Characterization Of Energetic Materials Research Articles

Evaluation of a CL‐20/TATB Energetic Co‐crystal

AbstractExploration of novel energetic‐energetic co‐crystals has greatly increased in recent years as the need for energetic materials with improved detonation performance and reduced sensitivity continues to grow. In 2015 a CL‐20/TATB co‐crystal was reported and touted sensitivity and detonation properties that would make it a potential replacement for the industry standard HMX. The confirmation, reproducibility, and characterization of energetic materials are still a widely debated topic especially when the material of interest has exceptional properties. In this work, CL‐20/TATB co‐crystals are attempted via solvent‐nonsolvent (S/NS) cocrystallization to assess the formation of a true co‐crystal. The prepared crystals were characterized via scanning electron microscopy (SEM), powder x‐ray diffraction (PXRD), fourier transform infrared spectroscopy (FTIR), raman spectroscopy, thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). This work reproduced S/NS cocrystallization similar to that reported in 2015, provides a solubility and thermodynamic explanation behind CL‐20/TATB cocrystallization, and assesses the future viability of CL‐20/TATB crystals.

Study on the compatibility of azo-tetrazolate high-energy materials using DSC

Compatibility is the ability of materials to resist chemical changes when they interact with other materials. Both the compatibility and interaction between energetic materials or between energetic and non-energetic materials are of great importance. Differential scanning calorimetry was performed to investigate the compatibility and the interaction between the energetic materials. The thermal characterization of energetic materials is important to indicate their stability as propellants, revealing necessary information regarding their thermal decomposition mechanisms during combustion and storage. The energetic materials include guanidinium azo-tetrazolate (GAT), aminoguanidinium azo-tetrazolate (AGAT), aminoguanidinium azo-tetrazolate monohydrate (AGATH), diaminoguanidinium azo-tetrazolate (DAGAT), triaminoguanidinium azo-tetrazolate (TAGAT), and ammonium azo-tetrazolate (AZT). Azo-tetrazolate salts and their derivatives were synthesized and fully characterized by multinuclear spectroscopy and Fourier transform infrared spectroscopy. The results present good compatibility between GAT–AGATH, GAT–DAGAT, GAT–TAGAT, GAT–AZT, AGAT–DAGAT, and DAGAT–TAGAT. The decomposition of AGATH and DAGAT was increased by adding GAT and TAGAT, respectively. There were poor compatibility between GAT and AGAT and fair compatibility between AGAT and TAGAT, and the mixtures of AGAT–AZT, DAGAT–AZT, and TAGAT–AZT might be hazardous. Adding any other energetic material to GAT accelerates the decomposition temperature of GAT, which may be useful in some applications.

Thermogravimetric analysis, kinetic study, and pyrolysis\u2013GC/MS analysis of 1,1\u02b9-azobis-1,2,3-triazole and 4,4\u02b9-azobis-1,2,4-triazole

BackgroundIn general, the greater the number of directly linked nitrogen atoms in a molecule, the better its energetic performance, while the stability will be accordingly lower. But 1,1ʹ-azobis-1,2,3-triazole (1) and 4,4ʹ-azobis-1,2,4-triazole (2) show remarkable properties, such as high enthalpies of formation, high melting points, and relatively high stabilities. In order to rationalize this unexpected behavior of the two compounds, it is necessary to study their thermal decompositions and pyrolyses. Although a great deal of research has been focused on the synthesis and characterization of energetic materials with 1 and 2 as the backbone, a complete report on their fundamental thermodynamic parameters and thermal decomposition properties has not been published.MethodsThermogravimetric–differential scanning calorimetry were used to obtain the thermal decomposition data of the title compounds. Kissinger and Ozawa–Doyle methods, the two selected non-isothermal methods, are presented for analysis of the solid-state kinetic data. Pyrolysis–gas chromatography/mass spectrometry was used to study the pyrolysis process of the title compounds.ResultsThe DSC curves show that the thermal decompositions of 1 and 2 are at different heating rates involved a single exothermic process. The TG curves provide insight into the total weight losses from the compounds associated with this process. At different pyrolysis temperatures, the compositions and types of the pyrolysis products differ greatly and the pyrolysis reaction at 500 °C is more thorough than 400 °C.ConclusionsApparent activation energies (E) and pre-exponential factors (lnA/s−1) are 291.4 kJ mol−1 and 75.53 for 1; 396.2 kJ mol−1 and 80.98 for 2 (Kissinger). The values of E are 284.5 kJ mol−1 for 1 and 386.1 kJ mol−1 for 2 (Ozawa–Doyle). The critical temperature of thermal explosion (Tb) is evaluated as 187.01 °C for 1 and 282.78 °C for 2. The title compounds were broken into small fragment ions under the pyrolysis conditions, which then might undergo a multitude of collisions and numerous other reactions, resulting in the formation of C2N2 (m/z 52), etc., before being analyzed by the GC/MS system.

