A novel high-energetic and good-sensitive cocrystal composed of CL-20 and TATB by a rapid solvent/non-solvent method

Abstract

Due to the insolubility of TATB in a majority of organic solvents, it is very difficult to prepare cocrystals of TATB. In this work, through a rapid nucleation solvent/non-solvent process, a novel cocrystal explosive, CL-20 (2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane)/TATB (1,3,5-triamino-2,4,6-trinitrobenzene), has been successfully prepared. The cocrystal is characterized with scanning electron microscopy (SEM), X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, thermogravimetric/differential scanning calorimetry (TG-DSC), and high performance liquid chromatography (HPLC). The SEM results indicate that the cocrystal particles are homogeneous with an average particle size of about 3–5 μm, and the morphology of the cocrystal is completely different from the primary materials. XRD and Raman analyses confirm that the cocrystal has unique peak patterns with large differences from CL-20 and TATB. IR and Raman spectra suggest that hydrogen-bonding interactions exist between CL-20 and TATB molecules. The density determination, the weight loss in one step and the single exothermic peak in the thermal analysis curves further illustrate that the CL-20/TATB cocrystal is a new substance instead of independent crystallization of CL-20 and TATB. In CL-20/TATB cocrystal, the molar ratio of CL-20 and TATB is 3 : 1 determined by HPLC. Thermal analysis and detonation parameters calculation shows that the cocrystal has excellent thermal stability and high energy-release efficiency. An impact sensitivity test indicates that the sensitivity of the cocrystal is sufficiently reduced relative to CL-20. For the CL-20/TATB cocrystal, its detonation performance is superior to HMX and impact sensitivity is almost the same as HMX.

---

1. Introduction

Energetic materials (EMs), i.e. explosives, propellants, and pyrotechnics, play an important role in both civilian and military applications.^1,2 As representatives of a category of compounds with plenty of stored chemical energy in their molecular structures, EMs exist as an inherent safety–power contradiction.³ Thus, improved performance, such as better thermal stability, higher power and detonation velocity, higher density, or enhanced insensitivity, has always been a prime requirement in the field of energetic materials. In order to tailor and improve EM properties, most researchers use some traditional strategies that include synthesizing new energetic compounds,^4,5 improving the quality of high explosive crystals,^6,7 preparing nanoscale particles of explosives^8–12 and adding insensitive compounds or coatings using physical techniques.^13–17 Although these methods have made some achievements, some problems still exist. For example, the synthesis of new materials is still unable to acquire an ideal simple substance explosive.⁴ Also, the fundamental problem of the sensitivity of explosives can’t be solved by recrystallization to improve the quality of explosive crystals.¹⁸ In addition, nanocrystallization of explosive particles is confronted with serious agglomeration, even though it can strongly change the sensitivity and performance of EMs. Plastic bonded explosives (PBXs) have been widely researched in EM fields. Nevertheless, they require lots of inert additives resulting in energy reduction.¹⁹

In recent years, an alternative way to improve the properties of explosives is cocrystallization, which is widely used for pharmaceutical chemicals,^20,21 attracting the interest of numerous related scientists and engineers.^22–35 Cocrystallization, consisting of two or more components in a defined ratio via non-covalent interactions including hydrogen bonds, π-stacking, or van der Waals force interactions,^36,37 is completely different from the traditional methods. It is emerging as an attractive approach to improve some of the key properties, including density, thermal stability, oxygen balance, sensitivity, and detonation performance, of energetic materials. Thus, cocrystal engineering is an effective way to modify the integrated performance of CL-20,^38,39 a novel caged nitramine explosive with the highest recorded energy density, good oxygen balance and high explosive power. According to actual measurements, many aspects of its performance, such as oxygen balance, detonation velocity and density, are all superior to the current military standard explosive HMX; its detonation energy release was found to be approximately 14% higher than that of HMX.⁴⁰ Its high detonation velocity and detonation pressure make CL-20 a suitable candidate for a wide range of military and commercial purposes. Unfortunately, its high mechanical sensitivity limits further application,^41,42 as it is relatively easily detonated by physical force in comparison to other secondary explosives.⁴⁰ Hence, increasing the insensitivity of CL-20 is becoming increasingly important. Cocrystallizing with an insensitive explosive is indeed a hopeful strategy to decrease its sensitivity. According to the literature, some CL-20 cocrystal explosives have been prepared to improve its insensitivity.^2,24–27 For example, Bolton and co-workers successfully obtained a CL-20/TNT cocrystal.²⁴ This cocrystal reduced the mechanical impact sensitivity relative to pure CL-20, but it also largely decreased the explosive power due to the incorporation of TNT. They then reported a CL-20/HMX cocrystal.²⁵ Although this cocrystal exhibit greater power, its sensitivity was not obviously improved. A CL-20/BTF cocrystal was also not an ideal cocrystal explosive because of its poor detonation properties.²⁶

