This work presents the first application of isotopically labeled LLM-105 (2,6-diamino-3,5-dinitropyrazine-1oxide) to investigate thermal decomposition pathways. Specially synthesized LLM-105 isotopologues were utilized to isolate the influence of labeled 15NO2 nitro groups on the formation of lightgas products. Simultaneous differential scanning calorimetry, thermo-gravimetric, and mass spectrometry measurements were employed to track the evolution of product gases, enabling the direct comparison of isotopically shifted species with unlabeled LLM-105. Key findings show that C2N2 production is mainly dependent on nitrogen sources from either the amine groups or the pyrazine ring (i.e., not the nitro groups). The formation of NO, N2, and N2O all involves the nitro groups to some extent. NO (nitric oxide) was found to be the predominant gas species directly formed from the nitro group of LLM-105. In contrast, mixed nitrogen isotopologues of N2 and N2O (i.e., 14N15N and 15NNO) formed more readily in comparison to their pure counterparts (i.e., 15N2 and 15N2O). This indicates the amine and/or pyrazine groups of LLM-105, in addition to the nitro group, are involved in the decomposition pathways forming N2 and N2O. In addition, our investigation led to the discovery of two previously unreported decomposition products (CHO and HNCO), which were confirmed through hydrogen labelling utilizing deuterium isotopes. These results provide detailed speciation trends of gaseous products during LLM-105 decomposition, offering new insights into reaction pathways. Experimental data reported here will support the development of a detailed chemical kinetics model for LLM-105, essential for the safe handling of high explosives. Novelty and significance statement: Revealing the thermal decomposition pathways of energetic molecules such as LLM-105 is a significant challenge, primarily because these molecules contain various functional groups that participate in complex chemical reactions. While previous research has identified most of the decomposition products of LLM-105, there remains a gap in the mechanistic understanding of its breakdown pathways. In this study, we utilized three distinct isotopologues of LLM-105 for the first time, allowing us to directly trace the contributions of specific functional groups to the formation of decomposition products. This approach enabled us to assign the generation of each product species (e.g., NO, N2, N2O, NO2, and C2N2) to individual functional groups (e.g., -NO2, -NH2, and pyrazine N). Furthermore, our investigation led to the discovery of two previously unreported decomposition products, CHO and HNCO, which expand the known decomposition profile of LLM-105 and enhance our understanding of its thermal behavior

Various small-scale experiments were performed to provide data for developing a model to predict the thermal response of LLM-105 over a wide range of conditions. The thermal decomposition of LLM-105 was studied as a function of sample mass, confinement of volatile products, and preheating time in both isothermal and ramped heating experiments. The thermal decomposition of LLM-105 is a two-step process, as shown by the two exothermic peaks in the heat flow profiles, which were fitted to two nth-order autocatalytic reaction models with a similar activation energy of similar to 289 kJ/mol. The magnitude and shape of these peaks varied with sample mass and confinement. Increasing sample mass enhanced the second exotherm with respect to the first one, while increasing the level of confinement promoted a transition from a sublimation-dominated regime towards thermal decomposition. The effect of LLM-105 particle size on the rate of weight loss was evident for open-pan experiments, where bigger particles sublimed at lower temperatures than smaller particles. Thermal response and solid residue composition of LLM-105 samples were analyzed following preheating for different durations. Longer preheating times caused a shift of the second exotherm to lower temperatures and a decrease in the reaction enthalpy, confirming that LLM-105 decay is a consecutive reaction mechanism, probably autocatalytic. The kinetic model derived from ramped experiments was validated against the measured LLM-105 fraction remaining and the enthalpy remaining of the solid residue as a function of preheating times and showed good agreement.

LLM-105 (2,6-diamino-3,5-dinitropyrazine-1-oxide) has been prepared at several different size quantities (similar to 10-70 Kg) and not subjected to further purification, such as recrystallization. Chemical and physical properties were compared-small-scale safety testing (impact, friction, ESD), thermal (chemical reactivity, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), one-dimensional time-to-explosion (ODTX)), morphological (particle-size distribution (PSD), scanning electron microscopy (SEM), powder x-ray diffraction (PXRD), skeletal density). Each preparation had similar properties to the other preparations except for PSD and PXRD. For PSD, all preparations exhibited a mono-modal distribution with a variation in median values from similar to 40 mu m to over 80 mu m. All PXRD values indicated the same morphology with minor variations in crystal orientations. Possible polymorphism was also observed in a few cases. SEM images and PXRD indicate all preparations to be diamond-type and X-type crystals with some twinning. Impact, friction, and ESD and thermal sensitivities values are consistent with these type of crystal habits as seen in vast literature studies.

In this paper we present measurements and analysis on the mechanical and thermomechanical properties of the LLM-105 based plastic bonded high explosive RX-55-DQ. Specifically we present uni-axial compression, and thermal measurements (CTE and ratchet growth), and for some of the measurements we provide a comparison to measurements on TATB-based PBX 9502. We also present the same mechanical property measurements performed on RX-55-DQ samples that underwent accelerated aging.

