New energetic materials (EMs) are the key to great advances in microscale energy-demanding systems as actuation part, igniter, propulsion unit, and power. Nanoscale EMs (nEMs) particularly offer the promise of much higher energy densities, faster rate of energy release, greater stability, and more security (sensitivity to unwanted initiation). nEMs could therefore give response to microenergetics challenges. This paper provides a comprehensive review of current research activities in nEMs for microenergetics application. While thermodynamic calculations of flame temperature and reaction enthalpies are tools to choose desirable EMs, they are not sufficient for the choice of good material for microscale application where thermal losses are very penalizing. A strategy to select nEM is therefore proposed based on an analysis of the material diffusivity and heat of reaction. Finally, after a description of the different nEMs synthesis approaches, some guidelines for future investigations are provided.

https://homepages.laas.fr/rossi/Publi/Nanoenergetics-Review-JMEMS-2.pdf

Nanoenergetic Materials for MEMS: A Review

Metal-based nanoenergetic materials: Synthesis, properties, and applications

Nano aluminum particles have received considerable attention in the combustion community; their physicochemical properties are quite favorable as compared with those of their micron-sized counterparts. The present work provides a comprehensive review of recent advances in the field of combustion of nano aluminum particles. The effect of the Knudsen number on heat and mass transfer properties of particles is first examined. Deficiencies of the currently available continuum models for combustion of nano aluminum particles are highlighted. Key physicochemical processes of particle combustion are identified and their respective time scales are compared to determine the combustion mechanisms for different particle sizes and pressures. Experimental data from several sources are gathered to elucidate the effect of the particle size on the flame temperature of aluminum particles. The flame structure and the combustion modes of aluminum particles are examined for wide ranges of pressures, particle sizes, and oxidizers. Key mechanisms that dictate the combustion behaviors are discussed. Measured burning times of nano aluminum particles are surveyed. The effects of the pressure, temperature, particle size, and type and concentration of the oxidizer on the burning time are discussed. A new correlation for the burning time of nano aluminum particles is established. Major outstanding issues to be addressed in the future work are identified.

https://www.yang.gatech.edu/publications/Journal/FGV%20(2015,%20Sundaram).pdf

Combustion of Nano Aluminum Particles (Review)

Review on synthesis and properties of high-energy-density liquid fuels: Hydrocarbons, nanofluids and energetic ionic liquids

Highly reactive metastable nano-scale composites of aluminum and metal oxides have been produced by arrested reactive milling (ARM), and their combustion performance has been preliminarily evaluated. Aluminum powder has been milled with powders of MoO3 and Fe2O3. The prepared composites are powders with particle sizes in the 1–100 μm range. Each individual particle comprises a fully dense, nano-scale mixture of the chemical reagents. These composites belong to a novel class of energetic materials characterized by an intimate mixing of reactive components on nanometer to atomic scale. Reactive components can be metal/metal oxide pairs or combinations of other materials capable of highly exothermic reactions such as B–Ti or B–Zr. High-energy milling of these components leads to mechanical initiation of the reaction. Highly reactive composites are obtained by arresting this process immediately before the initiation would occur if milling were allowed to proceed. An experimental parametric study of reactive milling in the Al–MoO3 and Al–Fe2O3 systems was conducted to establish at which milling times the reaction is spontaneously initiated under various conditions. Samples of nano-composite powders were synthesized by arresting the milling process, and characterized using electron microscopy, X-ray diffraction, and particle size analysis. Ignition temperatures of the materials were determined at heating rates in the range of 300–3000 K/s using an electrically heated filament. Activation energies of ignition were determined to be 152 ± 19 and 170 ± 25 kJ/mol for the Al-MoO3 and Al-Fe2O3 nano-composites, respectively. The activation energy obtained for the Al-Fe2O3 nano-composite is consistent with a previously reported value for the Al-Fe2O3 thermite reaction. Combustion tests were conducted in a constant volume pressure vessel in argon for both Al-Fe2O3 and Al-MoO3 and compared to respective blends of initial powders and to partially milled powders. The nano-composites showed higher respective reaction rates. Linear burning rates measured in an open channel of 2.5 × 2.5 mm cross-section were also higher for the ARM-prepared powders compared to partially milled materials.

Fully dense nano-composite energetic powders prepared by arrested reactive milling

Enhanced burn rate results are presented for ammonium perchlorate/Al nanoparticle strand burners at atmospheric (and higher) pressure and for the comparative combustion in a high pressure closed vessel of a solid propellant containing 15% of either conventional micrometer-scale Al or nanometric Al The burn rate at the smallest nanometric Al particle size appears to be asymptotically approaching an inverse particle-diameter-squared dependence

Enhanced Propellant Combustion with Nanoparticles

Nitroglycerin (NG) is commonly used as an ingredient in propellant formulations. In this study, a first automatically generated detailed kinetic model of this energetic material has been developed. The construction of this model was made possible by performing computations with the open source software package Reaction Mechanism Generator (RMG). To enable a faster convergence, significant intermediate species of NG decomposition and optimized operating conditions were indicated in the RMG input parameters. Thermochemical data related to significant decomposition species were derived from ab initio calculations at the DFT B3LYP/6-31 G(d,p) level of theory. To validate the RMG-built mechanism, simulations were performed with CHEMKIN-Pro. Computed species profiles from simulations were compared with flash pyrolysis measurements from the literature. Sensitivity analyses were performed on species mole fraction, and the most significant elementary reactions were identified. Some rate constant parameters were adjusted within the reaction rate uncertainty to improve the predictability of the model. Ignition delay times were computed for NG, and consistent trends were obtained when compared against to calculations for RDX and TNT using referenced model available in the literature. Although experimental data are scarce, this automated kinetic generation approach, applied to energetic materials, is to be highly promising. 

B. Baschung

Papers

Enhanced Propellant Combustion with Nanoparticles

Estimating ignition delay times of nitroglycerin: A chemical kinetic modeling study