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Nitrocellulose (NC) has been used since the late 1800ʹs in numerous energetic formulations; however, the effect of processing agents (solvents, etc.) on performance has not been thoroughly detailed. For illuminate applications, this is critical as spectral purity and dominant wavelength must meet specifications. In this effort, six processing agents (water, ethanol (EtOH), isopropyl alcohol (IPA), ethyl acetate (EtAc), acetone, and tetrahydrofuran (THF)) are evaluated and the effect they have on the NC fibers and subsequent performance is detailed. XRD and FTIR analysis indicates that the choice of processing agent directly affects the molecular integrity of the NC fibers due to the inhibition of NO2 bonds as well as freeing of hydrogen bonds between polymer chains during solubilization. Time-step FTIR analysis indicated that the weak nitrate ester bond (RCH2-ONO2) is targeted when processed in tetrahydrofuran, ethyl acetate, or acetone, and if heavy solvent interaction occurs, can lead to the autocatalytic decomposition of NC, when heat treated at 110°C. Spectral performance is detrimentally impacted as a result of such interactions. While all six processing agents for red-light illuminant formulations met the military requirements (i.e., spectral purity and wavelength), only ethanol and isopropyl alcohol processed formulations met the military required wavelength of 540 ± 20 nm for green-light illuminants. The IPA processed formulations exhibited the best results with spectral purity values of 69.0% and 94.8% for green and red-light illuminants, respectively. [ABSTRACT FROM AUTHOR]

Flexoelectricity is often studied at the macroscopic scale for energy conversion and harvesting. The fact that microstructural heterogeneities can have a profound impact on a material's flexoelectric response has been under-appreciated and largely unexplored. To capture the effects of microstructure on both the macroscopic flexoelectric behavior and the development of microscopic electric field that drives such microscale processes, we develop a computational framework that enables the quantification of how the microstructure can influence the flexoelectric behavior of heterogeneous materials. The specific material evaluated is a porous composite of tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride polymer and aluminum (Al) particles. The models explicitly resolve the Al particles and voids within the microstructure. The focus of the analysis is on assessing the physical mechanisms that enhance the macroscopic flexoelectric output and determining the effective flexoelectric coefficient of the inhomogeneous material. The approach also allows the contributions of individual strain gradient components to the effective flexoelectric coefficient to be delineated and offers a method of determining the flexoelectric coefficients associated with individual strain gradient components using measurements of the macroscopic flexoelectric responses of microstructures with different concentrations of Al particles and voids. It is concluded that the enhancement of local strain gradients near the Al particles and voids and the activation of contributions from multiple strain gradient components are the primary mechanisms for the increase in the macroscopic flexoelectric output of the composites. The macroscopic flexoelectric coefficient under cantilever beam bending is found to rise linearly with the Al content, consistent with the experimental measurements. [ABSTRACT FROM AUTHOR]

Fluoropolymers have weak electroactive properties but are often paired with other materials (inclusions) to form a composite with enhanced electroactive properties and when those inclusions are a metal or metalloid fuel (e.g., Al, Si, B) they can then function as electroactive reactive materials. There is strong interest in understanding the electromechanical (piezo, flexo, dielectric) properties toward the development of multifunctional energetics. Specifically, in this effort, we report the influence of magnesium diboride (MgB2) on the electroactive and combustion properties in a composite system with the fluoropolymer tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride (THV). The dielectric, flexoelectric, piezoelectric, burning rate, and heat of reaction are investigated for composites with 50–70 wt. % MgB2 loading. It is observed that with an increase in solids loading that the dielectric, flexoelectric, and burning rate increase. For example, at 70 wt. % MgB2, the measured dielectric constant was 298 ± 10, and the flexoelectric coefficient was 16.6 ± 1.2 nC/m. Unexpectedly, a true piezoelectric coefficient (d33) was measured between 11.4 ± 0.2 and 13.0 ± 0.3 pC/N at these solids loadings. Due to the mechanical properties of these composite systems, an apparent piezoelectric coefficient of 108 pC/N was calculated indicating that these reactive materials are highly electroactive. The multifunctional properties are demonstrated by applying the force of the human body (via jumping) to a THV/MgB2 (50 wt. %) film. A peak voltage of 0.75 V was observed. This work indicates that a variety of reactive materials may offer multifunctional capabilities. [ABSTRACT FROM AUTHOR]

Reactive Ni−Al materials have been developed using a variety of methods, with high energy ball milling (HEBM) being one of the most common means for tailoring reaction behavior. Powder production limitations associated with HEBM, including the addition of process control agents, have inspired the exploration of an alternate manufacturing technique: acoustic dry milling with the Resodyn Laboratory Resonant Acoustic Mixer (LabRAM). The influence of acoustic milling time, intensity, and media size with respect to microstructure and reactive behavior of Ni−Al powders were evaluated in this work. After just 20 min of milling, a reactive composite Ni−Al microstructure was produced. Milling intensity and media size were directly proportional to the formation of more homogeneous composite powders. The reaction onset temperature was decreased to 446 °C, or ≈200 °C lower than that of unprocessed material. The method shows promise for the production of reactive powder for a host of applications. [ABSTRACT FROM AUTHOR]

The combustion of mixed homogeneous pyrotechnic compositions and heterogeneous charges is studied experimentally with the aim of producing a selectable wavelength signal flare. The heterogeneous charge was perceived as a mixed color by a distant observer. A model for color chromaticity coordinates of homogeneous mixtures was derived that includes the mass, mass‐based burn rate and luminous intensity ratios of the constituting color compositions. This model can predict the expected dominant wavelength of a mixed composition. It can also handle the spacing of chromaticity coordinates of mixed compositions on a straight line in the CIE diagram between chromaticity coordinates of constituting colors. With two series of color composition mixtures, it was demonstrated that the chromaticity coordinates of the mixtures could be at, or slightly deviate, from the straight line connecting the chromaticity coordinates of the constituting compositions. It indicates there is little to no influence of flame temperature and mutual pyrotechnic reactions. [ABSTRACT FROM AUTHOR]

