Fluorine-based inorganic oxidizers for use in metal-based reactive materials

This work explores inorganic fluorides as oxidizers for fuel-rich reactive materials. A preliminary assessment of metal fluorides accounting for their enthalpy of formation points to bismuth (III) fluoride, BiF3 and cobalt (II) fluoride, CoF2 as oxidizers of interest. Initially, composite powders of aluminum with chosen fluorides at 50-50 wt. % are prepared by arrested reactive milling. Despite an increase in reactivity and lowtemperature ignition, the prepared composite powders are insensitive to initiation by electro-static discharge (ESD), making them attractive alternative to analogous thermites having very high ESD sensitivity. In air, the composite powder particles burn faster than reference aluminum particles of the same size. Very high combustion temperatures are observed suggesting gasification of a significant fraction of the fluorinated combustion products. However, in hydrogenated environments, fluorination of the fuel is hindered due to cannibalistic side-reaction between fluoride and water vapor; as a result the burn rates for composite particles are the same or even lower than for pure Al. Further, nickel (II) fluoride is considered as an oxidizer in more aluminum-rich compositions. Milling protocol is refined to achieve low ignition temperatures for the selected composition. Similar fast burn times and low ignition temperatures in air is achieved with only 30 wt. % of NiF2 suggesting it is possible to prepare even more fuelrich composites with attractive reactivities by further refining the mixing scale between fuel and oxidizer. The aerosol of aluminum-nickel fluoride composite burns with higher efficiency than spherical aluminum powder with comparable size distribution. Boron-based compositions with 50 wt. % of both fluoride oxidizers are similarly prepared and characterized. The nascent hydrated boron oxide layer is found to react with the fluoride and initiates low-temperature ignition. The composites burned in air faster than boron yielding gaseous reactive fluorinated products of interest to chemical and biological agent-defeat applications. The fluoride content is reduced to characterize the effect of composition to develop boron-replacement fuel. Additionally, solvent-based nanometric BiF3 coating is deposited on boron particle to homogenously disperse smaller quantity of fluoride. It is observed that only 10 wt. % of fluoride is sufficient for both milled, and coated boron powders to ignite readily and burn much faster than boron in air. During combustion, the reduced metal, Bi, functions as a catalytic oxygen-shuttle accelerating the particle burn rate. Finally, silicon-based compositions with the same fluoride oxidizers are prepared and characterized. For all the three fuels, ignition is found to be driven by lowtemperature oxidation initiated by fluorination. The fluorination mechanism is based on multiple factors such as fluoride stability in air, fuel reactivity and alloying tendency between metal fuel and metal reduced from the fluoride. Fluoride decomposition-driven ignition is observed in boron and silicon-based composites for different fluorides. For composites of Al with CoF2 and NiF2, fluorination occurs through redox-reaction; for Al·BiF3, the reaction was driven by decomposition of BiF3. Directions of possible future work are outlined based on the results and properties of different inorganic fluorides

Development and analysis of aluminum-PTFE reactive composite material

The shortcomings of micron sized aluminum due to the oxide barrier and two phase loses pose a hindrance for its efficient use as a fuel. In this study a fluoropolymer; Teflon’s inclusion in micron sized -325 mesh aluminum is suggested as a replacement to aluminum. Aluminum Teflon based energetic material see great potential for use in pyrotechnics, propellants and even explosives. A composite with composition Al-PTFE (90-10 wt. %) is prepared through Cryomilling and is shown to be a better method of preparation as compared to room temperature milling. The prepared materials are studied to identify best conditions. The analysis methods include thermal studies both aerobic and anaerobic, Mass Spectrometry, XRD analysis and ESD experiments. The best materials are shown to retain the Teflon till higher temperatures as compared with other materials such as nano powder mixtures and milled composites of Al-PTFE, both of composition (70-30 wt. %). The milled material exhibits two exothermic peaks at 405.4°C and 540°C which correspond to the phenomena of fluorine’s interaction with the oxide to form aluminum fluoride and the phase transition into a more stable fluoride of aluminum respectively. The activation energy for these reactions are on the higher side at 145.8 and 266.4 kJ/mol. This study offers a better milling process to make more reactive composites of micron sized Al and granular Teflon (PTFE)