As we all know, TATB, the so-called wood explosive, is widely used in military and civilian applications because of its moderate power, thermal stability, and insensitivity.^43,44 It is more insensitive than TNT, and its energy density is higher than TNT. The density of TATB is 1.938 g cm⁻³, much higher than that of TNT, 1.654 g cm⁻³.⁴⁵ Pure TATB is an inert explosive towards heat, light, friction, and mechanical impact, which can be attributed to its graphite-like layered structure. This layered structure of TATB with strong inter-molecular and intra-molecular hydrogen bonds, makes it difficult to form hot spots as external stir energy can be easily transferred to the slide between neighboring layers.^46,47 So, we expect that the CL-20/TATB cocrystal will have better comprehensive performance, such as higher energy and lower sensitivity. In our previous work, a cocrystal of HMX and TATB was prepared through a slow solvent/non-solvent method. Since the molar ratio of HMX : TATB is 8 : 1, it may be more reasonable to name it as a kind of doped cocrystal.²³ Besides this example, cocrystals of TATB have not been reported, and a possible reason can be attributed to the insolubility of TATB in most organic solvents.⁴⁸ In this work, we selected and prepared specific solvents to increase the solubility of TATB and made CL-20 and TATB precipitate at the same time to prepare a CL-20/TATB cocrystal through a rapid nucleation solvent/non-solvent (S/NS) process. Compared to conventional methods for the preparation of cocrystal explosive, using slow evaporation solvents, this method has an obvious advantage in its facile high-yielding production. The structure and performance of the CL-20/TATB cocrystal have been characterized by various methods. The effective characterization results give us sufficient confidence in the successful preparation of the CL-20/TATB cocrystal, even lacking the crystallography data of single crystal.

2. Experimental

2.1 Materials

Raw CL-20 (the ε polymorph) and TATB (Fig. 1), provided by the Institute of Chemical Materials, Chinese Academy of Engineering Physics (CAEP), are white and fluorescence green crystalline powders, respectively. DMSO was purchased from the Chengdu Ke Long Chemical Reagent Factory and ultrapure water acted as the solvent and non-solvent, respectively.

Fig. 1 Chemical structures of raw CL-20, C₆H₆N₁₂O₁₂ and TATB, C₆H₆N₆O₆.

2.2 Preparation of CL-20/TATB cocrystal

The cocrystal explosive was prepared using a solvent/non-solvent (S/NS) method, a rapid nucleation process. Firstly, two specific solutions of CL-20 and TATB were prepared at 25 °C.

The two solutions were rapidly poured into the ultrapure water at the same time. After that, the mixed solution was stirred 1.5 hours and then left standing overnight. Then, the mixed solution was filtered and the product was washed 3–5 times with ultrapure water to remove the solvent. At last, the sample was freeze-dried and the production rate was 75.5%.

2.3 Characterizations

Scanning electron microscopy (SEM) was conducted on an ULTRA 55 (ZEISS, Germany) field emission scanning electron microscope operating at an accelerating voltage of 5 kV, equipped with energy dispersive X-ray spectroscopy (EDS). The powder X-ray diffraction (XRD) patterns were recorded with a PANalytical X’Pert PRO instrument (Cu Kα, λ = 0.15406 nm, 45 kV, 50 mA, Rigaku D/max-RB, Netherlands). Images were integrated from 3° to 80° with a 0.05° step size using AreaMax 2 software. Raman spectra were measured with an inVia Raman spectrometer using an Ar laser (λ = 514.5 nm) and a semiconductor laser (λ = 785 nm). The maximum output power is 1.7 mW of the light spot of the inVia Raman spectrometer and the spectral resolution is 1 cm⁻¹. Fourier transform infrared spectroscopy (FT-IR) spectra were measured at 0.4 cm⁻¹ resolution on a Spectrum One (PE, USA) spectrometer and the IR data were collected in the range of 400–4000 cm⁻¹. High performance liquid chromatography (HPLC) analysis was conducted on an Agilent 1260 HPLC system using a 20 RBAX SB-C18 analytical column (150 × 4.6 mm ID) at 30 °C column temperature.

