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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]

Metal-based reactive composites are high energy-density materials that have potential uses as multifunctional energetics. However, when composed of micron size particles they can be difficult to ignite and have slow reaction rates. Recent work has shown that mechanically activated (MA) materials can have increased ignition sensitivity and reaction rate, yet the role of microstructure refinement (i.e., mechanical activation duration) in controlling combustion behavior is not well understood. In this work, the combustion velocities and flame temperatures were measured for equiatomic MA Ni/Al reactive powders produced using different milling durations in a two-step dry/wet milling process. For MA Ni/Al pellets pressed to 70% of the theoretical maximum density, it was shown that the combustion velocities increase as the milling time increases from ∼9.4 cm/s at 25% of the critical reaction milling time (t cr ) to ∼20 cm/s at a milling time of 97% t cr . For the cases considered, the average maximum flame temperatures were measured to be ∼1873 ± 30 K for samples milled for 25% t cr to 1786 ± 30 K at 97% t cr . It was also found that hydrocarbon contaminants are milled into the MA Ni/Al composite particles during the wet milling step and result in expansion of the pellets during combustion. Differential scanning calorimetry coupled with Fourier transform infrared spectroscopy showed that the release of hydrocarbon contaminants occurs at a temperature of ∼630 K. It was also shown that the concentration of hydrocarbon contamination decreased as the dry milling times increased, which suggests particle structure and mechanical property evolution during initial dry milling also affects contamination during subsequent wet milling. [ABSTRACT FROM AUTHOR]