the sidewall when burned in oxygen. They consider sonochemistry to be a simple
method to functionalize SWNTs.
Nikitenko has succeeded recently in preparing iron nanoparticles that are airstable [70]. Iron is easily oxidized in ambient conditions, but when it comes to iron
nanoparticles they are pyrophoric and burn spontaneously in air. That is why obtaining iron nanoparticles that are air-stable is important. On the other hand, it is
known that iron nanoparticles obtained sonochemically from alkane solutions are
not stable in contact with air. In his study, Nikitenko prepared coated iron nanoparticles by the sonochemical decomposition of [Fe(CO) 5 ] in diphenylmethane
(DPhM), an aromatic solvent with physicochemical properties (m.p. 25
C, b.p.
265
C, vapor pressure 1 kPa at 77
C) that are suitable for sonochemistry. The sonolysis of the neat DPhM forms a polymer-like solid product. It is proposed that small
amounts of this product generated in situ would coat the surface of iron nanoparticles formed simultaneously from Fe(CO) 5 . The as-prepared material contained
17.6 wt% C and 1.5 wt% H. The reaction yield was 53% with respect to iron. The
presence of a significant amount of carbon and hydrogen indicates that the asprepared material contains the sonolytic decomposition products of DPhM. At this
stage the as-prepared product is annealed at 700
C in argon. An air-stable, dark
gray magnetic powder is formed as a result of the annealing. The annealed material contains 5.6 wt% C and 0.08 wt% H. The annealed product is air-stable. Its
stability in air was checked once a month for the first 6 months after preparation
by (1) Mo ¨ssbauer spectroscopy, (2) XRD, and (3) magnetization measurements.
No changes were observed in the measured parameters during this period. The
annealed material is ferromagnetic, as follows from the magnetization curve. The
saturation magnetization M s and coercive force H c are 212 emu g
À1 and 40 Oe,
respectively. The M s value of the material is unexpectedly high and is close to that
of bulk bcc Fe (222 emu g
À1 ). The air-stability of the product originates from a
Fe 3 C/C layer surrounding the core of the iron nanoparticle.
6.1.2
Sonochemical Fabrication of Nano-Metallic Oxides
6.1.2.1 Sonochemical Synthesis of Transition Metal Oxides from the Corresponding
Carbonyls
Sonication of a decalin solution of Fe(CO) 5 in air yields amorphous nanoparticles
of Fe 2 O 3 [71]. This paper presents another advantage of using sonochemistry for
preparation of an amorphous product. It is well known that, unlike iron, which can
be obtained in the amorphous form by the cold quenching technique, amorphous
iron oxide cannot be prepared in this way. Higher cooling rates are needed for iron
oxides and other metal oxides. This is because the thermal conductivities of metal
oxides are usually much lower than those of the metals. This is the reason that
glass formers, whose purpose is to prevent crystallization, are added if the
quenching method is applied. Amorphous metal oxides can be prepared by rapidly
quenching the molten mixture of metal oxides only if a glass former, such as P 2 O 5 ,
V 2 O 5 , Bi 2 O 3 , SiO 2 , and CaO, is added to the mixture [72–74]. As mentioned above,
6.1 Sonochemistry 129
method to functionalize SWNTs.
Nikitenko has succeeded recently in preparing iron nanoparticles that are airstable [70]. Iron is easily oxidized in ambient conditions, but when it comes to iron
nanoparticles they are pyrophoric and burn spontaneously in air. That is why obtaining iron nanoparticles that are air-stable is important. On the other hand, it is
known that iron nanoparticles obtained sonochemically from alkane solutions are
not stable in contact with air. In his study, Nikitenko prepared coated iron nanoparticles by the sonochemical decomposition of [Fe(CO) 5 ] in diphenylmethane
(DPhM), an aromatic solvent with physicochemical properties (m.p. 25
C, b.p.
265
C, vapor pressure 1 kPa at 77
C) that are suitable for sonochemistry. The sonolysis of the neat DPhM forms a polymer-like solid product. It is proposed that small
amounts of this product generated in situ would coat the surface of iron nanoparticles formed simultaneously from Fe(CO) 5 . The as-prepared material contained
17.6 wt% C and 1.5 wt% H. The reaction yield was 53% with respect to iron. The
presence of a significant amount of carbon and hydrogen indicates that the asprepared material contains the sonolytic decomposition products of DPhM. At this
stage the as-prepared product is annealed at 700
C in argon. An air-stable, dark
gray magnetic powder is formed as a result of the annealing. The annealed material contains 5.6 wt% C and 0.08 wt% H. The annealed product is air-stable. Its
stability in air was checked once a month for the first 6 months after preparation
by (1) Mo ¨ssbauer spectroscopy, (2) XRD, and (3) magnetization measurements.
No changes were observed in the measured parameters during this period. The
annealed material is ferromagnetic, as follows from the magnetization curve. The
saturation magnetization M s and coercive force H c are 212 emu g
À1 and 40 Oe,
respectively. The M s value of the material is unexpectedly high and is close to that
of bulk bcc Fe (222 emu g
À1 ). The air-stability of the product originates from a
Fe 3 C/C layer surrounding the core of the iron nanoparticle.
6.1.2
Sonochemical Fabrication of Nano-Metallic Oxides
6.1.2.1 Sonochemical Synthesis of Transition Metal Oxides from the Corresponding
Carbonyls
Sonication of a decalin solution of Fe(CO) 5 in air yields amorphous nanoparticles
of Fe 2 O 3 [71]. This paper presents another advantage of using sonochemistry for
preparation of an amorphous product. It is well known that, unlike iron, which can
be obtained in the amorphous form by the cold quenching technique, amorphous
iron oxide cannot be prepared in this way. Higher cooling rates are needed for iron
oxides and other metal oxides. This is because the thermal conductivities of metal
oxides are usually much lower than those of the metals. This is the reason that
glass formers, whose purpose is to prevent crystallization, are added if the
quenching method is applied. Amorphous metal oxides can be prepared by rapidly
quenching the molten mixture of metal oxides only if a glass former, such as P 2 O 5 ,
V 2 O 5 , Bi 2 O 3 , SiO 2 , and CaO, is added to the mixture [72–74]. As mentioned above,
6.1 Sonochemistry 129