New chemometrics in laser-induced breakdown spectroscopy for recognizing explosive residues

Detection of explosives in traces is an important area for preventing terrorist attacks and for anticipating their disastrous consequences. Laser-induced breakdown spectroscopy (LIBS) has been demonstrated to be an effective analytical technique for the detection and characterization of energetic materials. However, the major obstacle in the identification of explosives is their elevated spectral similarity with those compounds that share an analogous elemental composition. Despite that a number of different chemometric methods have been developed in the past for the detection of explosives, this hurdle remains latent today. Our recent efforts have been focused on the use of an alternative chemometric approach for improving the sensitivity and selectivity of LIBS for residue explosives identification. Through the survey of the spectral responses from the analysis of a variety of organic residues (either explosive or potential confusant materials) located on the surface of a support, relationships between the optical emission behaviors of residues and their corresponding hazardous nature have been extracted. By using the original intensities of the most relevant emission signals (C : CN : C2 : H : N : O) properly projected onto 2D subspaces, different machine learning classifiers have been designed and trained. This approach has been demonstrated to be capable for the identification of organic explosive residues against several potential confusant materials when they are placed on the surface of an aluminum support. False positive and false negative rates better than 5% are achieved. These results evidence a great stride in solving this particular problem, enabling the LIBS technology as a practical tool in complex applications related to homeland security.

The High‐Pressure Characterization of Energetic Materials: 2‐Methyl‐5‐Nitramino‐2H‐Tetrazole

AbstractThe isothermal structural properties, equation of state, and vibrational dynamics of 2MNT were studied under high‐pressure using synchrotron XRD and optical Raman and IR microspectroscopy. Analysis of the XRD patterns revealed no indication of a phase transition to near 15 GPa and the pressure‐volume isotherm remained smooth to 15 GPa. Near 15 GPa, significant sample damage was observed from the X‐ray beam which precluded the acquisition of patterns above this pressure. XRD and Raman spectroscopic measurements showed the monoclinic ambient condition phase of 2MNT remains the dominant phase to near 20 GPa, although a shift of the NO2 IR active vibrational modes to lower frequencies suggested a subtle geometry modification not reflected in the XRD data.

The High‐Pressure Characterization of Energetic Materials: 1‐Methyl‐5‐Nitramino‐1H‐Tetrazole

AbstractPressure–volume relations and optical Raman and Infrared spectra of polycrystalline 1MNT have been obtained under quasi‐hydrostatic conditions up to 16 and 40 GPa, respectively, by using diamond anvil cell, synchrotron‐based angle‐resolved X‐ray diffraction, and microspectroscopy. The X‐ray measurements show that the pressure–volume relations remain smooth up to 16 GPa at room temperature, while vibrational measurements show no evidence of a phase transition to near 40 GPa. Anomalous increases of several vibrational intensities and bandwidths suggest that subtle molecular distortions and structural modifications occur in the crystal as pressure increases. Decompression experiments indicate the structural modifications are reversible.

