Modified Nanoenergetic Composites with Tunable Combustion Characteristics for Propellant Applications

This work reports on the synthesis and tunable characteristics of nanothermite compositions based on mesoporous Fe₂O₃ as an oxidizer and Al nanoparticles as a fuel. The reactivity (rate of increase of pressure) and the combustion wave speed were determined to evaluate the performance of these composites for various applications. A gas generating polymer, (acrylamidomethyl) cellulose acetate butyrate (AAMCAB), was loaded in the mesopores of Fe₂O₃ matrix following wet‐impregnation technique. The samples prepared in this work were characterized by a number of analytical techniques such as Fourier transform infrared (FTIR) absorption spectroscopy, transmission and scanning electron microscopy (TEM, SEM), energy dispersive X‐ray analysis, X‐ray diffraction, and nitrogen adsorption–desorption isotherms. Then, mesoporous Fe₂O₃ powder was mixed with Al nanoparticles to prepare nanoenergetic composites. The main characteristics such as peak pressure, reactivity, combustion wave speed, and pressure sustenance were determined as a function of polymer loading. The dependence of combustion wave speed on the pressure was established following the well‐known Vieille's law. The small value of 0.408 for the pressure exponent indicates the suitability of these nanothermite compositions for propellant applications. By reducing the percentage of polymer, the characteristic properties of nanoenergetic composite can be suitably tuned for other applications.     

Nanoenergetic Composites of CuO Nanorods,Nanowires, and Al‐Nanoparticles

This paper reports on the synthesis of the nanoenergetic composites containing CuO nanorods and nanowires, and Al‐nanoparticles. Nanorods and nanowires were synthesized using poly(ethylene glycol) templating method and combined with Al‐nanoparticles using ultrasonic mixing and self‐assembly methods. Poly(4‐vinylpyridine) was used for the self‐assembly of Al‐nanoparticles around the nanorods. At the optimized values of equivalence ratio, sonication time, and Al‐particle size, the combustion wave speed of 1650 m s⁻¹ was obtained for the nanorods‐based energetics. For the composite of nanowires and Al‐nanoparticles the speed was increased to 1900 m s⁻¹. The maximum combustion wave speed of 2400 m s⁻¹ was achieved for the self‐assembled composite, which is the highest known so far among the nanoenergetic materials. It is possible that in the self‐assembled composites, the interfacial contact between the oxidizer and fuel is higher and resistance to overall diffusional process is lower, thus enhancing the performance.     

Combustion of Energetic Porous Silicon Composites Containing Different Oxidizers

We present a quantitative investigation of combustion of on‐chip porous silicon (PS) energetic materials using oxidizers with improved moisture stability and/or minimized environmental impact compared to sodium perchlorate (NaClO₄). Material properties of the PS films were characterized using gas adsorption porosimetry and profilometry to determine specific surface area, porosity, and etch depth. PS energetic composites were formed using melt‐penetrated or solution‐deposited oxidizers into the pores. Combustion was characterized by high speed imaging and bomb calorimetry. The flame speeds quantified for PS/sulfur and PS/nitrate systems varied in the ranges of 2.9–3.7 m s⁻¹and 3.1–21 m s⁻¹, respectively. The experimental combustion enthalpies are reported for different oxidizer systems in both inert and oxidizing environments. For the PS/sulfur and the PS/nitrate systems, the experimental heats of combustion were comparable to those calculated for the thermodynamic equilibrium and taking into account an increased reactivity of PS due to the hydrogen terminated silicon surface.     

Combustion Synthesis of Boron Nitride via Magnesium Reduction Under Low Nitrogen Pressures

A combustion synthesis process was developed for the synthesis of h‐BN powder. B₂O₃, Mg, NH₄Cl, and NaN₃ were used as the reactants and they were mixed and pressed into a reactant compact, which was then wrapped up with an igniting agent (i.e., a mixed powder of Mg and Fe₂O₃). With the presence of NH₄Cl and NaN₃ in the reactant compact and the wrapping of the igniting agent, the combustion synthesis reaction could be carried out under low N₂ pressures (<1.0 MPa) with high product yields (up to 79%) and high specific surface areas (SSA) of the product powder (up to 151 m²/g). Effects of process parameters on the product yield, SSA, and combustion temperature were investigated and a reaction mechanism was proposed to explain the effects. The synthesized h‐BN was platelike crystals and their SSA was found to increase with decreasing maximum combustion temperature under most of the experimental conditions. This is explained by the growth time of the crystals, which is considered to be shorter under the condition with a lower maximum combustion temperature.     

