Figure 5 XRD results of residues after TG-DSC tests
3.4 Ignition and combustion
Ignition and combustion
performance represent the practical characteristics for energetic
materials future application. In this work, we carried out the ignition
and combustion by using fast heating wire test as well as high-speed
camera. The detailed ignition and combustion performance for each sample
is shown in Figure 6. The first picture of a firelight is defined as the
beginning time, set as 0 us. The DC power supplier is selected, and the
current value for ignition moment is recorded as the ignition energy
threshold.
In Figure 6(a), when the current
rise to 1.192 A, the Al/MnO2 nanothermite sample without
any additive successfully ignites. The speed of flame grow is very
rapid, and at about 350 us, the size of flame reaches the maximum. Then,
the flame fades away gradually with clear flying sparks (Supplementary
movie 1).
In Figure 6(b), the sample with 10wt%- P(VDF-ter-HFP-ter-TFE)
terpolymer additive ignites at about 1.137A current value. The speed of
flame growth is still relatively fast, and at about 1 ms, the size of
flame reaches the maximum. However, comparing to the
Al/MnO2 nanothermite sample in Figure 6(a), the speed of
flame grow and the size of maximum flame are decreased clearly. The
addition of terpolymer can help reduce the number of flying sparks to
concentrate the flame. Besides, the duration of combustion is longer
than that of Al/MnO2 nanothermite sample (Supplementary
movie 2).
Furthermore, when the contents of terpolymer reach 20wt% and 30wt%,
the current value at ignition moment are 1.083A and 1.075A,
respectively. As for Al/MnO2/20wt%-terpolymer sample,
in Figure 6(c), (Supplementary movie 3) the flame grows pretty slow, and
the maximum flame appears at about 7 ms. After the maximum flame moment,
the flame seems not to fade away gradually but further forms a certain
burning flame shape, which might be caused by the unevenly distributed
terpolymer, leading to the ignition delay phenomenon [31-32]. Such
phenomenon is also found in the last sample, in Figure 6(d)
(Supplementary movie 4). After the maximum flame moment at about 8 ms
~9 ms, a small but clear bulge appears at the top of
flame.
When the contents of terpolymer are below or equal to 10wt%, the
phenomenon of ignition delay is not obvious, and the shapes of flame are
mainly concentrated sphere. In contrast, once the terpolymer content is
over 20wt%, the ignition delay phenomenon and different shapes of flame
can be captured. Besides, the addition of P(VDF-ter-HFP-ter-TFE)
terpolymer can reduce the ignition energy threshold from the current
value at ignition moment, but it has a greatly negative influence on
flame growth, leading to the long combustion duration time.