The difficulty synthesizing new co-crystals has made the development of efficient methods for screening co-formers a high priority. Co-crystals have been realized as a new generation of materials with tuneable solubility, stability, and performance. Energetic co-formers have exceptionally weak intermolecular interactions making selection of co-crystallization method and parameters critical to forming a true co-crystal. COSMO-RS calculations coupled with the COSMOtherm software suite were used to screen common solvents and co-formers for CL-20. The predicted favorable solvates and co-crystal formers were compared to experimentally confirmed solvates and co-crystals to assess the accuracy of the COSMO method for CL-20-based materials. It was found that screening solvents using excess enthalpy and solvent cavity volume were able to predict experimentally confirmed CL-20 solvates. Co-crystal formation was difficult to predict using the COSMO method, highlighting the importance of entropy and solid-state interactions. The selection of good solvents is perhaps the best method for maximizing entropy. Understanding the dependence on entropy for energetic-energetic cocrystal formation coupled with an accurate method for screening co-crystal formation allows for intelligent design of co-crystallization methods. [ABSTRACT FROM AUTHOR]

The ever‐present threat of biological weapons has encouraged the development of novel pyrotechnic formulations that release gaseous iodine upon combustion, which acts as a potent active agent capable of countering bio‐agents (e. g. anthrax). These formulations typically contain a fuel (Al, B, Al/B4C) and an iodate serving as an oxidizer. However, the percentage of free iodine generated is relatively low and aging of these formulations remains an issue. In this work, the role of particle size on the combustion velocities, iodine output, and combustion products are detailed for a boron carbide/sodium periodate formulation. Formulations are studied with and without the addition of binder (protectant) and the role of particle size on achieving 3‐D printable energetics is detailed. It is found that altering the fuel particle size (boron carbide) had little effect on the combustion velocity and iodine recovery. However, by reducing the particle size of the oxidizer, NaIO4, drastic improvements in iodine recovery are achieved. A reduction in mean particle size from 215 to 3 μm resulted in a 47 % increase in observed iodine recovery for powder formulations. Combustion velocities appear to be unaffected and were 1.4–1.6 mm/s. An in‐depth discussion of the decomposition pathway of pure NaIO4 as well as when paired with a B4C fuel source is also discussed. [ABSTRACT FROM AUTHOR]

In this work, replacement of barium chromate (BaCrO4) in the traditional tungsten delay (W/BaCrO4/KClO4/Diatomaceous Earth (DE)) with strontium molybdate (SrMoO4) is explored both mechanistically and as an environmentally friendly alternative to currently fielded time delays. Delay performance and aging characteristics are examined at similar diameters (4.7 mm) to common delay housings. Measured maximum combustion temperatures ranged from 1507 K to 1628 K as a function of tungsten content. The measured combustion velocities ranged from 1.36 to 29.87 mm/s in 4.7 mm inner diameter aluminum housings for the alternative system. Activation energies were determined for both the traditional tungsten delay and the alternative formulation and ranged from 74.6 to 240.5 kJ/mol. The maximum measured gas production was 4.1 mL/g for all alternative formulations. Combustion products were characterized with powder X-ray diffraction and are relatively benign based upon known compound information and current regulations. Lastly, based on the data, general reaction mechanisms for pyrotechnic time delays are discussed toward design decisions of a good time delay. [ABSTRACT FROM AUTHOR]

The development of smart energetics is at the forefront of the research community. The desire is to have energetics that could have ON/OFF capability, tunable performance, and/or targeted energy delivery. Therefore, efforts have been focused on designing systems that respond to stimuli in a controlled manner. In this paper, nanoscale aluminum (nAl)/fluoropolymer reactive systems are studied and the piezoelectric nature of the fluoropolymers is used as a means to sensitize the system. Using a capacitor type setup, and drawing on our previous efforts, three fluoropolymer/nAl systems are studied and their sensitivities upon application of a DC voltage are quantified using BAM drop weight as the indicator. It is found, upon application of 1.0 kV, that for all three fluoropolymer/Al systems the sensitivity is greatly increased. For example, for the THV221/nAl system the impact energy required for ignition is reduced from 63 to 10 J. Further increasing the applied voltage is shown to further increase the sensitivity for all systems studied. The role of electroactive phase content and sensitization time is also discussed. [ABSTRACT FROM AUTHOR]

Engineering reactive materials is an ever present goal in the energetics community. The desire is to have energetics configured in such a manner that performance is tailored and energy delivery can be targeted. Additive manufacturing (3‐D printing) is one area that could significantly improve our capabilities in this area, if adequate formulations are developed. In this paper, fluoropolymer based reactive inks are developed with micron (mAl) and nanoscale aluminum (nAl) serving, as the fuel at high solids loading (up to 67 wt%) and their viscosity required for 3‐D printing is detailed. For the pen‐type technique and valves used in this work, it is required to have viscosities on the order of 104–105 cP. For printed traces with apparent diameters under <500 μm, the combustion velocities for both micron and nano scale aluminum formulations, are approximately identical: 30 ± 3 versus 32 ± 2 mm s−1, respectively. Further increasing the apparent diameter is shown to increase the combustion velocity in the case of the nanoscale aluminum formulation by four‐fold over that of the micron scale aluminum formulation, but it plateaus as it approaches an apparent diameter of 2 mm. The results suggest with proper architecture that tailorable combustion rates and energy delivery are feasible. [ABSTRACT FROM AUTHOR]