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

*† Metal-CO2 propulsion is less known than other Mars in-situ resource utilization (ISRU) technologies This concept, based on using Martian carbon dioxide as an oxidizer in jet or rocket engines, offers the advantage of no chemical processing for CO2 and thus requires less power consumption than ISRU alternatives In this paper, we review various aspects of metal-CO2 propulsion, such as combustion of magnesium and aluminum in CO2, engine types and characteristics, production of liquid CO2 and metal fuel on Mars, and potential missions Lunar and terrestrial applications are also discussed I Introduction N-SITU Resource Utilization (ISRU) is recognized as an enabling technology for exploration of Mars, which can significantly reduce the mass, cost, and risk of robotic and human missions The critical element in future missions is the large mass of propellant for a Mars ascent vehicle, while power and propellant to accommodate a long stay and mobility on Mars are also important Transportation of propellant from Earth to Mars requires tremendous increase in the initial mass of hardware in low Earth orbit (and hence mission cost) as compared to prior no-return missions Fortunately, Mars possesses resources that can be used for propellant production The Martian atmosphere consisting of 95% CO2 is the obvious and most promising in-situ resource I

Metal-CO2 Propulsion for Mars Missions : Current Status and Opportunities

Correlating ignition mechanisms of aluminum-based reactive materials with thermoanalytical measurements

Flame propagation behaviours in nano-metal dust explosions

This study investigates the heating and cooling of a shell−core structured Ni−Al functional particle through a molecular dynamics simulation. The functional nanoparitcle is constructed from their perfect crystal measuring 5.6 nm in diameter with a shell thickness of 0.5 nm. The simulation is carried out within a Nose−Hoover thermostat scheme of the NVT canonical ensemble and performed by an Embedded-Atom-Method (EAM) force field. The thermodynamic properties and structure evolution during continuous heating and cooling processes are investigated through the characterization of the gyration radius, radial distribution function (RDF), atom number distribution, mean-square-distance (MSD), and layered potential energy distribution. Some unique behaviors related to nanometer scale functional particles are identified that include two-way diffusion of aluminum and nickel atoms, enhanced melting of the aluminum core through the shell structure, glass phase formation for the fast cooling rate, and the Ll2 Ni3Al ph...

Molecular Dynamics Simulation of a Core−Shell Structured Metallic Nanoparticle

Ignition mechanism of nickel-coated aluminum particles

Combustion of titanium particles in air may potentially be used for the in situ synthesis of nanoscale TiO2 particles, which can photocatalytically degrade chemical and biological air pollutants. The knowledge of Ti particle reactions in O2-containing atmospheres is required to develop this method. In the present work, large (∼3 mm) single Ti particles were heated by a laser in O2/N2 and O2/Ar environments. High-speed digital video recording, thermocouple measurements and quenching at different stages of the process were used for diagnostics. Analysis of the obtained temperature-time curves and quenched particles does not show a significant influence of nitrogen on the oxidation of solid Ti. In all experiments, noticeable surface oxidation started at temperatures between ∼850 and ∼950 °C, leading to a sharp temperature rise at ∼1400 °C. During prolonged heating at the Ti melting point (1670 °C), a liquid TiO2 bead formed and, after an induction period, ejected fragments. It was shown that this phenomenon may result from an excess of oxygen in the liquid bead. Fragment ejection in O2/N2 atmospheres was more intense than in O2/Ar, indicating that N2 accelerates the oxidation of liquid Ti.

On the Mechanisms of Titanium Particle Reactions in O2/N2 and O2/Ar Atmospheres

In aluminized solid propellants, the use of Al particles coated by certain transition metals may improve engine performance characteristics, owing to decreased agglomeration and lower ignition temperature of the particles. For this application, a detailed knowledge of particle ignition is required. Earlier, we reported the ignition mechanism of single ∼2.5-mm Ni-coated Al particles heated by a laser in Ar and CO 2 atmospheres. In the present work, using the same apparatus, we investigate the ignition mechanism of Fe-coated Al particles. The results show that intermetallic reactions contribute to the heating rate upon Al melting at 660°C, but the particles ignite at 1350-1500°C under normal-gravity conditions. The ignition mechanism includes the formation of a solid Fe 2 Al 5 phase at the interface between liquid Al and the coating, with subsequent melting of Fe 2 Al 5 , formation of a solid FeAl layer, and conversion of the Fe coating to a Fe-Al solid solution. Microgravity (10 -3 -10 -2 g) experiments with Fe-coated and Ni-coated Al particles were conducted to reduce convection inside the particles, which may influence phase mixing during ignition. In microgravity, both Ni-coated and Fe-coated Al particles ignited at 1250-1400°C. The significantly lower ignition temperature, compared with conventional oxide-coated Al, suggests that Fe-coated and Ni-coated Al particles are promising candidates for propulsion applications.

Ignition of Iron-Coated and Nickel-Coated Aluminum Particles Under Normal- and Reduced-Gravity Conditions

We report a compact microgravity flight apparatus for characterization of high-temperature chemical reactions in single particle systems. The apparatus employs an infrared CO2 laser to ignite 1–5mm samples while video images, thermocouple measurements, laser on/off status, and XYZ accelerometer signals are synchronously recorded. Different operating modes permit preignition quenching, ignition, and combustion experiments to be performed. The apparatus was successfully utilized during microgravity experiments on board NASA research aircraft.

Apparatus for studies of high-temperature chemical reactions in single particle systems

*† ‡ The use of coated Al particles in solid rocket prop ellants may improve engine performance characteristics. For this application, a detailed knowledge of single particle ignition and combustion is required. Our p rior study on ~2.5-mm Ni-coated Al particles revealed useful information on ignitio n mechanisms. In the current work, we use microgravity to further clarify the me chanisms and particularly understand the roles of buoyancy and diffusion in p hase mixing inside the droplet. The ignition of Fe-coated Al particles in normal an d reduced gravity is also examined, owing to the non-toxicity of Fe as compared to Ni. The results show that dramatic differences exist between the ignition of the Fe-Al and Ni-Al particle systems. Specifically, the atmosphere and gravity e nvironments influence the ignition of Fe-coated Al particles but do not affec t the ignition of Ni-coated Al particles. The revealed ignition mechanism for Fe-c oated Al particles includes formation of solid Fe 2Al 5 phase at the interface between liquid Al and coati ng, with subsequent melting of Fe 2Al 5, formation of solid FeAl, and conversion of the Fe coating to αFe.

Timothy A. Andrzejak

Papers

Ignition mechanism of nickel-coated aluminum particles

On the Mechanisms of Titanium Particle Reactions in O2/N2 and O2/Ar Atmospheres

Ignition of Iron-Coated and Nickel-Coated Aluminum Particles Under Normal- and Reduced-Gravity Conditions

Apparatus for studies of high-temperature chemical reactions in single particle systems

Ignition of Aluminum Particles Coated by Nickel or Iron: Studies under Normal and Reduced Gravity Conditions