Page 91 - Book Hosokawa Nanoparticle Technology Handbook

2.2 PARTICLE SIZE FUNDAMENTALS
Table 2.2.4
Examples of metal oxide nanoparticles synthesized by MC
reaction.
Starting mixtures Reaction products
2AlCl 3 CaO Al O 3CaCl 2
2
3
ZrCl 4 2CaO ZrO 2CaCl 2
2
GdCl 3 3NaOH Gd O 3NaCl 1.5H O
3
2
2
CeCl 3 NaOH CeO 3NaCl H O
2
2
Na Cr O S Cr O Na SO 4
3
7
2
2
2
2
2NbCl 5 5Na CO 3 Nb O 10NaCl 5CO 2
2
2
5
SnCl 2 Na CO O SnO 2NaCl CO 2
3
2
2
2
2FeCl 3 3Ca(OH) 2 Fe O 3CaCl 2 3H O
2
3
2
ZnCl 2 Na CO 3 ZnO 2NaCl CO 2
2
Figure 2.2.21
Size of CeO nanoparticles as a function of temperature in
2
heating operation.

CeCl 3NaOH 12NaCl Ce(OH) 15NaCl
3 3
(2.2.20)
The role of heating is to form CeO from Ce(OH) ,
2
3
and it is found from this photo that the mean particle
size of CeO is around 10 nm and its size distribution
2
is quite narrow. Effect of heating temperature on the
particle size of CeO is shown in Fig. 2.2.21 [13], it is
2
noted that the size of CeO can be maintained in the
2
nanometer range when the temperature is not elevated.
c) Complex metal oxide nanoparticles
50 nm Ito et al. [14] have synthesized fine complex metal
oxide having nanometer size range by a MC method.
The method is to grind a mixture of metal chloride
and NaOH to produce metal hydroxide and NaCl. The
Figure 2.2.20
TEM photo of CeO nanoparticles. product ground is subjected to heating to form com-
2
plex oxide in which fine particles of NaCl are dis-
persed in the oxide phase. Subsequently, the heated
The addition of the dilute agent has a drawback of sample is washed with water to remove NaCl from the
difficulty in improving the volume ratio of nanopar- sample. This washing operation implies purification
ticles in the product. However, it is very important of the metal complex oxide. The temperature in the
because it plays a significant role to prevent from heating operation must be reduced more than that for
both crystalization of material and sintering during the mixture without grinding. The MC reaction equa-
heating. As an example, in the solid-phase reaction tion is shown by Eq. (2.2.21), as below:
shown by equation (2.2.19), only relatively large par-
ticles of SnO have been produced by heating the LaCl CoCl 5NaOH La(OH) Co(OH) 5NaCl
2
ground product, due to sintering of fine SnO synthe- 3 2 3 2
2
sized by the MC reaction. On the contrary, it is pos- (2.2.21)
sible to form SnO fine particles of 40 nm in size The ground product consists of (La(OH) Co(OH)
2
when the mixture is subjected to grinding with CaCl , NaCl), so that heating the product at 600 C makes 2
3
2
followed by its heating.
it possible to form (LaCoO NaCl) in the heated
3
sample. Consequently, nanoparticles of LaCoO are
3
SnCl Ca(OH) 0.5O SnO CaCl H O obtained at high yield by washing the heated sample
2 2 2 2 2 2
with water. The final product, LaCoO is very fine and
(2.2.19) 3
well-dispersed in comparison with the product
Figure 2.2.20 [12] is a TEM photo of CeO nanoparti- synthesized by the MC treatment of a mixture of
2
cles obtained by washing the heated product at 500 C, (La O Co O ). Especially, the specific surface area
3
2
2
3
after grinding the mixture of (CeCl NaOH NaCl). of the former final product is about three times higher
3
67