The thermal stability of the polymorphs of hexanitrohexaazaisowurtzitane, part II

Foltz, M. Frances; Coon, Clifford L.; Garcia, Frank; Nichols, Albert L.

doi:10.1002/prep.19940190305

Cited by 112 publications

(94 citation statements)

References 3 publications

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“…This peak is assigned to solid-solid α → γ phase transition and the peak temperature of solid-solid ε → γ phase transition is observed at 160 ± 1 °C Fig. 5(b), which are well comparable with value in reported literature 18 . Later than the solid-solid phase transition, the DSC profile exhibits a single step exothermic thermal decomposition for both raw CL-20 and ε-CL-20.…”

Section: Introductionsupporting

confidence: 79%

“…Due to the presence of different molecular conformations and arrangements in lattice, CL-20 has been reported to exist in five different polymorphic forms. Four polymorphs (ε, β, α, and γ) exist at ambient condition and one (ζ) exists at high pressure [3][4][5] . Due to the high energetic performance, high density, and low sensitivity compared to the other polymorphs, ε-CL-20 is more desirable for use in propellant and weapons systems 2,3 .…”

Section: Introductionmentioning

confidence: 99%

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Preparation and Characterisation of ε-CL-20 by Solvent Evaporation and Precipitation Methods

Ghosh¹,

Venkatesan²,

Sikder³

et al. 2012

DSJ

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, et al. studied the crystal quality of ε-CL-20 obtained from different precursors and solvent systems.In the present study, it is focused to prepare and characterisation by both solvent evaporation and precipitation methods. The present evaporation method also relates for obtaining agglomeration free fine ε-CL-20 crystals by in-situ use of ultrasound to crystallisation solution. The obtained crystals were characterised using HPLC, FTIR, Raman, Powder XRD, SEM and DSC techniques. Particle size measurement of obtained ε-CL-20 was carried out using particle size analyser and true density by Helium gas pycnometer. EXPERIMENTAL WORKRaw CL-20 sample was obtained from Premier Explosive's Laboratories, India. All the solvents and allied chemicals used for the processes are of analytical grade with > 99 % purity. ε-CL-20 is prepared using both solvent evaporation and precipitation techniques. Raw CL-20 is dissolved in ethyl acetate solvent and then antisolvent, n-heptane is added into the solution to induce the crystallisation. For the effective recovery in the drowning-out crystallisation, the fraction of raw CL-20, ethyl acetate and n-heptane was applied as about from 1 : 15 : 35, AbSTRACT ε-CL-20 is prepared from raw CL-20 by solvent evaporation and precipitation methods. Experiments were also done using solvent evaporation coupled with in-situ ultrasonication method. Using precipitation method, ε-CL-20 is scaled up to 500 g batch. Raw CL-20 was assigned to α-CL-20. The chemical and polymorphic purity of prepared ε-CL-20 was found to be about 98 per cent and > 95 per cent, respectively. ε-CL-20 was obtained agglomeration free with well defined geometry in comparison with raw CL-20 and its crystal morphology is dominantly bi-pyramidal or lozenge crystal shapes. The obtained mean particle size of prepared ε-CL-20 by solvent evaporation method with and without in-situ ultrasonication and also by precipitation methods is about 30 µm -40 µm, 150 µm -200 µm and 150 µm -300 µm, respectively. The measured true density of prepared ε-CL-20 by precipitation method with 100 g and 500 g batch scale using Helium gas pycnometer was 2.038 g/cm 3 and 2.043 g/cm 3 , respectively. The lower value of calculated void percentage of ε-CL-20 (0.05-0.29%) indicate better crystal quality. Conclusively, prepared ε-CL20 has high true density with less percentage of voids, less total moisture content and free from agglomeration as compared with the starting raw CL-20 material.

