Page 116 - Book Hosokawa Nanoparticle Technology Handbook

FUNDAMENTALS CH. 2 STRUCTURAL CONTROL OF NANOPARTICLES
Table 2.4.3
Major principles used to produce particle composites by the mechanical process [2].
Principle Example of products developed
as a composing machine
Application of pulverizer High-speed impact type pulverizer
Pin mill Hybridization system
Disc mill (Nara machinery Co., Ltd.)
Centrifugal classification type Cosmos (Kawasaki Heavy Industries, Ltd.)
Mechanofusion system
Attrition-type mill (Hosokawa Micron Corp.)
Ball mill
Tumbling type
Vibration type
Planetary type
Centrifugal fluidized type
Media agitating-type mill
Agitation vessel type
Jet mill
Fluidized-bed type
Others Motar and pestle:
Bottom plate of cylindrical vessel Mechanomill (Okada Seiko Co., Ltd.)
containing particles rapidly rotates
Elliptic cylindrical vessel rotor rapidly Thetacomposer (Tokuju Co., Ltd.)
rotates in a slowly rotating elliptic
cylindrical vessel

should be sufficiently larger than that of the guest its bonding condition to some extent by changing the
nanoparticles. Most of the particle-composing processing time and other factors.
machines shown in Table 2.4.3, the mechanical force
is given onto the particles by the rotational motion of 2.4.4.2 Factors to control the particle composing
the rotor. The nanoparticles are composed onto the The operating parameters of the machine affect the
surface of core particle depending upon the contact particle composing, including mechanical intensity,
number between the particles and various effects, processing temperature, ambient conditions, and the
including the mechanical and thermal ones, at the type of the machine, and so on. These parameters are
contact points caused by the rotor movement. often difficult to control independently. Furthermore,
Figure 2.4.23 shows the modeling of composing from the viewpoint of particles, the particle size and
nanoparticles onto the particle surface [2]. As shown combination ratio of core particles to the guest
in the figure, it proceeds in two steps. In the first step, nanoparticles and the way to add nanoparticles also
the surfaces of the core particles are activated and the influence the composing behavior considerably. As an
different kinds of nanoparticles adhere to it one after example, the remarkable effects of mechanical condi-
another. As a result, the adhesion ratio R of the tions and the processing temperatures on the particle
nanoparticles to the core particles increases, while the composing are explained below.
specific surface area S w of the powder mixture First regarding the mechanical effect, it is considered
decreases. In the second step, after sufficient nanopar- that the higher the revolution of the machine is, the
ticles being built-up, the nanoparticle layer itself is stronger is the force on the powder and on the particles
strongly pressed and bonded onto the core particle sur- between the interfaces. In addition, with the increasing
face. The boundary surface between the composite revolution, the frequency of giving the mechanical
particles made by this process becomes very strong. force on the particles also increases. Therefore, the
For example, in case of composing silica-based adhesion ratio in Fig. 2.4.23 increases generally with
glass beads with titanium dioxide using the the increase of machine revolution, which in turn
MechanoFusion system in Table 2.4.3, strong bonding reduces the specific surface area of the powder.
was observed at the interface between the two com- However, the composing effect of the mechanical
ponents due to the electron transfer. Therefore, it is force may differ depending on the combination of
possible to control the structure of coating layer and the core particles and the nanoparticles. For example,

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