Test of a stand-off laser-induced breakdown spectroscopy sensor for the detection of explosive residues on solid surfaces

The detection and characterization of energetic materials at distances up to 45 m using stand-off laser induced breakdown spectroscopy (LIBS) has been demonstrated. A field-portable open-path LIB spectrometer working under a coaxial configuration was used. A preliminary study allowed choosing a single-pulse laser source over a double-pulse system as the most suitable source for the stand-off analysis of organic samples. The C2 Swan system, as well as the hydrogen, oxygen and nitrogen emission intensity ratios were the necessary parameters to identify the analyte as an organic explosive, organic non-explosive and non-organic samples. O/N intensity ratios of 2.9 and 2.16 with relative standard deviations of 4.03% and 8.36% were obtained for 2,4-dinitrotoluene and aluminium samples, respectively. A field test with known samples and a blind test were carried out at a distance of 30 m from the sample. Identification of energetic compounds in such conditions resulted in 19 correct results out of 21 samples.

Theoretical Chemical Characterization of Energetic Materials

AbstractOur research is focused on developing computational capabilities for the prediction of properties of energetic materials associated with performance and sensitivity. Additionally, we want to identify and characterize the dynamic processes that influence conversion of an energetic material to products upon initiation. We are attempting to achieve these goals through the use of standard atomistic simulation methods. In this paper various theoretical chemistry methods and applications to energetic materials will be described. Current capabilities in predicting structures, thermodynamic properties, and dynamic behavior of these materials will be demonstrated. These are presented to exemplify how information generated from atomistic simulations can be used in the design, development, and testing of new energetic materials. In addition to illustrating current capabilities, we will discuss limitations of the methodologies and needs for advancing the state of the art in this area.

Surface characterization of energetic materials using point-to-point contact FTIR-ATR

Surface characterization of energetic materials and their components has been a useful tool for resolving many research and quality control issues. An important application for gun propulsion is the understanding of plasma-propellant interactions (PPIs) in order to exploit plasma ignition, which offers the potential for rapid, controlled ignition of high-energy density charges. Toward this end, surface characterization using Fourier-transform infrared (FTIR) microscopy has been performed on propellants exposed to plasma in extinguished closed-bomb and open-air plasma experiments. These experiments are being performed to elucidate the properties of plasmas that enhance energy transfer and ignition, ultimately with the goal of designing an electrothermal-chemical (ETC) igniter-propellant charge for the next-generation weapon for the Future Combat System. However, analytical techniques capable of low detection limits for propellant degradation products are needed for characterizing the nature (e.g., radiation, convective heat transfer, hot particle flow, etc.) and distribution (in a packed bed or charge to ensure uniform and repeatable ignition) of plasma interaction with the propellant. Knowledge of such phenomena is valuable for validating simulations of plasma dynamics and optimizing igniter design. Reflectance spectroscopy has been used previously in our laboratory in closed-bomb studies to characterize the morphology and chemical composition of the grains from extinguished closed-bomb and open-air plasma experiments, but degradation products had proved difficult to detect. Recently, the same samples were reanalyzed using point-to-point contact attenuated total reflectance (PPC-ATR) in order to improve diagnostics for plasma-propellant interaction. Commercially available attachments have been designed to exert greater pressure on the sample for greater contact with the ATR crystal, improving sensitivity. With PPC-ATR, it was possible not only to detect but to identify the components of JA2 most likely associated with plasma degradation. Decomposition products were limited to less than a millimeter into the sample, involved secondary carbon denitration, and apparently did not migrate, strongly suggesting that plasma-propellant interaction involved denitration of nitrocelluose (NC). A chemical species with infrared absorption at /spl sim/1570 cm/sup -1/ is apparently specific to plasma ignition (i.e., not observed with conventional ignition) and could serve as a marker compound for the extent of plasma interaction in charges with ETC igniters.