Al NPs Research Articles

The influence of various additives on coagulation process at different dosing point: From a perspective of structure properties

Structure properties of flocs (size, fractal dimension (Df), etc.) have a high impact on coagulation efficiency. In this work, the influences of three different additives (ferric salt (Fe), phosphate (P), and citric acid (CA)) on coagulation process/efficiency were investigated. Results showed that a small amount of extra Fe can facilitate the growth of Al flocs by providing more ‘active sites’. Although zeta potential and Df showed a limited change, the average floc size increased apparently and the increment was more obvious when Fe was added after the formation of the flocs. In contrast, P addition during the rapid mixing period will decrease the final average floc size, while the influence is less significant when P was added after the growth of the flocs. In terms of CA, a more striking negative effect on the growth ability of the flocs was observed compared to P. The strong complexing/coordination interactions between CA and aluminum hydroxide is the main reason behind the influence. CA also significantly decreased the Df value of the flocs compared to P, and Df showed a comparatively higher decrease when P or CA was added during the rapid mixing stage compared to the addition after the flocs formation. These results indicated that the addition of CA or P during the rapid mixing stage ‘inactivated’ or occupied more ‘active sites’ on the preliminarily formed Al NPs during the hydrolysis process, and therefore presented stronger impact on the morphology/size of the formed flocs.

Fabrication and characterization of Al–CuO nanocomposites prepared by sol-gel method

In this study, Al–CuO nanocomposites were fabricated by sol-gel method. As a contrast, the thermite was prepared by physical mixing at the equivalence ratio of 0.5, 1, 2, respectively. The intermediates and samples as prepared were characterized by SEM and XRD. The exothermic properties of the two samples prepared at different equivalence ratios were tested and the reaction products were characterized by XRD. The SEM results show that the sample prepared by the sol-gel method demonstrates a micron-sized agglomerated sphere formed by a mutual wrapping of Al NPs and CuO NPs, and the particles are evenly distributed in the agglomerate. In addition, when the content of Al powder is seriously insufficient, the heat release of the sample prepared by physical mixing is 1.6 times that of by sol-gel method. With the increase of Al powder content, the exothermic properties of Al/CuO NPs prepared by sol-gel method began to increase significantly compared with physical mixing and the difference is 1.5 times when the equivalence ratio increases to 2. It can be concluded that the reason for this result may be attributed to the different mass transfer modes of components due to the different morphologies of samples.

Synthesis and Multipole Plasmon Resonances of Spherical Aluminum Nanoparticles.

In comparison to Au and Ag, the high plasma frequency of Al allows multipole plasmon resonances from the ultraviolet to visible (UV-vis) range to be achieved by its nanoparticles with much smaller sizes and even a spherical shape. Herein, we report the high-supersaturation growth of monodisperse spherical Al nanoparticles (Al NPs) from 84 to 200 nm and their distinctive size-dependent multipole plasmon resonance properties in the UV-vis range. Linear relationships between the particle diameter and resonance peak positions of the dipole, quadrupole, and octupole were observed experimentally and confirmed by finite-difference time-domain (FDTD) calculations. FDTD calculations further reveal the high scattering-to-extinction ratio of multipole modes for the particle diameters >100 nm. The extinction coefficients of spherical Al NPs with different diameters were also determined. The excellent matching between the experimental and simulated results in the present work not only offers a standard for the synthesis and characterization of high-quality Al NPs but also provides new insight into the multipole plasmonic properties of Al NPs for advanced optical and sensing applications.

