64 4 Gas-Phase Synthesis of Nanoparticles
as is depicted in Figure 4.23. Figure 4.24 displays two designs for plasma processes
using electrodes.
For processes depicted in Figure 4.24, the precursor is either gaseous or a
powder blown with a carrier gas into the plasma flame. Even when this type of
process is used for the production of large quantities, it must be stated that the
quality is, with respect to the very special requirements for most of the applications
of nanoparticles, very poor. In this respect, the electrodeless RF processes are
significantly more successful. Such devices are, in the meantime available industrially as turnkey products. Figure 4.25 displays such a design.
The advantage of a design according to Figure 4.25 is the extended residence
time of the precursor in the plasma. This is important in cases where the reaction
Figure 4.21 Dependency of the size of FePt particles on the duration of the radio-frequency,
RF, pulse in an equipment according to Figure 4.20 [13].
0
10
20
30
plasma pulse duration [s]
0
30
60
90
120
mean
particle
diameter
[nm]
Figure 4.22 Hard magnetic FePt particles synthesized in a plasma system according to
Figure 4.20. The very narrow distribution of particle sizes, visible in the electron micrograph,
is remarkable [13]. (Reproduced by permission of Springer.)
200 nm
200 nm
200 nm
200 nm