''Performance Analysis Under Double Sided Clipping and Real Time Implementation of DCO-GFDM in VLC Systems

In the context of visible light communications (VLC), DC biased optical generalized frequency division multiplexing (DCO-GFDM) is a recently emerged waveform relying on block based transmission and employs pulse shaping using a circularly rotating prototype filter. In this work, we analyze the bit error rate (BER) performance of DCO-GFDM under double sided clipping induced by front end light emitting diode (LED) transmitters. The effect of clipping on BER performance is studied under different biasing conditions for different prototype filters. Additionally, we experimentally verify the real time performance of DCO-GFDM using different pulses. Simulations are performed in MATLAB software and experiments are conducted in a Lab-view environment using hardware. Two independent universal software radio peripherals (USRP)s are utilized as transmitter and receiver boards. It is observed that the simulation results match well with the corresponding theoretical results. Meanwhile, the experimentally achieved results for error vector magnitude (EVM), the received constellations, and the received spectrum along with BER in different cases are presented for the validation of DCO-GFDM waveform and are compared with DCO orthogonal frequency division multiplexing (DCO-OFDM). © 1983-2012 IEEE

Fluorine-containing oxidizers for metal fuels in energetic formulations

Fluorine containing oxidizers, primarily polymers, are extensively used in pyrotechnic compositions. Fluorinated oxidizers are less explored for metalized propellants and explosives despite a potential advantage of substantial heat release combined with gaseous combustion products. This review summarizes different types of fluorinated oxidizers used in energetic formulations or of potential interest for such systems, including gases, polymers, and inorganic compounds. Types of energetic formulations employing metals and fluoropolymers are discussed in more detail, including methods used to prepare composites and resulting salient features of the obtained materials. Laboratory experiments characterizing such materials, in particular, electron microscopy and thermal analysis, are discussed, showing characteristic morphologies and reaction sequences observed in different metal-fluorinated oxidizer composites. Striking similarities are noted in reaction sequences for diverse compositions hinting at possible similarities in the respective reaction mechanisms. Experiments probing ignition and combustion of metal-fluorinated oxidizer composites in laboratory conditions are also reviewed, including impact, flash heating and shock ignition. Finally, some practical performance tests for energetic formulations are described following by a brief discussion of the reaction mechanisms expected to govern ignition and combustion in various metal-fluorinated oxidizer composites. The conclusions are combined with recommendation for future research in the area of reactive metal-fluorinated oxidizer composites. Keywords: Reactive materials, Composites, Redox reactions, Pyrotechnics, Propellants, Explosive

Preparation and Characterization of Silicon-Metal Fluoride Reactive Composites

Fuel-rich composite powders combining elemental Si with the metal fluoride oxidizers BiF3 and CoF2 were prepared by arrested reactive milling. Reactivity of the composite powders was assessed using thermoanalytical measurements in both inert (Ar) and oxidizing (Ar/O2) environments. Powders were ignited using an electrically heated filament; particle combustion experiments were performed in room air using a CO2 laser as an ignition source. Both composites showed accelerated oxidation of Si when heated in oxidizing environments and ignited readily using the heated filament. Elemental Si, used as a reference, did not exhibit appreciable oxidation when heated under the same conditions and could not be ignited using either a heated filament or laser. Lower-temperature Si fluoride formation and oxidation were observed for the composites with BiF3; respectively, the ignition temperature for these composite powders was also lower. Particle combustion experiments were successful with the Si/BiF3 composite. The statistical distribution of the measured particle burn times was correlated with the measured particle size distribution to establish the effect of particle sizes on their burn times. The measured burn times were close to those measured for similar composites with Al and B serving as fuels

