Investigation on the thermal expansion of α-CL-20 with different water contents

Abstract

The thermal expansions of three kinds of a-CL-20 crystals have been investigated in the temperature range from 30 to 130°C by means of various-temperature X-ray powder diffraction (XRD) together with Rietveld refinement. The crystals were characterized by SEM, XRD, FTIR, and DSC/TG. The results show that the three samples contain 1/2, 1/4 mol, and none structural water, respectively. The a-CL-20 crystals all perform linear and anisotropic thermal expansion, while some differences exist. The unit-cell axes increase linearly with increasing temperature except for the a-axis. The expansion along the a-axis switches from positive to negative thermal expansion at 90°C for a-CL-20Á1/2H 2 O. The a-axis exhibits positive thermal expansion (PTE) with thermal irresilience for a-CL-20Á1/4H 2 O while PTE with thermal resilience for the anhydrous a-CL-20. The differences are caused by the structural water. The removal of structural water leads to the collapse of a-axis, further results in structural changes of the unit cell. Different water contents can cause different degree of structural changes, leading to the difference of thermal expansion behaviors.

Molecular Inclusion of Small Aging Products into the Hexanitrohexaazaisowurtzitane (CL‐20) Lattice: Part I, Infrared Spectra

“…It shares the same molecular unit as γ CL-20 but its lattice structure contains voids. α, β, and ɛ polymorphs all undergo a phase transition to γ CL-20 prior to thermal decomposition [6][7][8]17].…”

“…The hydrated α form of CL‐20 is generally found to be a 0.25 hydrate [1, 18], although other CL‐20/water ratios, in particular anhydrous α CL‐20, have been observed [17, 19]. The crystal structure of the α polymorph [18] shows four large void spaces that can each accommodate two water molecules for a total of eight possible water sites per unit cell.…”

Smart Host–Guest Energetic Material Constructed by Stabilizing Energetic Fuel Hydroxylamine in Lattice Cavity of 2,4,6,8,10,12-Hexanitrohexaazaisowurtzitane Significantly Enhanced the Detonation, Safety, Propulsion, and Combustion Performances

“…Unlike cocrystallization, the host–guest inclusion strategy is a type of crystal engineering based on the comprehensive theories of supramolecular recognition interactions and space matching, which has become a promising method for the development of novel intermolecular HEDMs. , Among the traditional HEDMs, the hydrated HNIW, namely, α-HNIW, is considered to be an ideal framework for constructing host–guest inclusion explosives, as its packing model can be retained after complete removal of the structural H 2 O. , Since 2010, some functional molecules such as H 2 O 2 , CO 2 , and N 2 O have successfully replaced the space of H 2 O without appreciably changing the lattice volume of α-HNIW. ,, Their crystal density, detonation performance, safety, thermal stability, and oxygen balance are significantly better than those of α-HNIW; in particular, the detonation velocity of HNIW/N 2 O and HNIW/H 2 O 2 host–guest explosives exceeded 9600 m/s, which is significantly higher than that of the well-known ε-HNIW. In addition to being used as a secondary explosive, HNIW is an ideal candidate for energetic oxidizers in rocket propellants because of its excellent oxygen balance and detonation performance. − Unlike its excellent detonation performance, its suboptimal combustion performance will severely limit its application in propellants, as combustion performance is critical for evaluating propulsion performance. , Therefore, selection and incorporation of functional guest molecules with excellent combustion performance is strategically critical for HNIW.…”

Solvate of 2,4,6,8,10,12‐Hexanitro‐2,4,6,8,10,12‐Hexaazaisowurtzitane (CL‐20) with both N2O4 and Stable NO2 Free Radical

“…However, as a rule, not all cavities in the crystal structure are occupied, and such a solvate can lose most of the inclusions without changing the crystal modification. The anhydrous α‐modification of CL‐20 described in contains less than 0.05 mol of H 2 O per mole of CL‐20. Similar studies with α‐CL‐20 ⋅ N 2 O 4 show a regular decrease in the vibrational intensity of 1749 cm −1 when the sample is held at elevated temperature (see the Supporting Information, Figure S), indicating a loss of N 2 O 4 , but the rest of the IR spectrum does not change and corresponds to the α‐modification until 85 % of initial N 2 O 4 is lost.…”