High Pressure–Temperature Phase Diagram of 1,1-Diamino-2,2-dinitroethylene (FOX-7)

Abstract

The pressure-temperature (P-T) phase diagram of 1,1-diamino-2,2-dinitroethylene (FOX-7) was determined by in situ synchrotron infrared radiation spectroscopy with the resistively heated diamond anvil cell (DAC) technique. The stability of high-P-T FOX-7 polymorphs is established from ambient pressure up to 10 GPa and temperatures until decomposition. The phase diagram indicates two near isobaric phase boundaries at ∼2 GPa (α → I) and ∼5 GPa (I → II) that persists from 25 °C until the onset of decomposition at ∼300 °C. In addition, the ambient pressure, high-temperature α → β phase transition (∼111 °C) lies along a steep boundary (∼100 °C/GPa) with a α-β-δ triple point at ∼1 GPa and 300 °C. A 0.9 GPa isobaric temperature ramping measurement indicates a limited stability range for the γ-phase between 0.5 and 0.9 GPa and 180 and 260 °C, terminating in a β-γ-δ triple point. With increasing pressure, the δ-phase exhibited a small negative dT/dP slope (up to ∼0.2 GPa) before turning over to a positive 70 °C/GPa slope, at higher pressures. The decomposition boundary (∼55 °C/GPa) was identified through the emergence of spectroscopic signatures of the characteristic decomposition products as well as trapped inclusions within the solid KBr pressure media.

A study of solvent selectivity on the crystal morphology of FOX-7 via a modified attachment energy model

“…Due to these attractive characteristics, many studies have been performed on its synthesis, 1,2 polymorphism, [3][4][5][6][7] thermal analysis, [8][9][10][11] and crystallization. Due to these attractive characteristics, many studies have been performed on its synthesis, 1,2 polymorphism, [3][4][5][6][7] thermal analysis, [8][9][10][11] and crystallization.…”

High‐Temperature Structural Transformations of 1,1‐Diamino‐2,2‐dinitroethene (FOX‐7)

“…In Step 3D SC and TG measurements were carried out during cooling of the sample from 499 Kt o3 23 K ( Figure 3). The exothermal process with DH = 4.5 Jg À1 and the rate maximum at 479 Kc orresponds to the transformation of ah igh-temperature polymorph (d-FOX-7,a ccording to [11]) into g-FOX-7 (according to our XRD and IR spectroscopic data).…”

“…Recent data indicate possiblee xistence of the fourth modification of this compound, d-FOX-7, which is stable above 453 Ku ntil the compound decomposes above 524 K [5,8,[11][12][13].I nt he cited papers, the conclusion on the existence of d-FOX-7 wasm ade based on IR spectroscopic data and on the enhancement of thermals tability of FOX-7 after heating at temperatures above 488 K. The heat effect of the g!d transformation was not reported since this process proceeds after the onset of thermal decomposition of FOX-7.…”

“…The pressure-temperature (P-T)p hase diagram of FOX-7 was determined basedo nt he data obtained by means of in situ synchrotron infrared radiations pectroscopya nd available literature values [11].A ccording to this diagram, at room temperature a-FOX-7 transforms in high-pressure modifications Ia nd II above 2and 4.5 GPa, respectively.The phased iagrams uggests the existence of two potential triple points at high P and T values: b + g + d and a + b + d.…”

“…At normal pressure the a-phase is stable below 373 K [ 1] and the stability range of the b-phase is 373-418 K [ 1,2]. The g-phase has been considered to exist from 435 Ku ntil rapid thermal decomposition at 504 K[ 2],b ut lateri tw as shown [1,3,4] that at ambient pressure the boundary between the areas of thermodynamics tability of b-a nd g-FOX-7 lies in the range of 418-423 K.High-temperature conversions of FOX-7, includingi ts thermal decomposition, have been investigated intensely [5][6][7][8][9][10].Recent data indicate possiblee xistence of the fourth modification of this compound, d-FOX-7, which is stable above 453 Ku ntil the compound decomposes above 524 K [5,8,[11][12][13].I nt he cited papers, the conclusion on the existence of d-FOX-7 wasm ade based on IR spectroscopic data and on the enhancement of thermals tability of FOX-7 after heating at temperatures above 488 K. The heat effect of the g!d transformation was not reported since this process proceeds after the onset of thermal decomposition of FOX-7.According to Refs. [8,9],d ecompositiono fF OX-7 in the temperature range 463-488Kis accompanied bym ass loss of 30-40 %a nd polymorphous transition of g-phase into hypothetical d-polymorph.The pressure-temperature (P-T)p hase diagram of FOX-7 was determined basedo nt he data obtained by means of in situ synchrotron infrared radiations pectroscopya nd available literature values [11].A ccording to this diagram, at room temperature a-FOX-7 transforms in high-pressure modifications Ia nd II above 2and 4.5 GPa, respectively.The phased iagrams uggests the existence of two potential triple points at high P and T values: b + g + d and a + b + d.[a] V.Abstract:S tucturalt ransformations of 1,1-diamino-2,2-dinitroethene( FOX-7) were investigated in the temperature range 298-513 Kbymeans of DSC,TG, isothermal calorimetry,P XRD, IR spectroscopy, and electron microscopy.T he data obtained confirmt he existenceo ft he high-temperature d-FOX-7 polymorph stable above 480 K. The heat effect of the g!d transformation is À 4.6 Jg À1 (À680 Jmol À1 ).…”