279
Characterization of Nanomaterials
12
Considering characterization methods, one has to distinguish methods delivering
information averaged over a large ensemble of particles, the global properties, and
those informing about one single or a limited number of particles, the local properties. The overall behavior of nanomaterials is controlled by their global properties, whereas the local properties help to understand why a material behaves in a
specific way. For a complete characterization of a batch of nanoparticles, both types
of methods are indispensable.
12.1
Specific Surface Area
The surface of an ensemble of nanoparticles, which is accessible from outside
bears a lot of information. Looking at the surface of perfectly separated particles
it is easy to calculate the surface of a given quantity. For the sake of comparison,
the surface A of an ensemble is given in square meters per gram (m
2 g
−1 ). (Even
though this is a non-SI unit, it will be used in this book, because this unit is
internationally accepted for comparison of powders.) Assuming spherical particles
with a diameter d, the specific surface A is given by:
A
d
d
d
=
=
[
]
−
6
6
3
2
1
π ρ
π
ρ
in m kg
2
,
(12.1a)
A
d
d
d
=
=
[
]
−
6
1
1000
6 1
1000
3
2
2
1
π ρ
π
ρ
in m g .
(12.1b)
In Eq. (12.1), the quantity ρ stands for the material density. Assuming separated
spherical particles; Figure 12.1 displays the specific surface for alumina using
density of 3.5 × 10
3 kg m
−3 . The assumption of a constant density for all particle
sizes is, possibly, not correct; however, to show the basic properties, these differences are not essential.
Looking at the huge specific surface areas that are expected from separated
nanoparticles and knowing that the largest specific surface areas determined
experimentally are in the range of a few hundred square meters per gram, one
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.
Characterization of Nanomaterials
12
Considering characterization methods, one has to distinguish methods delivering
information averaged over a large ensemble of particles, the global properties, and
those informing about one single or a limited number of particles, the local properties. The overall behavior of nanomaterials is controlled by their global properties, whereas the local properties help to understand why a material behaves in a
specific way. For a complete characterization of a batch of nanoparticles, both types
of methods are indispensable.
12.1
Specific Surface Area
The surface of an ensemble of nanoparticles, which is accessible from outside
bears a lot of information. Looking at the surface of perfectly separated particles
it is easy to calculate the surface of a given quantity. For the sake of comparison,
the surface A of an ensemble is given in square meters per gram (m
2 g
−1 ). (Even
though this is a non-SI unit, it will be used in this book, because this unit is
internationally accepted for comparison of powders.) Assuming spherical particles
with a diameter d, the specific surface A is given by:
A
d
d
d
=
=
[
]
−
6
6
3
2
1
π ρ
π
ρ
in m kg
2
,
(12.1a)
A
d
d
d
=
=
[
]
−
6
1
1000
6 1
1000
3
2
2
1
π ρ
π
ρ
in m g .
(12.1b)
In Eq. (12.1), the quantity ρ stands for the material density. Assuming separated
spherical particles; Figure 12.1 displays the specific surface for alumina using
density of 3.5 × 10
3 kg m
−3 . The assumption of a constant density for all particle
sizes is, possibly, not correct; however, to show the basic properties, these differences are not essential.
Looking at the huge specific surface areas that are expected from separated
nanoparticles and knowing that the largest specific surface areas determined
experimentally are in the range of a few hundred square meters per gram, one
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.