Flake Particles Research Articles

Shape-controllable Synthesis of Ultrafine ZnO Powders of Different Morphologies

By employing zinc acetate and sodium hydroxide as raw materials, ultrafine ZnO powders with different morphologies were successfully synthesized through hydrothermal method. The influences of the reaction temperature, the OH−/Zn2+ mol ratio and the reaction time on the morphologies of the ZnO powders were discussed. The reaction conditions were obtained, under which the ZnO of flower-like particles, micro-rods and flake particles was synthesized, respectively. The crystal structures and morphologies of those ZnO particles were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The ZnO with flower-like structures was composed of lots of micro-rods with hexagon morphology. The XRD patterns indicated that the ZnO powders were hexagonal wurtzite structures with high purity. Finally, the growth mechanism of the ZnO particles was discussed.

Influence of binder viscosity on the control of infrared emissivity in low emissivity coating

Low emissivity is the complex system and polymer binder is one of the most important factors that affect optical and mechanical properties of the coating. Low infrared emissivity coatings were prepared by using flake aluminum particles and three types of polymer resins as fillers and binders, respectively. The influence of polymer binder viscosity on pigment particles distribution, surface morphology and infrared emissivity of the coating was systematically investigated. The results indicate that infrared emissivity of the coating can be strongly affected by the resin viscosity at the same preparation condition, which induces different aluminum particles distribution and surface morphology of the coating. Low resin viscosity is helpful for aggregating pigments and reducing the top polymer layer thickness near the surface, thus the infrared emissivity is reduced. If the resin viscosity value is decreased by two orders of magnitude, the infrared emissivity values would be reduced as much as 0.2. Additionally, a theoretical model is proposed to account for this mechanism, which indicates that sedimentation, evaporation and diffusion play important roles in forming different aluminum particles distribution during the drying process of the coating.

Flexography Printing of Silver Tracks on LTCC Tapes – Effect of Printing Direction on Line Properties

The originality of this work is to print with flexography process conductive silver lines suitable for Low Temperature Co-fired Ceramics (LTCC) multilayer systems. Screen printing conductive paste with 65% silver flake particles was optimised for flexography process. Patterns with different line widths – from 100 to 600 μm – were printed in two directions, parallel and perpendicular to printing orientation. Printed lines withstood temperature as high as 875°C for one hour, relative to conventional sintering profile of LTCC multilayer systems. Line width, thickness and roughness decreased after sintering. A minimum line width of 153 μm was measured on sintered lines. Line thickness varied from 1.8 to 3.8 μm and line roughness from 0.7 to 0.9 μm after sintering. Conductive silver lines along 34 cm length were accomplished after sintering. Very low values of electrical resistivity were measured on the sintered lines. This study demonstrates the huge potential of flexography printing for LTCC multilayer systems.

A novel biodegradable nicotinic acid/calcium phosphate composite coating on Mg–3Zn alloy

A novel biodegradable composite coating is prepared to reduce the biodegradation rate of Mg–3Zn alloy. The Mg–3Zn substrate is first immersed into 0.02molL−1 nicotinic acid (NA) solution, named as vitamin B3, to obtain a pretreatment film, and then the electrodeposition of calcium phosphate coating with ultrasonic agitation is carried out on the NA pretreatment film to obtain a NA/calcium phosphate composite coating. Surface morphology is observed by scanning electron microscopy (SEM). Chemical composition is determined by X-ray diffraction (XRD) and EDX. Protection property of the coatings is evaluated by electrochemical tests. The biodegradable behavior is investigated by immersion tests. The results indicate that a thin but compact bottom layer can be obtained by NA pretreatment. The electrodeposition calcium phosphate coating consists of many flake particles and ultrasonic agitation can greatly improve the compactness of the coating. The composite coating is biodegradable and can reduce the biodegradation rate of Mg alloys in stimulated body fluid (SBF) for twenty times. The biodegradation process of the composite coating can be attributed to the gradual dissolution of the flake particles into chippings.

