Page 218 - Book Hosokawa Nanoparticle Technology Handbook

FUNDAMENTALS CH. 4 CONTROL OF NANOSTRUCTURE OF MATERIALS
[4] http://www.iza-structure.org/databases/ structure [1]. For example, it is possible to make nano-
[5] D.W. Breck: Zeolite Molecular Sieves, Wiley (1974). sized pores below 100 nm inside the material by bond-
[6] R.M. Barrer, P.J. Denny: J. Chem. Soc., 971–982 (1961). ing 10 nm nanoparticles together. As the particle size
[7] G.T.Kerr, G. Kokotailo: J. Am. Chem. Soc., 83, decreases, the number of atoms located at the particle
surface approaches to the total amount of atoms con-
4675–4675 (1960).
structing the particle. Therefore, nanoparticles are
[8] M.E. Davis, R.F. Lobo: Chem. Mater., 4, 756–768
expected to be bonded together at lower temperatures
(1992).
than the bulk materials. By applying strong mechanical
[9] P.P.E.A. de Moor, T.P.M. Beelen, B.U. Komanschek,
energy to nanoparticles, their surfaces can be activated
L.W. Beck, P. Wagner, M.E. Davis and R.A.V. Santen: and they can be bonded together in the dry state.
Chem. Eur. J., 5, 2083–2088 (1999). Using this method, bulk nanoporous components
[10] M. Ogura, Y. Kawazu, H. Takahashi and T. Okubo: can be produced by bonding nanoparticles alone; but,
Chem. Mater., 15, 2661–2667 (2003). they are often reinforced with fibrous materials like
fiberglass to improve their strength and workability.
Figure 4.3.6 shows the process to prepare composite
4.3.2 Preparation of nanoporous material by dry particles for the production of nanoporous materi-
processing als [2]. During the material processing, the nanoparti-
cles are bonded onto the surface of the fibrous
particles to make composite particles, which can form
(1) Preparation methods for nanoporous materials a layer with nanosized pores. These nanocomposite
It is known that the nanoporous materials having a particles can be prepared by using the above-
pore size below about 100 nm show completely dif- mentioned strong mechanical energy in a dry state.
ferent properties from the conventional materials The flowability of the composite particles consist-
with micron-sized pores. For example, the convective ing of the nanoparticles and fibrous particles can be
heat transfer becomes extremely difficult inside the improved by controlling their structures. As a result,
porous materials with pore sizes less than about the shaping die can be filled with the dry composite
70 nm, which is the mean free path of the molecules particles uniformly; and, the porous materials with
in the air. Also, various other properties, like catalytic high uniformity and stable strength can be produced
or absorptive properties, etc., exhibit different char- by subsequent press-forming operation.
acteristics in the nanosized space from those of their
bulk counterparts.
Many methods have been proposed to prepare the
porous materials with nanosized pores so far. The
method introduced here is to create nanoporous mate- Nanopore
rials with nanoparticles by using the dry mechanical < 100 nm
processing. Since the whole processing, from the
preparation of the starting material to its forming, is
conducted in a dry state, neither solvent nor liquid Nanoparticle
binder is used. Consequently, the residual contamina-
tion inside the porous material can be avoided and the 10~50 nm
process becomes quite simple. Furthermore, it is an
environment-friendly process because of no dying
and no gas to exhaust. Nanoparticle bonding structure
Furthermore, since it is desirable to use the
nanoparticles as close as possible to their produced Figure 4.3.5
condition, it is expected to be a low cost, environ- A schematic structure showing how to control the
ment-friendly process. As to the nanoparticles, prac- nanosized pores by the nanoparticle bonding [1].
tically there is no restriction on whether they are
inorganic or organic materials. Moreover, this Nano particle 50-100 nm
process seems to have relatively high possibility for
commercialization from the industrial viewpoints,
because the material-forming method can be scaled
up by proper equipment design. The formed
nanoporous components have advantages in lightness
and good workability because of their stable strength Fibrous particle
and high porosity.
The key point of this method for producing the porous Figure 4.3.6
materials is to create nanosized pores by direct bonding Production of nanoporous component by composing
of the nanoparticles. Figure 4.3.5 shows its schematic nanoparticles and fibrous particles [2].

194