Page 59 - Book Hosokawa Nanoparticle Technology Handbook

FUNDAMENTALS CH. 1 BASIC PROPERTIES AND MEASURING METHODS OF NANOPARTICLES
[4] G.C. Benson, T.A. Claxton: J. Chem. Phys., 48, 1356 decrease in particle size, which results from decrease in
(1968). flaw size in the particle [1]. Although such phenomena
[5] A . Taroni, D. Haneman: Surf. Sci., 10, 215 (1968). have been reported in the strength of a whisker, the
[6] M. Chikazawa, T. Takei: J. Soc. Powder Technol., Jpn., mechanical properties of a nanoparticle was limited
because of difficulty of measurement unlike in the case
14, 18 (1977).
of the optical, electrical and magnetic properties which
[7] N. Harnb, A.E. Hawkins, I. Opalinski: Trans.
can be evaluated as nanoparticle ensemble.
IChemE, 74, 605 (1996).
However, because of advancement in technology on
[8] M. Chikazawa, T. Kanazawa and T. Yamaguchi: KONA
high-precision determination of very small load and
(Powder & particle), 2, 54 (1984). displacement, the mechanical properties of a nanoparti-
[9] L.J.M. Schlangen, L.K. Koopal, M.A. CohenStuart, cle also has been measured in recent years. It has been
J. Lyklema: Colloid Surface A, 89, 157 (1994). reported that elastic modulus of Au cluster is as small as
[10] R.H. Yoon, T. Salman, G. Donnay: J. Colloid Interf. 2/3 of that of Au bulk as a result of nano indentation and
Sci., 70, 483 (1979). scanning probe microscopy [2]. This result was caused
by high internal compressive stress of a nanoparticle.
Such inherent compressive stress suggests the possibil-
1.10 Mechanical property ity of super-hard material. Mechanical properties of a Si
nanoparticle of 20–50nm also have been directly meas-
ured. While the hardness of a bulk is 12 GPa, that of
Mechanical properties vary with the decrease in parti- a nanoparticle increases with decrease in particle size,
cle size as well as optical, electrical and magnetic prop- which varied from 20 to 50 GPa (Fig. 1.10.2) [3].
erties. It is well known that the strength of metal and
ceramic material improves by decreasing grain size to
nano size or by making compositie in nano-scale. In
metallic materials, yield stress increases with decrease
in grain size (Hall–Petch relation) and then decreases
with further decrease in grain size (Inverse Hall–Petch
relation). Not only the mechanical property of such a
bulk composed of nanoparticles but also that of a par-
ticle itself depend on the particle size. Fig. 1.10.1
shows the dependence of the strength of an alumina
particle on its particle size. The strength increases with

5

4

3

[GPa]
2x10 0

3 4 5 6789 1 2 3 4 5 6 7
Particle size [ m] Figure 1.10.2
Mechanical properties of a Si nanoparticle evaluated by
Figure 1.10.1 nano indentation technique. (a) Load–displacement curve,
Dependence of the strength of an alumina particle on its (b) load dependence of the hardness of a Si nano particle
particle size. with different particle size.
36