The influence of geometry in 2D simulation on the charge/discharge processes in Li-ion batteries

A two dimensional simulation approach is proposed for examining the influence of geometry and morphology on current and potential distribution in Li-ion batteries at a microscopic scale. The study was focused on two different geometries of graphite anodes: close packed spheres and flakes (in different aspect ratios). The simulation output, which includes charge/discharge curves, concentration and voltage gradients in the cells, and the current density at each point in the cells, allows studying the significance of the particles’ geometry and the layered structure of composite electrodes. We found that at high electrolyte solutions conductivities, when the secondary aspect of current distribution is dominant, interspacing the particles in the same layer, perpendicular to the ion flow (e.g. from 0.2μm to 0.4μm), leads to a significant moderation of the maximum solution current density (e.g. from 190A/m2 to 97A/m2). The results also show that when the cells are changed from an anode containing spherical particles to an anode containing flaky particles, the intercalation reaction becomes intensively nonuniform with anodes comprising flaky particles and the solution over-potential increases, so that the cell voltage decreases by up to ∼70mV. In addition, a small vertical increase in the interspacing between the graphite flake particles leads to a significant increase in the cell voltage (i.e. decreasing the solution overvoltage), and we also show that 10% expansion of the particles active surface area, leads to an additional improvement of ∼150mV in the cell voltage. However, there is no significance change in the solution’s current density.

Formulation and screen printing of water based conductive flake silver pastes onto green ceramic tapes for electronic applications

Abstract Environmentally friendly, water-based silver pastes, adapted for screen printing, were formulated with different silver contents (67–75%). These pastes allowed screen printing onto low temperature co-fired ceramic (LTCC) of narrow conductive tracks with a 60 μm line width and a 3 × 10−8 Ω m electrical resistivity. Inks were formulated with a mixture of spherical and flake shape silver particles with 2–4 μm mean diameter. Rheological behaviour of pastes was studied in order to determine its effect on printed lines properties. Prepared inks were then screen printed and sintered under normal atmosphere at 875 °C. As expected, electrical properties depended on silver content. Resistivity values varying from 1.6 × 10−8 to 3.3 × 10−8 Ω m were calculated over 36.3 cm line length. These values are very close to bulk silver resistivity (1.6 × 10−8 Ω m). Compared to previous research and commercial pastes, the newly formulated pastes reached equivalent or even better conductivities with lower silver content (70% by weight).

Hydrothermal Synthesis of Li<sub>2</sub>MnSiO<sub>4</sub> Powders as a Cathode Material for Lithium Ion Cells

Li2MnSiO4 cathode materials were prepared by hydrothermal reaction at 150°C using LiOH, Si(OC2H5)4 and Mn(Ac)2.4H2O as raw materials followed by a low temperature heat annealing at 650°C. The samples were characterized by X-ray diffraction, scanning electron microscopy, FTIR. The powders electrochemical performance was investigated in terms of cycling behavior. Nanometer-sized flake crystalline particles of Li2MnSiO4 are obtained with some degree of agglomeration and little impure phases are detected after annealing. The charge capacity of the Li2MnSiO4 samples is 306 mAh/g (about 1.84 Li+ per unit formula extracted), and the discharge capacity is 114 mAh/g (about 0.68 Li+ per unit formula inserted) in the first cycle in the voltage range of 1.5–4.8 V under a rate of C⁄20. With increasing cycle number, the cell exhibits a well cycle performance with more than 95% coulombic efficiency and the maintenance of 61% of its discharge capacity after 50 cycles.