Probing the reaction mechanism of Al/CuO nanocomposites doped with ammonium perchlorate

The oxide shell of Al nanoparticles (Al NPs) prevents further reaction of Al/CuO nanothermites which reduces Al utilization efficiency and the performance of the nanothermites. However, the performance of Al/CuO nanothermites can be improved by adding ammonium perchlorate (AP). In this work, in order to confirm and explain the enhancement mechanism of AP on Al/CuO nanothermites, Al/CuO/NC and Al/CuO/NC/AP composites were prepared using the electrospray method. The composites were characterized by differential scanning calorimetry/thermogravimetric, x-ray diffraction, scanning electron microscope and transmission electron microscopy. Meanwhile, the ignition temperature and the time-resolved analysis of the rapid pyrolysis chemistry of the composites were tested using T-jump and time-of-flight mass spectrometry, respectively. The results show that Al NPs of Al/CuO/NC/AP composite are hollow compared to Al/CuO/NC composite after reaction. Al NPs and CuO NPs reduce the decomposition temperature and facilitate the rapid decomposition of the AP, and the decomposition products of the AP can destroy the oxidation layer of Al NPs. This result facilitates the further conduct of the thermite reaction. A mutually reinforcing relationship exists between the Al/CuO/NC composites and AP.

Thermodynamics and performance of Al/CuO nanothermites with different storage time

The storage stability of energetic materials is important for their application. In our previous work, Al/CuO nanothermites was applied to a MEMS-based solid propellant micro thruster (SPM) array because of its short ignition delay and high reaction rate.In the current work, the storage stability of Al/CuO nanothermites, which were prepared by electrospray method and stored with different storage time, was systematically researched. The activation energy of Al/CuO nanothermites were measured by DSC. The ignition temperature and the curve pressure history of Al/CuO nanothermites were measured using T-jump and constant-volume pressurization tests, respectively. Further, the nanothermites were characterized by XRD, XPS, SEM and TEM.The results show that the morphology and mixture uniformity of the nanothermites after a long-time storage did not change significantly. The slow decomposition of NC and the thickening of oxide layer of Al NPs existed in the storage of Al/CuO nanothermites, analysed by XPS. The activation energy (Ea ) of Al/CuO nanothermites after storage for different time was determined using the method of Kissinger, as shown in Figure 1. Ea was decreased from 272.8 kJ/mol to 154 kJ/mol after storage for 13 months. When stored for 0, 7 and 13 months, the peak pressures of Al/CuO nanothermites were 685.8 kPa, 626.3 kPa and 625.5 kPa, respectively. In addition to the ignition temperature, it was 775 °C, 739 °C and 754 °C, respectively. This result indicated that the ignition and combustion properties of Al/CuO nanothermites are obviously reduced when stored for a long time, at room temperature.The full version of this extended abstract will appear in Defence Technology in 2020.

Modulation of Synaptic Plasticity Mimicked in Al Nanoparticle‐Embedded IGZO Synaptic Transistor

AbstractDiverse artificial synapse structures and materials are widely proposed for neuromorphic hardware systems beyond von Neumann architecture owing to their capability to mimic complex information processing tasks such as image recognition, natural language processing, and learning. Nevertheless, temporal and spatial randomness in the movement of ion and electron particles that exist in materials usually prevents the solid‐state‐based synaptic devices from enabling the reliable modulation of synaptic plasticity. An aluminum nanoparticle (Al NP)‐embedded indium gallium zinc oxide (IGZO) synaptic transistor whose spike peak level and conductance change can be precisely modulated by the density of Al NPs within the IGZO channel is demonstrated. Essential synaptic functions including excitatory or inhibitory postsynaptic current, paired pulse facilitation, and short‐term potentiation or depression are also thoroughly emulated in the synaptic transistor device with the most optimized Al NP density: IGZO:Al NPs (6 nm). Moreover, controllable switching from short‐term to long‐term memory regimes essential for a learning task is demonstrated. Simulation results prove that this transistor can provide a decent recognition accuracy for neuromorphic computing. Indeed, the integrated IGZO:Al NP synaptic circuit with the effective synaptic plasticity will facilitate the implementation of a reconfigurable neuromorphic computing system.

