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Continuous flow supercritical water synthesis and crystallographic characterization of anisotropic boehmite nanoparticles
Author(s) -
Lock Nina,
Hald Peter,
Christensen Mogens,
Birkedal Henrik,
Iversen Bo Brummerstedt
Publication year - 2010
Publication title -
journal of applied crystallography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.429
H-Index - 162
ISSN - 1600-5767
DOI - 10.1107/s0021889810019187
Subject(s) - boehmite , crystallite , supercritical fluid , materials science , nanoparticle , aluminium nitrate , transmission electron microscopy , chemical engineering , crystallography , mineralogy , composite material , aluminium , nanotechnology , chemistry , metallurgy , organic chemistry , engineering
Crystalline boehmite nanoparticles have been prepared in a few minutes from thermal decomposition of aluminium nitrate in near‐ and supercritical water. Highly anisotropic nanoparticles are formed under continuous flow conditions using T‐piece mixing and a large size tube diameter. The shapes and sizes of the synthesized nanocrystals were determined from peak shape analysis of powder X‐ray diffraction data. The crystallite morphology is pressure dependent, and the size increases with temperature for constant reaction time and pressure. The modelled crystallite sizes and anisotropic shapes are in good agreement with transmission electron microscopy studies. At lower synthesis pressures the boehmite crystallite morphology is a mixture of platelets and bar‐shaped crystals. The bar‐shaped crystals align into polycrystalline fibre‐like long thin needles, which again align sidewise in bundles. At higher pressures, only the polycrystalline fibres are formed. Full conversion of dried boehmite to γ‐Al 2 O 3 is observed after short‐term heating to 773 K with an overall conservation of the morphology.