Nanoenergetic Materials Research Articles

Fabrication and Characterization in Composites of Nanoenergetic Materials and Porous Metal with UV Ink Method

The preparations of composites of porous metal and nanoenergetic materials were studied. Composites of porous metal (nickel, aluminum and magnesium) and nano-scale aluminum powder and CL-20 have been synthesized with UV (ultraviolet) ink method, respectively. The structure, morphology, infrared characteristic, thermal decomposition of composites were characterized by using Mercury Injection Apparatus, Scanning Electron Microscope, Fourier Transform Infrared Spectroscopy, and Differential Scanning Calorimeter. The results showed that nanoenergetic materials could deposit into pores of porous metal without collapsing after solidification. Constituents of the composites could coexist with each other without chemical changes. Thermal decomposition temperature was lower after the addition of nanoenergetic materials. System enthalpy increased significantly with the addition of CL-20 and reactive porous metal. The new composites have potential applications in the field of structural and energetic materials.

Fluid dynamic modeling of nano-thermite reactions

This paper presents a direct numerical method based on gas dynamic equations to predict pressure evolution during the discharge of nanoenergetic materials. The direct numerical method provides for modeling reflections of the shock waves from the reactor walls that generates pressure-time fluctuations. The results of gas pressure prediction are consistent with the experimental evidence and estimates based on the self-similar solution. Artificial viscosity provides sufficient smoothing of shock wave discontinuity for the numerical procedure. The direct numerical method is more computationally demanding and flexible than self-similar solution, in particular it allows study of a shock wave in its early stage of reaction and allows the investigation of “slower” reactions, which may produce weaker shock waves. Moreover, numerical results indicate that peak pressure is not very sensitive to initial density and reaction time, providing that all the material reacts well before the shock wave arrives at the end of the reactor.

Linking molecular level chemistry to macroscopic combustion behavior for nano-energetic materials with halogen containing oxides

Coupling molecular scale reaction kinetics with macroscopic combustion behavior is critical to understanding the influences of intermediate chemistry on energy propagation, yet bridging this multi-scale gap is challenging. This study integrates ab initio quantum chemical calculations and condensed phase density functional theory to elucidate factors contributing to experimentally measured high flame speeds (i.e., >900 m∕s) associated with halogen based energetic composites, such as aluminum (Al) and iodine pentoxide (I2O5). Experiments show a direct correlation between apparent activation energy and flame speed suggesting that flame speed is directly influenced by chemical kinetics. Toward this end, the first principle simulations resolve key exothermic surface and intermediate chemistries contributing toward the kinetics that promote high flame speeds. Linking molecular level exothermicity to macroscopic experimental investigations provides insight into the unique role of the alumina oxide shell passivating aluminum particles. In the case of Al reacting with I2O5, the alumina shell promotes exothermic surface chemistries that reduce activation energy and increase flame speed. This finding is in contrast to Al reaction with metal oxides that show the alumina shell does not participate exothermically in the reaction.

Ultra-rapid elimination of biofilms via the combustion of a nanoenergetic coating

BackgroundBiofilms occur on a wide variety of surfaces including metals, ceramics, glass etc. and often leads to accumulation of large number of various microorganisms on the surfaces. This biofilm growth is highly undesirable in most cases as biofilms can cause degradation of the instruments and its performance along with contamination of the samples being processed in those systems. The current “offline” biofilm removal methods are effective but labor intensive and generates waste streams that are toxic to be directly disposed. We present here a novel process that uses nano-energetic materials to eliminate biofilms in < 1 second. The process involves spray-coating a thin layer of nano-energetic material on top of the biofilm, allowing it to dry, and igniting the dried coating to incinerate the biofilm.ResultsThe nanoenergetic material is a mixture of aluminum (Al) nanoparticles dispersed in a THV-220A (fluoropolymer oxidizer) matrix. Upon ignition, the Al nanoparticles react with THV-220A exothermically, producing high temperatures (>2500 K) for an extremely brief period (~100 ms) that destroys the biofilm underneath. However, since the total amount of heat produced is low (~0.1 kJ/cm2), the underlying surface remains undamaged. Surfaces with biofilms of Pseudomonas aeruginosa initially harboring ~ 107 CFU of bacteria /cm2 displayed final counts of less than 5 CFU/cm2 after being subjected to our process. The byproducts of the process consist only of washable carbonaceous residue and gases, making this process potentially inexpensive due to low toxic-waste disposal costs.ConclusionsThis novel method of biofilm removal is currently in the early stage of development. However, it has potential to be used in offline biofilm elimination as a rapid, easy and environmentally friendly method.