Effects of excess NaClO4 on phases,size and magnetic properties of Ni–Zn ferrite powders prepared by combustion synthesis

Ni_0.4Zn_0.6Fe₂O₄ powders were prepared by combustion synthesis with different amount of NaClO₄. Phases, particle size and magnetic properties of the powders and annealed powders were systematically investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive spectrometer (EDS) and vibrating sample magnetism (VSM). The excess content of NaClO₄ offered significant advantages with respect to the size, morphology and magnetic properties of the powders. After annealing, sub-micro ferrite spherical powders with spinel phase in a range of 500–800 nm can be obtained. With the increase of the NaClO₄ content, the saturation magnetization of the powders shows a maximum value at 68.8 emu/g when w=0.4, whereas the coercivity stayed nearly constant. The maximum saturation of annealed powders by combustion synthesis is much higher than the range reported in the literature.     

Bottom‐up vs reactive sintering of Al2O3–YAG–YSZ composites via one or three‐phase nanoparticles (NPs). Bottom‐up processing wins this time

The bottom‐up approach describes the synthesis of bulk materials from the finest possible length scales to obtain the best global properties. This approach was adapted to the synthesis of multi‐phase ceramic composites produced from metal oxides produced by liquid‐feed flame spray pyrolysis (LF‐FSP). The effect of length scale of mixing was tested through two processing schemes, mixed single metal‐oxide nanopowders (NPs) and nanocomposite NPs having the desired composition within single particles. For the Al₂O₃–Y₂O₃–ZrO₂ ternary system, composites prepared from nanostructured nanoparticles sinter to finer grain sizes (<410 nm) at equivalent densities of 95%TD than those prepared from mixed nanoparticle processing. These contrast with our previous studies in this area where mixed NP processing gave the best or equivalent results. The nanocomposite NPs produced in this study exhibit novel nanostructures with three phases contained within single particles <26 nm average particle size (APS). This nanostructure may directly explain the enhanced sintering of the nanocomposite NPs and may provide an impetus for future synthesis of similarly structured NPs.     

Preparation of Fine-grained Silicon from Serpentine Mineral by Magnesiothermic Reduction of Silica in the Presence of Reaction Products as Diluents

In the work, the preparation of fine-grained silicon was performed in combustion mode by magnesiothermic reduction of silica, obtained from serpentine mineral, which is characterized by a high specific surface area (about 560 m²/g) and high reaction activity. It is manifested by the fact that the measured combustion temperature exceeded the adiabatic combustion temperature calculated with the ISMAN THERMO software, by about 200 °C. In order to mitigate the synthesis conditions, combustion products (Si+2MgO) were used as diluting agents allowing a significant decrease of combustion temperature and a finer silicon powder without contaminating the target product with incidental reagents and without decreasing the yield of the target product. Based on the measured values of combustion parameters (combustion temperature and combustion wave propagation velocity) vs diluent amount, it was estimated that the effective activation energy for SiO₂+2Mg reaction by the solid+liquid mechanism in the temperature interval 1400–2100 °C was about 65±3 kJ/mol.     

Nanoenergetic Gas‐Generators: Design and Performance

Nanoenergetic gas‐generator (NGG) mixtures may have various potential military applications from aircraft fuels to rocket propellants, explosives, and primers. To find reactions generating the highest pressure peak, we studied eight nanoenergetic reactions. The Al/Bi₂O₃ reaction generated the highest pressure pulse among the eight thermite reactions. We developed a highly efficient, one step process for synthesis of Bi₂O₃ nanostructured particles. Its use generated about a three times higher peak pressure (∼10 MPa) than when using commercial bismuth oxide nanoparticles (3 MPa). The pressure in the vessel rose very rapidly to a peak value for a duration of ∼0.02 ms and ΔP/Δt of up to 500 GPa s⁻¹. Increasing the crystallinity of the bismuth oxide nanoparticles increased the peak gas pressure by 25%. The maximum pressure×volume (PV) value obtained at m=0.1 g with our synthesized Bi₂O₃ was 707 Pa m³ much higher than that reported in the literature (33 Pa m³) for the same sample mass. Addition of carbon to the reactant mixtures did not increase the peak pressure. Addition of up to 3 wt.‐% of boron to the thermite systems increased the peak pressure by ∼50%.     

