Micron-sized Composite Particles Research Articles

Construction of micro-nano structured Si/C anode armed with rGO hollow spheres for high-performance lithium-ion hybrid capacitors

Because of the unique ability to combine high energy density with high power density, lithium-ion hybrid capacitors (LICs) have generated significant interest. Among the various anodes being explored for LICs, silicon (Si) stands out as a particularly promising anode material due to its high theoretical capacity. Nevertheless, the formidable challenge lies in the rapid capacity fade resulting from substantial volume expansion. Herein, a simple and efficient spray drying technique was used to fabricate a Si@rGO@NC composite with micro-nano structure. In this composite, Si nanoparticles are encapsulated between reduced graphene oxides (rGO) hollow spheres and a layer of carbon is coated on the surface of both the Si and the micron-sized composite particles, forming a rigid and mechanically stable structure. The composite combines the high activity of nano-Si with the industrially easy handling of micron-scale particles. Moreover, the rGO hollow spheres not only enhance the electrical conductivity but also buffer the volume expansion of the electrode and provide channels for the rapid transport of electrolyte/ions. Thanks to its advantageous structural features, the constructed LICs with activated carbon as cathode can achieve a Max. energy/power density of 253.1 Wh kg−1/10,824.1 W kg−1 and maintain 84.3 % of its initial capacitance after 8000 cycles. The micro-nano structured design concept of Si-based materials developed in our work could offer new insights and directions for the future development of Si-based energy storage devices.

Cold spray deposition of high density polyethylene composite powders

In this paper, we investigate the use of the cold spray additive manufacturing technique to deposit micron-sized composite particles of high-density polyethylene (HDPE) compounded with either micron or nanometer sized particles of silicon dioxide (SiO2) or copper (Cu). In this study, the mass fraction of the SiO2 and copper particles added into the final composite powders was varied between 0.5 % and 9.1 % and the deposition efficiency of each composite powder was measured. Deposition of the composite powders onto an HDPE substrate was successful even at the highest particle loadings tested. In each case, an optimal mass fraction of silicon dioxide or copper particles was observed with a maximum value of deposition efficiency larger than that of the pure HDPE. For the silicon dioxide composite powders, the deposition efficiency nearly doubled compared to the pure HDPE powders. The improvement of deposition efficiency at moderate particle loadings is likely due to the increase in the impact kinetic energy of the particles resulting from the increase in the density of the composite powders. While the decrease in deposition efficiency at high particle loadings is likely the result of the increased coverage of the silicon dioxide and copper particles on the surface of the HDPE powders limiting the interaction between the HDPE of the composite powder with the HDPE substrate. SEM images show that it is possible to create a smooth, dense, and uniform thin-film polymer composite coating using cold spray.

Combustion of explosively dispersed Al-Mg-Zr composite particles

Micron-sized composite particles consisting of an Al-Mg alloy and Zr were produced via mechanical milling. Three different particle chemistries were prepared with varying ratios of the Al-Mg alloy to Zr. In addition, the prepared powders were size selected using mechanical sieves. Explosively launched combustion properties of these powders were independently measured as a function of the particle stoichiometry and particle size. Ignition temperatures were measured utilizing a heated filament experiment while combustion efficiency was characterized by measuring the dynamic pressure produced in a closed bomb in which the powder was explosively dispersed under fixed enthalpy conditions. Commercial Al powder, Valimet H-2, was also tested alongside these materials as a benchmark. High-speed video and thermocouple measurements were also obtained for the closed bomb experiments. We observed an increase in combustion efficiency from 30% to 80–90% in the composite materials compared to the pure Al. Furthermore, reaction products were collected and analyzed by powder x-ray diffraction to gain further insight into combustion efficiency and reaction pathways. We observed significant improvement of combustion under these experimental conditions, including higher quasi-static pressures and higher rates of pressure rise, with composite fuels compared to pure Al, even without a secondary oxidizer additive.

Custom particle morphology in energetic nanocomposites prepared by arrested reactive milling in immiscible liquids

The effect of polar and nonpolar liquid process control agents (PCA) on properties of metal rich Al/CuO thermites prepared by Arrested Reactive Milling was studied. Acetonitrile and hexane, and their mixtures were used as PCA. Milling in nonpolar hexane results in fully dense, micron-sized composite particles of 100nm-scale CuO inclusions in an Al matrix. Using polar acetonitrile results in a mixture of nano-sized, largely unagglomerated Al and CuO particles. Porous composites, agglomerated to different degrees, formed in hexane-acetonitrile mixtures. In particular, micron-sized porous spherical composite particles formed in a mixture with 25% acetonitrile. Such spherical composites may result from interaction of suspended powder particles with stressed droplets of a Pickering emulsion forming when immiscible liquids serve as PCA. Despite dramatic changes in the powder morphology, all composites were reactive. Systematic differences, discussed in the text, were observed in their ignition temperatures and oxidation kinetics.