Interfacial Chemistry in Al/CuO Reactive Nanomaterial and Its Role in Exothermic Reaction

Interface layers between reactive and energetic materials in nanolaminates or nanoenergetic materials are believed to play a crucial role in the properties of nanoenergetic systems. Typically, in the case of Metastable Interstitial Composite nanolaminates, the interface layer between the metal and oxide controls the onset reaction temperature, reaction kinetics, and stability at low temperature. So far, the formation of these interfacial layers is not well understood for lack of in situ characterization, leading to a poor control of important properties. We have combined in situ infrared spectroscopy and ex situ X-ray photoelectron spectroscopy, differential scanning calorimetry, and high resolution transmission electron microscopy, in conjunction with first-principles calculations to identify the stable configurations that can occur at the interface and determine the kinetic barriers for their formation. We find that (i) an interface layer formed during physical deposition of aluminum is composed of a mixture of Cu, O, and Al through Al penetration into CuO and constitutes a poor diffusion barrier (i.e., with spurious exothermic reactions at lower temperature), and in contrast, (ii) atomic layer deposition (ALD) of alumina layers using trimethylaluminum (TMA) produces a conformal coating that effectively prevents Al diffusion even for ultrathin layer thicknesses (∼0.5 nm), resulting in better stability at low temperature and reduced reactivity. Importantly, the initial reaction of TMA with CuO leads to the extraction of oxygen from CuO to form an amorphous interfacial layer that is an important component for superior protection properties of the interface and is responsible for the high system stability. Thus, while Al e-beam evaporation and ALD growth of an alumina layer on CuO both lead to CuO reduction, the mechanism for oxygen removal is different, directly affecting the resistance to Al diffusion. This work reveals that it is the nature of the monolayer interface between CuO and alumina/Al rather than the thickness of the alumina layer that controls the kinetics of Al diffusion, underscoring the importance of the chemical bonding at the interface in these energetic materials.

Optical ignition of nanoenergetic materials: The role of single-walled carbon nanotubes as potential optical igniters

We demonstrate the effective optical ignition of nanoenergetic materials (nEMs) by adding single-walled carbon nanotubes (SWCNTs) as an optical ignition agent into an nEM matrix composed of Al/CuO nanoparticles (NPs). The measured burn rate and pressurization rate of SWCNT (optical igniter)-Al NP (fuel)-CuO NP (oxidizer) composites were found to attain maximum values of ∼240m/s and ∼5.9±0.8psi/μs, respectively, in the case of SWCNT (1wt.%)-nEM composites. As the amount of SWCNTs added into the nEM matrix was further increased (i.e., SWCNT>2wt.%), both the burn rate and the pressurization rate of the as-prepared SWCNT-nEM composites decreased significantly. This was because the large amount of SWCNTs in the nEM matrix increased the heat dissipation through the SWCNT agglomerates, so that the temperature increase in the SWCNT-nEM composite was limited, thus hindering the oxidation and subsequent ignition of the nEMs. This suggests that the remote optical ignition and controlled-explosion reactivity of nEMs can be performed by incorporating SWCNTs as a potential optical ignition agent with nEMs.

Fabrication, characterization, and application in nanoenergetic materials of uncracked nano porous silicon thick films

The porous silicon (PS) film has gained increasing attention in recent years as advanced nanoenergetic materials (nEMs). A simple fabrication method to prepare uncracked PS thick films was successfully realized with precisely controlled electrochemical etching, and the relationship between the current density and the concentration of electrolytes was found in its fabrication. Additionally, the capillary stresses resulted from the liquids in nanopores of PS films was another factor resulted in its crack. The nanopores composed of uncracked PS thick films distributed regularly and their diameters ranged from 2nm to 6nm. Its Sa (average roughness) of PS film surface was 6.53nm, and its thickness ranged from 102.41μm to 205.75μm. The specific surface area was 587m2/g and the average diameter of nanopores was 4.3nm. The PS film was found to be monocrystal and it was same as the substrate. The crack mechanism of PS films was discussed: the porous structure reduced the strength of PS films comparing the silicon bulk and the capillary effect hastened the crack of PS films. PS films filling with sodium percholorate in nanopores were ignited by laser and the stable combustion showed that they were advantageous to be applied as micro-electromechanical systems (MEMS) compatible devices, such as silicon-based chips of mircothruster and microigniter.

