Flake-like Shape Research Articles

Tunable magnetic and microwave absorption properties of Sm1.5Y0.5Fe17-xSix and their composites

In this work, we report the magnetic and microwave absorption properties of the Sm1.5Y0.5Fe17-xSix (0.0 ≤ x ≤ 1.5) and their paraffin composites. It was found that the introduction of Si can remarkably tune the intrinsic magnetic properties of the Sm1.5Y0.5Fe17-xSix, making the Sm1.5Y0.5Fe17-xSix-paraffin composites excellent microwave absorption materials. The milled Sm1.5Y0.5Fe17-xSix powders have flake-like shape with length of 5 μm and thickness of 100 nm, consisting of sphere-like crystalline grains with size of about 11 nm. In the tested frequency region, the permeability μ′ of the composites shows, especially at higher frequency, little decrease after introducing the Si, while the permittivity ε′ decreases by about 40% with Si content increasing from x = 0.0 to x = 1.5, which is advantageous to improve the impedance match and enhance the performance of the microwave absorption. The peak frequency (fp) of the reflection loss (RL) peak with same composite thickness increases with increasing the Si content, in accordance with the variation of the calculated resonance frequency *fr = f(Ms, Haθ, Haφ, μi). Moreover, the qualified bandwidth (QB, RL ≤ −10 dB) also increases remarkably with increasing the Si content due to a better impedance match. An extraordinary dielectric microwave absorption peak was also found in the composites, which can further increase the QB in some degree. A maximum RL of −55.1 dB and a QB of 3.7 GHz (12.7–16.4 GHz) are obtained for the Sm1.5Y0.5Fe15.5Si1.5-paraffine composite, suppressing many reported microwave absorbing materials.

Study on the RF inductively coupled plasma spheroidization of refractory W and W-Ta alloy powders

Spherical powders with good flowability and high stacking density are mandatory for powder bed additive manufacturing. Nevertheless, the preparation of spherical refractory tungsten and tungsten alloy powders is a formidable task. In this paper, spherical refractory metal powders processed by high-energy stir ball milling and RF inductively coupled plasma were investigated. By utilizing the technical route, pure spherical tungsten powders were prepared successfully, the flowability increased from 10.7 s/50 g to 5.5 s/50 g and apparent density increased from 6.916 g cm−3 to 11.041 g cm−3. Alloying element tantalum can reduce the tendency to micro-crack during tungsten laser melting and rapid solidification process. Spherical W-6Ta (%wt) powders were prepared in this way, homogeneous dispersion of tantalum in a tungsten matrix occurred but a small amount of flake-like shape particles appeared after high-energy stir ball milling. The flake-like shape particles can hardly be spheroidized in subsequent RF inductively coupled plasma process, might result from the unique suspended state of flaky particles under complex electric and magnetic fields as well as plasma-particle heat exchange was different under various turbulence models. As a result, the flake-like shape particles cannot pass through the high-temperature area of thermal plasma torch and cannot be spheroidized properly.

Synthesis and characterization of poly(2-chloroaniline) by chemical oxidative polymerization

Nano-scaled P2ClAn was synthesized via chemical oxidation polymerization. The effects of oxidant concentration, surfactant type and concentration on the synthesized P2ClAn were investigated. Electrical conductivity results revealed that the undoped P2ClAn synthesized by APS at the monomer:oxidant mole ratio of 1:1 was the most suitable condition to yield the highest P2ClAn electrical conductivity. The morphological structures of P2ClAn changed from an irregular-shaped structure to a cylinder shape or a flake-like shape depending on the surfactant type and concentration. P2ClAn in the presence of SDS, used as a surfactant template, provided particles with an average nanosize of 56.2 nm and higher electrical conductivity than using CTAB. Further doping process of P2ClAn was studied using HClO4. The electrical conductivity of the doped dP2ClAn/SDS50 increased by three orders of magnitude, at the monomer:doping mole ratio of 1:25 possessing the highest electrical conductivity of 10.47 S cm−1, relative to the synthesized P2ClAn without doping.

