The structure of Al(III) in strongly alkaline aluminate solutions — A review

Sipos, Pál

doi:10.1016/j.molliq.2009.01.015

Cited by 127 publications

(106 citation statements)

References 91 publications

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“…In this process, the hard oxide shell covering the aluminum is dissolved with the metal becoming free and active to be leached 51,56 . Thereby, the aluminum speciation in solution reveals the presence of monomeric and oligomeric aluminates ranging from 6-to 5-and 4-coordination numbers [57][58][59] . The aluminum coordination in solution has been considered as an important feature for phase structure when organic additives or solvents are employed 59,60 .…”

Section: Synthetic Approachmentioning

confidence: 99%

A Novel Synthesis Route of Mesoporous γ-Alumina from Polyoxohydroxide Aluminum

et al. 2018

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Mesoporous gamma-aluminas (γ-Al 2 O 3 ) were synthesized starting from an unusual precursor of polyoxohydroxide aluminum (POHA). This precursor was obtained from aluminum oxidation in alkaline water-ethanol solvent in the presence of d-glucose that induces the formation of a gel, which leads to the POAH powder after ethanolic treatment. Precipitated POHAs were calcined at different temperatures (300, 400, 700 and 900 °C) resulting in the metastable γ-Al 2 O 3 phase. Whereas at 300 °C no γ-Al 2 O 3 phase was formed, unexpectedly, mesoporous γ-Al 2 O 3 was obtained at 400 ºC having a high specific surface area (282 m 2 /g) and a narrow pore size distribution. At higher temperatures, the aluminas had the expected decrease in surface area: 166 m 2 /g (700 °C) and 129 m 2 /g (900 °C), respectively. The structural change from POHA to alumina calcined at 400 ºC occurs directly without the need to isolate the hydroxide or oxyhydroxide aluminum precursors. Both POHA and transition aluminas were characterized by Fourier Transform Infrared spectroscopy (FTIR), X-ray diffraction (XRD), N 2 sorption and Scanning Electron Microscopy (SEM). These findings show an alternative route to produce high standard aluminas.

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Section: Synthetic Approachmentioning

confidence: 99%

A Novel Synthesis Route of Mesoporous γ-Alumina from Polyoxohydroxide Aluminum

et al. 2018

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“…In this process the hard oxide shell recovering the metal is first dissolved 46,47 with the metal becoming free and active to be oxidized 41,42,48 , hence generating a complex mixture of aluminum complexes in solution. For instance, studies on aluminum chemical speciation reveal the presence of monomeric and oligomeric aluminates ranging from 6-to 5-and 4-coordination numbers, all of them in a very narrow pH range [49][50][51] . Apart from this, aluminum solution chemistry is an unresolved theme with several open questions 50,51 .…”

Section: Water-ethanol Mixture Aluminum and Base Effects On Al-ntcdamentioning

confidence: 99%

“…For instance, studies on aluminum chemical speciation reveal the presence of monomeric and oligomeric aluminates ranging from 6-to 5-and 4-coordination numbers, all of them in a very narrow pH range [49][50][51] . Apart from this, aluminum solution chemistry is an unresolved theme with several open questions 50,51 . Taking into account the aforementioned, four main points can be considered for the Al-NTCDA/OH -reduction system in water-ethanol mixtures: i) in strong aqueous alkaline media besides the NTCDA high hydrolysis rate constant and its lower solubility, aluminate species are soluble and therefore no bayerite is formed in short reaction times; ii) in pure alcoholic media, as in other organic solvents, no aluminum corrosion and consequently no NTCDA reduction occurs; iii) in mixed water-ethanol media these two constraints are relaxed and so, solubilization of NTCDA and its redox reaction are highly favorable; iv) at the same time, in the specific H 2 O-EtOH 1:3 mixture ratio, electron adduct NTCDA species are formed and the aluminate solution is destabilized, leading to the precipitation of bayerite.…”

Section: Water-ethanol Mixture Aluminum and Base Effects On Al-ntcdamentioning

confidence: 99%

Synthesis and properties of new paramagnetic hybrid bayerite from Al(0)/naphthalene dianhydride reaction

et al. 2010

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The reaction of Naphthalene 1,4,5,8-dianhydride (NTCDA) with elemental aluminum(0) powder is studied in an aqueous alcoholic KOH mixture to search for the NTCDA anion and dianion electron-adducts. After analyzing various reaction conditions it was found that the reaction yielded a greenish precipitate in 3:1 (v:v) ethanol:water mixture. This powder is composed mainly of aluminum trihydroxide crystallites of bayerite [a-Al(OH 3 ) (s) ] and the organic content is approximately 6%. This hybrid material proved to be paramagnetic even after exposure to air for one year and at temperatures up to 200 °C. Typical carbonylic bound to metal IR bands and reflectance UV-VIS spectra demonstrate the entrapment of NTCDA radical anion into the aluminum trihydroxide, hence rendering its green color and a paramagnetic behavior. Thus, besides the understanding of an aluminum reaction in suspension, the entrapment of an organic material (NTCDA) that stays stable as the corresponding radical can provide an interesting option for the synthesis of aluminum trihydroxide composites.

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“…The speciation of Al (III) has been reviewed and ascertained by Sipos (2009) who considers that: ''four solution species (all aquated), i.e., Na þ , OH À , Al(OH) 4 À and a dimeric complex (most probably (OH) 3 Al-O-Al(OH) 3 2 À ) along with their ion pairs, are sufficient to account qualitatively and, where appropriate, quantitatively for all the experimental observations collected for concentrated alkaline aluminate solutions at temperatures up to 100 1C''. After many authors (including Wesoloski), we equated in the above described work: ½AlðOHÞ À 4 % A (1) and ½OH À ¼ CÀ½AlðOHÞ À 4 (3): this is a rough approximation, even at high pH because of ion pairing and oligomerization.…”

Section: Chemical Interpretation Toward a Chemically Based Modelmentioning

confidence: 99%