4.5. Thermal decomposition studies
TG curves of various samples of AP and NTO are depicted in Figure 5.
Thermal decomposition of N0, N1, and N2 samples takes place between
200-300 oC in a single step. The incorporation of
additives in pure NTO causes the TG curve of NTO to shift towards the
left side (i.e., lower temperature region). The order of thermal
decomposition temperature was: N0>N2>N1. The
TG curve reveals that the mass loss of N2 was 4 % higher and that in
the case of N1 was 5 % lower compared to the pure N0 sample. As the
mass ratio of the additive: pure NTO was 95:5, both the samples
containing additives (i.e., N1 and N2) must have decomposed to yield a
total mass loss that corresponds to 5 % lower than pure N0. However,
the plausible explanation for higher mass loss in N1 could be that N1
must have catalyzed the residue that may have remained un-reacted when
pure N0 was decomposed leading to greater mass loss than expected. The
mass loss of N2 was 5 % lower that was because of the presence of the 5
% additive.
A0 decomposes in two steps; (i) between 250-330oC
leading to a mass loss of 18 % called low-temperature decomposition
(LTD) and (ii) between 331-450 oC with a mass loss of
82 % called high-temperature decomposition (HTD). In the presence of
the additives (A1 and A2), the TG curve of AP shifts to lower
temperatures compared to A0. The TG curve of AP was changed drastically
when the additives were incorporated. A2 decomposes in two steps at a
lower temperature range, but the LTD step of A2 becomes more influential
than LTD in A0. The mass loss in LTD of A2 was 13 % higher than in LTD
of A0. The LTD step in A1 becomes the major decomposition step of AP
with a mass loss of 90 % and other small decomposition takes place with
only 7 % mass loss.
Figure 5. TG curve of NTO (a), and AP (b) with and without BZC,
and BZC/rGO additiveDTA curves of A0-A2 and N0-N2 are depicted in Figure 6. N0, N1, and N2
decompose in a single exothermic event with a maximum curve temperature
(Tm) of 276, 230, and 239 oC,
respectively. DTA curve of N0 in the presence of additive was shifted to
the left side, and the corresponding temperature value of DTA curves are
depicted in Table 2. DTA curve of A0 exhibit three peaks, one
endothermic peak ~242 oC corresponding
to the phase transformation of AP from orthorhombic to cubic, and two
exothermic peaks belonging to the decomposition of AP. In the presence
of additives, the endothermic peak of AP was varied by only 1-2oC, but LTD and HTD peaks of AP were affected
drastically. LTD and HTD peaks of A2 were decreased by 21 and 71oC, respectively. In A1, two exothermic peaks of AP
merge into a single exothermic peak at 292 oC. The
difference between onset temperature (To) and maximum
temperature (Tm) also plays an important factor in
determining the thermal performance of energetic materials (Table 2). ∆T
of A1 and A2 was lower than A0, indicating the faster decomposition of
AP in the presence of additives. N1 and N2 increase the ∆T of N0 by 3,
and 26 oC, respectively. The TG and DTA results
suggest that BZC was a more suitable catalyst for influencing the
thermal performance of both NTO and AP compared to BZC/rGO. The
comparisons of previously reported additives (3 % by mass) on the
thermal decomposition of AP is given in Table 3.27–30From Table 3, it was evident that BZC containing AP composition
decomposes at low temperature and hence, it can influence the burning
rate properties of AP based propellants and formulations to compare to
other catalysts with same content reported in Table 3.Figure 6. DTA curve of (a) NTO, and (b) AP with and
without BZC, and BZC/rGO additive
Table 2. DTA and TG data of AP, and NTO with and without catalyst ( β=10oC min-1)