Fabrication of Si nanopowder from Si swarf and application to high-capacity and low cost Li-ion batteries

Si nanopowder is expected as a high capacity anode active material for Li-ion batteries (LIBs) due to its superior theoretical capacity of ∼3600 mA h/g, which is approximately one order of magnitude higher than that of conventional graphitic materials. We have succeeded in fabrication of Si nanopowder from Si swarf using the cost-effective beads milling method. The Si nanopowder consists of Si nano-crystals having flake-like shape with two largely different sizes, i.e., several hundred nm sizes and sizes less than 15 nm. The mode diameter of Si crystallites fabricated from Si swarf is 6.3 nm. The performance of the nano-Si electrode for Li ion batteries is greatly improved by carbon-coating on Si nanomaterials and addition of fluoroethylene carbonate (FEC) in an electrolyte solution. By addition of 10–15 wt% FEC, a stable and thin (10–20 nm) solid-electrolyte interphase (SEI) layer is formed on the electrode, and the number of cracks on the electrode surfaces after the 100th cycle greatly decreases. Addition of FEC improves the cyclability and decreases the SEI resistance (RSEI) and the charge transfer resistance (Rct). However, excess FEC (25 wt%) suppresses free volume expansion of Si nanopowder due to formation of thick SEI, leading to smooth Si surfaces, and resulting in an increase in Rct. Carbon-coating on Si nanopowder greatly improves the cyclability even with the low C/Si ratio of 0.1. In the case of excess carbon-coating, Si nanopowder agglomerates during carbon-coating, which causes peeling-off of a part of carbon-coated Si nanopowder during lithiation, resulting in a decrease of the capacity. The delithiation capacity higher than 1600 mA h/g after the 100th cycle with the current density of 1800 mA/g is achieved by setting the C/Si ratio at 0.1 and the FEC concentration at 10 wt%.

Alloying Behavior and Properties of Al-Based Composites Reinforced with Al85Fe15 Metallic Glass Particles Fabricated by Mechanical Alloying and Hot Pressing Consolidation

In this study, Al85Fe15 metallic glass particles with high onset crystallization temperature (1209 K) were synthesized by a mechanical alloying method. High-quality 6061Al-based composites reinforced with Al85Fe15 metallic glass particles were fabricated by a vacuum hot-pressing sintering technique. The glass particles with flake-like shape are distributed uniformly in the Al matrix. The bulk composites possess high relative density, excellent hardness and strength. The microhardness values of the Al-based bulk composites with the additions of 20 vol.% and 30 vol.% Al85Fe15 particles are 204 MPa and 248 MPa, respectively, which are much higher than that of 6061Al (61 MPa). The compressive yield strength of the 30 vol.% glass-reinforced composite is 478 MPa, which is enhanced by 273% compared with 6061Al. The amorphous characteristic and homogeneous dispersion of glass particles account for the excellent mechanical properties of the Al-based composites. In addition, the corrosion behavior of Al-based composites in a seawater solution has been investigated by electrochemical polarization measurements. Compared to 6061Al, the 30 vol.% glass-reinforced composite shows the lower corrosion/passive current density and larger passive region, indicating the greatly enhanced corrosion resistance.

Microstructural and magneto-transport properties of Bi1.6Pb0.4Sr2Ca1−xGdxCu2O8+δ superconducting ceramics

This study aims to investigate the effect of Gd doping on the phase formation, microstructure, transport and magnetic properties of the Bi(Pb)-2212 system. A series of superconducting bulks with a nominal composition of Bi1.6Pb0.4Sr2Ca1−xGdxCu2O8+δ with x=0, 0.05, 0.10 and 0.15 are synthesized by the solid state synthesis route. The formed samples are characterized by means of X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectrometer (EDS), electrical transport and magnetic measurements. The experiment results reveal that all the samples doped are composed of Bi-2212 phase and traces of Bi-2201 secondary phase when compared to the undoped sample. The refinement of cell parameters shows that the doping reduces the cell volume of the samples. The texture degree decreases with doping while the degree of orthorhombicity increases. Quantitative EDS analysis confirms that Gd atoms are successfully introduced into crystalline structure. The SEM micrographs show randomly distributed grains with a flake-like shape. The highest value of onset critical transition temperatures is obtained for x=0.10 and is about 90.22K, which correlates well with the observed slope of resistivity and the hole concentration of the CuO2 layers. Magnetic hysteresis loops suggest that the diamagnetism, remanant magnetization and lower critical field are better for x=0.10. Based on the enhancements of both grain boundary weak-links and flux pinning centers, improvement of the critical current densities and flux pinning density is obtained with this kind of doping.

