Page 180 - Book Hosokawa Nanoparticle Technology Handbook

FUNDAMENTALS CH. 3 CHARACTERISTICS AND BEHAVIOR OF NANOPARTICLES AND ITS DISPERSION SYSTEMS

Figure 3.5.29
Powder yield locus (PYL) and internal friction angle . i

but adhesion force between particles is proportionate to
1 powers or square of particle size. Nanoparticles make
the dendrite-like structure by the larger adhesion force
than particle weight and so nanoparticles show the quite
larger porosity than 0.95 or more, and very difficult to
achieve high-packing density. If this phenomenon is uti-
lized, the characterization of the nanoparticle can be
quantized with simple packing test.
On the other hand, particles can penetrate into the
space which is 7–10 times larger than the particle
size, but difficult to flow into the opening less than 7
because of the powder bridge formation. The
nanoparticle is easy to leak from the tiny space, and to
Figure 3.5.30 entrain with micro airflow from the microscopic
Powder yield locus and unconfined yield stress . opening, because particle size of nanoparticle is very
f
small. The nanoparticles show specific floodability
when they are packed in the cell or container such as
yield stress . The Mohr’s stress circle passes the ori- in shearing test, caution during operation is necessary.
f
gin of stress plane and is tangential to PYL. The flow
factor F is given by
f
References

F f f [1] J. Tsubaki, M. Suzuki and Y. Kanda: Nyuumon Ryushi
f g 1 ( p ) g (3.5.65)
b Funtaikougaku, Nikkankogyo Shinbunsya, p. 38
(2002).
where and are the apparent and particle densi- [2] P.S. Roller: Ind. Eng. Chem., 22, 1206–1208 (1930).
b
p
ties, respectively, and g the gravitational acceleration. [3] S. Toyama: J. Soc. Powder Technol., 7, 57–62 (1970).
The powder with high value of F can stack high, and [4] R.L. Carr : Chem. Eng., 72, 163–168 (1965).
f
the high F value means high adhesive and low-flowa- [5] H. Yanagida et al.: Biryushi Kogaku Taikei, Vol. 1,
f
bility powder. Kihongijyutyu, Fuji-Techno-System, p. 526 (2001).
[6] H. Rumpf: Chem. Ing. Tech., 42, 538–544 (1970).
f) Packing characteristics and flowability of nanoparticles
[7] A.W. Jenike, P.J. Elsey and R.H. Wooley: Proc. Am.
The nanoparticle is very fine powder and has unique Soc. Test. Mat., 1168–1190 (1960).
packing characteristics and flowability. Generally, the [8] International Standard Organization: 11697(1994)
packing characteristics depend on the force balance of
packing force such as powder weight and external force [9] M. Hirota, T. Kobayashi and T. Oshima: J. Soc.
and impeditive force such as the wall friction and cohe- Powder Technol., 20, 493–499 (1983).
sion of powder. When particle size becomes small, [10] M.D. Ashton, D.C.H. Cheng, R. Farley, F.H.H.
the relative adhesion force increases because the parti- Valentin: Reologica. Acta, 4, 206–212 (1965).
cle weight is proportionate to cubic of particle diameter, [11] A.W. Jenike: Bull. Univ. Utah, 53, 1–198 (1964).
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