Nanocomposite Catalysts Obtaining by Mechanochemical Technique for Synthesizing Carbon Nanotubes

In the current research reactive milling was employed to fabricate the nanocomposite precursors for the catalytic growth of carbon nanostructures. For this purpose several mixtures of iron oxide and aluminum powders along with different amounts of graphite powders were mechanically milled for different times. The adiabatic temperature and the heat released from exothermic reaction during milling were controlled by varying the percentage of graphite. Synthesized powders were analyzed by X-ray diffraction, scanning electron microscope, transmission electron microscope, and thermogravimetric analysis. Propane gas was used in a chemical vapor deposition technique as a source of carbon to synthesize carbon nanotubes (CNTs). The results show that decomposition efficiency of propane promotes in the case of using milled powders and leads to a high yield of CNTs formation. The mechanical induced reaction between aluminum and iron oxide in the presence of graphite was used to produce micron-sized composite particles. These particles contain separated iron nanoparticles and dispersed in the matrix of ball milled graphite and alumina. It was found that the yield of fabrication of CNTs increased as decomposition temperature of propane increased from 625 to 850°C. Microscopic evaluation by SEM proved that the productivity of CNTs grown on milling derived catalysts was much high at higher annealing temperatures (700°C and 850°C) rather than that of lower temperature (625°C). The results of TGA tests showed that the amount of produced carbon nanotube depends on annealing temperature and as annealing temperature changed from 652 to 850°C carbon nanotube content increased from 13 to 85 wt%. TEM results demonstrated that CNTs were grown according to tip-growth mechanism.

Peculiarities of photonic nanojet formation from multilayer spherical microparticles

The main characteristics of “photonic nanojets” (the cross-section size, length, and peak intensity) formed in the vicinity of micron-sized composite particles consisting of a core and several shells with different refractive indices are considered. It is shown that it is possible to manipulate the parameters of a “photonic nanojet”, in particular, extend its size or increase its peak intensity by changing the refractive index of the neighboring shells in the composite spherical microparticles.

Controlling the parameters of photon nanojets of composite microspheres

We consider the spatial and amplitude characteristics of PNJ forming in the neighborhood of the shadow surface of micron-sized composite particles consisting of a nucleus and a shell with various refraction indices when laser radiation scatters on them. We study the longitudinal and transverse dimensions of a photon flux and its peak intensity depending on the microparticle shell thickness. We show that a certain choice of the refraction index of the shell relative to the nucleus in two-layer composite spherical microparticles can significantly lengthen the forming PNJ or increase their peak intensity. The width of the photon flux during this changes insignificantly.

Nanocomposite thermite powders prepared by cryomilling

Reactive nanocomposite materials have been recently prepared by Arrested Reactive Milling (ARM), a method based on mechanical milling of component powders to form micron-sized composite particles where components are mixed on a scale of about 100 nm. The milling temperature affects both the refinement rate and the final product properties. In this paper we report an effort to prepare Al–CuO reactive nanocomposite powders at cryogenic temperatures. The material was processed in a liquid nitrogen bath using steel vials and balls of different sizes as milling media. The number and dimensions of the milling balls as well as the milling time were systematically varied. The products were characterized by X-ray diffraction, particle size analysis, and scanning electron microscopy. Thermal characteristics were studied using a custom wire-ignition setup and differential scanning calorimetry. Results show that the uniformity of mixing and reactivity of the nanocomposite powders can be improved using milling at cryogenic temperatures.

New micrometer-sized monodispersed self-assembled amphiphilic polystyrene/poly( n-butyl methacrylate) composite particles of hemispherical morphology: synthesis and characterization

Uniform micron-sized polystyrene template particles surface grafted with polyvinylpyrrolidone were prepared by dispersion polymerization of styrene in alcoholic solvents in the presence of polyvinylpyrrolidone as stabilizer. Poly(acrylic acid, sodium salt) derivatized polystyrene/ poly( n-butyl methacrylate) micron-sized composite particles of hemispherical morphology and narrow size distribution were formed by a single-step swelling of the uniform polystyrene template microspheres dispersed in water with emulsion droplets of the monomer n-butyl methacrylate containing the initiator benzoyl peroxide. n-Butyl methacrylate was then polymerized at 73 °C within the template microspheres in the presence of the water-soluble monomer acrylic acid, sodium salt. The sodium ions of the poly(acrylic acid) derivatized composite particles were then replaced with dodecylammonium ions by interacting these composite particles with excess dodecylamine hydrochloride. As a result of this process the surface of the hemispherical composite particles composed of hydrophilic polyvinylpyrrolidone chains on the polystyrene phase and hydrophobic dodecyl groups on the poly(acrylic acid) derivatized poly( n-butyl methacrylate) phase. These newly formed micron-sized composite particles show amphiphilic characteristics and aggregate to form micelle-like spherical clusters. The ability to control the template polystyrene microspheres’ dimensions and various polymerization parameters may open a wide variety of self-assembled spherical and other structures composed of micron-sized particles for various fundamental and practical applications such as self-assembly processes and the formation of photonic bandgap crystals.

Preparation of electrically conducting particles consisting of a polymer core and a metallic copper shell

Micron-sized composite particles consisting of spherical polymer cores and metallic copper shells were prepared. Basic cupric carbonate was coated on sulfonated polymer particles by pH-controlled hydrolysis of cupric nitrate. The thickness of the coating layer was controlled by the number of polymer particles. Addition of CO2 during aging increased the shell thickness. Electrically conducting particles were obtained by reduction with hydrogen of the composite particles obtained.