Effect of different annealing atmospheres on the structural and luminescence properties of Ce3+-doped YAG phosphors synthesized by sol–gel method

Cerium trivalent doped yttrium aluminum garnet (YAG:Ce3+) yellow phosphors have been successfully synthesized by sol–gel process and heat-treat at 900°C for 2h in different atmospheres such as vacuum, air and nitrogen gas. The objective of the present paper is to study the effects of annealing atmosphere on the structural, morphological and luminescence properties of YAG:0.5% Ce3+ powders. After elaboration, the samples were characterized by X-ray diffraction, field emission scanning electron microscopy (FESEM), Fourier transforms infrared spectroscopy (FTIR) and photoluminescence measurements. The XRD results confirmed the presence of single cubic phase for all samples independent of annealing atmosphere. FE-SEM micrograph results revealed that the particles present flake-like shapes. The YAG:Ce3+ phosphors showed broad green–yellow emission band in the range of 460–700nm with maximum intensity at 530nm assigned to the 5d→4f transitions of Ce3+ ion. It is found that the annealing in vacuum atmosphere is the most suitable annealing condition for obtaining high quality YAG:Ce3+ powder with stronger emission intensity.

Tunable electromagnetic properties and enhanced microwave absorption ability of flaky graphite/cobalt zinc ferrite composites

In this study, the flaky graphite/cobalt zinc ferrite composites were synthesized by the coprecipitation method. The XRD results showed that the flaky graphite/cobalt zinc ferrite composites can be obtained and there is no impurity when the graphite weight ratio is less than 20 wt%. The FE-SEM results exhibited that the flaky graphite/cobalt zinc ferrite composites possessed flake-like shape with high aspect ratio. Moreover, the electromagnetic properties could be tuned by varying the graphite weight ratio. In the series of as-prepared flaky graphite/cobalt zinc ferrite composites, the sample with 10 wt% graphite possessed excellent impedance matching performance. As a result, the it exhibited the best microwave absorption properties. The reflection loss was less than −10 dB in frequency range of 10.3–13.5 GHz and the maximum reflection loss was reach to −33.85 dB at 11.7 GHz when the coating thickness was 2.5 mm. Moreover, the electromagnetic analysis demonstrated that the electromagnetic loss properties and the electromagnetic impedance matching performance should be both satisfied to obtain the excellent microwave absorption properties. This study was meaningful to design the ferrite/carbon composites based microwave absorbers.

La and F co-substituted hydroxyapatite bioactive coating reinforced by SiC nanowire/ZrO2 hybrid materials for carbon/carbon composites

La and F co-substituted hydroxyapatite (LFH) bioactive coatings reinforced by SiC nanowire/ZrO2 (SZ) hybrid materials were applied on carbon/carbon composites using a combination method of chemical vapor deposition, slurry process, electrochemical deposition and immersion process. Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), Raman spectroscope and X-ray photoelectron spectroscopy (XPS) were adopted to investigate the morphology, microstructure and composition of the coating. The adhesion strength of the coating was investigated by tensile test and the in-vitro bioactivity of the coating was studied using simulated body fluid (SBF) immersion test. The results showed that SZ hybrid reinforcement exhibited a porous and latticed structure, which favored the infiltration of LFH crystals and the integration between SZ and LFH. LFH showed a flake-like shape with a thickness of 20–60nm and a length of 1–3μm. The average adhesion strengths of unreinforced and SZ reinforced LFH coating were 2.97±0.32MPa and 12.37±0.84MPa, respectively. The in-vitro bioactivity test confirmed that the SZ reinforced LFH coating could induce the nucleation and growth of bone-like apatite on its surface in SBF. It was suggested that the SZ reinforced LFH coating might be an effective method to improve the surface bioactivity of carbon/carbon composites with excellent adhesion strength.

