Highly reactive energetic films by pre-stressing nano-aluminum particles

Energetic films were synthesized using stress altered nano-aluminum particles (nAl). The nAl powder was pre-stressed to examine how modified mechanical properties of the fuel particles influenced film reactivity. Pre-stressing conditions varied by quenching rate. Slow and rapid quenching rates induced elevated dilatational strain within the nAl particles that was measured using synchrotron X-ray diffraction (XRD). An analytical model for stress and strain in a nAl core–Al2O3 shell particle that includes creep in the shell and delamination at the core–shell boundary, was developed and used for interpretation of strain measurements. Results show rapid quenching induced 81% delamination at the particle core–shell interface also observed with Transmission Electron Microscopy (TEM). Slower quenching elevated dilatational strain without delamination. All films were prepared at approximately a 75:25 Al:poly(vinylidene fluoride) PVDF weight ratio and were 1 mm thick. A drop weight impact test was performed to assess ignition sensitivity and combustion. Stress altered nAl exhibited greater energy release rates and more complete combustion than untreated nAl, but reaction dynamics and kinetics proceeded in two different ways depending on the nAl quenching rate during pre-stressing

A slice of an aluminum particle: Examining grains, strain and reactivity

Micron-scale aluminum (Al) particles are plagued by incomplete combustion that inhibits their reactivity. One approach to improving reactivity is to anneal Al particles to increase dilatational (volumetric) strain which has also been linked to increased combustion performance. While optimal annealing temperatures have been identified (roughly 300 °C), little is known about cooling rate effects on particle combustion performance. This study examines the effect of quenching after annealing Al microparticles to 100, 200 and 300 °C on intra-particle dilatational strain and reactivity. Synchrotron X-ray diffraction analysis of the particles reveals the cooling rates in the range from 0.007 to 0.38 K/s have little effect on the dilatational strain of the aluminum-core, alumina-shell particles. The annealed and quenched Al particles were then combined with a metal oxidizer (copper oxide) to examine reactivity. Flame propagation experiments follow the same trend: flame speeds are unchanged until a critical annealing temperature of 300 °C is reached and performance is maintained for each annealing temperature regardless of cooling rate. These results show that altering the mechanical properties and combustion performance of Al particles is strongly dependent on the annealing temperature and unchanged with variation in cooling rate. The contributions from elastic and plastic deformation mechanisms on strain are also considered and additional experimental results are shown on the microstructure of an Al particle. Focused ion beam milling of an Al particle to electron transparency was combined with transmission electron microscope imaging in order to examine the microstructure of the Al particles. This confirmed that the Al microparticles have a polycrystalline structure shown by grains all exceeding 100 nm in size

Edge-Oriented Graphene on Carbon Nanofiber for High-Frequency Supercapacitors

Abstract High-frequency supercapacitors are being studied with the aim to replace the bulky electrolytic capacitors for current ripple filtering and other functions used in power systems. Here, 3D edge-oriented graphene (EOG) was grown encircling carbon nanofiber (CNF) framework to form a highly conductive electrode with a large surface area. Such EOG/CNF electrodes were tested in aqueous and organic electrolytes for high-frequency supercapacitor development. For the aqueous and the organic cell, the characteristic frequency at − 45° phase angle was found to be as high as 22 and 8.5 kHz, respectively. At 120 Hz, the electrode capacitance density was 0.37 and 0.16 mF cm−2 for the two cells. In particular, the 3 V high-frequency organic cell was successfully tested as filtering capacitor used in AC/DC converter, suggesting the promising potential of this technology for compact power supply design and other applications

Preparation and microstructural characterization of oriented titanosilicate ETS-10 thin films on indium tin oxide surfaces

Oriented polycrystalline ETS-10 thin films (average thickness similar to 1.50-1.75 mu m) were prepared on the ITO glass substrates using secondary growth of ETS-10 multilayers with a partial a(b)-out-of-plane preferred crystal orientation. After secondary growth, the films showed a columnar grain microstructure, and a significantly increased degree of a(b)-out-of-plane orientation. This orientation is desirable for advanced applications of ETS-10 films. The prepared films were strongly attached to the ITO glass substrates as evidenced by the absence of discernible differences in the substrate coverage with film after a 60-min ultrasonication in water

Highly reactive energetic films by pre-stressing nano-aluminum particles

Energetic films were synthesized using stress altered nano-aluminum particles (nAl). The nAl powder was pre-stressed to examine how modified mechanical properties of the fuel particles influenced film reactivity. Pre-stressing conditions varied by quenching rate. Slow and rapid quenching rates induced elevated dilatational strain within the nAl particles that was measured using synchrotron X-ray diffraction (XRD). An analytical model for stress and strain in a nAl core–Al2O3 shell particle that includes creep in the shell and delamination at the core–shell boundary, was developed and used for interpretation of strain measurements. Results show rapid quenching induced 81% delamination at the particle core–shell interface also observed with Transmission Electron Microscopy (TEM). Slower quenching elevated dilatational strain without delamination. All films were prepared at approximately a 75:25 Al:poly(vinylidene fluoride) PVDF weight ratio and were 1 mm thick. A drop weight impact test was performed to assess ignition sensitivity and combustion. Stress altered nAl exhibited greater energy release rates and more complete combustion than untreated nAl, but reaction dynamics and kinetics proceeded in two different ways depending on the nAl quenching rate during pre-stressing.This article is published as Bello, Michael N., Alan M. Williams, Valery I. Levitas, Nobumichi Tamura, Daniel K. Unruh, Juliusz Warzywoda, and Michelle L. Pantoya. "Highly reactive energetic films by pre-stressing nano-aluminum particles." RSC Advances 9, no. 69 (2019): 40607-40617. DOI: 10.1039/C9RA04871E. Posted with permission.</p