Effect of boron content in B·BiF 3 and B·Bi composites on their ignition and combustion

Composite powders combining boron with BiF3 and Bi in different amounts were prepared by high energy milling. Thermal analysis in an argon-oxygen mixture showed significant oxidation starting about 200 K lower than for pure boron. Selective oxidation of metallic Bi at low temperatures was observed. Composites containing either Bi or BiF3 ignited more readily than pure boron when heated by a CO2 laser beam. The composites containing BiF3 ignited more readily than boron when in contact with a hot wire. Burn times of particles aerosolized in air and ignited using the CO2 laser were measured as durations of the recorded emission pulses produced by burning particles. Statistical distributions of the measured burn times were correlated with the respective powder's particle size distributions. Compared to elemental boron, burn times of all prepared composites were shorter, including those containing only 10 wt.% of BiF3 or ca. 8 wt.% of Bi, and for most composites combustion temperatures were higher

Boron-rich composite thermite powders with binary Bi2O3·CuO oxidizers

Mixed oxide powders of Bi2O3 and CuO were prepared by mechanical milling as well as calcination of mixed nitrates. Arrested reactive milling was used to prepare boron-rich thermite composite powders with a constant equivalence ratio using these mixed oxides as oxidizers. Thermal analysis showed lower reaction onset temperatures for exothermic reactions and a greater energy release for these binary oxidizer energetic composites compared to composites with the same equivalence ratio but using either Bi2O3 or CuO as the oxidizer. The greatest effect was observed for a mixed oxidizer with 25 wt % Bi2O3. Heated filament ignition tests showed that the ignition temperatures for all mixed oxidizer composites are higher than those measured for the composites with individual Bi2O3 but lower than those for the composites with individual CuO serving as oxidizers. A weak trend of increasing ignition temperatures as the CuO content of the binary oxidizer increases is noted. Correlations between thermal analysis and ignition experiments suggest the early oxidation onset as the reaction leads to ignition. Particle burn times as determined by laser-ignited single particle combustion tests are near 400 μs for 1 μm particles, less than for similarly sized pure boron, but with no discernible effect of oxidizer composition

IL-17 and IL-22 production in HIV+ individuals with latent and active tuberculosis

Abstract Background IL-17 and IL-22 cytokines play an important role in protective immune responses against Mycobacterium tuberculosis (Mtb) infection. Information on the production of these cytokines and the factors that regulate their production in the context of human immunodeficiency virus (HIV) and latent tuberculosis infection (LTBI) or active tuberculosis disease (ATB) is limited. In the current study, we compared the production of these two cytokines by PBMC of HIV-LTBI+ and HIV + LTBI+ individuals in response to Mtb antigens CFP-10 (culture filtrate protein) and ESAT-6 (Early Secretory Antigenic Target). We also determined the mechanisms involved in their production. Methods We cultured Peripheral Blood Mononuclear Cells (PBMCs) from HIV- individuals and HIV+ patients with latent tuberculosis and active disease with CFP-10 and ESAT-6. Production of IL-17, IL-22 and PD1 (Programmed Death 1), ICOS (Inducible T-cell Costimulator), IL-23R and FoxP3 (Forkhead box P3) expression on CD4+ T cells was measured. Results In response to Mtb antigens CFP-10 and ESAT-6, freshly isolated PBMCs from HIV+ LTBI+ and HIV+ active TB patients produced less IL-17 and IL-22 and more IL-10, expressed less IL-23R, and more PD1 and expanded to more FoxP3+ cells. Active TB infection in HIV+ individuals further inhibited antigen specific IL-17 and IL-22 production compared to those with LTBI. Neutralization of PD1 restored IL-23R expression, IL-17 and IL-22 levels and lowered IL-10 production and reduced expansion of FoxP3 T cells. Conclusions In the current study we found that increased PD1 expression in HIV + LTBI+ and HIV+ active TB patients inhibits IL-17, IL-22 production and IL-23R expression in response to Mtb antigens CFP-10 and ESAT-6