Effects of metal oxide nanoparticles on combustion and gas-generating performance of NaN3/Al composite powders ignited using a microhotplate platform

We investigated the effects of different metal oxide (MO) nanoparticles (e.g., CuO, KIO4, Fe2O3) on the combustion and gas-generating characteristics of sodium azide microparticle (NaN3 MP; gas-generating agent) and aluminum nanoparticle (Al NP; heat source) composite powders. The NaN3 MP/Al NP/MO NP composite powders were stably ignited using a microhotplate (MHP) heater. The addition of CuO and KIO4 to the NaN3 MP/Al NP composite powders resulted in relatively high burn rates and high pressurization rates upon MHP-assisted ignition. This suggests that the highly reactive CuO and KIO4 NPs significantly increased the combustion of the Al NPs; as a result, sufficient heat energy was generated via the active aluminothermic reaction to thermally decompose the NaN3 MPs. Finally, the gas generating properties of NaN3 MP/Al NP composite powders mixed with various MO NPs were tested using homemade inflatable small airbags. The airbags were fully inflated within ~20 ms when CuO and KIO4 NPs were added to the NaN3 MP/Al NP composite powders. However, the addition of Fe2O3 NPs to the NaN3 MP/Al NP composite powder resulted in a slow and only partial inflation of the airbag due to an incomplete aluminothermic reaction, which was due to a slow combustion reaction between the Al NPs and relatively weak oxidizer of the Fe2O3 NPs. This suggests that the rapid, stable, and complete thermal decomposition of NaN3 MP/Al NP composites can be effectively achieved by employing highly reactive nanoscale oxidizers.

Synthesis of Aluminium Nanoparticles Using Electrochemical Method

Aluminium nanoparticles (Al NPs) have been synthesized using electrochemical method. The synthesis was conducted by electrolysis of aluminium metal in a sodium citrate solution as an electrolyte solution. Formation of Al NPs was investigated on the variation of potential (5-50 V), concentration of electrolyte solution (0.02-0.42 M), and electrolysis time (15-75 minutes). The obtained product was characterized by X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM), Energy Dispersive X-Ray (EDX), and UV-Vis Spectrophotometer. XRD pattern indicate that the obtained product was aluminium nanoparticles. The result show that the size of Al NPs were 56-63 nm with the Al compositions of 7.08%. The optimum condition was reached at 40 V with 0.18 M sodium citrate solution during 45 minutes electrolysis process. The plasmon band peak was found at 234 nm. In this condition Al Nps is more stable.

Toxic effects of cutaneous and oral exposure to aluminum and magnesium nanoparticles on brain tissue in rats

In this study, it was aimed to research the effects of cutaneous and oral exposure to aluminum nanoparticles (Al-NPs) and magnesium nanoparticles (Mg-NPs) on the brain tissue, which is vitally important in terms of its structure and functions. The study was performed on Wister-Albino rats, which were divided into 10 groups, such as control groups (groups 1 and 2), groups, to which Al and Mg NPs were applied as 500 mg/kg and 1500 mg/kg orally (groups 3-6) and 1000 mg/kg and 2000 mg/kg cutaneously (groups 7-10). The dosages were administered as a single dose. While brain tissue and serum MDA levels as well as brain tissue TNF-α and IL-6 levels have significantly increased in the group, to which 1500 mg/kg Mg-NPs was applied orally, significant decreases have also been observed in brain tissue GPX and SOD levels of the same group. Additionally, meaningful decreases in brain tissue SOD levels and significant increases in TNF-α and IL-6 levels have been observed in the group, to which 1500 mg/kg Al-NP was applied orally. On the other hand, it was found that brain tissue GPX and SOD levels of the group, to which 2000 mg/kg Mg-NP was applied cutaneous, have been decreased significantly. Histopathological examinations have also supported these findings. At the end of the study, it was observed that the toxic effect of Al and Mg NPs has varied, depending on the application method, dosage and duration.