Comparison of engineered nanocoatings on the combustion of aluminum and copper oxide nanothermites

Water-repellent nano-coatings for submerged combustion of nano-energetic composite materials were developed. These coatings may have applications for oceanic power generation, underwater ordnance, propulsion, metal cutting, and torch technologies. Nano-coatings were deposited on thermite pellets by a vapor-phase technique. Two types of deposition techniques studied were chemical vapor deposition (CVD) and atomic layer deposition (ALD). A total of six types of nano-coatings were applied on the thermite pellets. Various process parameters to produce the coatings were explored. Characterization of the nano-coatings was carried out using Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), and contact angle goniometry. Submerged combustion tests of the nano-coated thermite pellets were performed as a function of submerged time. The pellets were submerged in de-ionized water for 3, 5, and 10days. The energy released by the thermite reaction was analyzed and compared to other types of nano-coated pellets. Initial results of a fluorocarbon self-assembled monolayer (FSAM) coating were compared with an ALD coating composed of Al2O3. Results show that with increasing submerged time, there was a decrease in the ratio of bubble energy to total energy of combustion (Kc=Kbubble/Kcombustion) for all coatings tested. The initial bubble energy of the pellets coated with FSAM and ALD with Al2O3 was 133.3 and 142.2 (KJ/Kg), respectively. After submersion for 10days, the bubble energy reduced to 10.4 and 15.6 (KJ/Kg), respectively. The value of Kc for the FSAM coating decreased by a factor of 12.8 whereas the ALD with Al2O3 coating decreased by a factor of 9.1. The hydrophobic coating is critical for energy generation because without it, the pellets do not ignite, resulting in 100% loss of energy.

An investigation into the fabrication and combustion performance of porous silicon nanoenergetic array chips

An investigation into the ignitions and combustions of porous silicon (PS) nanoenergetic material array chips (nECs) at different ignition voltages was performed. The PS nECs were fabricated by integrating PS nanoenergetic material (nEMs) matrices and Cr-microbridges (microigniters) on the surface of silicon substrates. The combustion of PS nECs was in ambient air. Its ignition and combustion were investigated by a testing system and an optical high-speed camera. Experimental results revealed that the combustion delay time of PS nEMs increased from 8.0 × 10−5 s to 1.1 × 10−4 s with the decrement of ignition voltages from 140 to 80 V. The scope of ignition energy ranged from 0.153 to 0.287 mJ by calculations. The reaction type was deflagration, from the analysis of the high-speed video of PS nECs. The comprehensive experimental results indicated that the combustion of PS nECs was ignited by the synergic effect of the heat and the plasma. The ignition experiments suggested that Cr-microbridges were reliable igniters to trigger the self-sustained combustion of PS nECs. The strong plume of flame emitted from the surface of PS nECs indicated that the PS nECs may be applied as micro/nano igniter chips and microthruster chips.

A micro initiator realized by integrating KNO3@CNTs nanoenergetic materials with a Cu microbridge

A micro initiator was developed by integrating KNO3@CNTs nanoenergetic materials with a Cu thin-film microbridge realized onto a glass substrate. It was fabricated by magnetron sputtering with Cu and subsequent electrophoretic deposition with KNO3@CNTs nanoenergetic materials, which were prepared by wet chemical method, embedding KNO3 in carbon nanotubes (CNTs). The samples were characterized by TEM, XRD, TG/DSC and SEM, respectively. The electrical explosion performances of the micro initiator under capacitor discharge were investigated. The process of electrical explosion was observed by high-speed photography and the temperature distribution versus time was acquired by a temperature measurement system with double line of atomic emission spectroscopy. The results show that the hollow cavities of the CNTs were filled with crystalline KNO3, and that the entire surface of the micro initiator was well distributed without large reunion. Compared with single-layer Cu thin-film microbridge, the micro initiator possessed more violent electrical explosion process, the electrical explosion duration was longer, and the peak temperature was higher, which indicate that chemical reactions of KNO3@CNTs nanoenergetic materials were involved in the electrical explosion process of the micro initiator, accompanied by more heat release.

