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An important proposed mechanism in nanothermites reactions - reactive sintering - plays a significant role on the combustion performance of nanothermites by rapidly melting and coalescing aggregated metal nanoparticles, which increases the initial size of the reacting composite powders before burning. Here, we demonstrate a high-speed microscopy/thermometry capability that enables ~ µs time and ~ µm spatial resolution as applied to highly exothermic reaction propagation to directly observe reactive sintering and the reaction front at high spatial and temporal resolution. Experiments on the Al+CuO nanocomposite system reveal a reaction front thickness of ~30 μm and temperatures in excess of 3000 K, resulting in a thermal gradient in excess of 107 K m-1. The local microscopic reactive sintering velocity is found to be an order of magnitude higher than macroscale flame velocity. In this observed mechanism, propagation is very similar to the general concept of laminar gas reaction theory in which reaction front velocity ~ (thermal diffusivity x reaction rate)1/2.

A fast, quantitative method for determining the dimensions of nanorods (i.e., length and diameter) is described, based on hyphenation of differential mobility analysis (DMA) with single particle inductively coupled plasma mass spectrometry (spICP-MS). Seven gold nanorod samples with different dimensions (diameters 11.8 nm to 38.2 nm, aspect ratios 1.8 to 6.9) were used to validate the method. We demonstrate that DMA-spICP-MS can (1) achieve quantification of both length and diameter comparable with TEM analysis, (2) make statistically meaningful measurements in minutes at low concentrations (

Silver-containing oxidizers are of interest as biocidal components in energetic application such as thermites due to their biocidal agent delivery. In this study, AgFeO2, was evaluated as an oxidizer in aluminum-based thermite system. This novel oxidizer AgFeO2 particles were prepared via a wet-chemistry method and its structure, morphologies and thermal behavior were investigated using X-ray diffraction, scanning electron microscopy, thermogravimetric analysis and differential scanning calorimetry, and time-resolved temperature-jump time-of-flight mass spectrometry. The results indicate the decomposition pathways of AgFeO2 vary with heating rates from a two-step at low heating rate to a single step at high heating rate. Ignition of Al/AgFeO2 occurs at a temperature just above the oxygen release temperature that is very similar to Al/Fe2O3 and Al/CuO. However, with a pressurization rate three times of Al/CuO, Al/AgFeO2 yields a comparable result as to Al/hollow-CuO or Al/KClO4/CuO, with a simpler preparation method. The post combustion products demonstrated that the Al/AgFeO2 thermite reaction produces a fine dispersion of elemental nanosized silver particles which coats the larger alumina particles and is thus bioavailable.

Cisplatin-complexed gold nanoparticles (PtII-AuNP) provide a promising strategy for chemo-radiation-based anticancer drugs. Effective design of such platforms necessitates reliable assessment of surface engineering on a quantitative basis and its influence on drug payload, stability, and release. In this paper, poly(ethylene glycol) (PEG)-stabilized PtII-AuNP was synthesized as a model antitumor drug platform, where PtII is attached via a carboxyl-terminated dendron ligand. Surface modification by PEG and its influence on drug loading, colloidal stability, and drug release were assessed. Complexation with PtII significantly degrades colloidal stability of the conjugate; however, PEGylation provides substantial improvement of stability in conjunction with an insignificant trade-off in drug loading capacity compared with the non-PEGylated control (

Particles from smoldering biomass burning (BB) represent a major source of carbonaceous aerosol in the terrestrial atmosphere. In this study, mass specific absorption spectra of laboratory-generated smoldering wood particles (SWP) from 3 hardwood and 3 softwood species were measured in situ. Absorption data spanning from λ = 500 to 840 nm were collected using a photoacoustic spectrometer coupled to a supercontinuum laser with a tunable wavelength and bandwidth filter. SWP were size- (electrical mobility) and mass-selected prior to optical characterization allowing data to be reported as mass-specific absorption cross sections (MAC). The median measured MAC at λ = 660 nm for smoldering oak particles was 1.1 (0.57/1.8) × 10-2 m2 g-1 spanning from 83 femtograms (fg) to 517 fg (500 nm ≤ mobility diameter ≤950 nm), MAC values in parentheses are the 16th and 84th percentiles of the measured data (i.e., 1σ). The collection of all six wood species (Oak, Hickory, Mesquite, Western redcedar, Baldcypress, and Blue spruce) had median MAC values ranging from 1.4 × 10-2 m2 g-1 to 7.9 × 10-2 m2 g-1 at λ = 550 nm with absorption Ångström exponents (AAE) between 3.5 and 6.2. Oak, Western redcedar, and Blue spruce possessed statistically similar (p > 0.05) spectra while the spectra of Hickory, Mesquite, and Baldcypress were distinct (p < 0.01) as calculated from a point-by-point analysis using the Wilcox rank-sum test.