2.4 Performance test

2.4.1 Thermal analysis. Simultaneous differential scanning calorimetry (DSC) and thermogravimetry (TG), namely simultaneous DSC-TG curves were conducted using United States SDT Q600 synchronous thermal analyzers at a heating rate of 10 °C min⁻¹ in a N₂ atmosphere over the range of 20–500 °C with Al₂O₃ as a reference. The sample (0.5–2 mg weighed to a precision of 0.0001 mg) was weighed into crimped aluminum pans, which were pierced to allow vapor to escape, and pressed to increase contact between the pan and sample.

2.4.2 Impact sensitivity. The impact sensitivity testing of the cocrystal was determined using an in-house-constructed drop-weight test with a BAM impact sensitivity instrument according to the international standard method. The bump head of the BAM impact sensitivity instrument is made of chilled steel (Rockwell hardness is 60–63), the minimum diameter is 25 mm, the impact loading included 0.5 kg, 1 kg, 2 kg, 5 kg, or 10 kg. The impact energy range is 0.5–10 J. The drop height ranged from 0–1000 mm, the atmospheric temperature was 25 °C and the humidity was 85% RH. The sample was measured with 30 mm³ of cylinder volume.

2.4.3 Density and detonation properties. The density was tested using the Crystal Density Gradient Instrument of the Institute of Chemical Materials, China Academy of Engineering Physics. The detonation properties, including detonation velocity and detonation pressure at theoretical maximum density (TMD), were calculated using the linear output thermodynamic user-friendly software code.

3. Results and discussion

3.1 Characterizations

3.1.1 Morphology. Crystal qualities such as crystal size, crystal shape, crystal surface, and crystal defects play an important role for the safe storage, transport, and handling of munitions items and explosives while maintaining their performance. These physicochemical parameters may also affect the detonation initiation spots of the explosive.⁴⁹ The crystal morphologies of the cocrystal and the raw materials are shown in Fig. 2. In Fig. 2, we can see that the morphology of the cocrystal is obviously different from those of the raw materials. The raw CL-20 crystals are colorless cambiform structures with integrated crystal surfaces (Fig. 2a), and the TATB raw material has irregular bulk crystals (Fig. 2b), whereas the CL-20/TATB cocrystals exhibit a colorless tetrahedron morphology with smooth and integrated surfaces (Fig. 2c–e). The top left inset (e) of the photograph in Fig. 2d shows a magnified image of the area outlined in red. The SEM images show unambiguously that particle size of the cocrystal is uniform and that the average particle size is about 3–5 μm.

Fig. 2 SEM micrographs of the raw CL-20, TATB and CL-20/TATB cocrystal: (a) raw CL-20; (b) TATB; (c) CL-20/TATB cocrystal; (d) and (e) higher magnifications of the CL-20/TATB cocrystal.

3.1.2 X-ray diffraction. The CL-20/TATB cocrystal structure can be distinguished from CL-20 and TATB via powder X-ray diffraction (PXRD). Fig. 3 shows the PXRD patterns of the cocrystal, raw CL-20 and TATB, and the different polymorphs of CL-20. From Fig. 3, we can find that the main diffraction angles of the CL-20/TATB cocrystal localized at 30.18°, 27.86°, 22.57°, and 14.89° are evidently different from the raw materials TATB and CL-20 with its different polymorphs. In the 2θ range of 10–40°, some of the peaks for CL-20 and TATB have disappeared, such as the peaks at 10.75°, 12.61°, and 25.79° for CL-20 and 20.75°, 23.84°, and 42.26° of TATB, and new peaks localized at 15.00° and 39.86° are observed in the diffraction pattern of the cocrystal. These differences enable easy distinction between the cocrystal and pure TATB or the various polymorphs of CL-20, as shown in Fig. 3. The unique XRD patterns of the cocrystal indicate that it is a new substance instead of the separate crystallization of the raw materials. Considering the rich polymorphism of CL-20, we compared the XRD peaks of the cocrystal with each kind of crystal type of CL-20. The results indicate that the peaks of the cocrystal were different from all of the types of CL-20.

