Anomalous reduction in surface area during mechanical activation of boehmite synthesized by thermal decomposition of gibbsite

Alex, T C; Kumar, Rakesh; Roy, Sunanda; Mehrotra, Shanta

doi:10.1016/j.powtec.2010.12.010

Cited by 38 publications

(31 citation statements)

References 26 publications

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“…658,667 Boehmite (g-AlOOH) prepared by thermal decomposition of gibbsite showed an anomalous decrease in its surface area from B264 m 2 g À1 to B65 m 2 g À1 after 240 min of planetary milling. 658 In sharp contrast, boehmite prepared by hydrothermal transformation of gibbsite showed an increase in specific surface area from B3 m 2 g À1 to 35 m 2 g À1 under identical conditions of milling. 668 The mechanically induced dehydroxylation in high-surface-area boehmite is accompanied by coalescence of fine pores (2 and 4 nm) to form bigger pores (20 nm) and an aggregation process.…”

Section: Role Of Water In Mechanochemistrymentioning

confidence: 99%

Hallmarks of mechanochemistry: from nanoparticles to technology

et al. 2013

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The aim of this review article on recent developments of mechanochemistry (nowadays established as a part of chemistry) is to provide a comprehensive overview of advances achieved in the field of atomistic processes, phase transformations, simple and multicomponent nanosystems and peculiarities of mechanochemical reactions. Industrial aspects with successful penetration into fields like materials engineering, heterogeneous catalysis and extractive metallurgy are also reviewed. The hallmarks of mechanochemistry include influencing reactivity of solids by the presence of solid-state defects, interphases and relaxation phenomena, enabling processes to take place under non-equilibrium conditions, creating a well-crystallized core of nanoparticles with disordered near-surface shell regions and performing simple dry time-convenient one-step syntheses. Underlying these hallmarks are technological consequences like preparing new nanomaterials with the desired properties or producing these materials in a reproducible way with high yield and under simple and easy operating conditions. The last but not least hallmark is enabling work under environmentally friendly and essentially waste-free conditions (822 references).

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Section: Role Of Water In Mechanochemistrymentioning

confidence: 99%

Hallmarks of mechanochemistry: from nanoparticles to technology

et al. 2013

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“…83-2384] used in the study was synthesized by thermal transformation of Bayer's process gibbsite as described in an earlier publication. [18] The median particle size (d 50 ) of the sample was 110 lm. The geometrical specific surface area (SSA Geo ) and BET specific surface area (SSA BET ) of the sample were 0.10 and 263 m 2 /g, respectively, indicating highly porous nature of the sample.…”

Section: A Boehmite Samplementioning

confidence: 99%

“…Gre´nman et al [14] observed only 4 pct dissolution after 3 hours of leaching in 6 M NaOH solution at 358 K (85°C). High solubility of boehmite (up to 60 pct) has been reported for nano-size (0.07 to 0.1 lm) boehmite by Packter [9] and high surface area (264 m 2 /g) boehmite by Alex et al [18,19] under ambient pressure leaching. In spite of different reported solubilities, the effect of nature of solid phase, e.g., purity (chemical and structural), specific surface area, porosity, crystallite size, etc., [20,21] have not been adequately addressed.…”

Section: Introductionmentioning

confidence: 97%

“…[4] Several investigations have focused on alkali leaching of boehmite. [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] The kinetics of alkali leaching is described in terms of 'shrinking core model with surface reaction' [4,13,19] and 'first-order chemical reaction.' [15][16][17] Most studies have focused on the effect of alkali concentration and temperature on boehmite solubility.…”

Section: Introductionmentioning

confidence: 99%

“…[2,18,[22][23][24][25][26][27][28][29][30][31] After 120 minutes of mechanical activation in a planetary mill, an increase in leachability from 58 to 88 pct and 12 to 92 pct is observed during alkali leaching (temperature-363 K (90°C), alkali concentration-180 g/l Na 2 O, leaching time-30 minutes) for boehmite prepared by thermal and hydrothermal transformation of gibbsite, respectively. [18,30] Kinetics of alkali leaching of mechanically activated boehmite has been explained in terms of 'second-order reaction model.' [31] The nature of solid phase may change continuously during leaching.…”

Section: Introductionmentioning

confidence: 99%

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Elucidation of the Nature of Structural Heterogeneity During Alkali Leaching of Non-activated and Mechanically Activated Boehmite (γ-AlOOH)

Kumar

Alex

2015

Metall Mater Trans B

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Crystal joints and faces in non-activated boehmite and, state of agglomeration of particles, degree of amorphization, microcrystallite dimension and, strain in mechanically activated boehmite are indicators of structural heterogeneity which influences reactivity of the solid phase. The focus of this paper is on understanding the manifestation of the heterogeneity during alkali leaching of a boehmite (specific surface area-263 m 2 /g), without and with mechanical activation using planetary milling up to 240 minutes. A two-prong strategy is used for this purpose which involved analysis of the kinetics of leaching by a model-free approach using 'isoconversional method' and, in parallel, characterization of the reacting solid after different durations of leaching. Unlike model-fitting methods, the kinetic analysis revealed sample-dependent variation of apparent activation energy with fraction leached. Changes observed in the morphology of samples (by SEM), particle size distribution (by laser diffraction), and crystalline nature (by powder X-ray diffraction) are used to explain activation energy changes and propose mechanisms of leaching. The effect of mechanical activation on rate constant is assessed and it has been found that up to~23-fold increase in rate is possible depending on the activation time, leaching temperature, and fraction leached. Further, based on binary correlations between activation energy at different fractions leached and initial characteristics of the samples, it is found that the leaching is predominantly influenced by structural changes during milling, namely, degree of amorphization, microcrystallite dimension, and strain, vis-a`-vis specific surface area. Significantly, the paper highlights limitation of model-fitting methods used by most researchers to analyze the kinetics of leaching, especially for mechanically activated minerals.

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Mechanical Activation of Al‐Oxyhydroxide Minerals – Physicochemical Changes, Reactivity and Relevance to Bayer Process

et al. 2012

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Overview of our research on 'structure and reactivity' of gibbsite and boehmite under varied conditions of mechanical activation, e.g. milling energy and presence of a second phase is presented. Bulk and surface changes induced in the solids by milling are characterized in terms of morphology, particle size distribution, specific surface area and nature of porosity, crystallite size and zeta potential. Results on enhanced amorphisation of gibbsite in presence of a second phase (quartz, hematite etc), changes in zeta potential of gibbsite due to loss of texture during milling and anomalous decrease in surface area of boehmite during milling are reported. Reactivity of the activated solids in sodium hydroxide and variation in thermal transformation temperatures is correlated with physicochemical characteristics of the samples and plausible explanation for the observed correlations presented. Significance of the results with specific reference to bauxite and alumina processing in Bayer process is highlighted.

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Anomalous reduction in surface area during mechanical activation of boehmite synthesized by thermal decomposition of gibbsite

Cited by 38 publications

References 26 publications

Hallmarks of mechanochemistry: from nanoparticles to technology

Hallmarks of mechanochemistry: from nanoparticles to technology

Elucidation of the Nature of Structural Heterogeneity During Alkali Leaching of Non-activated and Mechanically Activated Boehmite (γ-AlOOH)

Mechanical Activation of Al‐Oxyhydroxide Minerals – Physicochemical Changes, Reactivity and Relevance to Bayer Process

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