Gas Sensing Behaviors of Hierarchically Structured Nickel Oxide Film by Electrophoretic Deposition

This work presents a simple route to fabricate p-type nickel oxide films. Different morphologies of NiO particles were prepared by using a precipitation method and a hydrothermal method. The preformed particles by both methods transformed to pure NiO phase after calcination at 300 °C. NiO particles with different morphologies such as flake-like, rod-like, and cube-like shape were deposited into films by electrophoretic deposition. Three different morphologies of NiO were found to exhibit p-type gas sensing properties against ethanol gas, leading to higher responses to ethanol with rod-like shape at 300 °C.

Influence of Mg on Solidification of Hypereutectic Cast Iron: X-ray Radiography Study

Radiography using a synchrotron radiation X-ray source was performed to examine solidification and melting behaviors in hypereutectic cast iron specimens containing 0.002 and 0.05mass pctMg. The solidification sequence in the alloy containing 0.002mass pctMg was (1) nucleation and growth of graphite particles of which transformed to a flake-like shape, (2) growth of γ-Fe dendrites, (3) nucleation of graphite particles ahead of the interface just prior to the eutectic solidification, and (4) the eutectic solidification. In contrast, (1) and (2) occurred nearly at the same time in the specimen containing 0.05 mass pct Mg. The addition of 0.05mass pctMg significantly reduced the temperature range in which the graphite particles grew as the primary phase. Image-based analysis of melting behavior showed that even 0.05 mass pct addition was sufficient to modify the phase equilibrium of the liquid, γ-Fe, and graphite phases. Thus, the observed influence of Mg on the solidification sequence was attributed to the modification of the phase equilibrium. The influence was consistently explained by considering the shift of the eutectic composition to the carbon side in the pseudo-ternary system. It was also suggested that supersaturation of carbon in the melt increased as the temperature decreased even though the primary graphite particles existed. The supersaturation may cause the nucleation of the graphite particles just before the eutectic solidification.

Synthesis of Graphene Oxide Nanosheets via Modified Hummers’ Method and Its Physicochemical Properties

The efficient synthesis of exfoliated graphene oxide nanosheets (GO) via modified Hummers’ method was successfully carried out. The physicochemical properties of GO were determined by Fourier transform infrared spectroscopy (FTIR), UV-visible spectrophotometry (UV-vis), x-ray diffraction analysis (XRD), Raman spectroscopy, and transmission electron microscopy (TEM). The graphite was fully oxidized by strong oxidizing agent caused the oxygen-containing functional groups such as C-O-C, C=O, and COOH were introduced into the graphite layers as analyzed by Raman and FTIR. XRD pattern of GO showed 2θ of 12.0o with interlayer spacing ~ 7.37A which describe non uniform crystal structure with the addition of oxygen containing functional groups. UV-vis spectrum of GO exhibit maximum absorption peak at ~ 234 nm corresponding to the aromatic C=C bond with π-π* transition. The morphology of GO was observed to have flake-like shape and less transparent layers by TEM. The properties of synthesized GO suggest high potential in producing the high quality of graphene which is can be applied as the electrocatalyst support for direct methanol fuel cell application.

Getting in shape: Molten wax drop deformation and solidification at an immiscible liquid interface

The controlled production of non-spherical shaped particles is important for many applications such as food processing, consumer goods, adsorbents, drug delivery, and optical sensing. In this paper, we investigated the deformation and simultaneous solidification of millimeter size molten wax drops as they impacted an immiscible liquid interface of higher density. By varying initial temperature and viscoelasticity of the molten drop, drop size, impact velocity, viscosity and temperature of the bath fluid, and the interfacial tension between the molten wax and bath fluid, spherical molten wax drops impinged on a cooling water bath and were arrested into non-spherical solidified particles in the form of ellipsoid, mushroom, disc, and flake-like shapes. We constructed cursory phase diagrams for the various particle shapes generated over a range of Weber, Capillary, Reynolds, and Stefan numbers, governed by the interfacial, inertial, viscous, and thermal effects. We solved a simplified heat transfer problem to estimate the time required to initiate the solidification at the interface of a spherical molten wax droplet and cooling aqueous bath after impact. By correlating this time with the molten wax drop deformation history captured from high speed imaging experiments, we elucidate the delicate balance of interfacial, inertial, viscous, and thermal forces that determine the final morphology of wax particles.