Fig. 3 XRD spectra of α-CL-20, β-CL-20, γ-CL-20, ε-CL-20, raw CL-20, TATB and the CL-20/TATB cocrystal.

3.1.3 Raman spectroscopy. Raman spectroscopy is another useful means for the characterization of the cocrystal that shows that the vibrational modes of the cocrystal are different from those of the starting materials.^50–53 A full understanding of the effects of the cocrystal formation on the vibrational modes of motion is obtained by the complete assignment of the spectra of the starting materials and of the cocrystal. The Raman spectra of raw CL-20, TATB, and the cocrystal are given in Fig. 4. A comparison of the spectra reveals that there are several band shifts occurring between the individual components and the cocrystal. As shown in Fig. 4, in the cocrystal, the band at 126.6 cm⁻¹ (NO₂ deformation) of CL-20 shifts to the lower wavenumber of 112.1 cm⁻¹, and the bands at 317.9 and 344.9 cm⁻¹ (NO₂ twisting vibration and the cage skeleton vibration) of CL-20 shift to 309.7 and 336.7 cm⁻¹, respectively. Moreover, the bands at 3032 and 3048 cm⁻¹ (C–H stretching) of CL-20 shift to the higher wavenumbers 3038 and 3055 cm⁻¹, the band at 1165 cm⁻¹ (C–N stretching in C–NH₂) of TATB shifts to 1169 cm⁻¹ and the band at 3222 cm⁻¹ (NH₂ stretching) of TATB shifts to 3228 cm⁻¹ shown in the top right inset (b) of Fig. 4. At the same time, the bands at 192.3 and 264.7 cm⁻¹ (cage deformation) of CL-20 and the band at 3322 cm⁻¹ of TATB have disappeared in the cocrystal, and a strong band at 281.2 cm⁻¹ is observed. On the other hand, the Raman peaks of cocrystal ring deformation at 386.0 and 881.8 cm⁻¹ have become more stronger compared to TATB. In addition, following the literature,⁵⁴ the Raman spectrum of this cocrystal is completely different from the four polymorphs of CL-20 as shown in the top left inset (a) of Fig. 4. All these changes may be mainly attributed to the hydrogen bond interactions between the –NO₂ of CL-20 and –NH₂ of TATB.

Fig. 4 Raman spectra of raw CL-20, TATB, and the CL-20/TATB cocrystal. Top left inset (a) is the literature data of the four polymorphic of CL-20 from ref. 54, and the top right inset (b) is the high wavenumber region.

3.1.4 FT-IR and HPLC. To determine whether impurities existed in the cocrystal and the interactions between the CL-20 and TATB molecules, the FT-IR spectra of raw CL-20, TATB and the CL-20/TATB cocrystal were measured. As a whole, the absorptions of the cocrystal (Fig. 5a) are similar to those of the raw materials, but they still have differences more or less. For the CL-20/TATB cocrystal (Fig. 5a), some absorptions at 979.3, 942.9, 883.4, 722.9, 659.0 and 566.3 cm⁻¹ representing the mixing vibrations of CL-20 are shifted to 989.9, 951.4, 879.7, 717.5, 657.2 and 563.7 cm⁻¹, respectively, and the peak strength has changed. Meanwhile, the peaks at 1223.3, 1175.2, 699.3, and 446.3 cm⁻¹ for the mixing vibrations of TATB are weakened and shifted to 1228.3, 1174.9, 717.5 and 447.5 cm⁻¹, respectively. As for the CL-20/TATB cocrystal, relative to the raw materials, the absorptions at 444.5, 566.3, 979.3 (mixing vibration of CL-20), 854.6 (C–C stretching of CL-20), and 1588.8 cm⁻¹ (N=O stretching of CL-20) are weakened or diminished. According to a previous report (see Fig. 5b),⁵⁵ a triplet-like feature near 850 cm⁻¹ (at 751, 835, and 880 cm⁻¹) and the low intensity absorption at 3695 cm⁻¹ that is shifted from the α-CL-20 sharp hydrate peak (3700 cm⁻¹), we infer that the molecular conformation of CL-20 in CL-20/TATB cocrystal is the same as that in the α-CL-20 polymorph. According to the above analysis, we can infer that there may exist hydrogen bond interactions between the CL-20 (–NO₂) and TATB (–NH₂) molecules. In addition, quantitative results from the HPLC determinations confirm that the mass percentages of CL-20 and TATB in the CL-20/TATB cocrystal are 83.5% and 16.5%, respectively, corresponding to a molar ratio of 3 : 1.

