In order to effectively model the behaviour of energetic materials under operational conditions it is essential to obtain detailed structural information for these compounds at elevated temperature and/or pressures. The structural characterisation of the high explosives RDX and CL-20 and a series of inorganic azides [Mn+(N3)n] at extreme conditions is described herein. In addition to the characterisation of a highly metastable β -form of RDX (1,3,5- trinitrohexahydro-1,3,5-triazine) at atmospheric pressure, the structure solution of a high-pressure/ high-temperature polymorph is described. This form, obtained above 4.3 GPa and 450 K, has been shown to be distinct from the β -form and has therefore been denoted - RDX. Furthermore, ε -RDX is sufficiently metastable to allow its recovery to ambient pressure at 150 K; it only transforms to the α -form upon warming to 230 K. Finally, the ambient-temperature compression of RDX has been investigated to a maximum pressure of 23.0 GPa, using methanol:ethanol (4:1) as the pressure-transmitting medium; no phase transition was observed under these conditions, other than the α → γ transition at 3.9 GPa. The structure of a high-pressure polymorph of CL-20 (2,4,6,8,10,12- hexanitrohexaazaisowurtzitane) has also been determined by a combination of powder and single-crystal X-ray diffraction. Compression of γ -CL-20 to above 0.7 GPa using Fluorinert (FC-77) as the pressure-transmitting medium results in a phase transition to the ζ -form, which has been found to display structural similarities with both theγ γ - and ε -forms. The high-pressure behaviour of CL-20, however, depends markedly on the starting polymorph and the pressure-transmitting medium selected. Compression of γ -CL-20 in MeOH:EtOH (4:1) results in the formation of a 2:1 CL-20:MeOH solvate at 0.5 GPa. This solvate is stable upon compression to P > 5.0 GPa. It may also be recovered to ambient pressure at 293 K. Meanwhile, no phase transition is observed during the compression of ε -CL-20 to a maximum pressure of 7.2 GPa. Finally, a series of inorganic azides [NaN3, CsN3, TlN3, NH4N3, AgN3 and Pb(N3)2] has been characterised under a range of pressure and temperature conditions. Of the six compounds studied, all displayed at least one polymorphic transition – 5 new forms have been structurally characterised in this work and evidence of another 5 is presented. The combined effect of pressure and temperature results in sodium azide adopting a tetragonal structure common to larger alkali metal azides. Caesium azide has been shown to undergo three phase transitions during compression to 6.0 GPa – the structure of the first high-pressure form is reported. A variable temperature X-ray powder diffraction study of TlN3 has allowed the structural characterisation of the low-temperature TlN3-IV (at 230 K) as well as providing evidence for a phase transition to a high-temperature form above 550 K. The high-pressure form III (obtained above 0.76 GPa) has also been determined by neutron powder diffraction. Silver, ammonium and lead(II) azides have all been shown to undergo a phase transition at high pressures. Compression of silver azide (P > 0.80 GPa) removes an orthorhombic distortion observed at atmospheric pressure, resulting in the tetragonal structure adopted by CsN3 and TlN3 under ambient conditions. Moreover, NH4N3 and Pb(N3)2 have been found to undergo phase transitions at 2.6 GPa, although their high-pressure structures have still to be determined.

La cristallisation en continu de nanoparticules énergétiques est un défi de longue date. Le Spray Flash Evaporation (SFE) est une technique majeure développée et brevetée en interne, pour la production en continu de matériaux énergétiques submicroniques ou nanométriques ; la technologie se base sur la surchauffe d’un solvant pulvérisé dans le vide et s’évaporant de manière flash. Ce présent travail de recherche a pour but de comprendre et contrôler la cristallisation au sein du procédé SFE. Le RDX et le cocristal CL-20:HMX 2:1 sont étudiés. La sursaturation, concernant le SFE, est une fonction du temps et de l’espace liée aux tailles et vitesses de gouttes : elle fut variée par un anti-solvant et par l’amélioration du SFE avec un système double buse. Ensuite, PVP 40K et PEG 400 ont été utilisés afin de contrôler la nucléation et la croissance. Les particules ont pu être ajustées d’une taille de 160 nm à 5 µm, avec des morphologies facettées ou sphériques et avec des sensibilités moindres. / The continuous formation of nanosized energetic material is a long-standing challenge. Spray Flash Evaporation (SFE) is a major technique, internally developed and patented, for continuously producing energetic materials at submicron or nano scale; it relies on the superheating of a solvent sprayed into vacuum and thus flashing. This present research project aims to understand and control the crystallisation occurring in the SFE process. RDX and the cocrystal CL-20:HMX 2:1 was studied overcome the limited in situ characterizations also. The supersaturation is a function of time and space in SFE, linked to the size distribution and velocity of droplets. Supersaturation was raised with an anti-solvent and by the enhancement of the SFE with a dual nozzle system. Then PVP 40K and PEG 400 were successfully used to alter the nucleation and the growth. The particles were subsequently tuned from 160 nm spheres to 5 µm grains and were less sensitive, especially toward electrostatic discharge.

A majority of research within the field of energetic materials have been centered around the stable crystalline phase, whilst there has been less about the amorphous phase and the implications of these types of material. In this study, Molecular Dynamics simulations with the General Amber Force Field (GAFF) is used to predict fundamental properties of the nitramine explosives HMX and CL-20 in the amorphous phase. Amorphous structures are obtained by compressing a molecular gas to 4 GPa followed by relaxation and equilibration. The simulations indicate that the amorphous phases of HMX and CL-20 have lower densities than the corresponding crystal phases, 12.7% and 7.3% respectively. Both HMX and CL-20 was found to compress more easily when subject to external pressure, the difference was most significant for HMX.As a second part of this study an amorphous composition of CL-20/HMX/Polyvinylacetate(PVAc) (50/45/5 -wt%) was studied. This was obtained by compressing a molecular gas to varying pressures followed by relaxation and equilibration. Results indicate that the simulated density around 1.64 [g/cm3 ] fall close to experimental observations of 1.7 [g/cm3 ]. The density was observed to not vary significantly for pressures higher than 0.4 [GP a] in accordance to experimental data.