Micro-Optical Initiation of Nanoenergetic Materials Using a Temporally Tailored Variable-Pulse-Width Laser

Nanoenergetic materials can provide a significant enhancement in the rate of energy release as compared with microscale materials. The energy-release rate is strongly dependent not only on the primary particle size but also on the level of agglomeration, which is of particular interest for the inclusion of nanoenergetics in practical systems where agglomeration is desired or difficult to avoid. Unlike studies of nanoparticles or nanometer-size aggregates, which can be conducted with ultrafast or nanosecond lasers assuming uniform heating, microscale aggregates of nanoparticles are more sensitive to the thermophysical time scale of the heating process. To allow control over the rate of energy deposition during laser initiation studies, a custom, temporally tailored, continuously variable-pulse-width (VPW) laser was employed for radiative heating of nanoenergetic materials. The laser consisted of a continuous-wave master oscillator, which could be sliced into desired pulses, and a chain of amplifiers to reach high peak power. The slicer allowed control over the time profile of the pulses via the combination of an arbitrary waveform generator and acousto-optic modulator (AOM). The effects of utilizing flat-top or ramped laser pulses with durations from 100 ns to 150 μs and energies up to 20 mJ at 1064 nm were investigated, along with a broad range of heating rates for single particles or nanoparticle aggregates up to 100-μm diameter. In combination with an optical microscope, laser heating of aggregates consisting of 70-nm diameter Al nanoparticles in a Teflon matrix showed significant dependence on the heating profile due to the sensitivity of nanoenergetic materials to heating rate. The ability to control the temporal pulse-intensity profile leads to greater control over the effects of ablative heating and the resulting shockwave propagation. Hence, flexible laser-pulse profiles allow the investigation of energetic properties for a wide size range of metal/metal-oxide nanoparticles, aggregates, and composites.

Preparation and Characterization of Nanoenergetic Materials Based on KNO&lt;sub&gt;3&lt;/sub&gt;-Filled Carbon Nanotubes

A novel nanoenergetic material was prepared by filling KNO3in the CNTs through a wet chemical method. The samples were characterized by TEM, XRD, and TG/DSC. The results show that KNO3with a mean diameter of ~9 nm were homogeneously filled into CNTs to form KNO3@CNTs nEMs. The TG/DSC curves indicate that the reaction enthalpy (ΔH) of KNO3@CNTs nEMs was 876.1 J/g and the characteristic temperature of the exothermic peak was 386.8 °C.

An in situ chemical reaction approach to synthesize zinc picrate energetic thin film upon zinc oxide nanowires array

Nanoenergetic materials are the key to great advances in microscale energy‐demanding systems as actuation part, igniter, propulsion unit, and power. An important challenge of energetic materials for microelectromechanical system (MEMS) is the compatibility of standard microsystem techniques with technology process employed in preparing energetic materials producing a large amount of gas and heat. Picric acid is known to react with metals to form highly unstable metallic picrate, which are often employed as explosive materials. In this study, films of zinc picrate were successfully produced with an ‘in‐situ chemical reaction’ method by introducing picric acid onto a ZnO nanowire array, which is fully compatible with technology for MEMS. The films were characterized by nuclear magnetic resonance, X‐ray diffraction, XPS, and SEM. The results demonstrate that picric acid reacted with ZnO to form zinc picrate thin film. Differential scanning calorimetry and thermogravimetric analysis measurements show that zinc picrate/ZnO films exhibit producing a large amount of gas, high energy output and lower ignition temperature, which will enhance the diversity of functions on MEMS devices. Therefore, this will open the door to integrate this traditional organic energetic material into microsystem, leading to new generation of MEMS devices. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Integration of nano-Al with Co3O4 nanorods to realize high-exothermic core–shell nanoenergetic materials on a silicon substrate

Nanoenergetic materials (nEMs) have better performance in ignition and energy release rate compared to conventional energetic materials. This makes them have promising applications in actuation, ignition, propulsion, power, fluidic, and electro-explosive devices at the micro and nanoscale. In this study, Co3O4 is used for the first time to achieve novel Al/Co3O4 based nEMs by integrating nano-Al with Co3O4 nanorods that are synthesized by a chemical method. The total heat of reaction, especially the exothermic reaction before Al melting, is greatly enhanced by using Co3O4 pure nanostructures (no microscale film exits). The nEMs are fabricated onto a silicon substrate, which is very convenient to achieve promising functional nanoenergetics-on-a-chip. The fabricated nEMs are confirmed to have nanoscale mixing, very high heat of reaction, and significantly reduced onset temperature of the major exothermic reaction by scanning electron microscopy, differential thermal/thermogravimetric analysis, and differential scanning calorimetry.