EFFECT OF COLLAGEN ON THE MORPHOLOGY AND STRUCTURE OF CALCIUM PHOSPHATE NANOPARTICLES

Collagen and noncollagenous proteins have an important role in the formation of mineral constituent of bone matrix. In this research, the morphology and phase characteristics of calcium phosphate nanoparticles in presence of collagen were investigated. The synthesis reaction was initiated by mixing H 3 PO 4 as phosphorous source and CaCl 2 as calcium source and type I collagen. Collagen concentration in suspension and Ca to P ratio was 1% and 1.67, respectively. The samples (with collagen and without collagen), were heat treated at 600°C and characterized by X-Ray diffraction (XRD), Fourier transformation infrared (FTIR) and scanning electron microscopy (SEM). More smaller and flake-like shape particles were observed in the SEM images of sample synthesized in the presence of collagen compared to the control sample which was constituted of larger granular particles. The XRD results revealed that the synthesized mineral powders with collagen were composed of hydroxyapatite and octacalcium phosphate. P – O and OH characteristic peaks were identified in FTIR spectra. In hybrid sample, the shift of amides band, revealed the electrostatic interactions between calcium phosphate ions and carboxyl or amino groups of collagen fibrils. The Ca to P molar ratio for sample with collagen was 1.9. It was found that the sample synthesized in the presence of collagen has a similar microstructure to natural bone.

FACILE SYNTHESIS AND OPTICAL PROPERTIES OF PbO NANOSTRUCTURES

PbO nanostructures were synthesized by the oxidation of lead sheets in a tube furnace under oxygen ambient using different temperatures, from 280 °C to 450 °C. X-ray diffraction patterns (XRD) indicated the formation of α-PbO nanostructures from the lead sheet with an increase in the temperature. Scanning electron microscope (SEM) results showed that flake-like shapes were starting to grow on the lead sheet that was placed in the 280 °C. In addition, the SEM studies showed nanoflake and nanoporous morphologies for the lead sheets that were placed at 330 °C and 450 °C, respectively. Raman measurements confirmed the XRD results and indicated two Raman active modes that belonged to the α-PbO phase for the nanoflakes and the nanoporous surface. The optical properties of the products were characterized using a photoluminescence (PL) technique. The PL results for the PbO nanoflakes and nanopores showed a peak in the visible region.

Nanoscale zero-valent iron flakes for groundwater treatment

Even today the remediation of organic contaminant source zones poses significant technical and economic challenges. Nanoscale zero-valent iron (NZVI) injections have proved to be a promising approach especially for source zone treatment. We present the development and the characterization of a new kind of NZVI with several advantages on the basis of laboratory experiments, model simulations and a field test. The developed NZVI particles are manufactured by milling, consist of 85 % Fe(0) and exhibit a flake-like shape with a thickness of <100 nm. The mass normalized perchloroethylene (PCE) dechlorination rate constant was 4.1 × 10−3 L/g h compared to 4.0 × 10−4 L/g h for a commercially available reference product. A transport distance of at least 190 cm in quartz sand with a grain size of 0.2–0.8 mm and Fe(0) concentrations between 6 and 160 g/kg (sand) were achieved without significant indications of clogging. The particles showed only a low acute toxicity and had no longterm inhibitory effects on dechlorinating microorganisms. During a field test 280 kg of the iron flakes was injected to a depth of 10–12 m into quaternary sand layers with hydraulic conductivities ranging between 10−4 and 10−5 m/s. Fe(0) concentrations of 1 g/kg (sand) or more [up to 100 g/kg (sand)] were achieved in 80 % of the targeted area. The iron flakes have so far remained reactive for more than 1 year and caused a PCE concentration decrease from 20.000–30.000 to 100–200 µg/L. Integration of particle transport processes into the OpenGeoSys model code proved suitable for site-specific 3D prediction and optimization of iron flake injections.

