Mo(CO) 6 appears to take place in the interfacial region: Thus, the water molecule
formed in the bubble may diffuse into the interfacial region or the water molecules
that are available from the atmospheric air, precursor, and solvent, and stabilize the
unusual pentavalent molybdenum oxide:
2MoðCOÞ 6 þ 17=2O 2 ! Mo 2 O 5 þ 12CO 2 ðSonolysisÞ
ð 3Þ
Mo 2 O 5 þ 2H 2 O ! Mo 2 O 5 Á2H 2 O
ð4Þ
The above possible mechanism for the formation of the blue oxide is consistent
with explanations in the literature for a sonochemical reaction.
Magnetite nanorods have been prepared by the sonication of aqueous iron (II)
acetate in the presence of b-cyclodextrin [77]. The as-prepared magnetite nanorods are ferromagnetic and their magnetization at room temperature is about 78
emu g
À1 . The particle sizes measured from transmission electron micrographs are
about 48/14 nm (L/W). A mechanism for the sonochemical formation of magnetite nanorods is discussed.
Only one report was found that discussed the effect of a magnetic field on sonication and sonication products [78]. The sonochemical irradiation of Fe(CO) 5 solution in decalin under argon has been carried out with and without an external
magnetic field. The sonication cell placed between the poles of a magnetic field of
7 kG which was applied during the sonication. We have already pointed out that
this reaction yields amorphous Fe 2 O 3 [9]. Direct TEM measurements reveal that
the sample obtained without a magnetic field consists of sponge-like particles with
a mean size of about 25 nm, whereas the sample synthesized in a 7 kG magnetic
field consists of highly acicular particles, 50 nm in length and 5 nm in width. Our
finding sheds light on the process of particle nucleation during sonication, which
cannot be a diffusion-assisted growth because of the very small time scale. We
conclude, therefore, that particles are forced to form an acicular entity by direct
magnetic interactions. The amorphous nature of the as-prepared substance was
verified by X-ray diffraction, selected area electron diffraction, and differential
scanning calorimetry. The magnetic moment vs. temperature measurements and
Mo ¨ssbauer spectroscopy reveal a large shift of the blocking temperature of about
70 K toward higher temperatures for the sample obtained in the magnetic field. We
attribute the observed shift to the significant enhancement of the particle shape
magnetic anisotropy.
6.1.2.2 Sonochemical Synthesis of Ferrites from the Corresponding Carbonyls
It was just a reasonable extension that a mixture of carbonyls would be sonicated
under air to yield the corresponding ferrites while the irradiation under argon
yielded the metallic alloy [37]. Indeed, nanosized amorphous NiFe 2 O 4 powder was
prepared by sonochemical decomposition of solutions of volatile organic precursors, Fe(CO) 5 and Ni(CO) 4 in decalin at 273 K, under an oxygen pressure of 100–
150 kPa [79]. The amorphous nature of these particles was confirmed by various
techniques. Magnetic measurements, Mo ¨ssbauer, and EPR spectral studies indi6.1 Sonochemistry 131
formed in the bubble may diffuse into the interfacial region or the water molecules
that are available from the atmospheric air, precursor, and solvent, and stabilize the
unusual pentavalent molybdenum oxide:
2MoðCOÞ 6 þ 17=2O 2 ! Mo 2 O 5 þ 12CO 2 ðSonolysisÞ
ð 3Þ
Mo 2 O 5 þ 2H 2 O ! Mo 2 O 5 Á2H 2 O
ð4Þ
The above possible mechanism for the formation of the blue oxide is consistent
with explanations in the literature for a sonochemical reaction.
Magnetite nanorods have been prepared by the sonication of aqueous iron (II)
acetate in the presence of b-cyclodextrin [77]. The as-prepared magnetite nanorods are ferromagnetic and their magnetization at room temperature is about 78
emu g
À1 . The particle sizes measured from transmission electron micrographs are
about 48/14 nm (L/W). A mechanism for the sonochemical formation of magnetite nanorods is discussed.
Only one report was found that discussed the effect of a magnetic field on sonication and sonication products [78]. The sonochemical irradiation of Fe(CO) 5 solution in decalin under argon has been carried out with and without an external
magnetic field. The sonication cell placed between the poles of a magnetic field of
7 kG which was applied during the sonication. We have already pointed out that
this reaction yields amorphous Fe 2 O 3 [9]. Direct TEM measurements reveal that
the sample obtained without a magnetic field consists of sponge-like particles with
a mean size of about 25 nm, whereas the sample synthesized in a 7 kG magnetic
field consists of highly acicular particles, 50 nm in length and 5 nm in width. Our
finding sheds light on the process of particle nucleation during sonication, which
cannot be a diffusion-assisted growth because of the very small time scale. We
conclude, therefore, that particles are forced to form an acicular entity by direct
magnetic interactions. The amorphous nature of the as-prepared substance was
verified by X-ray diffraction, selected area electron diffraction, and differential
scanning calorimetry. The magnetic moment vs. temperature measurements and
Mo ¨ssbauer spectroscopy reveal a large shift of the blocking temperature of about
70 K toward higher temperatures for the sample obtained in the magnetic field. We
attribute the observed shift to the significant enhancement of the particle shape
magnetic anisotropy.
6.1.2.2 Sonochemical Synthesis of Ferrites from the Corresponding Carbonyls
It was just a reasonable extension that a mixture of carbonyls would be sonicated
under air to yield the corresponding ferrites while the irradiation under argon
yielded the metallic alloy [37]. Indeed, nanosized amorphous NiFe 2 O 4 powder was
prepared by sonochemical decomposition of solutions of volatile organic precursors, Fe(CO) 5 and Ni(CO) 4 in decalin at 273 K, under an oxygen pressure of 100–
150 kPa [79]. The amorphous nature of these particles was confirmed by various
techniques. Magnetic measurements, Mo ¨ssbauer, and EPR spectral studies indi6.1 Sonochemistry 131