Synthesis of aluminum nanoparticles as additive to enhance ignition and combustion of high energy density fuels

High energy density fuels are critical for hypersonic aerospace propulsion but suffer from difficul- ties of ignition delay and incomplete combustion. This research reports aluminum nanoparticles （A1 NPs） assisted ignition and combustion of high energy density JP-10 fuel. A1NPs with a size of 16 nm were fabricated through a mild and simple method by decomposing AIH3. Et20 with the addition of a surfactant ligand. The uniform size distribu- tion, nanoscaled size and surface ligand make A1 NPs stably suspend in JP-10, with 80% NPs being dispersed in the liquid fuel after six months. A shock tube test shows that the presence of 1 wt-% A1 NPs can significantly shorten ignition delay time at temperature of 1500 to 1750 K, promote the combustion, and enhance energy release of JP-10. This work demonstrates the potential of A1 NPs as ignition and combustion additive for high energy density fuel in hypersonic applications.

Monitoring micro-structural evolution during aluminum sintering and understanding the sintering mechanism of aluminum nanoparticles:A molecular dynamics study

In this work, molecular dynamics simulations have been performed to explore the structural evolution and underlying sintering mechanism of aluminum nanoparticles. The structural evolution during sintering was firstly monitored through radial distribution function and atomic migration, and the underlying sintering mechanism was further quantitatively characterized in terms of average displacement, mean squared distance(MSD), radius ratio(i.e., the ratio of the neck radius to the particle radius), shrinkage and radius of gyration, crystalline orientations, particle size, etc. Results show that the surface atoms of nanoparticles are more active than the internal atoms, favoring the mechanical rotation of nanoparticles during sintering. During the sintering process, average displacement, radius ratio and the shrinkage rate have undergone three stages with increasing the temperature:(1) a slow increase and subsequent abrupt hike after reaching the sintering temperature;(2) an almost plateau region over a wide span of temperature;(3) finally a sharp increase again after reaching the melting temperature. In contrast, MSD remains basically unchanged before melting, close to zero, followed by a sudden increase after melting temperature. Although the radius of gyration also experiences three stages, nonetheless it exhibits almost completely contrary trend. It has also been found that both sintering temperature and melting temperature demonstrate an almost linear increase with the increase of nanoparticle size ranging from4.0, 6.0, 8.0 to 10.0 nm in diameter. Finally, we also found that the particle direction has limited effect on neck growth during sintering.

Anti-sintering behavior and combustion process of aluminum nano particles coated with PTFE:A molecular dynamics study

The characteristic of easy sintering of aluminum nanoparticle(ANP)limits its application in solid propellants.Coating ANP with fluoropolymer could effectively improve its combustion performance.To find out how the coating layer inhibits sintering and promotes complete combustion of particles from an atomic view,a comparative study has been done for bare ANP and PTFE coated ANP by using reactive molecular dynamics simulations.The sintering process is quantified by shrinkage ratio and gyration radius.Our results show that,at the same heating rate and combustion temperatures,bare ANPs are sintered together after the temperature exceeds the melting point of aluminum but the decomposition of PTFE coating layer pushes particles away and increases reaction surface area by producing small Al-F clusters.The sintering of ANPs which are heated in PTFE is alleviated compared with particles heated in oxygen,but particles still sinter together due to the lack of intimate contact between PTFE and alumina surface.The effect of temperature on the combustion of PTFE coated ANPs is also studied from 1000 to3500 K.The number density analysis shows the particles will not be sintered at any temperature.Aluminum fluoride prefers diffusing to the external space and the remained particles are mainly composed of Al,C and O.Fast ignition simulations are performed by adopting micro canonical ensemble.With the expansion of aluminum core and the melting of alumina shell,bare ANPs are sintered into a liquid particle directly.For PTFE coated ANPs,the volatilization of gaseous aluminum fluoride products continually endows particles opposite momentum.

Dual-Wavelength Passively Q-Switched Ytterbium-Doped Fiber Laser Based on Aluminum Oxide Nanoparticle Saturable Absorbers

We report on generation of a dual-wavelength, all-fiber, passively Q-switched ytterbium-doped fiber laser using aluminum oxide nanoparticle （Al2O3-NP） thin film. A thin film of Al2O3 was prepared by embedding Al2O3-NPs into a polyvinyl alcohol （PVA） as a host polymer, and then inserted between two fiber ferrules to act as a saturable absorber （SA）. By incorporating the Al2O3-PVA SA into the laser cavity, a stable dual-wavelength pulse output centered at 1050 and 1060.7nm is observed at threshold pump power of 80mW. As the pump power is gradually increased from 80 to 300mW, the repetition rate of the generated pulse increases from 16.23 to 59 kHz, while the pulse width decreases from 19 to 6μs. To the best of our knowledge, this is the first demonstration for this type of SA operating in the 1 μm region.

Potential acute effects of suspended aluminum nitride (AlN) nanoparticles on soluble microbial products (SMP) of activated sludge

The study aims to identify the potential acute effects of suspended aluminum nitride（Al N）nanoparticles（NPs） on soluble microbial products（SMP） of activated sludge.Cultured activated sludge loaded with 1,10,50,100,150 and 200 mg/L of Al N NPs were carried out in this study.As results showed,Al N NPs had a highly inverse proportionality to bacterial dehydrogenase and OUR,indicating its direct toxicity to the activated sludge viability.The toxicity of Al N NPs was mainly due to the nano-scale of Al N NPs.In SMP,Al N NPs led to the decrease of polysaccharide and humic compounds,but had slight effects on protein.The decrease of tryptophan-like substances in SMP indicated the inhibition of Al N NPs on the bacterial metabolism.Additionally,Al N NPs reduced obviously the molecular weight of SMP,which might be due to the nano-scale of Al N.