Preparation and Combustion Performance of B/PVDF/Al Composite Microspheres

AbstractIn order to solve the problems that boron nanoparticles (B NPs) are easy to agglomerate, low in combustion efficiency and difficult to ignite, 80 nm B NPs were doped with 50 nm aluminum nanoparticles (Al NPs) by electrospraying using 10 wt % PVDF as binders. The prepared B/PVDF/Al composite microspheres with diameter of 1∼5 μm were examined by scanning electron microscopy (SEM). Elemental maps confirmed the uniform distribution of B and Al NPs with the coating of polyvinylidene fluoride (PVDF). The thermal properties were tested by thermogravimetry‐differential scanning calorimetry (TG‐DSC), and the combustion process of samples in air was recorded by a high‐speed camera. The results showed that PVDF can reacted with the oxide layer on the surface of Al (Al2O3) and B (B2O3) NPs to promote the combustion and energy release of B/PVDF/Al. In addition, the thermal reactivity of B/PVDF/Al increased as the Al NPs content increases. Al NPs could reduce the ignition energy of B/PVDF/Al, allowing it to burn stably in air. A thermal reaction mechanism was proposed to explain qualitatively the four‐stage pattern of B/PVDF/Al decomposition observed in TG‐DSC curves.

Ultrafast relaxation dynamics of aluminum nanoparticles in solution

Colloidal aluminum nanoparticles (Al NPs) can support surface plasmon resonances spanning ultraviolet to near-infrared wavelengths because of the high electron density of Al metal and the favorable position of its interband transitions. Free-standing colloidal Al particles can be synthesized using a variety of methods and suspended in solution, but there are still few investigations of its ultrafast decay processes. We used transient absorption spectroscopy (TAS) to examine the ultrafast relaxation dynamics of colloidal Al NPs suspended in ethanol. The electron-phonon (e-p) coupling times of Al NPs are equivalent or even longer than the e-p coupling times of Ag nanocubes or Au bipyramids in solution. The prolonged hot-electron transfer in Al NPs is likely due to the presence of the Al2O3 shell, which causes excited charge carrier trapping-detrapping at the metal core-oxide shell interface.

Oxidation of Levitated exo-Tetrahydrodicyclopentadiene Droplets Doped with Aluminum Nanoparticles

Advancement of the next generation of air-breathing propulsion systems will require developing novel high-energy fuels by adding high energy-density materials such as aluminum to enhance fuel performance. We present original measurements, obtained by exploiting the ultrasonic levitation technique, to elucidate the oxidation of exo-tetrahydrodicyclopentadiene (JP-10; C10H16) droplets doped with 80 nm-diameter aluminum nanoparticles (Al NPs) in an oxygen-argon atmosphere. The oxidation was monitored by Raman, Fourier-transform infrared (FTIR), and ultraviolet-visible (UV-Vis) spectroscopies together with high-speed optical and IR thermal-imaging cameras. The addition of 0.5 wt % of the Al NPs was critical for ignition under our experimental conditions occurring at 540 ± 40 K. Diatomic radicals such as OH, CH, C2, and AlO were observed during the oxidation of the doped JP-10 droplets, thus providing insight into the reactive intermediates. The influence of the Al NPs on the reaction mechanism is discussed.

Detachable surface plasmon substrate to enhance CH3NH3PbBr3 lasing

Surface plasmons can make highly spatial confinement and near-field enhancement at the metal/dielectric interface and decrease optical loss. Here, we introduced detachable aluminum nanoparticles (Al NPs) substrate to enhance CH3NH3PbBr3 perovskite lasing performances, and compared the lasing actions between Al-CH3NH3PbBr3 and prime CH3NH3PbBr3 microcuboid to understand the mechanism. Based on Al surface plasmons coupled excitation in Al-CH3NH3PbBr3 hybrid system, the lasing threshold is dramatically reduced more than 27% and the stimulated emission of CH3NH3PbBr3 improved 10 times.

Al-In nanoparticles and their clusters as solar spectrum plasmonic resonators

Noble metal nanoparticles are the most widely used systems of plasmonic scatterers. They have been used for applications involving light harvesting, optical filters etc. However, scalability of technologies is impacted; this has to do with their prohibitive costs. Use of earth-abundant elements is thereby worth exploring. Al NPs, standalone is a reasonable solar spectrum scatterer, over a broad wavelength range (400–800 nm). But Al plasmonic response is sensitive to surface oxidation and corrosion, which compromises its performance when deployed in a device. Here we show that Al-In alloys are plausible choices. Al-In nanoalloys of diameter 85 nm show a scattering cross section of nearly 8 × 10−14 m2. Al-In nanoparticles scattering cross-sections are invariant with In concentration. Furthermore, all features of Al plasmon resonance are retained making it relevant for solar applications. Al-In heptamers of diameter 150 nm show resonance and anti-resonance peaks at 510 nm and 590 nm wavelengths respectively; making it relevant for prospective filter applications.