Soybean-derived hierarchical porous carbon with large sulfur loading and sulfur content for high-performance lithium-sulfur batteries

© 2016 The Royal Society of Chemistry. cc-byAn hierarchical porous carbon nanostructure with intrinsic O- and N-dopants and an ultrahigh specific surface area of 1500 m2 g-1 is reported towards the goal of designing and achieving a better sulfur electrode for lithium-sulfur batteries (LSBs) that can provide both large sulfur loading and large sulfur content and are based on a facile fabrication process. This nanostructure was derived from crude soybeans in a facile pyrolysis process. Using it as a sulfur host, the S/C active composite with 80% sulfur content was made. Cells with different sulfur loadings were investigated and were found to demonstrate large capacity, high coulombic and energy efficiencies, and high cycling stability. In particular, for a sulfur loading of 5.5 mg cm-2 and a sulfur content of 80%, cells displayed a specific capacity of ca. 950 mA h g-1, which corresponds to an areal capacity of 5.2 mA h cm-2. Such a performance moves LSB technology closer to practical applications

Direct evidence of advantage of using nanosized zeolite Beta for ISFET-based biosensor construction

Analytical characteristics of urease- and butyrylcholinesterase (BuChE)-based ion sensitive field-effect transistor (ISFET) biosensors were investigated by the incorporation of zeolite Beta nanoparticles with varying Si/Al ratios. The results obtained by the zeolite-modified ISFET transducers suggested that the Si/Al ratio strongly influenced the biosensor performances due to the electrostatic interactions among enzyme, substrate, and zeolite surface as well as the nature of the enzymatic reaction. Using relatively small nanoparticles (62.7 +/- 10, 76.2 +/- 10, and 77.1 +/- 10 nm) rather than larger particles, that are widely used in the literature, allow us to produce more homogenous products which will give more control over the quantity of materials used on the electrode surface and ability to change solely Si/Al ratio without changing other parameters such as particle size, pore volume, and surface area. This should enable the investigation of the individual effect of changing acidic and electronic nature of this material on the biosensor characteristics. According to our results, high biosensor sensitivity is evident on nanosize and submicron size particles, with the former resulting in higher performance. The sensitivity of biosensors modified by zeolite particles is higher than that to the protein for both types of biosensors. Most significantly, our results show that the performance of constructed ISFET-type biosensors strongly depends on Si/Al ratio of employed zeolite Beta nanoparticles as well as the type of enzymatic reaction employed. All fabricated biosensors demonstrated high signal reproducibility and stability for both BuChE and urease

Investigation of characteristics of urea and butyrylcholine chloride biosensors based on ion-selective field-effect transistors modified by the incorporation of heat-treated zeolite Beta crystals

Urea and butyrylcholine chloride (BuChCl) biosensors were prepared by adsorption of urease and butyrylcholinesterase (BuChE) on heat-treated zeolite Beta crystals, which were incorporated into membranes deposited on ion-selective field-effect transistor (ISFET) surfaces. The responses, stabilities, and use for inhibition analysis of these biosensors were investigated. Different heat treatment procedures changed the amount of Bronsted acid sites without affecting the size, morphology, overall Si/Al ratio, external specific surface area, and the amount of terminal silanol groups in zeolite crystals. Upon zeolite incorporation the enzymatic responses of biosensors towards urea and BuChCl increased up to similar to 2 and similar to 5 times, respectively; and correlated with the amount of Bronsted acid sites. All biosensors demonstrated high signal reproducibility and stability for both urease and BuChE. The inhibition characteristics of urease and BuChE were also related to the Bronsted acidity. The pore volume and pore size increases measured for the heat-treated samples are very unlikely causes for the improvements observed in biosensors' performance, because urease and BuChE are approximately one order of magnitude larger than the resulting zeolite Beta pores. Overall, these results suggest that the zeolites incorporated into the biologically active membrane with enhanced Bronsted acidity can improve the performance of ISFET-based biosensors

Confining Sulfur Species in Cathodes of Lithium–Sulfur Batteries: Insight into Nonpolar and Polar Matrix Surfaces

To alleviate the polysulfides shuttle effect in lithium–sulfur batteries (LSBs), the use of a functionalized carbon matrix with a polar surface has been widely reported to chemically bind the soluble polysulfides. However, whether and how such a polar carbon surface affects the overall cathode performance, particularly the initial discharge corresponding to the reduction of cyclooctasulfur (S₈), has not caught enough attention. By combining polar and nonpolar carbon matrix surfaces in different configurations through sandwiching sulfur species between two carbon matrix membranes, we found cells with dramatically different performance. The discharge process at different states, particularly the charge-transfer resistances corresponding to nonpolar S₈ and polar polysulfide intermediates and the final Li₂S, were investigated. The experimental results, further supported by first-principles density functional theory calculations, indicate that the adsorption energy and barrier for electron transfer together affect the electrochemical performance of LSBs, and therefore, a rational design that combines polar and nonpolar surfaces should be adopted