Fig. 5 FT-IR spectra of raw CL-20, TATB and the CL-20/TATB cocrystal are shown in (a). Right inset (b) is the literature data of the four polymorphs of CL-20 from ref. 55.

3.2 Performance test

3.2.1 Thermal analysis. The thermal behavior of the cocrystal was examined using simultaneous DSC-TG. From the DSC and TG curves in Fig. 6, it is clear that the thermal behaviour of the cocrystal is obviously different from its raw materials, and the differences in the thermal stability of raw CL-20 and TATB further suggest the formation of a cocrystal. The DSC profile curve reveals a strong exothermic peak at 231.8 °C, attributed to the decomposition event of the cocrystal, which is distinctly lower than that of pure CL-20 (245.57 °C) or TATB (380.89 °C). The exothermic peak of the cocrystal is in advance of those of CL-20 and TATB, indicating that the thermal decomposition activity of cocrystal is higher than those of CL-20 and TATB. In addition, a weak endothermic peak at 208.15 °C is observed in the cocrystal with an increase of approximately 50 °C relative to the phase transition temperature (ε → γ) of CL-20, 161.93 °C.⁵⁶ The peak at 208.15 °C may demonstrate the phase transition temperature of the cocrystal. In the TG profile of the cocrystal, a constant weight is observed in the temperature range from 0–228.53 °C, implying no solvent molecules. Then a rapid weight loss in one step appears from 228.53 to 240 °C, corresponding to a drastic exotherm in the DSC trace of the cocrystal. At the same time, it also illustrates that this is our target cocrystal compound instead of a mixture, and this is further confirmed by the thermal behavior of the physical mixture of the CL-20 and TATB, which has an obvious two-step weight loss in the TG curve.

Fig. 6 TG and DSC curves of raw CL-20, TATB and the CL-20/TATB cocrystal and mechanical mixture of CL-20 and TATB.

3.2.2 Sensitivity test. In order to evaluate the CL-20/TATB cocrystal for potential utilization in the application of explosives, the mechanical sensitivity of the raw CL-20, CL-20/TATB cocrystal, and the physical mixture of CL-20 and TATB were investigated using a BAM impact sensitivity instrument, an in-house constructed drop-weight test, and the 30 mm³ samples were struck with a drop weight 0.5 kg. With this method, the minimum energy value of the detonation of CL-20 was 2.25 J, of the physical mixture was 2.5 J, and of the CL-20/TATB cocrystal was 3 J (see Fig. 7). Apparently, the minimum energy value of the CL-20/TATB cocrystal detonation is higher than raw CL-20 and the physical mixture. This result is in keeping with most of the cocrystals reported before and further confirms that cocrystallization provides an effective method to ameliorate the sensitivity of explosives. In addition, the cocrystal has a similar sensitivity to HMX, which has best comprehensive properties and is widely used.

Fig. 7 Results for the sensitivity of raw CL-20, the mechanical mixture of CL-20 and TATB, and the CL-20/TATB cocrystal. MED is the minimum energy value of detonation in the figure.

3.2.3 Density and detonation properties. In terms of energetic materials, there are many important properties of explosives related to the density, including detonation properties, sensitivity and thermal stability, etc. So, finding a high density explosive is beneficial to the design and synthesis of the ideal explosive. Density is one of the characteristics of materials and each material has its unique density. Therefore, we tested the densities of the CL-20/TATB cocrystal, raw CL-20 and TATB at room temperature, and the results are shown in Table 1. There is no stratification phenomenon during the testing process of the CL-20/TATB cocrystal and the single density value of 1.960 g cm⁻³ means a pure phase. The density of the cocrystal is between the two densities of the raw materials. For energetic materials, the density is a favorable factor to evaluate their detonation performance. According to the relationship between the detonation properties and density of the explosive, we can predict the value of the detonation velocity and detonation pressure of the cocrystal by using the linear output thermodynamic user-friendly software code^57–59 as follows:

P = ρ₀D²(1 − 0.713ρ₀^0.07) (3)

where F is the detonation factor, D is the detonation velocity in km s⁻¹, P is the detonation pressure in GPa. nO, nN, nH are the numbers of oxygen, nitrogen and hydrogen atoms in a molecule. nB is the number of oxygen atoms in excess of those already available to form CO₂ and H₂O. nC is number of oxygen atoms doubly bonded directly to carbon, as in carbonyl, nD is the number of oxygen atoms singly bonded directly to carbon, and nE is the number of nitro groups existing either as a nitrate ester configuration or as a nitric acid salt, such as hydrazine mononitrate. A = 1 if the compound is aromatic, otherwise A = 0; G = 0.4 for a liquid explosive and G = 0 for a solid explosive. ρ₀ is the initial density of the unreacted explosive in g cm³.