Volume holographic recording in Al nanoparticles dispersed phenanthrenequinone-doped poly(methyl methacrylate) photopolymer

High-performance material plays a crucial role in holographic data storage, which is a noteworthy technology with potential applications in the field of high capacity data storage. We report on a new kind of holographic storage material based on aluminum nanoparticles (Al NPs) dispersed phenanthrenequinone-doped poly(methyl methacrylate) (PQ/PMMA) photopolymer. Al NPs are efficiently synthesized in a monomer solvent using laser ablation in liquids without chemical precursors. It is shown that an increase in diffraction efficiency and recording sensitivity is achieved in both traditional holography and polarization holography by doping with Al NPs. After 4 h of ablation, the new material exhibited an improvement in the diffraction efficiency for both traditional holography and polarization holography from 2.85% to 57.15% and from 0.6% to 4.07%, respectively. We also investigated the image recording and reconstruction performance for both traditional and polarization holography and the results indicate that the proposed material has noticeable potential as a holographic storage material. Additionally, it also possesses excellent potential for holographic position multiplexing recording. We conclude that laser ablation in a liquid is a promising option for processing low-cost nano-doped holographic storage material.

Comparison study of the ignition and combustion characteristics of directly-written Al/PVDF, Al/Viton and Al/THV composites

The aluminum–fluorine reaction is attracting growing interest due to its higher density over aluminum–oxygen. Fluorine rich polymers are particularly interesting for their applications as an energetic binder in advanced additive manufacturing of energetic materials. In this paper, three soluble polymers of PVDF (59 wt% F), Viton (66 wt% F) and THV (73 wt% F) are incorporated with aluminum nanoparticles (Al NPs) and prepared as free-standing films using solvent-based direct writing. The three composite films are compared for their mechanical properties as well as the ignition and combustion performance. Tensile stress was found to order as Al/PVDF > Al/THV > Al/Viton while the elasticity of Al/Viton is much higher than the other two. The burn rate of different composite films increases with Al content, while the flame temperature peaks slightly fuel-rich. The Al/PVDF had the highest burn rate, however, the flame temperature ordered as Al/THV (∼2500 K) > Al/Viton (∼2000 K) > Al/PVDF (∼1500 K), consistent with fluorine content. With higher fluorine and lower hydrogen content, THV releases more CFx gas than HF, which generates higher temperature. However, HF which is predominantly produced from PVDF has the lowest ignition by far and may be responsible for its high flame speed.

On the promotion of high temperature AP decomposition with silica mesoparticles

Silica particles are known to enhance the combustion of aluminum (Al) and ammonia perchlorate (AP) based energetic materials although the role of silica remains unknown. In this paper, AP/SiO2 mesoparticles ((AP/SiO2)m) and Al/(AP/SiO2)m composite particles were prepared and the thermal properties/reactivity evaluated. Composites with 7 wt% SiO2 have a reactivity ∼7 times higher than that of Al/AP. The ignition temperature of Al/(AP/SiO2)m was also found to be ∼100 °C lower compared to that of Al/AP. The thermal decomposition process of (AP/SiO2)m and Al/(AP/SiO2)m composite particles were investigated using both low and high heating rates. During slow heating, with the addition of silica, the decomposition of AP transitioned from a slow two-stage to a rapid one-step process. At high heating rate, the release temperature of ClO2 and O2 from AP is below ∼400 °C, while for (AP/SiO2)m case, the peak release temperature is much higher at ∼650 °C, when Al NPs reach its melting point and are ready to react. This may explain why Al/(AP/SiO2)m shows higher reactivity than Al/AP composite particles.