Novel synthesis and antimicrobial studies of nanoscale titania particles

In the present investigation, a novel strategy of continuous microwave assisted flow synthesis (CMFS) has been adopted in comparison to traditional synthesis procedures (sol-gel and chemical precipitation method) for the quick production of TiO₂ nanoparticles with very fine particle properties. The X-ray powder diffraction analysis (XRPD) and transmission electron microscopy (TEM) were two techniques used for analysing the properties related to structure and particle morphology of the resultant samples. It was observed that the particles formed by using continuous flow route were less agglomerated, and particle size (~ 6?nm) was smaller in comparison with others obtained using sol-gel (~ 9?nm) and chemical precipitation method (~ 15?nm). X-ray diffraction impressions established the generation of Anatase phase with preferential [101] dimension. Zeta potential computations were taken to inspect the colloidal stability of nanoparticles. Antimicrobial nature of TiO₂ nano-samples was analyzed by using various bacterial and fungal strains. The nanostructured TiO₂ particles confirmed outstanding uniformity with respect to chemical and structure. This new ceramic substance with strong antimicrobial activity promised magnificent potential in bone tissue engineering.     

Enhanced Combustion Characteristics of Bismuth Trioxide‐Aluminum Nanocomposites Prepared through Graphene Oxide Directed Self‐Assembly

We present a facile, spontaneous, and surfactant‐free method to controllably self‐assemble aluminum and bismuth trioxide nanoparticles through the introduction of graphene oxide as a self‐assembly directing agent. The self‐assembled nanocomposites demonstrate significant combustion performance improvements in comparison to randomly mixed aluminum and bismuth trioxide nanoparticles with enhanced pressure generation from 60 to 200 MPa, pressurization rate from 3 to 16 MPa μs⁻¹, burning rate from 1.15 to 1.55 km s⁻¹, and specific impulse from 41 to 71 s. The sensitivity of the self‐assembled aluminum and bismuth trioxide to electrostatic discharge was reduced by four orders of magnitude, without decreasing the combustion performance. Graphene oxide directed self‐assembly can be used to synthesize nanocomposites with diverse combustion properties and controlled ignition sensitivity, which lays the foundation for preparing multi‐functional, highly‐reactive, combustion systems in the future.     

Effect of Solids Loading on Resonant Mixed Al‐Bi2O3 Nanothermite Powders

Sensitive nanoenergetic powders, such as nanothermites, have traditionally been processed by ultrasonic mixing of very low solids loaded suspensions in organic solvents, which has restricted their use and application due to high solvent content and associated handling issues. In this work, we report on the performance and mixing quality of nanothermite mixtures prepared in a LabRAM resonant mixer at high solids loadings as compared to ultrasonic mixing. Specifically, the aluminum‐bismuth(III) oxide (Al/Bi₂O₃) system processed in the polar solvent N,N‐dimethylformamide (DMF) was investigated. It was found that the performance and overall quality of mixing was strongly correlated to the volumetric solids loading during processing; increasing volumetric solids loading decreases separation of particles, leading to more particle interaction and more intimate mixing. The measured performance of this system processed at 30 vol‐% was similar to traditionally ultrasonicated mixtures. Increasing the solids loading above 30 vol‐% yielded diminishing returns in performance and may introduce additional safety concerns since dry powders are very sensitive to electrostatic discharge. This mixing approach uses significantly less solvent than traditional ultrasonic mixing, results in a higher density final material, and is amenable to scaling. In addition, solvent wetted nanothermite mixed at 30 vol‐% solids loading can be mixed and deposited from a single applicator and was observed to be over five orders of magnitude less sensitive to electrostatic discharge than dry powders. This relative insensitivity enables the safe deposition of high density nanothermite ink onto devices.     

Phase formation in gas-phase combustion and pyrolysis reactions under spark and radio-frequency discharge conditions

Doped ultrafine silicon dioxide powder with a narrow particle size distribution was obtained by RF discharge-stimulated dichlorosilane (SiH₂C) oxidation at a low pressure using isobutylene as the combustion inhibitor and chromium hexacarbonyl (Cr(CO)₆) as the dopant. The formation and morphology of the ultrafine particles are governed by the parameters of the RF discharge and by the chemical mechanism of the combustion reaction yielding the aerosol. Submicron-sized filamentous carbon structures can be obtained by isobutylene decomposition under spark discharge conditions in the presence of a molybdenum metal catalyst.     

