TY - JOUR
T1 - Microstructural changes in porous hematite nanoparticles upon calcination
AU - Johnsen, Rune
AU - Knudsen, Kenneth D.
AU - Molenbroek, Alfons M.
PY - 2011
Y1 - 2011
N2 - This combined study using small-angle neutron scattering (SANS), X-ray
powder diffraction (XRPD), transmission electron microscopy (TEM) and
adsorption isotherm techniques demonstrates radical changes in the microstructure
of porous hematite (-Fe2O3) nanoparticles upon calcination in air.
TEM images of the as-synthesized hematite sample show that it consists of
subrounded nanoparticles [50 (8)–61 (11) nm in average minimum and
maximum diameters] with an apparent porous structure of nanosized pores/
channels or cracks. SANS data confirm the presence of two characteristic sizes,
one originating from the particle size and the other from the pore/void structure.
Furthermore, the TEM images show that the particle sizes are nearly unaffected
by calcination at 623 K, whereas their pore/void structure changes radically to
an apparently pitted or spongy microstructure with cavities or/and voids. The
change in microstructure also causes a reduction in the surface area as calculated
by gaseous adsorption. The XRPD and SANS data show that the crystallite and
SANS particle sizes are virtually unchanged by calcination at 623 K. Calcination
at 973 K induces a significant alteration of the sample. The XRPD data reveal
that the crystallite size increases significantly, and the SANS and adsorption
isotherm studies suggest that the specific surface area decreases by a factor of
5–6. The TEM images show that the particles are sintered into larger
agglomerates, but they also show that parts of the porous microstructure
observed in the sample calcined at 623 K are retained in the sample calcined at
973 K.
AB - This combined study using small-angle neutron scattering (SANS), X-ray
powder diffraction (XRPD), transmission electron microscopy (TEM) and
adsorption isotherm techniques demonstrates radical changes in the microstructure
of porous hematite (-Fe2O3) nanoparticles upon calcination in air.
TEM images of the as-synthesized hematite sample show that it consists of
subrounded nanoparticles [50 (8)–61 (11) nm in average minimum and
maximum diameters] with an apparent porous structure of nanosized pores/
channels or cracks. SANS data confirm the presence of two characteristic sizes,
one originating from the particle size and the other from the pore/void structure.
Furthermore, the TEM images show that the particle sizes are nearly unaffected
by calcination at 623 K, whereas their pore/void structure changes radically to
an apparently pitted or spongy microstructure with cavities or/and voids. The
change in microstructure also causes a reduction in the surface area as calculated
by gaseous adsorption. The XRPD and SANS data show that the crystallite and
SANS particle sizes are virtually unchanged by calcination at 623 K. Calcination
at 973 K induces a significant alteration of the sample. The XRPD data reveal
that the crystallite size increases significantly, and the SANS and adsorption
isotherm studies suggest that the specific surface area decreases by a factor of
5–6. The TEM images show that the particles are sintered into larger
agglomerates, but they also show that parts of the porous microstructure
observed in the sample calcined at 623 K are retained in the sample calcined at
973 K.
KW - Materials characterisation and modelling
KW - Materialekarakterisering og modellering
U2 - 10.1107/S0021889811016050
DO - 10.1107/S0021889811016050
M3 - Journal article
SN - 0021-8898
VL - 44
SP - 495
EP - 502
JO - Journal of Applied Crystallography
JF - Journal of Applied Crystallography
IS - 3
ER -