Graphitic coated Al nanoparticles manufactured as superior energetic materials via laser ablation synthesis in organic solvents

The large heat release predicted in the early investigations of energetic aluminum nanoparticles (Al NPs) used in solid-state propulsion and pyrotechnics has been offset by hindered diffusion-limited detonation rates due to excess oxide shell formations and surface area loss from aggregations. We address these challenges by manufacturing graphitic shell coated Al NPs (<20 nm sizes) via laser ablation synthesis in solution (LASiS) to preserve high surface areas and interfacial properties of Al NPs. Specifically, we use a high-energy laser to ablate Al pellets confined in either acetone or toluene to coat the laser-ablated Al NPs with graphitic shells generated from the thermal pyrolysis of the organic solvents. Energetic activities of the C/Al NPs were tested via the laser-induced air shock from energetic materials (LASEM) technique. We demonstrate that synthesis parameters such as organic solvents, laser flux and ablation times can be tuned to provide superior control of NP sizes/aggregation with the aid of the C shell formations and, in turn, their energetic behavior. This study unveils the synthesis-structure-property relations in LASiS-based manufacturing of energetic nanocapsules within graphitic shells that are safe to handle and can undergo kinetically controlled spontaneous energy release under desired conditions.

Nanoscale surface reactions by laser irradiation of Al nanoparticles on MoO3 flakes

Surface reactions between heated aluminum nanoparticles (Al NPs) and thin α-MoO3 sheets are investigated. Localized photothermal heating on Al NP clusters is provided by a Raman spectrometer laser, while enhanced heating rates and imaging resolution are enabled by the use of a plasmonic grating substrate. Prominent linear reaction zones extending from Al NPs in the 〈001〉 crystal direction are observed on the surface of the host MoO3 sheets after heating. Raman spectroscopy and x-ray diffraction indicate that α-Al2O3 is generated within these extended reacted regions, while AFM and SEM indicate that the topology of the reaction regions are indistinguishable from the MoO3 host. We hypothesize that these Al2O3 zones are formed by surface diffusion and subsequent sub-surface adsorption of heated Al adatoms along the low-energy 〈001〉 MoO3 direction. Understanding and controlling these reaction mechanisms could lead to enhanced combustion of Al/MoO3 nanothermite systems.

Effect of aluminum micro- and nanoparticles on ignition and combustion properties of energetic composites for interfacial bonding of metallic substrates

In this study, the effect of micro- and nanoscale energetic materials in the formulation of aluminum microparticles (Al MPs)/aluminum nanoparticles (Al NPs)/iron oxide nanoparticles (Fe2O3 NPs) as a heat energy source for melting solder microparticles (SAC 305 MPs) on the interfacial bonding properties of Cu metallic substrates, is investigated. The optimized mixing ratio is Al MP:Al NP:Fe2O3 NP = 30:30:40 wt%, which generates a maximum total exothermic energy of ∼2.0 kJ g−1. The presence of Al NPs is essential to make stable ignition and initiation of Al MPs, which enable to attain relatively long combustion duration. The use of highly reactive Al NPs/Fe2O3 NPs can improve the aluminothermic reaction, while the addition of Al MPs to the Al NPs/ Fe2O3 NPs is also required to maintain their high thermal energy for a longer duration. An energetic material (EM) layer composed of Al MP/Al NP/Fe2O3 NP composites is employed as a heat source between solder material (SM) layers composed of SAC305 MPs. The SM/EM/SM multilayer pellets are assembled and ignited between interfacial Cu substrates for bonding. Thus, interfacial bonding between the Cu substrates is successfully achieved, and the resulting maximum mechanical strength for the bonded Cu substrates using the SM/EM/SM multilayer pellets increases by ∼40% compared to that when using a pure SM layer pellet. Hence, EM layers can act as both an effective heat energy generation source and a mechanical reinforcing medium, while the interfacial bonding process using SM/EM/SM multilayer pellets demonstrated herein provides an easy and versatile means of welding and jointing for industrial applications.