Effect on wear resistance of nanoparticles addition to a powder polyester coating through ball milling

The wear properties of a textured polyester powder coating with pyrogenic silica nanoparticles addition were evaluated. Raw powders of a commercial, textured polyester organic coating were mixed with low amounts of SiO₂ nanoparticles (0.5–3 wt%) using ball milling, a simple and economical method. Nanoparticles were mixed into the powder of thermoset organic coating for 10 min in a two-body planetary ball mill. Particle size distribution of the powder was measured to evaluate the milling effect. The coatings were applied and cured in an industrial installation on aluminum substrates. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) images of the coatings were taken to analyze the homogeneity of the organic coating. Roughness, gloss and color were measured in order to evaluate their appearance. The effect of nanoparticles on abrasive and erosion wear performances was measured. Pin-on-disk wear tests were carried out. Erosion measurements were performed with free fall of sand on the samples, a test based on ASTM D968 standard. The results showed that the milling process provides a good distribution of nanoparticles as no agglomerates were found. The addition of 0.5 wt% silica nanoparticles allows for improvement of the wear resistance of the coatings.     

Study of a new polymer electrolyte poly(ethylene oxide): NaClO3 with several plasticizers for battery application

Sodium ion conducting thin film polymer electrolytes based on poly(ethylene oxide) (PEO) complexed with NaClO₃ were prepared by a solution‐casting method. Characterization by XRD, IR spectroscopy and AC conductivity has been carried out on these thin film electrolytes to analyse their properties. The conductivity studies show that the conductivity value of PEO:NaClO₃ complex increases with the increase in salt concentrations. Increase in conductivity was found in the electrolyte system by the addition of low molecular weight polymer poly(ethylene glycol) (PEG) and the organic solvents dimethylformamide (DMF) and propylene carbonate (PC). Using these electrolyte systems, cell parameters were measured from the discharge study with the application of load 100 kΩ at room temperature with common cell configuration Na|electrolyte|C:I₂:electrolyte. The open circuit voltage (OCV) ranges from 2.81 to 3.23 V and the short circuit current (SCC) ranges from 340 to 1180 µA. © 2001 Society of Chemical Industry     

Effect of reactant composition on the production of MoSi2 by self-propagating high-temperature synthesis

The effect of reactant composition, particle size of silicon, density of powdered compacts, and reaction atmosphere on the characteristics of molybdenum disilicide produced from molybdenum and silicon powders by self-propagating high-temperature synthesis, was studied in a pressurized reaction chamber at 1.5 bar. The atomic ratio of silicon to molybdenum (Si/Mo) was changed from 1.0 to 2.6 in order to investigate the effect of reactant composition on the characteristics of self-propagating high-temperature synthesis. Stable combustion was observed for the values of atomic ratios of silicon to molybdenum from 1.8 to 2.2 and SHS-produced material consisted of a uniform and single-phased MoSi₂. In the meantime unstable combustion such as oscillatory, spinning, and surface combustion was detected for the values of atomic ratios of silicon to molybdenum less than 1.8 or larger than 2.2. SHS-produced material under unstable combustion includes the impurities of Mo₅Si₃, Mo₃Si, unreacted Mo and Si resulting from the layered or reacted-on-surface structures, which give lower degree of reaction and possibly poor electrical properties of heating element MoSi₂. The value of criterion α suggested by Shkadinskii et al. to differentiate stable combustion from unstable one, is found to be 0.74 for producing molybdenum disilicide by self-propagating high-temperature synthesis. Stable combustion was detected for the values of α greater than 0.74 (α>0.74) to give the uniform and single-phased product while unstable combustion was observed for the values of α less than 0.74 (α<0.74) to result in a non-uniform and multiphase product. This critical value will help the industry to produce uniform and high-purity molybdenum disilicide by self-propagating high-temperature synthesis processes.     

Simultaneous high-frequency induction heated combustion synthesis and consolidation of nanostructured HfSi2–SiC composite

Dense nanostructured HfSi₂–SiC composite was synthesized by high-frequency induction heated combustion synthesis (HFIHCS) method in one step from powders of mechanically activated HfC and Si. Simultaneous combustion synthesis and densification were accomplished under the combined effects of an induced current and mechanical pressure. Highly dense HfSi₂–SiC was produced under simultaneous application of a 60 MPa pressure and the induced current. The average grain size and mechanical properties (hardness and fracture toughness) of the composite were investigated.     

