Figure 7 The diagram of different combustion phenomenon, (a)
Al/MnO2 nanothermite, (b)
Al/MnO2/10wt%-terpolymer nanothermite, (c)
Al/MnO2/20wt%-terpolymer nanothermite (d)
Al/MnO2/30wt%-terpolymer nanothermite
As for Al/MnO2nanothermite (Figure 7(a)), without any addition of terpolymer, the
ignition point should be near the heating wire and between the Al NPs
and MnO2 NRs, and then theoretically the flame travels
equally fast in each direction.
In Figure 7(b), the 10wt% content of P(VDF-ter-HFP-ter-TFE) terpolymer
exists in the gaps among components, decreasing the heat spread and
direct contact of nanothermite components. It can be the reason for the
delay of flame growth. But the content of terpolymer is not high, so the
negative effect on flame growth is not terrible, either. Each coin has
two sides. Based on ignition test, the addition of terpolymer can reduce
the ignition energy threshold from the current value at ignition moment.
The terpolymer is very sensitive
to the temperature increment. On one hand, high temperature can lead the
process of thermal decomposition with heat release. On the other hand,
the decomposition of terpolymer can release the fluoride. The fluoride
can directly react with nanothermite components at early stage.
Besides, since fluorine is the
most electronegative element, it can deal with the alumina shell covered
on the Al NPs, leading to the increasing active aluminum directly react
with oxidizer.
Figure 7(c) and (d) shows the combustion diagram of
Al/MnO2/20wt%-terpolymer and
Al/MnO2/30wt%-terpolymer nanothermite, respectively.
Comparatively, the negative effect on flame growth become increasing
great with the increasing content of terpolymer. Terpolymers even
totally cover the nanothermite components in some parts, which leads to
the clear ignition delay phenomenon. At the same time, much more heat
will release at an early stage due to the more content of terpolymer
decomposition as well as reaction with components from TG-DSC results,
resulting in a lower ignition energy threshold accordingly.