Memory effects in gel-solid transformations: Coordinately unsaturated Al sites in nanosized aluminas

Journal Article · Wed Sep 01 04:00:00 EDT 1993 · Chemistry of Materials; (United States)

DOI:https://doi.org/10.1021/cm00033a004· OSTI ID:5040630

Coster, D; Fripiat, J J ^[1]

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1. Univ. of Wisconsin, Milwaukee, WI (United States)

Precursors of aluminas rich in pentacoordinated aluminum are generated by a new sol-gel route. The critical step of the process is a limited hydrolysis of aluminum tri.sec.butoxide in non-aqueous media. The gel-solid transformation is investigated by [sup 27]Al high-resolution MAS NMR and nitrogen adsorption. The structural and textural evolutions of the gel by thermal activation up to 700[degrees]C are self-determined. As the octahedral condensation in the gel increases, the Al[sup V] concentration in the solid increases: This observation evidences a structural memory. The percentage of small pores (d<6 nm) in the transition alumina is correlated to the chemical shift of the Al[sup VI] line in the gel. Thus, a textural memory effect is also observed. A general mechanism for the Al[sup V] formation is proposed, and the metastability of this coordinately unsaturated aluminum site is demonstrated. 12 refs., 9 figs., 5 tabs.

• OSTI ID: 5040630
• Journal Information: Chemistry of Materials; (United States), Journal Name: Chemistry of Materials; (United States) Vol. 5:9; ISSN CMATEX; ISSN 0897-4756
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360201 -- Ceramics
Cermets
&amp; Refractories-- Preparation &amp; Fabrication
360202* -- Ceramics
Cermets
&amp; Refractories-- Structure &amp; Phase Studies
ALUMINIUM COMPOUNDS
ALUMINIUM OXIDES
CHALCOGENIDES
MAGNETIC RESONANCE
NUCLEAR MAGNETIC RESONANCE
OXIDES
OXYGEN COMPOUNDS
PHASE TRANSFORMATIONS
RESONANCE
SOL-GEL PROCESS
SORPTIVE PROPERTIES
SURFACE PROPERTIES