000861705 001__ 861705 000861705 005__ 20210130000942.0 000861705 0247_ $$2doi$$a10.1007/s11051-018-4285-4 000861705 0247_ $$2ISSN$$a1388-0764 000861705 0247_ $$2ISSN$$a1572-896X 000861705 0247_ $$2WOS$$aWOS:000438821500001 000861705 037__ $$aFZJ-2019-02135 000861705 082__ $$a570 000861705 1001_ $$00000-0002-1158-1491$$aKhodan, A.$$b0$$eCorresponding author 000861705 245__ $$aPorous monoliths consisting of aluminum oxyhydroxide nanofibrils: 3D structure, chemical composition, and phase transformations in the temperature range 25–1700 °C 000861705 260__ $$aDordrecht [u.a.]$$bSpringer Science + Business Media B.V$$c2018 000861705 3367_ $$2DRIVER$$aarticle 000861705 3367_ $$2DataCite$$aOutput Types/Journal article 000861705 3367_ $$0PUB:(DE-HGF)16$$2PUB:(DE-HGF)$$aJournal Article$$bjournal$$mjournal$$s1553776203_27223 000861705 3367_ $$2BibTeX$$aARTICLE 000861705 3367_ $$2ORCID$$aJOURNAL_ARTICLE 000861705 3367_ $$00$$2EndNote$$aJournal Article 000861705 520__ $$aWe present a study on the chemical and structural transformations in highly porous monolitic materials consisting of the nanofibrils of aluminum oxyhydroxides (NOA, Al2O3·nH2O) in the temperature range 20–1700 °C. A remarkable property of the NOA material is the preservation of the monolithic state during annealing over the entire temperature range, although the density of the monolith increases from ~0.02 up to ~3 g/cm3, the total porosity decreases from 99.3 to 25% and remains open up to 4 h annealing at the temperature ~1300 °C. The physical parameters of NOA monoliths such as density, porosity, specific area were studied and a simple physical model describing these parameters as the function of the average size of NOA fibrils—the basic element of 3D structure—was proposed. The observed thermally induced changes in composition and structure of NOA were successfully described and two mechanisms of mass transport in NOA materials were revealed. (i) At moderate temperatures (T ≤ 800 °C), the mass transport occurs along a surface of amorphous single fibril, which results in a weak decrease of the length-to-diameter aspect ratio from the initial value ~24 till ~20; the corresponding NOA porosity change is also small: from initial ~99.5 to 98.5%. (ii) At high temperatures (T > 800 °C), the mass transport occurs in the volume of fibrils, that results in changes of fibrils shape to elliptical and strong decrease of the aspect ratio down to ≤ 2; the porosity of NOA decreases to 25%. These two regimes are characterized by activation energies of 28 and 61 kJ/mol respectively, and the transition temperature corresponds to the beginning of γ-phase crystallization at 870 °C. 000861705 536__ $$0G:(DE-HGF)POF3-6G4$$a6G4 - Jülich Centre for Neutron Research (JCNS) (POF3-623)$$cPOF3-623$$fPOF III$$x0 000861705 536__ $$0G:(DE-HGF)POF3-6G15$$a6G15 - FRM II / MLZ (POF3-6G15)$$cPOF3-6G15$$fPOF III$$x1 000861705 588__ $$aDataset connected to CrossRef 000861705 65027 $$0V:(DE-MLZ)SciArea-180$$2V:(DE-HGF)$$aMaterials Science$$x0 000861705 65017 $$0V:(DE-MLZ)GC-1601-2016$$2V:(DE-HGF)$$aEngineering, Industrial Materials and Processing$$x0 000861705 693__ $$0EXP:(DE-MLZ)KWS2-20140101$$1EXP:(DE-MLZ)FRMII-20140101$$5EXP:(DE-MLZ)KWS2-20140101$$6EXP:(DE-MLZ)NL3ao-20140101$$aForschungs-Neutronenquelle Heinz Maier-Leibnitz $$eKWS-2: Small angle scattering diffractometer$$fNL3ao$$x0 000861705 693__ $$0EXP:(DE-MLZ)KWS3-20140101$$1EXP:(DE-MLZ)FRMII-20140101$$5EXP:(DE-MLZ)KWS3-20140101$$6EXP:(DE-MLZ)NL3auS-20140101$$aForschungs-Neutronenquelle Heinz Maier-Leibnitz $$eKWS-3: Very small angle scattering diffractometer with focusing mirror$$fNL3auS$$x1 000861705 7001_ $$0P:(DE-Juel1)130863$$aNguyen, T. 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