Table 1 Detonation properties and densities for raw CL-20, TATB and the CL-20/TATB cocrystal

Samples	Density (g cm^−3)	Detonation properties
		Detonation velocity (m s^−1)	Detonation pressure (GPa)
Raw CL-20	2.038	9382	46.6
TATB	1.913	8036	31.4
CL-20/TATB cocrystal	1.960	9127	41.3
HMX	1.906	9110	39.5

---

The results shown in Table 1 indicate that the detonation velocity and detonation pressure of the cocrystal are slightly reduced relative to CL-20, but are much higher than those of TATB. The detonation properties of the cocrystal are better than the current military standard explosive HMX due to the higher density of 1.960 g cm⁻³.

4. Conclusions

A novel energetic cocrystal explosive CL-20/TATB with a 3 : 1 molar ratio has been successful prepared by applying a rapid nucleation solvent/non-solvent method. Different from the raw materials, the CL-20/TATB cocrystal presents as a colorless tetrahedron with a smooth and integrated surface, and the particle size is very uniform with an average particle size of about 3–5 μm. The differences in the XRD pattern and Raman spectrum of the CL-20/TATB cocrystal from CL-20 and TATB means the formation of a new crystal phase, which is further verified by the density determination and the thermal analysis. The density of the CL-20/TATB cocrystal is 1.960 g cm⁻³, between CL-20 and TATB. The single exothermic peak at 231.8 °C is at a distinctly lower temperature than the peaks of CL-20 (245.57 °C) and TATB (380.89 °C), and the phase transition temperature, located at 208.15 °C, is 46.22 °C higher relative to CL-20 (161.93 °C). Based on the density value, the detonation velocity and detonation pressure of the CL-20/TATB cocrystal are calculated to be 9127 m s⁻¹ and 41.3 GPa, respectively, a slight decrease compared to CL-20. These data indicate that the CL-20/TATB cocrystal exhibits a high energy release efficiency and excellent thermal stability. The mechanical sensitivity of the CL-20/TATB cocrystal decreased from 2.25 J for CL-20 to 3 J. Compared with the current military standard explosive HMX, the detonation properties of the CL-20/TATB cocrystal are obviously improved and the sensitivity is almost the same. In addition, the rapid nucleation solvent/non-solvent method in this work has prominent advances in giving a high purity cocrystal, a short crystallization time, and easily scaled technology, which provide a strong foundation for the practical application of the CL-20/TATB cocrystal explosive.

Acknowledgements

We are very grateful for the financial help from the Sichuan Province Key Laboratory for Nonmetal Composites and Functional Materials (No. 11zxfk23), the Postgraduate Innovation Fund Project by Southwest University of Science and Technology (No. 15ycx006), and the Innovation Team Construction Program of Southwest University of Science and Technology (No. 14tdfk06).

