4.6
Flame Aerosol Process
Among all of the processes used to produce nanoparticulate powders, the flame
aerosol process is the oldest. Additionally, it is the only one to be used for mass
production in the kiloton range. Although this well-established industrial process
has been used for many decades, the basic principles are still not well understood,
not least because the processes of powder synthesis and particle formation take place
at extremely high temperatures and over very short times.
Since prehistoric times, in China, carbon black (as a pigment for inks) has been
produced by flame aerosol processes, and today this same technology – or one of its
many variants – is still used to produce thousands of metric tons of carbon black, fumed
silica, and titania (TiO 2 ) pigments. In addition, during recent years the application of
this process has been expanded to incorporate many highly specialized products (for
excellent reviews, see [19,20]). As the aerosol flame process has such a long history and
broad application, many highly specific variants, leading to the production of particles
with different morphology, size, and crystallinity, have been developed.
In the simplest case, a flame reactor set-up is as shown in Figure 4.30a and b. The
flame reactor consists of a primary flame that is fueled with hydrogen, methane, or
another hydrocarbon fuel. In most cases, the gaseous fuel is premixed with oxygen or
air in the burner. In the case shown in Figure 4.30a, many small primary flames
surround the secondary flame, where the reaction for particle formation occurs. Both
Figure 4.30a and b demonstrate the synthesis of silica, and, therefore, silane (SiH 4 )
or silicon tetrachloride (SiCl 4 ) were selected as the precursor compounds. Reaction of
Figure 4.30 Typical arrangements for flame
synthesis of nanoparticles. (a) Primary flames
surrounding a secondary flame, in which the
powder is produced, characterize this
arrangement. (b) In this design, the vaporized
precursor is introduced into the primary flame
for reaction.
72j 4 Gas-Phase Synthesis of Nanoparticles
Flame Aerosol Process
Among all of the processes used to produce nanoparticulate powders, the flame
aerosol process is the oldest. Additionally, it is the only one to be used for mass
production in the kiloton range. Although this well-established industrial process
has been used for many decades, the basic principles are still not well understood,
not least because the processes of powder synthesis and particle formation take place
at extremely high temperatures and over very short times.
Since prehistoric times, in China, carbon black (as a pigment for inks) has been
produced by flame aerosol processes, and today this same technology – or one of its
many variants – is still used to produce thousands of metric tons of carbon black, fumed
silica, and titania (TiO 2 ) pigments. In addition, during recent years the application of
this process has been expanded to incorporate many highly specialized products (for
excellent reviews, see [19,20]). As the aerosol flame process has such a long history and
broad application, many highly specific variants, leading to the production of particles
with different morphology, size, and crystallinity, have been developed.
In the simplest case, a flame reactor set-up is as shown in Figure 4.30a and b. The
flame reactor consists of a primary flame that is fueled with hydrogen, methane, or
another hydrocarbon fuel. In most cases, the gaseous fuel is premixed with oxygen or
air in the burner. In the case shown in Figure 4.30a, many small primary flames
surround the secondary flame, where the reaction for particle formation occurs. Both
Figure 4.30a and b demonstrate the synthesis of silica, and, therefore, silane (SiH 4 )
or silicon tetrachloride (SiCl 4 ) were selected as the precursor compounds. Reaction of
Figure 4.30 Typical arrangements for flame
synthesis of nanoparticles. (a) Primary flames
surrounding a secondary flame, in which the
powder is produced, characterize this
arrangement. (b) In this design, the vaporized
precursor is introduced into the primary flame
for reaction.
72j 4 Gas-Phase Synthesis of Nanoparticles