Preparation and characterization of novel optically active poly(amide‐imide)/α‐Fe2O3 nanocomposites containing l‐alanine moieties

An optically active poly(amide‐imide) (PAI) was synthesized from the polymerization reaction of N,N′‐(Pyromellitoyl)‐bis‐l ‐alanine diacid chloride with 2,5‐diaminotoluene. The obtained inorganic metal oxide nanocomposites composed of PAI/nanostructured hematite (α‐Fe₂O₃) were synthesized through ultrasonic irradiation. The resulting nanocomposites were characterized by Fourier transform infrared spectroscopy, powder X‐ray diffraction, transmission electron microscopy (TEM) and thermogravimetric analysis (TGA). The TEM results indicated that the nanoparticles were dispersed homogeneously in PAI matrix on nanoscale. TGA confirmed that the heat stability of the nanocomposites was improved in the presence of α‐Fe₂O₃ nanoparticles. POLYM. COMPOS., 37:1805–1811, 2016. © 2014 Society of Plastics Engineers     

Hydrothermal Synthesis of Si‐doped Hydroxyapatite Nanopowders: Mechanical and Bioactivity Evaluation

Si‐doped hydroxyapatite nanoparticles (n‐Si_xHA) were prepared by hydrothermal synthesis from calcium nitrate tetrahydrate and diammonium hydrogen orthophosphate. A rod‐like morphology was obtained for all the powders irrespective of the incorporated Si‐doping level. But the crystallinity of the n‐Si_xHA powders, the density achieved upon sintering powder compacts and their mechanical properties (three‐point‐bending strength), as well as their biomineralization activity evaluated by immersing them into simulated body fluid (SBF) were found to be dependent on the Si‐doping amount.     

Fabrication of polymeric nanoparticles of poly(ethylene‐co‐vinyl acetate) coated with chitosan for pulmonary delivery of carvedilol

Carvedilol is a drug with low oral bioavailability due to its high first‐pass metabolism. The purpose of the present study was to prepare a mucoadhesive dry powder inhaler of this drug loaded in poly(ethylene‐co‐vinyl acetate)(PEVA) nanoparticles for pulmonary delivery. PEVA nanoparticles were prepared by an O/W solvent evaporation method and coated with different concentrations of chitosan as a mucoadhesive polymer. Encapsulation efficiency, particle size, zeta potential, release efficiency, and mucoadhesive properties of the different formulations were evaluated on mucin substrate. The optimized formulation of nanoparticles was spray dried using lactose and mannitol as carrier powders. The flowability of the obtained powders was checked by Carr's Index and Hausner ratio and the in vitro deposition of the aerosolized drug was investigated using a Next Generation Impactor. Increasing in the particle size and zeta potential of nanoparticles confirmed the settling of the chitosan coating layer on the surface of nanoparticles. The in vitro drug release from coated nanoparticles decreased with increasing of chitosan concentration. Mucoadhesive property of chitosan‐coated PEVA nanoparticles was higher than noncoated ones. Spray‐dried powders had different aerosilization behavior. Mannitol‐based formulation was found to have low density, better flow ability, smaller aerodynamic diameter (d_aer) and higher fine powder fraction. The results of the present study allow concluding that mannitol spray dried, mucoadhesive nanoparticles of PEVA are suitable inhaler powder for pulmonary delivery of carvedilol. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39694.     

Nanostructured phenolic matrices: Effect of different nanofillers on the thermal degradation properties and reaction to fire of a resol

In this work, the effect of 6 different fillers as a nanomodifier of phenolic matrix was evaluated in thermal stability and reaction to fire. The chosen nanoparticles were montmorillonite, silica, carbon black, and 3 carbides—boron, silicon, and zirconium carbides. The nanofillers were mechanically dispersed in the matrix, and the dispersion and distribution of the nanosized particles in the matrix was evaluated by transmission electron microscopy. The thermal stability of nanocomposites was investigated by thermogravimetric analysis both in nitrogen and in air while the thermal combustion properties were measured using a microscale combustion calorimeter. The experimental data highlighted the remarkable effects of nanoboron carbide on the thermal properties it can confer to the phenolic matrix. Rheological behavior of the blends was also investigated to evaluate the effect of the different fillers on the viscosity of the nanostructured matrices.