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@ARTICLE{Khodan:861705,
author = {Khodan, A. and Nguyen, T. H. N. and Esaulkov, M. and
Kiselev, M. R. and Amamra, M. and Vignes, J.-L. and Kanaev,
A.},
title = {{P}orous monoliths consisting of aluminum oxyhydroxide
nanofibrils: 3{D} structure, chemical composition, and phase
transformations in the temperature range 25–1700 °{C}},
journal = {Journal of nanoparticle research},
volume = {20},
number = {7},
issn = {1572-896X},
address = {Dordrecht [u.a.]},
publisher = {Springer Science + Business Media B.V},
reportid = {FZJ-2019-02135},
pages = {194},
year = {2018},
abstract = {We 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.},
cin = {JCNS-FRM-II / Neutronenstreuung ; JCNS-1},
ddc = {570},
cid = {I:(DE-Juel1)JCNS-FRM-II-20110218 /
I:(DE-Juel1)JCNS-1-20110106},
pnm = {6G4 - Jülich Centre for Neutron Research (JCNS) (POF3-623)
/ 6G15 - FRM II / MLZ (POF3-6G15)},
pid = {G:(DE-HGF)POF3-6G4 / G:(DE-HGF)POF3-6G15},
experiment = {EXP:(DE-MLZ)KWS2-20140101 / EXP:(DE-MLZ)KWS3-20140101},
typ = {PUB:(DE-HGF)16},
UT = {WOS:000438821500001},
doi = {10.1007/s11051-018-4285-4},
url = {https://juser.fz-juelich.de/record/861705},
}