Nanoparticles (NPs) dispersed within a conductive host are essential for a range of applications including electrochemical energy storage, catalysis, and energetic devices. However, manufacturing high quality NPs in an efficient manner remains a challenge, especially due to agglomeration during assembly processes. Here we report a rapid thermal shock method to in situ synthesize well-dispersed NPs on a conductive fiber matrix using metal precursor salts. The temperature of the carbon nanofibers (CNFs) coated with metal salts was ramped from room temperature to ∼2000 K in 5 ms, which corresponds to a rate of 400,000 K/s. Metal salts decompose rapidly at such high temperatures and nucleate into metallic nanoparticles during the rapid cooling step (cooling rate of ∼100,000 K/s). The high temperature duration plays a critical role in the size and distribution of the nanoparticles: the faster the process is, the smaller the nanoparticles are, and the narrower the size distribution is. We also demonstrated that the peak temperature of thermal shock can reach ∼3000 K, much higher than the decomposition temperature of many salts, which ensures the possibility of synthesizing various types of nanoparticles. This universal, in situ, high temperature thermal shock method offers considerable potential for the bulk synthesis of unagglomerated nanoparticles stabilized within a matrix.

Alkali metal borohydrides present a rich source of energy dense materials of boron and hydrogen, however their potential in propellants has been hitherto untapped. Potassium borohydride is a promising fuel with high gravimetric energy density and relatively low sensitivity to air and moisture. Problems arise due to the dehydrogenation of the borohydride on heating with minimal energy release. Common methods to extract both boron and hydrogen by means of borane species involve direct reaction of boron trifluoride species with alkali borohydrides. However, these methods face storage and safety issues due to rapid release of diborane on mixing the reactants. We propose a method of diborane release through controlled release of boron trifluoride by means of a tetrafluoroborate based ionic liquid. The trifluoride is released from the ionic liquid at elevated temperatures and enables safe mixture of the reactants at room temperature. It was found that the reaction between borohydride and boron trifluoride proceeds well above room temperature with potassium borohydride releasing diborane and potassium fluoride. The reaction pathway shows a primary reaction releasing diborane and potassium fluoride and a second less energy efficient step leading to the formation of potassium tetrafluoroborate. A 3D printed propellant formulation was also tested. [ABSTRACT FROM AUTHOR]

In this study, free‐standing composites consisting of 90 wt% nanoenergetic mesoparticles are fabricated and their combustion characteristics are investigated. The findings reveal that the integrity of the mesoparticles remains intact during the printing process and a reduction in sintering is observed for the composite of mesoparticles compared to the physical mixture. However, the composite of mesoparticles exhibits noncontinuous and oscillating propagation behavior at a steady frequency of ≈5 Hz. This is attributed to insufficient heat feedback from the flame to the unburnt material. To address this issue, carbon fiber (C.F.) is introduced into the composite to enhance heat feedback to the reaction front by intercepting hot agglomerates near the burning surface. Incorporating C.F. leads to steady propagation of the composite. Agglomerate residence time and characteristic heat transfer time analysis near the burning surface indicate that while the composite without C.F. has agglomerate residence time on the same order of magnitude as the characteristic heat transfer time, the composite with C.F. has significantly increased overall agglomerate residence time compared to the characteristic heat transfer time. This confirms the enhanced heat feedback through C.F. inclusion. This study demonstrates the crucial role of heat feedback in the combustion behavior of energetic composites. [ABSTRACT FROM AUTHOR]

Nanoparticles hosted in conductive matrices are ubiquitous in electrochemical energy storage, catalysis and energetic devices. However, agglomeration and surface oxidation remain as two major challenges towards their ultimate utility, especially for highly reactive materials. Here we report uniformly distributed nanoparticles with diameters around 10 nm can be self-assembled within a reduced graphene oxide matrix in 10 ms. Microsized particles in reduced graphene oxide are Joule heated to high temperature (∼1,700 K) and rapidly quenched to preserve the resultant nano-architecture. A possible formation mechanism is that microsized particles melt under high temperature, are separated by defects in reduced graphene oxide and self-assemble into nanoparticles on cooling. The ultra-fast manufacturing approach can be applied to a wide range of materials, including aluminium, silicon, tin and so on. One unique application of this technique is the stabilization of aluminium nanoparticles in reduced graphene oxide film, which we demonstrate to have excellent performance as a switchable energetic material.

Optical absorption spectra of laboratory generated aerosols consisting of black carbon (BC) internally mixed with nonabsorbing materials (ammonium sulfate, AS, and sodium chloride, NaCl) and BC with a weakly absorbing brown carbon surrogate derived from humic acid (HA) were measured across the visible to near-IR (550 to 840 nm). Spectra were measured in situ using a photoacoustic spectrometer and step-scanning a supercontinuum laser source with a tunable wavelength and bandwidth filter. BC had a mass-specific absorption cross section (MAC) of 7.89 ± 0.25 m(2) g(-1) at λ = 550 nm and an absorption Ångström exponent (AAE) of 1.03 ± 0.09 (2σ). For internally mixed BC, the ratio of BC mass to the total mass of the mixture was chosen as 0.13 to mimic particles observed in the terrestrial atmosphere. The manner in which BC mixed with each material was determined from transmission electron microscopy (TEM). AS/BC and HA/BC particles were fully internally mixed, and the BC was both internally and externally mixed for NaCl/BC particles. The AS/BC, NaCl/BC, and HA/BC particles had AAEs of 1.43 ± 0.05, 1.34 ± 0.06, and 1.91 ± 0.05, respectively. The observed absorption enhancement of mixed BC relative to the pure BC was wavelength dependent for AS/BC and decreased from 1.5 at λ = 550 nm with increasing wavelength while the NaCl/BC enhancement was essentially wavelength independent. For HA/BC, the enhancement ranged from 2 to 3 and was strongly wavelength dependent. Removal of the HA absorption contribution to enhancement revealed that the enhancement was ≈1.5 and independent of wavelength.