4.5 Plasma Processes 65
Figure 4.23 Process schema for high-temperature plasma processes. To obtain top-quality
products, the design of the quenching step is of essential importance. For economic reasons,
process gas recycling is necessary.
ReacƟon zone
plasma
Quenching
Powder
collecƟon
Process-gas
recirculaƟon
Carrier and
process gas
Precursor
Quenching
gas
Product
Off-gas
Figure 4.24 Two basic designs for plasma
processes applying electrodes. The two
designs differ in the feed of the precursor;
either coaxial into the plasma burner (a) or
the precursor is blown perpendicular into the
plasma flame (b). Such systems are powered
either by DC or AC sources.
Power
supply
Gas
feed
Precursor
feed
Precursor
feed
Plasma
Power
supply
(a)
(b)
rate of particle formation is low. The capacity of such systems reaches from grams
to kilograms per hour. A typical example of a product of such an industrial equipment is shown in Figure 4.26, displaying GeO powder with a surprisingly narrow
particle-size distribution. Additionally, this figure documents the importance of
and the opportunities to influence the particle size of the product. In these micrographs, the influence of the quenching conditions is clearly visible. Obviously,