Notes and references

1. K. B. Landenberger and A. J. Matzger, Cryst. Growth Des., 2012, 12, 3603–3609.
2. D. I. A. Millar, H. E. Maynard-Casely, D. R. Allan, A. S. Cumming, A. R. Lennie, A. J. Mackay, I. D. H. Oswald, C. C. Tang and C. R. Pulham, CrystEngComm, 2012, 14, 3742.
3. A. K. Sikder and N. Sikder, J. Hazard. Mater., 2004, 112, 1–15.
4. H. Hofmann and K. Rudolf, US Pat., 20040216822 A1, 2004.
5. A. Elbeih, A. Husarova and S. Zeman, Cent. Eur. J. Energ. Mater., 2011, 8, 173–182.
6. A. E. D. M. van der Heijden, R. H. B. Bouma and A. C. van der Steen, Propellants, Explos., Pyrotech., 2004, 29, 304–313.
7. H. Kröber and U. Teipel, Propellants, Explos., Pyrotech., 2008, 33, 33–36.
8. Y. Bayat, M. Zarandi, M. A. Zarei, R. Soleyman and V. Zeynali, J. Mol. Liq., 2014, 193, 83–86.
9. Y. Bayat and V. Zeynali, J. Energ. Mater., 2011, 29, 281–291.
10. J. Liu, W. Jiang, Q. Yang, J. Song, G.-z. Hao and F.-s. Li, Def. Technol., 2014, 10, 184–189.
11. X. D. Guo, G. Ouyang, J. Liu, Q. Li, L. X. Wang, Z. M. Gu and F. S. Li, J. Energ. Mater., 2015, 33, 24–33.
12. G. Yang, F. Nie, H. Huang, L. Zhao and W. Pang, Propellants, Explos., Pyrotech., 2006, 31, 390–394.
13. B. C. Tappan and T. B. Brill, Propellants, Explos., Pyrotech., 2003, 28, 223–230.
14. S. S. Samudre, U. R. Nair, G. M. Gore, R. Kumar Sinha, A. Kanti Sikder and S. Nandan Asthana, Propellants, Explos., Pyrotech., 2009, 34, 145–150.
15. C.-W. An, F.-S. Li, X.-L. Song, Y. Wang and X.-D. Guo, Propellants, Explos., Pyrotech., 2009, 34, 400–405.
16. A. K. Nandi, M. Ghosh, V. B. Sutar and R. K. Pandey, Cent. Eur. J. Energ. Mater., 2012, 9, 119–130.
17. Z. Ma, B. Gao, P. Wu, J. Shi, Z. Qiao, Z. Yang, G. Yang, B. Huang and F. Nie, RSC Adv., 2015, 5, 21042–21049.
18. J. H. Urbelis and J. A. Swift, Cryst. Growth Des., 2014, 14, 1642–1649.
19. L. Yu, H. Ren, X. Y. Guo, X. B. Jiang and Q. J. Jiao, J. Therm. Anal. Calorim., 2014, 117, 1187–1199.
20. N. Chieng, M. Hubert, D. Saville, T. Rades and J. Aaltonen, Cryst. Growth Des., 2009, 9, 2377–2386.
21. D. R. Weyna, T. Shattock, P. Vishweshwar and M. J. Zaworotko, Cryst. Growth Des., 2009, 9, 1106–1123.
22. K. B. Landenberger and A. J. Matzger, Cryst. Growth Des., 2010, 10, 5341–5347.
23. J. P. Shen, X. H. Duan, Q. P. Luo, Y. Zhou, Q. L. Bao, Y. J. Ma and C. H. Pei, Cryst. Growth Des., 2011, 11, 1759–1765.
24. O. Bolton and A. J. Matzger, Angew. Chem., Int. Ed., 2011, 50, 8960–8963.
25. O. Bolton, L. R. Simke, P. F. Pagoria and A. J. Matzger, Cryst. Growth Des., 2012, 12, 4311–4314.
26. Z. Yang, H. Li, X. Zhou, C. Zhang, H. Huang, J. Li and F. Nie, Cryst. Growth Des., 2012, 12, 5155–5158.
27. C. Y. Guo, H. B. Zhang, X. C. Wang, J. J. Xu, Y. Liu, X. F. Liu, H. Huang and J. Sun, J. Mol. Struct., 2013, 1048, 267–273.
28. H. Zhang, C. Guo, X. Wang, J. Xu, X. He, Y. Liu, X. Liu, H. Huang and J. Sun, Cryst. Growth Des., 2013, 13, 679–687.
29. H. Lin, S.-G. Zhu, L. Zhang, X.-H. Peng and H.-Z. Li, J. Energ. Mater., 2013, 31, 261–272.
30. B. Gao, D. Wang, J. Zhang, Y. Hu, J. Shen, J. Wang, B. Huang, Z. Qiao, H. Huang, F. Nie and G. Yang, J. Mater. Chem. A, 2014, 2, 19969–19974.
