Suhithi M. Peiris

Isothermal equations of state of beta octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine at high temperatures

Isothermal pressure-volume equations of state of beta HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine) at temperatures of 30, 100, and 140°C under both hydrostatic and nonhydrostatic compressions have been obtained using synchrotron angle-dispersive x-ray diffraction experiments. The samples were heated to the isotherm temperature and compressed up to 5.8GPa. At all temperatures HMX remained in the beta phase up to 5.8GPa. However, at 140°C upon decompression to ambient from nonhydrostatic pressures above 4GPa, HMX underwent a phase transition to the delta phase. The same transition was seen upon decompression to ambient from hydrostatic compression; however, parts of the sample remain in the β phase, resulting in a mixed-phase sample. The diffraction data were analyzed to yield unit-cell dimensions at each pressure, and further analyzed to yield thermal expansion, bulk modulus, and the pressure derivative of the bulk modulus.

Equation of state and structural changes in diaminodinitroethylene under compression

Structural changes in 1,1-diamino-2,2-dinitroethylene (DADNE, FOX-7) compressed to high pressure in diamond anvil cells were investigated using angle-dispersive x-ray diffraction analysis, Raman spectroscopy, and optical polarizing microscopy. The x-ray results show several changes above 1 GPa. When the x-ray data are indexed according to the ambient-pressure structure, DADNE shows anisotropic compression, with higher compression along the b axis than along the a or c axis. An ambient-temperature isothermal equation of state of DADNE was generated from these data. In addition, the experimentally obtained Raman spectra were matched with vibrational normal modes calculated using quantum chemistry calculations. The shifts in vibrational modes indicate changes in H-wagging vibrations with pressure.

Phase transitions and isothermal equations of state of epsilon hexanitrohexaazaisowurtzitane (CL-20)

The phase stability of epsilon hexanitrohexaazaisowurtzitane at high pressure and temperature was investigated using synchrotron angle-dispersive x-ray diffraction experiments. The samples were compressed at room temperature using a Merrill–Bassett diamond anvil cell. For high-temperature compression experiments a hydrothermal diamond anvil cell developed by Bassett was used. Pressures and temperatures of around 5 GPa and 175 °C, respectively, were achieved. The epsilon phase was determined to be stable under ambient pressure to a temperature of 120 °C. A phase transition to the gamma phase was seen at 125 °C and the gamma phase remained stable until thermal decomposition above 150 °C. Pressure-volume data for the epsilon phase at ambient and 75 °C were fitted to the Birch–Murnaghan formalism to obtain isothermal equations of state.

Equations of state of 2,6-diamino-3,5-dinitropyrazine-1-oxide

2,6-diamino-3,5-dinitropyrazine-1-oxide (LLM-105) is an energetic ingredient that has an impact sensitivity close to that of TATB, yet a calculated energy content close to HMX. Reported tests of formulated LLM-105 reveal that it is a good candidate for a new insensitive high-performance explosive. As use of LLM-105 increases, thermodynamic parameters and phase stability will need to be determined for accurate modeling. In order to accomplish this goal, isothermal equations of state of LLM-105 at static high-pressure and temperature were investigated using synchrotron angle-dispersive x-ray diffraction and diamond anvil cells. Data at ambient temperature, 100 °C (373 K), and 180 °C (453 K) were used to obtain isothermal equations of state, and data at ambient pressure were used to obtain the volume thermal expansion coefficient. At ambient temperature, 100 °C (373 K), and 180 °C (453 K) no phase change was evident up to the highest measured pressure; and at ambient pressure, LLM-105 was stable up to 240 °C (513 K) and thermally decomposed by 260 °C (533 K).

Ab initio 0 K isotherm for crystalline 1,1-diamino-2,2-dinitroethylene

The ab initio calculation of the 0 K isotherm of the organic molecular crystal 1,1-diamino-2,2-dinitroethylene (C2H4N4O4), also known as FOX-7, is accomplished by means of solutions of the many-body Schrodinger equation in a periodic crystal lattice. It was found that the Hartree–Fock method is adequate to represent the behavior of the material and that, in general, density functional methods give inferior results. Initially, calculations were done assuming rigid molecules under compression. In further calculations the internal molecular bond lengths were optimized for each value of compression. Finally, calculations were performed in which all the molecular coordinates were optimized. The results are compared with experimental x-ray diffraction data obtained by compressing samples in diamond anvil cells. Excellent agreement is obtained when the molecular coordinates are completely optimized. In addition, FOX-7 is highly anisotropic and this anisotropy must be taken into account to obtain good agreement w...

