Page 115 - Book Hosokawa Nanoparticle Technology Handbook

2.4 COMPOSITE STRUCTURE FUNDAMENTALS
The composite materials are required widely in the Structure control of
industrial and medical fields and expected to become fine particle layer Heterogeneous
a key technology for the development of nanotechnol- fine particle
ogy. The application of the supercritical fluid is
expected to advance as a technology indispensable for
the creation of such composite materials in the future.

References
Multi-
[1] H. Uchida: NanoTechnology with Supercritical Fluids, layering
p. 64, CMC Publishing Co., Ltd., Tokyo (2004). (a) Core-shell type (b) Fine-particle dispersed type
[2] R. Viswanathan, G.D. Lilly, W.F. Gale and R.B. Gupta:
Figure 2.4.22
Ind. Eng. Chem. Res., 42, 5535–5540 (2003).
The structures of composite particles obtainable by the
[3] K. Sue, N. Kakinuma, T. Adschiri and K. Arai: Ind.
mechanical process.
Eng. Chem. Res., 43, 2073–2078 (2004).
[4] X.-R. Ye, Y. Lin, C. Wang and C.M. Wai: Adv. Mater.,
15, 316–319 (2003).
by bonding different components or gradients onto
[5] X.-R. Ye, Y. Lin and C.M. Wai, Chem. Commun.,
the particle surface.
642–643 (2003).
On the other hand, Fig. 2.4.22(b) shows the com-
[6] X.-R. Ye, Y. Lin, C. Wang, M.H. Engelh, Y. Wang and posite structure (fine-particle dispersed type) made
C.M. Wai: J. Mater. Chem., 14, 908–913 (2004). by burying or dispersing nanoparticles in the coarser
[7] Z. Liu, X. Dai, J. Xu, B. Han, J. Zhang, Y. Wang, particles. The mechanical alloying applied in the field
Y. Huang and G. Yang: Carbon, 42, 458–460 (2004). of powder metallurgy is one of the technologies for
[8] X.-R. Ye, H.-F. Zhang, Y. Lin, L.-S. Wang and C.M. Wai: producing this type of composite particles.
J. Nanosci. Nanotechnol., 4, 82–85 (2004). The major principles used for producing composite
particles by the mechanical methods are summarized
[9] Y. Wang, R.N. Dave and R. Pfeffer: J. Supercrit.
in Table 2.4.3 [2], which classifies the particle com-
Fluids, 28, 85–99 (2004).
posing methods into three categories. The first cate-
[10] J. Zhang, Z. Liu, B. Han, D. Liu, J. Chen, J. He and
gory is the composing machines conventionally used
T. Jiang: Chem. Eur. J., 10, 3531–3536 (2004).
as grinding mills. Although grinding is the mechani-
[11] Z. Li, J. Zhang, J. Du, T. Mu, Z. Liu, J. Chen and cal operation to break solid particles, most of their
B. Han: J. Appl. Polym. Sci., 94, 1643–1648 (2004). size reduction principles have effective functions to
[12] Z. Li, J. Zhang, T. Mu, J. Du, Z. Liu, B. Han and make composite particles as seen in the table. It
J. Chen: Collids. Surf. A, 243, 63–66 (2004). becomes obvious to explore the possibility of apply-
[13] Y.-P. Sun, H.W. Rollins and R. Guduru: Chem. Mater., ing mechanical effects for making particle compos-
11, 7–9 (1999). ites. As a result, some particle composing machines
have been developed based on the basic grinding
[14] M.J. Meziani, H.W. Rollins, L.F. Allard and Y.-P. Sun:
mechanisms, as shown in the right column of the
J. Phys. Chem. B, 106, 11178–11182 (2002).
table. On the other hand, machines taking new
[15] M.J. Meziani, Y.-P. Sun: J. Am. Chem. Soc., 125,
mechanical principles and equipment design are also
8015–8018 (2003).
being developed and listed as others in the table.
Since these mechanical processes are normally car-
2.4.4 Mechanical processes ried out in a dry state, there is no solvent contamina-
tion on the composite particles and its production
Among the methods to customize the structure of par- process is simple and environment friendly in compar-
ticles, a technique can produce composite particles by ison to the wet processing. Consequently, most of the
direct bonding the nanoparticles onto the surface of particle-composing machines are used in a dry state.
fine particles using mechanical treatment. In the following, the mechanical particle-composing
Figure 2.4.22 schematically shows two typical struc- processes and their critical operating parameters for
tures of composite particles obtainable by this method controlling the structure of particle composites as
[1]. Figure 2.4.22(a) illustrates the core–shell type of shown in Fig. 2.4.22 will be explained.
composite particle with nanoparticles on the surface of
the core particle. This particle structure is widely used 2.4.4.1 Particle-composing process
in the particle surface modification and the like. To make composite particles, the mechanical force
Using the mechanical processing, it is possible to needs to be exerted on the powder. In this case, the
design various particle surface structures from dense powder is a mixture of core particles and the guest
to porous ones. It can also make multi-layer structure nanoparticles. In general, the size of the core particles
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