity of powder produced by Cases-2 and 3 was higher than that by Case-1.

Gibbsite growth kinetics on gibbsite, kaolinite, and muscovite substrates: atomic force microscopy evidence for epitaxy and an assessment of reactive surface area

New experimental data for gibbsite growth on powdered kaolinite and single crystal muscovite and published data for gibbsite growth on gibbsite powders at 80°C in pH3 solutions show that all growth rates obey the same linear function of saturation state provided that reactive surface area is evaluated for each mineral substrate. Growth rate (mol m −2 s −1) is expressed by Rate ppt = (1.9 ± 0.2) × 10 −10|Δ G r |/ RT (0.90±0.01), which applies to the range of saturation states from Δ G r = 0 to 8.8 kJ mol −1, where Δ G r = RT[ln( Q/ K)] for the reaction Al 3+ + 3H 2O = Al(OH) 3 + 3H +, and equilibrium defined as Δ G r = 0 was previously determined. Identification of the growth phase as gibbsite was confirmed by rotating anode powder x-ray diffraction. Rates on kaolinite were determined using steady-state measured changes between inlet and outlet solutions in single-pass stirred-flow experiments. Rates on muscovite were determined by measuring the volume of precipitated crystals in images obtained by Tapping Mode™ atomic force microscopy (TMAFM). In deriving the single growth rate law, reactive surface area was evaluated for each substrate mineral. Total BET surface area was used for normalizing rates of gibbsite growth onto powdered gibbsite. Eight percent of the BET surface area, representing the approximate amount occupied by the aluminum octahedral sheet exposed at crystal edges, was used for powdered kaolinite. The x - y area of the TMAFM images of the basal surface was used for single crystal muscovite. Linearity of growth rates with saturation state suggests that the dominant nucleation and growth mechanisms are two dimensional. Such mechanisms are supported by observations of the morphologies of gibbsite crystals grown on muscovite at Δ G r = 8.8 kJ mol −1. The morphologies include (1) apparent epitaxial films as determined by hexagonal outlines of edges and thicknesses of 30 to 40 Å, (2) elongate crystals 30 to 40 Å thick aligned with the structure of the distorted Si-tetrahedral sheet of the 2 M 1 muscovite, and (3) micrometer-scale three-dimensional clumps of intergrown crystals. Reactive surface area as defined now for heterogeneous crystal growth in reactive-transport models must be modified to include substrates other than that of the growing mineral and to account for the role of structural and chemical controls on epitaxial nucleation and growth.

Effect of Dry-Grinding and Addition of Seed on .ALPHA.-Alumina Formation from Gibbsite.

Effect on α-alumina formation from gibbsite powder by heating was investigated for dry-grinding of gibbsite powder and the gibbsite powder added α-alumina fine powder as a seed. Two powder samples were prepared so as to adjust α-alumina formation temperature to nearly the same temperature at 1100°C. The transformation of intermediate alumina to α-alumina in the ground sample proceeded more homogeneous than that in the seeded sample. The particle size distribution of α-alumina powder calcined from the ground sample become narrower than that from the seeded sample, leading to the formation of sintered body with homogeneous grain size. This may be due to both the formation of much more fine α-alumina particles as nuclei of transformation and to a good dispersion in the intermediate alumina powder by the grinding in comparison with seeding.

Use of X-Ray Powder Diffraction Rietveld Pattern-Fitting for Characterising Preferred Orientation in Gibbsites

AbstractA study has been conducted with gibbsite specimens, on the use of Rietveld X-ray powder diffraction (XRPD) pattern fitting for quantitating preferred orientation in powders. This study has shown that an earlier formula gives results which correlate closely with an empirical measure of morphology proposed recently for gibbsite powders, viz., the ratio of the XRPD intensities for the (002) line and the (110, 200) doublet lines. A method is proposed on the basis of this correlation for the correction for preferred orientation of line intensities in gibbsite powder patterns. The correction method appears to have excellent potential for XRPD quantification of gibbsite levels in mixtures, and could have general application for coping with preferred orientation effects in the quantitation of other phases.

Strategies for Preferred Orientation Corrections in Xray Powder Diffraction Using Line Intensity Ratios

AbstractLi et al (1990) reported experiments with gibbsite powder specimens on the use of Rietveld pattern-fitting, involving the March preferred orientation model, to characterise preferred orientation according to the March r parameter. It was shown that intensity corrections may be applied with the March r parameter derived from Rietveld analysis or with the related line intensity ratio MR which is sensitive to preferred orientation. The present paper reports an analytic expression involving r and MR which has proved highly reliable for the correction of preferred orientation bias in quantitative phase analysis of gibbsite. Similar expressions may be readily derived for other materials for which the March model is appropriate. Therefore the line ratio approach has considerable potential for rapid correction of intensities for preferred orientation.

Studies on recrystallised aluminium trihydroxide precipitates: The energetics of dissolution by sodium hydroxide solutions

Aluminium hydroxide gels were recrystallised in high pH solution for 2–1000 hr to give a series of gibbsite powders of different surface areas, 1`11/2, P11/8, P11/48, P11/360 and P11/X; their average platelet lengths were 30, 60, 130, 260 and 450 nm. The dissolution equilibria of these powders in sodium hydroxide solutions of C=1-8 M were studied at 20° to 80°C.

Kinetics and mechanism of the heterogeneous reactions of crystallized Gibbsite powders with aqueous sodium hydroxide solutions

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTKinetics and mechanism of the heterogeneous reactions of crystallized Gibbsite powders with aqueous sodium hydroxide solutionsA. Packter and H. S. DhillonCite this: J. Phys. Chem. 1973, 77, 25, 2942–2947Publication Date (Print):December 1, 1973Publication History Published online1 May 2002Published inissue 1 December 1973https://doi.org/10.1021/j100643a003RIGHTS & PERMISSIONSArticle Views139Altmetric-Citations10LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (722 KB) Supporting Info (1)»Supporting Information Supporting Information Get e-Alerts

The Heterogeneous Reactions of Gibbsite Powders with Aqueous Hydroxide Solutions—Kinetics and Mechanism

The Heterogeneous Reactions of Gibbsite Powders with Aqueous Hydroxide Solutions—Kinetics and Mechanism