Page 275 - Book Hosokawa Nanoparticle Technology Handbook

FUNDAMENTALS CH. 4 CONTROL OF NANOSTRUCTURE OF MATERIALS
References

[1] Y. Sakka, T. Uchikoshi: Mater. Sci. Technol., 41,
205–210 (2004).
[2] K. Uematsu: Ceram. Jpn., 40, 686–702 (2005).
[3] J. Cesarano III, I.A. Aksay: J. Am. Ceram. Soc., 71,
1062–1067 (1988).
[4] F. Kitahara, K. Furusawa: Bunsan-Nyuka-Kei no
Kagaku, Kogyo Shuppan, Tokyo, p. 104 (1991).
[5] Y. Hirata, S. Nakagama and Y. Ishihara: J. Ceram.
Soc. Jpn., 98, 316–321 (1990).
[6] O. Vasylkiv, Y. Sakka and V.V. Skorokhod: J. Am.
Ceram. Soc., 86, 299–304 (2003).
[7] O. Vasylkiv, Y. Sakka, Y. Maeda and V.V. Skorokhod:
J. Euro. Ceram. Soc., 24, 469–473 (2004).
[8] Y. Sakka: Ceram. Jpn., 30, 1017–1020 (1995).
Figure 4.5.45 [9] Y. Sakka, K. Hiraga: Nippon Kagaku Kaishi, 497–508
SEM photograph of porous -Al O . (1999).
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[10] F. Tang, F. Fudouzi, T. Uchikoshi and Y. Sakka:
J. Euro. Ceram. Soc., 24, 341–344 (2004).
for obtaining a homogeneous microstucture. For the
dispersed suspension, segregation during colloidal fil-
tration is a common problem due to differences in the 4.6 Self-assembly
sedimentation rate, but it can be minimized using a
suspension with a high solid loading.
As an example of the multi-component system, 4.6.1 Self-organization of nanoparticles
some colloidal processing trials of SiO added 3YTZ It is expected that various kinds of functions can be
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are described. The addition of SiO is one method for realized by thin films consisting of two- or three-
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enhancing the superplastic elongation by modifica- dimensional structures of nanoparticles on a sub-
tion of the 3YTZ grain-boundary. Using commercial strate. One of the most realistic methods of ordering
3YTZ powder with an aggregate size of 90 nm, the nanoparticles is coating and drying process [1]. It is a
following three types of suspensions were prepared typical bottom-up method based on self-organization
[9]; SiO -coated 3YTZ particles used for the colloidal of nanoparticles in solution. The self-organization
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processing in which the composite particle is pre- method observed anywhere in nature is not well-
pared by an alkoxide precipitation method, coating by understood. The nanomaterials design from an engi-
SiO , a hetero-coagulated suspension is used, and a neering point of view can be established by
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well-dispersed suspension with 30 vol% solids load- understanding the mechanisms of self-organization in
ing. In either case, a homogeneous microstructure nature. As a result, the innovation of nanoprocessing
with a fine grain size of 0.2 m and high density is to fabricate nanomaterials can be established. The
established by the low-temperature sintering [9]. nanostructure control is essential to design sophisti-
The hetero-coagulation method is also applicable cated functional materials. In fact, nanostructures
for the preparation of porous materials. This is based observed in functional materials are not well-
on the template-assisted approach of a core–shell designed but obtained by chance. It is the same as a
composite [10]. Monodispersed polymer spheres are recipe of cooking accumulated as personal skills.
used as templates, and ceramic particles act as the tar- Nanoparticles consisting of metals, ceramics, semi-
get materials. By particle surface modification, well- conductors, organics, carbons, and polymers are syn-
dispersed suspensions of the polymer and ceramic thesized by various kinds of methods for realizing
particles with a high opposite charge could be desired both physical properties and functions. The
obtained at the same pH. The flocculated particles are necessary conditions to explore new functions by
subsequently closely packed by vacuum filtration. employing nanoparticles are as follows.
The polymers are finally removed by calcination at
round 500 C for 4 h, resulting in the porous struc- 1. The size of nanoparticles is preferable less than
tures. Figure 4.5.45 shows porous -Al O with a par- 10 nm.
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ticle size of about 30 nm from a 350-nm template
after heating at 850 C. This method is applicable for 2. The size distribution of nanoparticles is smaller
obtaining various types of porous ceramics with a than 10 % in CV value whose definition is the
controlled pore size and porosity by changing the par- ratio of the standard deviation to the average
ticle sizes of both the ceramic and polymer [10]. value.
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