39
Gas-Phase Synthesis of Nanoparticles
4
4.1
Fundamental Considerations
The first nanoparticles were synthesized using gas-phase processes. Significantly
earlier, colloid chemistry was used to synthesize nanoparticles in suspensions
(=colloids); however, separating of the particles from the liquid is difficult; the
colloidal particles form agglomerates.
In gas-phase processes, a vapor of the material condenses in a gas phase forming
small particles. These particles may be isolated particles or agglomerates.
Nanoparticles – Nanocomposites – Nanomaterials: An Introduction for Beginners, First Edition. Dieter Vollath.
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA. Published 2013 by Wiley-VCH Verlag GmbH & Co. KGaA.
Box 4.1 Processes of Particle Formation
An environment containing a gas and atoms or molecules that can condensate
in a low concentration is assumed. These are the assumptions for a random
process (Poisson process) forming particles. Generally, particle formation is
described by four major steps:
• Nucleation. A nucleus is the smallest stable unit. Usually, it consists of at
least three atoms or molecules. Such nuclei are formed if three atoms collide
coincidently. This nucleus acts as a core for further
• condensation of atoms or molecules at the surface of the nucleus. Therefore,
the nucleus grows and forms a cluster and later a particle. Condensation is
a random process ruled by the dynamics of the gas species. Colliding cluster
or small particles may coagulate. During
• coagulation by exchange of surface energy, a new, larger particle is formed.
Having reached a certain size, the difference of surface energy will be so
small that further coagulation of particles is impossible. Now the process of
• agglomeration starts. Agglomerates consist of two or more individual particles. Often, one distinguishes soft and hard agglomerates. Soft agglomerates are bound by van der Waals bonds; hard agglomerates are sintered. If
at all, only soft agglomerates can be separated.
Gas-Phase Synthesis of Nanoparticles
4
4.1
Fundamental Considerations
The first nanoparticles were synthesized using gas-phase processes. Significantly
earlier, colloid chemistry was used to synthesize nanoparticles in suspensions
(=colloids); however, separating of the particles from the liquid is difficult; the
colloidal particles form agglomerates.
In gas-phase processes, a vapor of the material condenses in a gas phase forming
small particles. These particles may be isolated particles or agglomerates.
Nanoparticles – Nanocomposites – Nanomaterials: An Introduction for Beginners, First Edition. Dieter Vollath.
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA. Published 2013 by Wiley-VCH Verlag GmbH & Co. KGaA.
Box 4.1 Processes of Particle Formation
An environment containing a gas and atoms or molecules that can condensate
in a low concentration is assumed. These are the assumptions for a random
process (Poisson process) forming particles. Generally, particle formation is
described by four major steps:
• Nucleation. A nucleus is the smallest stable unit. Usually, it consists of at
least three atoms or molecules. Such nuclei are formed if three atoms collide
coincidently. This nucleus acts as a core for further
• condensation of atoms or molecules at the surface of the nucleus. Therefore,
the nucleus grows and forms a cluster and later a particle. Condensation is
a random process ruled by the dynamics of the gas species. Colliding cluster
or small particles may coagulate. During
• coagulation by exchange of surface energy, a new, larger particle is formed.
Having reached a certain size, the difference of surface energy will be so
small that further coagulation of particles is impossible. Now the process of
• agglomeration starts. Agglomerates consist of two or more individual particles. Often, one distinguishes soft and hard agglomerates. Soft agglomerates are bound by van der Waals bonds; hard agglomerates are sintered. If
at all, only soft agglomerates can be separated.