Preparation and Thermal Decomposition Properties of Multi-scale Interface-Tunable Al/RDX Energetic Composites

doi:10.12382/bgxb.2022.0618

Abstract

Abstract:

Based on the integrated design concept of oxidant/metal fuel (Al) in propellants and the surface modification of aluminum particles, the multi-scale interface-tunable semi-embedded Al/RDX and fully-embedded Al@RDX composites were prepared by resonant acoustic mixing and spray drying. The morphology, true density and heat of combustion of the composites were characterized by scanning electron microscopy (SEM) and other techniques, and the thermal decomposition process and its gas products were studied by simultaneous thermal analyzer (DSC-TG-FT-IR). The results showed that compared with the mechanical mixture, the true density of the composites remained basically unchanged, but the heat of combustion of these two composites was higher, which were 17.31 kJ/g and 18.82 kJ/g. The DSC results showed that the heat of thermal decomposition of RDX can be increased by these two ways. Although the embedding of aluminum particles does not change the types of gas-phase products of RDX decomposition, it is more conducive to generate more HCHO. After the embedding of aluminum particles, the first decomposition stage of RDX changed from the random nucleation model (A2) to the random chain scission model (L2), while the second decomposition stage of the fully-embedded Al@RDX composites was transformed into the autocatalytic model (AC).

Key words: multi-scale Al-RDX composites, interface modification, resonant acoustic mixing technology, spray drying technology, thermal decomposition characteristics

XU Ruixuan, XU Jiaxing, XUE Zhihua, LÜ Jieyao, YAN Qilong. Preparation and Thermal Decomposition Properties of Multi-scale Interface-Tunable Al/RDX Energetic Composites[J]. Acta Armamentarii, 2023, 44(3): 691-701.

Figures/Tables 12

Fig. 1 Schematic diagram of the structure of the resonant acoustic mixing equipment

Fig. 2 SEM, EDS and TEM images of the composite particles

Table1 Results of the true density and heat of combustion of RDX and the composites with different structures

样品	真密度 /(g·cm^-3)	单位质量燃烧热/(kJ·g^-1)
样品	真密度 /(g·cm^-3)	第1次	第2次	第3次	平均值	标准差
RDX	1.82	9.40	9.81	9.47	9.56	0.22
Al+RDX	2.25	16.84	16.44	16.98	16.75	0.28
Al/RDX	2.25	17.30	17.45	17.17	17.31	0.14
Al@RDX	2.26	19.20	18.57	18.69	18.82	0.33

Fig. 3 Comparison of the true density and the heat of combustion of the composites with different structures

Fig. 4 Comparison of DSC curves of different composite particles

Table 2 DSC characteristic parameters of RDX, Al+RDX, Al/RDX and Al@RDX composites

样品	T_m/°C	T_i/°C	T_p/°C	T_e/°C	W/°C	△H/(J·g^-1)
RDX^[19]	205.1	226.7	248.7	255.7	29.0	1 747.0
RDX^[21]	204.1		242.3			1 812.0
Al+RDX	205.3	227.4	247.7	254.7	24.8	771.2
Al/RDX	189.4	228.4	251.8	278.6	40.0	779.4
Al@RDX	205.3	223.8	243.0	257.4	30.9	775.2

Fig. 5 Comparison of TG-DTG curves of different composite particles

Table 3 Thermal decomposition kinetic parameters of RDX, Al+RDX, Al/RDX and Al@RDX composites

样品	阶段	联合动力学法				Friedman法		Kissinger法
样品	阶段	m	n	E_a(1)	cA/min⁻¹	E_a(2)	r	E_a(3)	Log A	r
RDX^[21]								196.5	13.79	0.998 5
RDX^[22,23,24]		0.021	0.997	159.6±0.7	3.7×10¹⁵	246.2		130.4	11.87	0.995 0
RDX/TAG-Ni^[21]		0.135	0.944	189.4±1.2	1.2×10¹⁷	192.2	0.995 4	186.5	13.18
RDX/TAG-Co^[21]		0.090	0.891	203.6±2.3	2.8×10¹⁸	156.7	0.999 9	195.3	14.02
Al+RDX	1st	0.461	0.631	153.0±0.7	4.5×10¹⁴	151.5	0.998 5	163.0	10.81	0.995 5
Al+RDX	2nd	0.646	1.053	58.2±2.4	5.2×10⁰⁴	16.0	0.995 3	144.7	8.70	0.992 7
Al/RDX	1st	0.347	1.109	152.0±2.3	1.4×10¹⁴	156.1	0.993 7	136.0	7.77	0.998 6
Al/RDX	2nd	0.606	1.076	148.8±2.1	8.4×10¹²	151.2	0.996 0	192.8	12.85	0.980 9
Al@RDX	1st	0.413	1.093	155.0±1.6	8.7×10¹⁴	150.5	0.989 3	137.1	8.22	0.999 9
Al@RDX	2nd	0.890	0.641	31.1±0.3	5.4×10⁰¹	29.4	0.994 4	155.6	9.85	0.999 0

Fig. 6 Dependence of activation energy on the conversion rate of composites by the Friedman method

Fig. 7 FT-IR results of the gas phase decomposition products of Al+RDX, Al/RDX and Al@RDX composites

Fig. 8 Competitive mechanism of the two paths in the thermal decomposition process of RDX

Fig. 9 Comparison of the normalized curves for the decomposition kinetic models of RDX、Al+RDX、 Al/RDX and Al@RDX composites obtained by the combined kinetic method (D2, two-dimensional diffusion model; F1, first order reaction, so-called unimolecular decay law, where random nucleation is followed by an instantaneous growth of nuclei; R2, phase boundary controlled reaction (contracting area), R3, phase boundary controlled reaction (contracting volume); L2, random chain scission model; A2 and A3, random two and three dimensional nucleation and nucleus growth models; AC, autocatalytic model.)

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