Phase stability of {epsilon} and {gamma} HNIW (CL-20) at high-pressure and temperature

Hexanitrohexaazaisowurtzitane (CL‐20) is one of the few ingredients developed since World War II to be considered for transition to military use. Five polymorphs have been identified for CL‐20 by FTIR measurements (α, β, γ, e, ζ). As CL‐20 is transitioned into munitions it will become necessary to predict its response under conditions of detonation, for performance evaluation. Such predictive modeling requires a phase diagram and basic thermodynamic properties of the various phases at high pressure and temperature. Therefore, the epsilon and gamma phases of CL‐20 at static high‐pressure and temperature were investigated using synchrotron angle‐dispersive x‐ray diffraction experiments. The samples were compressed and heated using diamond anvil cells (DAC). Pressures and temperatures achieved were around 5 GPa and 240 °C, respectively. The epsilon phase was stable to 6.3 GPa at ambient temperature. When heated at ambient pressure the epsilon phase was sustained to a temperature of 120 °C then underwent a tr...

High‐Pressure Structural Study of Epsilon HNIW (CL‐20)

The structure of epsilon CL‐20 at room temperature was investigated using synchrotron angle‐dispersive x‐ray diffraction experiments and Raman spectroscopy. For x‐ray diffraction, the samples were compressed up to 6.3 GPa using a Merrill‐Bassett diamond anvil cell (DAC) under both hydrostatic and non‐hydrostatic conditions. Pressure — volume data were then fit to the Birch‐Murnaghan equation of state to obtain an isothermal equation of state. No phase transition was observed within this pressure range.Raman spectroscopy was performed in the range of 50–1650 cm−1. The samples were compressed non‐hydrostatically to 7.1 GPa. Changes in peak positions with increasing pressure were observed. Vibrational spectra were calculated using Hartree‐Fock and density functional theory and a comparison was made with the experimental spectrum.

T‐JUMP/FTIR STUDIES OF POLY‐GLYCIDYL NITRATE (PGN) PYROLYSIS

In an effort to understand the effects of hydroxyl end‐modification and isocyanate curing, decomposition of PGN prepolymer has been investigated using T‐Jump/FTIR (Fourier transform infrared) spectroscopy of PGN allowing real‐time analysis of decomposition gas products under simulated deflagration conditions. Our results identify decomposition products including: CH2O, H2O, CO2, CO, N2O, NO, NO2, HCN and HONO. Kinetic rates relative to CO2 formation lead to calculated activation energies of 22 kcal/mol and 18 kcal/mol. Much higher activation energies (32 kcal/mol) were calculated relative to CH2O formation rates, in agreement with DSC data, indicating that CH2O formation is likely an initial decomposition step while CO2 formation is due to side gas phase reactions. Additional FTIR and optical microscopy studies indicate that condensed phase, backbone scission reactions also occur, causing time delays prior to major gas production.

Comparison of Reaction Kinetics of I‐RDX® and RDX at High Pressure

Reactions and kinetics of the new less‐sensitive form of RDX developed by Eurenco (known as I‐RDX®) need to be compared to standard RDX, especially at shock pressures and temperatures. To evaluate the effect of pressure samples of I‐RDX® and standard RDX were compressed to various static pressures in anvil cells. To evaluate the effect of temperature samples were initiated with different fluences of a 5ns pulsed Nd:YAG laser. As a measure of global reaction rate, changes in transmittance through the samples were monitored during reaction. Both RDX and I‐RDX® were initially transparent under pressure, becoming opaque soon after initiation and then clear as the final gaseous products are formed. A comparison of the global reaction times obtained under various pressure and fluence conditions for I‐RDX® and RDX samples are presented.

HMX (Beta Phase): Laser‐Ignited Reaction Kinetics and Isothermal Equations of State

Reaction rates of laser‐initiated HMX (beta phase) at high pressure have been measured using time‐resolved absorbance spectroscopy. Over 20 samples of HMX were compressed to various initial pressures between 0.6 – 3.7 GPa and laser‐initiated with various laser‐pulse fluence between 1.4 – 8.5 J/cm2. Under these P,T conditions, the complete reaction of HMX to the product gases takes 12–14 microseconds. Our time‐resolved absorbance data show that HMX reactions are multi‐step processes, demonstrated by an initial increase in absorbance followed by a later decrease in absorbance. In addition, isothermal equations of state of HMX at 30°C, 100°C and 140°C have been obtained using synchrotron angle‐dispersive x‐ray diffraction experiments. The samples were heated to the isotherm temperature and compressed up to 6 GPa. At all temperatures HMX remains in the beta phase up to 5 GPa. However, at 140°C when compressed above 4 GPa, upon decompression to ambient pressure, HMX undergoes a phase transition to the delta ph...