Geoscience Reference
In-Depth Information
Figure 10.83 SEM photographs of BiFeO
3
powders
[392]
.
Source: Courtesy of S. Komameni.
BiFeO
3
and CsAl
2
PO
6
using microwave-hydrothermal conditions and found an
enhancement of kinetics. BiFeO
3
has a perovskite structure and can be prepared at
194
C under microwave-hydrothermal conditions only. The other phase CsAl
2
PO
6
is
useful in nuclear waste disposal and is accomplished at 138
C under microwave-
hydrothermal conditions.
Figure 10.83
shows SEM photographs of BiFeO
3
powders:
(a) highly crystallized agglomerated BiFeO
3
powder prepared by microwave-
hydrothermal process at
194
C with a duration of 2
3h.
Figure 10.84
shows SEM
photographs of CsAl
2
PO
6
[392]
. These results clearly indicate that the use of micro-
wave field catalyzes crystallization of
B
inorganic phases under hydrothermal
conditions.
Recently, D'Arrigo et al.
[393]
and Kim et al.
[394]
have synthesized nano-
phase ferrites such as ZnFe
2
O
4
,NiFeO
4
,MnFe
2
O
4
,andCoFe
2
O
4
under
microwave-hydrothermal conditions. Multicomponent oxides like spinel phase
Co-, Co
Zn ferrite nanoparticles have been prepared using
microwave-hydrothermal method. The average particle size obtained by such a pro-
cess is about 10 nm. In the Co-ferrite system, single-phase ferrites with a spinel struc-
ture began to form at a relatively low temperature (100
C) in a short holding time
(30 min).
Figure 10.85
shows TEM images of Co
1
x
Zn
x
Fe
2
O
4
and Ni
1
x
Zn
x
Fe
2
O
4
nanoparticles obtained using the microwave-hydrothermal method
[395]
. Nanophase
ferrites with high surface areas, in the range of 72
Zn and Ni
247 m
2
/g,havebeensynthesized
in a matter of a few minutes at temperatures as low as 164
C. The rapid synthesis of
nanophase ferrites via an acceleration of
reaction rates under microwave-
