The high-pressure phase behavior and compressibility of 2,4,6-trinitrotoluene

Abstract

The phase stability and isothermal compression behavior of 2,4,6-trinitrotoluene (TNT) have been established to 26.5 GPa using angle-dispersive x-ray diffraction. P-V isotherms derived from the high-pressure x-ray spectra displayed a slight density hysteresis around 4.0 GPa and a sharp discontinuity at ∼20.0 GPa. The latter transition is ascribed to a monoclinic-to-orthorhombic first-order phase transition in TNT. The conversion of the isothermal P-V data to the shock velocity-particle velocity plane revealed a deviation from linearity at low up, a cusp associated with the phase transition at high up, and general agreement with the wealth of unreacted Hugoniot data on TNT.

Topological pressure-temperature state diagram of the crystalline dimorphism of 2,4,6-trinitrotoluene

“…9, the monoclinic form would only become stable above -17.2 ´298 + 5690 = 564 MPa. This would in principle still be in contradiction with the observation of Stevens et al [4] of the formation of the orthorhombic polymorph at or below a pressure of 34 GPa,; however, because the observation was carried out under atmospheric pressure, the pressure range from 564 to 0 MPa, would leave the system with a considerable pressure window to crystallize in the orthorhombic system either from the amorphous state or even from the monoclinic form damaged by the pressure.…”

“…Another observation, which may be deceptive, is the paper by Stevens et al on the behavior of TNT under pressure [4]. It is shown in the paper that when TNT is subjected to pressures above 23 GPa and in particular up to 35 GPa, it has turned into the orthorhombic form on returning to zero pressure [4].…”

“…According to Vrcelj et al in 2003, the orthorhombic form is metastable and converts to the stable monoclinic form [1,2]. Bowden et al added to this in 2014: "the orthorhombic phase is metastable at ambient pressure/temperature and was observed at high pressure" [3], while referring to Stevens et al, who in fact had mentioned: "the high pressure-temperature(P-T) stability of TNT has not been investigated in detail" [4].…”

Chemical stability of molten 2,4,6-trinitrotoluene at high pressure

“…5,6 Previously, we described the room temperature isotherm and compressibility of monoclinic TNT, and observed a solid-solid phase transition near 23 GPa, which was irreversible upon decompression. 7,8 There has also been limited experimental evidence of an ambient-pressure phase transition at 337-338 K marked by dilatometric expansion, 9 and subtle pressure-induced changes to vibrational spectra at $2 GPa and 298 K suggested structural modifications to the parent monoclinic phase. 10 The chemical stability of molten TNT at ambient pressure has been studied previously by Brill and James 11 and Beckman et al 12 TNT's low T M arises from its weak intermolecular interactions, and low crystal symmetries.…”

Material Point Method Simulation of the Equation of State of Polymer-Bonded Explosive under Impact Loading at Mesoscale

“…The determination of an EOS for a PBX is typically based on experimental studies, although the constitutive models of each component have also been studied by computational approaches. To obtain an EOS for an unreacted high explosive, various attempts have been reported involving static compression experiments [3][4][5][6], where the experimental data under static high pressure and room temperature conditions were derived from X-ray diffraction measurements. Analyses of isotherms from an empirical EOS allow for the determination of the isothermal bulk modulus (K 0 ) and its pressure derivative (K 0 ) for PBXs.…”