211
up as high as 6000 MPa, an increase of a factor of 3. Individual
nanowires and tubes are even stronger. The figure shows data
for carbon nanotubes and nanowires of copper, silver, and gold.
Reported strengths here extend up to 60 GPa.
We end by returning to the “ideal strength” diagram shown as Figure
4.37 of Chapter 4. It is replotted in Figure 7.12 with nanostructured,
nanolayered, and amorphous materials added. Their properties lie
within a factor of about 3 of the ideal. We are approaching a fundamental limit here. It is going to be very difficult to make materials
that are stronger than this.
7.2 therMal ProPerties
of nanoMaterials
Melting Point
As discussed in Section 4.4, the melting point of a material is a
fundamental point of reference because it directly correlates with
the bond strength. In bulk systems the surface-to-volume ratio is
small and the curvature of the surface is negligible. Therefore, for
a solid, in bulk form, surface effects can be disregarded. On the
other hand, for the case of nanoscale solids, for which the ratio of
surface to mass is large, the system may be regarded as containing
Figure 7.12
The ideal strength diagram from Chapter 4 with
data for nanomultilayers and amorphous metals
added. Their strength approaches the ideal.
Metals
Polymers
Ceramics
Yield strength,
σ
y / Young's modulus, E
10 -4
10 -3
1
10 -2
10 -1
Ideal strength
PTFE
PE
PP
PS
PVC
PET
ABS
PA
Ti alloys
Lead
Copper
Al alloys
Mild steel
Brass
Glass
Zirconia
Alumina
Concrete
Brick
Nano multilayers and
amorphous metals
Thermal Properties of Nanomaterials