Over the past two decades, the diversity of metal and metalloid oxide materials prepared using sol–gel techniques has increased significantly. This transformation can be attributed in part to the development of the technique known as epoxide-assisted gelation. The process utilizes organic epoxides as co-reactants for the sol–gel polymerization of simple inorganic metal salts in aqueous or alcoholic media. In this approach, the epoxide acts as a proton scavenger, which drives hydrolysis and condensation of hydrated metal species in the sol–gel reaction. This process is generalizable and applicable to the synthesis of a wide range of metal and metalloid oxide aerogels, xerogels, and nanocomposites. In addition, modification of synthetic parameters allows for control over the structure and properties of the sol–gel product. The method is particularly amenable to the synthesis of multicomponent and nanocomposite sol–gel systems with intimately mixed nanostructures. This chapter describes both the reaction mechanisms associated with epoxide-assisted gelation and an overview of materials that have been prepared using this technique.

In the last 20 years, there have been a significant number of investigations of the application of aerogels and sol–gel-derived materials and methods to the field of energetic materials (e.g., explosives, propellants, thermites, and pyrotechnics) specifically through the synthesis and characterization of nanostructured energetic composites. Aerogels have unique density, composition, porosity, and particle sizes as well as low temperature and benign chemical synthetic methods all of which make them attractive for energetic nanomaterials candidates. The application of these materials and methods to this technology area has resulted in three general types of sol–gel energetic materials: (1) sol–gel inorganic oxidizer/metal fuel thermite-like composites; (2) sol–gel-derived porous pyrophoric metal powders, films, and monoliths; and (3) sol–gel metal or organic fuel/inorganic oxidizer nanocomposites (propellant, explosive, thermite, and pyrotechnic composites). This chapter summarizes results from synthesis and characterization research in all three areas. General trends are detailed, analyzed, and discussed. In general, all sol–gel nanostructured energetic material behaviors are highly dependent on several factors including the nanomorphology of the network, its surface area, the degree of mixing and contact area between phases, the type of mixing (sol–gel, physical mixing, interpenetration), solids loading, and the presence of impurities. Sol–gel methods are attractive to the area of nanostructured energetics because they offer a great deal of many processing options such as monoliths, powders, and films and have broad compositional versatility. These attributes coupled with strong synthetic control of the microstructural properties of the sol–gel matrix enable the preparation of energetic nanocomposites with tunable performance characteristics. Various aspects of the present literature work are reviewed and future challenges for this technological area are presented and discussed.

1H nuclear magnetic resonance (NMR) experiments were performed on the proposed insensitive high-explosive 2,6-diamino-3,5-dinitropyrazine-1-oxide (LLM-105) at high-speed magic-angle spinning rates of up to 60 kHz. These rapid speeds produce well-resolved spectra that aid in the study of the chemical and structural properties of this material. Extraordinarily long 1H T1 values were observed for the main amine peaks from the LLM-105 explosive and can be used to differentiate between peaks from the main compound and those of impurities. Further, advanced NMR measurements and simulations reveal unique spectral properties due to the strong network of intramolecular and intermolecular hydrogen bonding and provide insights in the structure of LLM-105.

The mixing of materials during additive manufacturing is a major benefit which allows one to compositionally and spatially tailor material properties, for example to locally control the reactivity in fuel – oxidizer systems known as thermites. This work characterizes an active mixing printhead used in conjunction with a 3D printing process known as Direct Ink Writing. Besides compositional control, a major benefit of this approach is that it offers a safe method for working with these materials, which can otherwise be hazardous once mixed. Custom fuel and oxidizer inks are fed at fixed volumetric rates into an active mixing printhead, and both the rotational speed of the mixing impeller as well as the fuel – oxidizer ratio are varied. Upon ignition, the propagation speed increases with the rotational speed of the mixer and plateaus above a critical value of ≈750 rpm. The critical mixing speed is corroborated by computational fluid simulations and an analytical expression that considers the inks’ complex fluid behavior. Additionally, varying the composition results in a wide range of propagation speeds with peak reactivity corresponding to a fuel‐rich formulation ( ϕ = 1.5). A test article incorporating a fast‐ and slow‐burning region demonstrates how spatial composition can manipulate the reactivity.

The objective of this numerical study is to demonstrate how the shock sensitivity of TATB-based explosives can be altered with the addition of sub-millimeter features. Such simulation-based studies are important because structure-property relationships are not well established for reacting energetic materials. For this study, we use LX-17 (92.5% wt TATB, 7.5% wt Kel-F 800) as the prototypical insensitive TATB-based explosive. Simulations are performed in the multi-physics hydrocode, ALE3D. The Lee-Tarver Ignition and Growth reactive flow model is used to simulate the shock initiation response of the explosives. Our metric for shock sensitivity in this study is run distance to detonation as a function of applied pressure. In the first part of our study, we examine changes to shock sensitivity of one dimensional TATB-HMX laminates where a thin HMX explosive layer has been inserted into the TATB explosive bulk. We investigate HMX layer thickness, HMX volume fraction, as well as uniform and non-uniform HMX layer spacing. Uniformly spaced TATB-HMX laminate calculations show increased shock sensitivity with higher HMX volume fraction. As HMX layer thickness decreases, the overall laminate shock initiation response becomes more TATB-like. Calculations demonstrate differences in shock sensitivity with the forward graded and reverse graded structures. In the second part of the study, we examine changes to shock sensitivity when tungsten chevron features are embedded in the TATB. The high shock impedance tungsten coupled to the unique chevron shape effectively amplifies the incoming shock in the TATB. High impedance tungsten is capable of amplifying the shock in TATB by nearly 2.5 times the input pressure without consideration of chevron shape. The addition of the chevron feature has a focusing effect that is directional in nature. This can accelerate the transition to detonation. Reactive calculations show the shock sensitivity increasing for all chevron geometries considered.