Phase separation in electrospun nanofibers controlled by crystallization induced self-assembly

Nanofibers from poly(lactic acid) (PLA) homopolymer and poly(p-dioxanone)-b-poly(ethylene glycol) multi-block copolymer (PPDO-b-PEG) with different phase separation morphologies depending on the crystallization induced self-assembly of PPDO-b-PEG are prepared by single spinneret electrospinning. Mixing solvents of chloroform–dimethyl formamide (CHCl3–DMF) with different compositions are used for controlling the crystallization of the PPDO block and therefore the phase separation in the obtained nanofibers. The crystallization of the PPDO block has a very important influence on the morphology of the PPDO-b-PEG nanoparticles in the spinning solution. In spinning solutions with low DMF content, nanoparticles with irregular shapes and non-compact inner structures are formed because the degree of crystallization of the PPDO block is relatively low, and a discontinuous sea-island phase separation is formed in the obtained electrospun nanofibers. Meanwhile, in spinning solutions with high DMF content, the copolymer can form flake-like nanoparticles with a relatively high degree of crystallization. The flake-like shape favors compact aggregation of the PPDO phase during formation of the nanofibers, and a continuous core–shell phase separation of the nanofibers is obtained.

Titanium catalyzed silicon nanowires and nanoplatelets

Silicon nanowires, nanoplatelets, and other morphologies resulted from silicon growth catalyzed by thin titanium layers. The nanowires have diameters down to 5 nm and lengths to tens of micrometers. The two-dimensional platelets, in some instances with filigreed, snow flake-like shapes, had thicknesses down to the 10 nm scale and spans to several micrometers. These platelets grew in a narrow temperature range around 900 celsius, apparently representing a new silicon crystallite morphology at this length scale. We surmise that the platelets grow with a faceted dendritic mechanism known for larger crystals nucleated by titanium silicide catalyst islands.

Cytotoxicity evaluations of pristine graphene and carbon nanotubes in fibroblastic cells

This study concentrates upon investigating differential cellular responses to carbon nanoparticles (CNPs) such as pristine graphene flakes, single-walled carbon nanotubes (SWCNTs) and multiwalled CNTs (MWCNTs), in human dermal fibroblasts (HDFs) vs. the L-929 fibroblast cell line. Characterizing the surface morphology of each CNP by using scanning electron microscopy, we determined their cytotoxicity profiles by quantifying the mitochondrial activity. Graphene was found to have an irregular flake-like shape with various lengths within the ranges of 50 ∼ 1500 nm. The estimated sizes of the SWCNTs and the MWCNTs were about 400 nm and 1000 nm in diameter, respectively and several µm in length. All the CNPs tested here exerted adverse effects on the viability of HDFs even at 15.6 ppm, through intracellular uptake whereas except MWCNTs, they did not show any cytotoxicity against L-929 cells at 250 ppm. This result suggests that CNPs can have a differential influence on normal fibroblasts vs. immortalized ones.

Aluminum-Metal Reactive Composites

Three binary Al-based reactive composite powders are prepared by mechanical milling. The particles have an aluminum matrix and inclusions of Fe, Ni, or Zn comprising 10 at % of the bulk composition. For additives of Ni and Zn, only short milling times can be used to prepare composites; intermetallic phases form at longer milling. Short milling times yield relatively coarse particles with flake-like shapes. Prepared powders are characterized using electron microscopy and X-ray diffraction. Oxidation and ignition of the materials are studied using thermal analysis and heated-filament ignition, respectively. Thermogravimetric analysis shows selective oxidation of Zn and Ni at low temperatures, prior to a characteristic first step of Al oxidation. At higher temperatures, the powders oxidize following, qualitatively, the stepwise process reported earlier for the pure Al powders. The magnitude and kinetics of the low-temperature aluminum oxidation steps are substantially affected by the presence of the metal inclusions. Heated-filament ignition experiments showed that all three prepared composite powders ignite at lower temperatures than pure Al powder. Comparison of the Al-metal composites with Al · Al2O3 reference composites prepared with similar milling conditions suggests that the altered Al morphology, such as developed grain boundary network produced in the milled powders, is primarily responsible for their accelerated low-temperature oxidation. It is further observed that simply an increase in the low-temperature oxidation rate detected in thermo-analytical experiments is insufficient to achieve ignition of the material under rapid heating conditions. It is concluded that the improved ignition dynamics for the prepared Al-metal composites is due to a combination of the accelerated low-temperature oxidation with reaction mechanisms altered by the presence of metal inclusions.