Page 270 - Book Hosokawa Nanoparticle Technology Handbook

4.5 STRUCTURE CONTROL OF NANOPARTICLE COLLECTIVES BY SINTERING AND BONDING FUNDAMENTALS
pressure sintering,
, is expressed by the following
equation:

appl (4.5.6)
sinter
3
where, sinter , is sintering stress, and appl is unidirec-
tional pressure stress applied. The sintering rate is
often evaluated using the following equation:

dl A
n fd ()exp ⎛ Q⎞
ldt a p ⎜ ⎝ kT ⎠ ⎟ (4.5.7)

where, dl/l is a coefficient of linear contraction, A a
constant, a particle size, f(d) a function of density d,
and Q apparent activation energy.
For example, it is reported that n is 2.2– 2.6 (20
MPa 100, 550 T C 750) in the case of TiO with
2
a particle size of 12 nm; n is 3 (5 MPa 50, T:
1,400 C) in the case of ZrO with a particle size of
2
25 nm [6]. The value of n is 1 for the sintering by dif-
fusion. Accordingly, the value of n larger than unity
suggests that plastic flow of crystalline particles, such
as sliding, occurs during the sintering process. For
TiO , the value of n is large, although the sintering
2
temperature is very low. This is a very interesting fea-
ture of nanoparticles.
Various techniques are available in the pressure sin-
tering method; centrifugal sintering is introduced here,
which has been developed recently [7]. Figure 4.5.37
Figure 4.5.36 shows the principle. The centrifugal sintering is a
Distribution of aggregates. method to sinter materials under centrifugal force; the

High speed rotating
Heater
r r

Sample
holder

Centrifugal
Ceramic rotor acceleration
Compact
Specificatious of centrifugal
nd
sintering apparatus (2 model)
Revolution : <10 000 min -1
Centrifugal acceleration temperature
Heating method : Induction heating
Temperature : <1000°C

Figure 4.5.37
Principal of centrifugal sintering.

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