Additive manufacturing (AM) has recently shown great promise as a means to tailor a wide range of material properties, both quasi-static and dynamic. An example of controlling the dynamic behavior is to tailor the chemical energy release rate in composite energetic materials such as thermites - which are a subset of pyrotechnics that use a metal fuel and a metal oxide as an oxidizer. Since these materials are most hazardous once finely mixed, the approach taken here is to formulate the fuel and oxidizer separately such that they can be mixed on-the-fly. Herein, the development, formulation, and characterization of two respective aqueous 3D printable inks consisting of Al and CuO are discussed. The rheological properties and ability of the material to span gaps are characterized. To demonstrate that the materials could be mixed and sustain a reaction, the inks are fed into a static mixing nozzle and extruded into a high-aspect ratio test strip. Upon drying, the material can be ignited and sustain a propagation through the part. These results present a facile, and safe, way to AM thermite which can be used for more detailed follow on studies looking at the role of architecture on the reactivity.

Metal powders are commonly added to explosive formulations to modify the blast behavior. Although detonation velocity is typically reduced compared to the neat explosive, the metal provides other benefits. Aluminum is a common additive to increase the overall energy output and high-density metals can be useful for enhancing momentum transfer to a target. Typically, metal powder is homogeneously distributed throughout the material; in this study, controlled distributions of metal powder in explosive formulations were investigated. The powder structures were printed using powder bed printing and the porous structures were filled with explosives to create bulk explosive composites. In all cases, the overall ratio between metal and explosive was maintained, but the powder distribution was varied. Samples utilizing uniform distributions to represent typical materials, discrete pockets of metal powder, and controlled, graded powder distributions were created. Detonation experiments were performed to evaluate the influence of metal powder design on the output pressure/time and the overall impulse.

Synthesis of chlorine-free, rare earth oxide aerogels from the lanthanide series was achieved using a modified epoxide-assisted sol-gel method. An ethanolic solution of the hydrated metal nitrate, propylene oxide, and ammonium carbonate was found to gel upon heating to 333 K. Critical point drying of the wet gel in CO 2 yielded monolithic aerogels. Most of the aerogels were amorphous as-prepared, but became nano-crystalline after calcination at 923 K in air. The aerogels had high surface areas (up to 150 m 2 /g), low densities (40–225 mg/cm 3 ), and were photoluminescent.

A description of the various approaches to the synthesis of the insensitive energetic compound, 2,6-dia-mino-3,5-dinitropyrazine-1-oxide (LLM-105), developed at LLNL over the past 20 years will be described.

The compounds 1,1′,2,2′- and 1,1′,3,3′-tetra-t-butylferrocene (1,2-BUT and 1,3-BUT, respectively) were oxidized with AgReO4 in dichloromethane and the ferrocenium(1+) salts were isolated, after recrystallization from acetone, as dark-blue or dark-green crystals of [1,2-BUT+][ReO4−] and [1,3-BUT+][ReO4−]·acetone, respectively, which were suitable for X-ray diffraction. As expected from the known structures of the neutral ferrocenes, the di-t-butylcyclopentadienyl (Cp′) rings are virtually parallel in the 1,2-BUT+ cation and are tilted by 11.6° in the 1,3-BUT+ cation. The FeC distances in both cations span a greater range and are, on average, longer than in the corresponding neutral ferrocenes. UV–Vis spectra revealed that λmax for yellow 1,2-BUT (442nm) is lower than for orange 1,3-BUT (466nm) and that λmax for blue 1,2-BUT+ (674nm) is lower than for green 1,3-BUT+ (682nm). In addition, E1/2(+/0) values determined by cyclic voltammetry in dichloromethane, reported here for the first time, show that 1,3-BUT (−0.24V versus Fe(Cp)2+/0) is 50mV easier to oxidize than 1,2-BUT (−0.19V versus Fe(Cp)2+/0). A comparison of the structure of [1,2-BUT+][ReO4−] with that of the literature compound [1,3-DEC+][ReO4−] shows that the shortest Fe⋯Re distances in the two salts are ca. 5.8Å, indicating that the effective ion-pairing radii of the two cations are essentially the same in spite of the much greater overall size of the 1,3-DEC+ cation (1,3-DEC+=1,1′,3,3′-tetra(2-methyl-2-nonyl)ferrocenium(1+)). This surprising result is significant as far as differences in anion-extraction equilibria reported previously.