31. D. Spitzer, B. Risse, F. Schnell, V. Pichot, M. Klaumunzer and M. R. Schaefer, Sci. Rep., 2014, 4, 1–6.
32. Y. P. Wang, Z. W. Yang, H. Z. Li, X. Q. Zhou, Q. Zhang, J. H. Wang and Y. C. Liu, Propellants, Explos., Pyrotech., 2014, 39, 590–596.
33. H. Lin, S.-G. Zhu, H.-Z. Li and X.-H. Peng, J. Phys. Org. Chem., 2013, 26, 898–907.
34. Z. Yang, H. Li, H. Huang, X. Zhou, J. Li and F. Nie, Propellants, Explos., Pyrotech., 2013, 38, 495–501.
35. C. Zhang, Y. Cao, H. Li, Y. Zhou, J. Zhou, T. Gao, H. Zhang, Z. Yang and G. Jiang, CrystEngComm, 2013, 15, 4003–4014.
36. A. D. Bond, CrystEngComm, 2007, 9, 833–834.
37. F. Lara-Ochoa and G. Espinosa-Pérez, Supramol. Chem., 2007, 19, 553–557.
38. A. T. Nielsen, R. A. Nissan, D. J. Vanderah, C. L. Coon, R. D. Gilardi, C. F. George and J. Flippen-Anderson, J. Org. Chem., 1990, 55, 1459–1466.
39. C. Zhang, X. Xue, Y. Cao, J. Zhou, A. Zhang, H. Li, Y. Zhou, R. Xu and T. Gao, CrystEngComm, 2014, 16, 5905–5916.
40. R. Simpson, P. Urtiew, D. Ornellas, G. Moody, K. Scribner and D. Hoffman, Propellants, Explos., Pyrotech., 1997, 22, 249–255.
41. D. I. A. Millar, H. E. Maynard-Casely, D. R. Allan, A. S. Cumming, A. R. Lennie, A. J. Mackay, I. D. H. Oswald, C. C. Tang and C. R. Pulham, CrystEngComm, 2012, 14, 3742–3749.
42. U. Nair, R. Sivabalan, G. Gore, M. Geetha, S. Asthana and H. Singh, Combust., Explos. Shock Waves, 2005, 41, 121–132.
43. V. M. Boddu, D. S. Viswanath, T. K. Ghosh and R. Damavarapu, J. Hazard. Mater., 2010, 181, 1–8.
44. A. K. Nandi, N. Thirupathi, A. K. Mandal and R. K. Pandey, Cent. Eur. J. Energ. Mater., 2014, 11, 295–305.
45. B. M. Dobratz, Properties of chemical explosives and explosive simulants, comp, California Univ., Lawrence Livermore Lab., Livermore, USA, 1972.
46. J. R. Kolb and H. Rizzo, Propellants, Explos., Pyrotech., 1979, 4, 10–16.
47. C. Zhang, X. Wang and H. Huang, J. Am. Chem. Soc., 2008, 130, 8359–8365.
48. W. Selig, Estimation of the Solubility of 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) in Various Solvents, California Univ., Lawrence Livermore Lab., Livermore, USA, 1977.
49. A. E. van der Heijden and R. H. Bouma, Cryst. Growth Des., 2004, 4, 999–1007.
50. M. A. Elbagerma, H. G. M. Edwards, T. Munshi, M. D. Hargreaves, P. Matousek and I. J. Scowen, Cryst. Growth Des., 2010, 10, 2360–2371.
51. H. G. Brittain, Cryst. Growth Des., 2009, 9, 2492–2499.
52. H. G. Brittain, Cryst. Growth Des., 2009, 9, 3497–3503.
53. H. G. Brittain, Cryst. Growth Des., 2010, 10, 1990–2003.
54. M. Ghosh, V. Venkatesan, N. Sikder and A. K. Sikder, Cent. Eur. J. Energ. Mater., 2013, 10, 419–438.
55. M. Ghosh, V. Venkatesan, S. Mandave, S. Banerjee, N. Sikder, A. K. Sikder and B. Bhattacharya, Cryst. Growth Des., 2014, 14, 5053–5063.
56. R. Turcotte, M. Vachon, Q. S. M. Kwok, R. Wang and D. E. G. Jones, Thermochim. Acta, 2005, 433, 105–115.
57. H. Muthurajan, R. Sivabalan, M. B. Talawar and S. N. Asthana, J. Hazard. Mater., 2004, 112, 17–33.
58. L. Rothstein and R. Petersen, Propellants, Explos., Pyrotech., 1979, 4, 56–60.
59. L. R. Rothstein, Propellants, Explos., Pyrotech., 1981, 6, 91–93.

---