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Section: Introductionsupporting

confidence: 79%

Section: Introductionmentioning

confidence: 99%

Preparation and Characterisation of ε-CL-20 by Solvent Evaporation and Precipitation Methods

Ghosh¹,

Venkatesan²,

Sikder³

et al. 2012

DSJ

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“…It can be seen that the initial phase transition temperature increases with increasing purity of the samples (note: if a lower temperature gradient is utilized, more accurate initial phase transition temperatures could be obtained). This is attributed to the presence of impurities reducing the energy barrier for phase transition, and the heat accumulation and energy release of impurities providing additional energy to promote the phase transition [10,11]. Therefore, purity is a key factor in ensuring the stability and safety of HNIW.…”

Section: Influence Of Purity On Crystal Structural Transformationmentioning

confidence: 99%

“…The different extended orientations of the nitro groups relative to the five-or six-membered rings of HNIW leads to different molecular packing models and different numbers of molecules in a cell, which defines several probable polymorphs of HNIW. So far, five different polymorphs (α, β, γ, ε, and ζ) have been reported and identified [10][11][12][13][14]. Four of the polymorphs (α, β, γ, and ε) exist at ambient pressure and temperature.…”

Section: Introductionmentioning

confidence: 99%

Thermally Induced Polymorphic Transformation of Hexanitrohexaazaisowurtzitane (HNIW) Investigated by in-situ X-ray Powder Diffraction

Liu¹,

Li²,

Ze-shan³

et al. 2016

Cent. Eur. J. Energ. Mater.

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Abstract:The ε→γ phase transition of HNIW induced by heat was investigated with in situ X-ray powder diffraction (PXRD). The effects of purity, particle size, insensitive additives and the time of isothermal heat treatment on the phase transition were evaluated. It was found that the phase transition is irreversible with changes in temperature, and the two phases can coexist in a certain temperature range. Moreover, the initial phase transition temperature increases with increasing purity and decreasing particle size of HNIW, and thus with the approximate crystal density. The addition of graphite and paraffin wax to HNIW as insensitive additives leads to a decrease in the initial phase transition temperature, but the addition of TATB does not affect the initial phase transition temperature. Thus, TATB is a suitable insensitive additive. Moreover, at the critical temperature, the isothermal time determined the efficiency of the ε-to γ-phase transition. This work lays the foundations for the choice of molding technologies, performance test methods, ammunition storage options, as well as the manufacture of HNIWbased explosive formulations.

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“…The DSC analysis shows an endothermic phenomenon in the temperature range 160-200 8C, which corresponds to a solid-solid phase transition from the CL20-CO 2 to the g-CL20 polymorph, followed by an exothermic phenomenon above 210 8C due to thermal decomposition of the g-CL20 polymorph (Figure 3 a). [20,25] TGA-MS characterization displays two weight-loss signals in the same temperature ranges (i.e., 160-200 8C and above 210 8C, Figure 3 b). The mass to charge ratio (m/z) of 44 that corresponds to CO 2 , demonstrates that CO 2 molecules are released during the solid-solid phase transition (Figure 3 c).…”

mentioning

confidence: 99%

Host–Guest Inclusion Compound from Nitramine Crystals Exposed to Condensed Carbon Dioxide

Martin

Marre

Guionneau

et al. 2010

Chemistry A European J

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HNIW or CL20 (2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane) is a nitramine, which is considered as the highest energetic molecular compound known to date, therefore, attracting increasing interest in propulsion applications. Additionally, CL20 is an interesting system for fundamental studies, exhibiting several polymorphs, which can behave as host lattices for trapping guest molecules. Herein, a new CL20 structure that contains inserted CO(2) molecules is reported. A combination of Fourier transform infra red (FTIR) spectroscopy, scanning electron microscopy (SEM), single-crystal X-ray diffraction, and thermal analyses (thermogravimetric analysis coupled with mass spectrometry and differential scanning calorimetry) was used to characterize this new material.

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The thermal stability of the polymorphs of hexanitrohexaazaisowurtzitane, part II

Cited by 112 publications

References 3 publications

Preparation and Characterisation of ε-CL-20 by Solvent Evaporation and Precipitation Methods

Preparation and Characterisation of ε-CL-20 by Solvent Evaporation and Precipitation Methods

Thermally Induced Polymorphic Transformation of Hexanitrohexaazaisowurtzitane (HNIW) Investigated by in-situ X-ray Powder Diffraction

Host–Guest Inclusion Compound from Nitramine Crystals Exposed to Condensed Carbon Dioxide

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