Laser-induced plasma chemistry of the explosive RDX with various metallic nanoparticles

The feasibility of exploiting plasma chemistry to study the chemical reactions between metallic nanoparticles and molecular explosives such as cyclotrimethylenetrinitramine (RDX) has been demonstrated. This method, based on laser-induced breakdown spectroscopy, involves the production of nanoparticles in a laser-induced plasma and the simultaneous observation of time-resolved atomic and molecular emission characteristic of the species involved in the intermediate chemical reactions of the nanoenergetic material in the plasma. Using this method, it has been confirmed that the presence of aluminum promotes the ejection process of carbon from the intermediate products of RDX. The time evolution of species formation, the effects of laser pulse energy, and the effects of trace metal content on the chemical reactions were also studied.

Modified Aerosol Routes to Core-Shell Nano-Energetic Materials Synthesis

ABSTRACTFollowing the generic strategy of creating core-shell structured nanoparticles reported by our group previously [1] and exploring its applications, an aerosol route combined with iron carbonyl decomposition was developed to encapsulate strong oxidizer within mild oxidizer particles. This modified method enables the application of hygroscopic nano-energetic materials by stabilizing them within a water-insoluble shell. Fe2O3/I2O5 composite oxidizers have been created. Some of the results obtained from combustion tests show that the composite system significantly outperforms the single metal oxide (Fe2O3) system in both pressurization rate and peak pressure. The time-resolved mass spectrometry shows that a significant amount of O2 and I2 are released from the composite oxidizers. These preliminary results suggest a supplement to the previous strategy of obtaining the core-shell structured composite oxidizers and the method still needs to be further optimized.

SIZE DEPENDENCE OF INTERBAND TRANSITIONS INAlNANOPARTICLE

The interband transition onset frequency of nanoaluminum is found to approximately, linearly decrease as reducing aluminum diameter in the 25–100 nm range. This linear relation is indicated to originate mostly from increased inner strain of nanoparticle caused by the small size effect. This relation realizes to introduce the size dependence of interband transitions into the metallic dielectric function and has its important application in the laser ignition of nanoenergetic materials.

Effect of nanostructures on the exothermic reaction and ignition of Al/CuOx based energetic materials

Al/CuOx based micro- and nanoenergetic materials (EMs) have been made by the thermal oxidation of Cu thin films deposited onto silicon substrates followed by Al integration through thermal evaporation. The micro- and nano-EMs are then characterized by scanning electron microscopy, energy dispersive X-ray analysis, X-ray diffraction, differential thermal analysis, and differential scanning calorimetry. By comparing the thermite reactions and ignition properties of Al with micro-CuOx and Al with nano-CuOx, we show experimentally that one-dimensional nanostructures (CuO nanowires) and nano-Al affect greatly the exothermic behaviors and ignition properties of the Al/CuOx based EMs. The higher surface energy associated with the CuO nanowires and the deposited nano-Al is believed to be a possible factor contributing to the enhanced exothermic reactions that occur below the melting point of Al and the smaller ignition delay and lower ignition energy.

A Micro Fuse Realized by Integrating Al/CuO-Based Nanoenergetic Materials on a Micro Wire

Nano energetic materials (nEMs) have improved performance in energy release, ignition, and mechanical properties compared to their bulk or micro counterparts. In this study a micro fuse developed by intergrating Al/CuO-based nanoenergetic materials on a micro wire. CuO nanowires are synthesized by thermally annealing Cu film deposited onto a micro wire. Nano-Al is integrated with the nanowires by thermal to realize an Al/CuO based nEMs. It allows batch and high level of integration and reliability. The micro fuse is tested by open-air combustion testing and characterized by scanning electron microscopy, x-ray diffraction, differential thermal analysis and differential scanning calorimetry.

Effect of a superhydrophobic coating on the combustion of aluminium and iron oxide nanothermites

There is an interest in broadening the range of applications of nanoenergetic composite materials to include their combustion and energy generation in submerged environments. Currently, their use is primarily limited to gas environments. Oceanic power generation, underwater ordnance, propulsion, metal cutting, and torch technologies are examples of applications that would significantly benefit from nanocomposite energetic materials. Recent research on superhydrophobic coatings has made it possible to coat nanoenergetic samples using a vapor-phase deposition process which significantly reduces the detrimental effects of water entering the composite that can occur during wet-chemistry based superhydrophobic processes. In this work, we discuss the process utilized to produce the superhydrophobic coating on nanoenergetic materials. We then analyze the bubble energy produced and compare this value to other energetic formulations. It was found that the ratio of the bubble energy to the total energy of combustion was an order of magnitude higher for the superhydrophobic coated materials compared to energetic composites containing a hydrophobic binder.