Effect of particle shape on hydrocyclone classification

Influence of particle shape on hydrocyclone classification was investigated. Classification tests using hydrocyclone and cyclosizer showed that coarse fractions of plate-like particles such as PTFE and glass flake used here were not necessarily recovered as underflow product, especially at relatively high inlet velocity. Settling velocity of the glass flake particles in centrifugal field was estimated using a centrifugal particle size analyzer, and it was revealed that differences in settling velocity between coarse and fine glass flake particles became smaller with increases in angular velocity. Moreover, settling test of glass plate in water or glycerin solution was conducted to know relationship between particle Reynolds number (Re) and settling velocity of the plate. At smaller Re condition, the glass plate settled straight and stably, and larger plate settled faster than smaller plate. However, oscillating motion of the plate occurred in the region of high Re, and settling velocities of the large plate became smaller than that of the small plate in such conditions. Drag coefficient (C) calculated based on the settling velocity of the glass plate is similar to that of glass spheres below Re of about 50, above which it became larger than that of glass sphere. Approximation formula of correlaton between Re and C suggests that the influence of the Re on C can be neglected in the region of high Re, and C increases with increases in the ratio of the particle diameter to thickness (D/T).The decrease of the difference in settling velocity recognized in the centrifugal settling test and the effect of the particle shape (D/T) on C at high Re region are considered to be able to affect the hydrocyclone classification. The misplacement of coarse plate-like particles in the hydrocyclone and cyclosizer tests could be ascribed to the particle shape effects.

Effects of processing parameters of tungsten–copper composites

Fabrication of net-shape tungsten–copper (W–Cu) composites has attracted more attention in recent years due to its good performance for wide applications. In this research, W–Cu composite including 20wt.%, 25wt.%, or 30wt.% Cu. was produced by powder metallurgy technique using wet mixtures of elemental powders. Cold compaction was carried out under pressures from 300 to 1200MPa, while sintering was achieved in vacuum at 1400°C for 1h, and 2h. The particle size and shape of powders, as well as the microstructure after wet mixing, compaction, and sintering were investigated by using SEM.Wet mixed powders were proved to be homogeneous, and the copper flake particles were found semi-coated by fine spherical tungsten particles. The relative green and the as-sintered densities were found to increase with increasing compaction pressure and copper content. After sintering, the composite revealed homogeneous structure. The relative as-sintered density was found to increase with sintering time. Tungsten–copper composite compacted under 1200MPa and sintered at 1400ºC for 2h exhibited the highest relative sintered density, hardness, and compression strength. Also, it exhibited the lowest electrical resistivity and coefficient of thermal expansion.

3-D self-assembly of flower-like particles via microwave irradiation for water treatment

Three-dimensional (3-D) flower-like shape (FLS) Fe3O4 and Fe particles were successfully synthesized using FLS precursor particles that are prepared through a facile microwave-assisted reaction. The mechanism underlying the self-assembly process and shape evolution of FLS particles was systematically investigated by changing reaction parameters such as reaction temperature, reaction time and reaction pressure. During the reaction, iron alkoxide, α-Fe2O3 and FeOOH nanoparticles are formed first and are subsequently transformed to 3-D hierarchical FLS particles by the self-assembly of the primary nanoparticles. Reaction temperature and pressure play critical roles in the formation of the hierarchical flower-like superstructure. There is an optimum window of the reaction temperature (∼180 °C) for the formation of 3-D FLS particles, which is attributed to the competition between the self-assembly process and growth process of the nanoparticles. Also, since FeCl3, ethylene glycol, and urea are used together as raw materials, the appearance of FLS particles is strongly dependent on the reaction pressure. As the reaction pressure becomes larger than 1 MPa, the flake type particles become more thermodynamically favorable than the FLS particles, due to the limited decomposition of urea. Brunauer–Emmett–Teller (BET) analysis shows that FLS particles have a large surface area (>40 m2 g−1). Because of their high specific surface area and intrinsic reactivity, FLS particles efficiently remove sulfur ions in aqueous solution. This suggests that these flower-like particles can be promising materials to treat toxic gas such as H2S in an environment-friendly way.

Fabrication of High-performance Sm–Fe–N isotropic bulk magnets by a combination of High-pressure compaction and current sintering

TbCu7-type Sm–Fe–N coarse powders in the flake form were consolidated without a bonding medium using a low-thermal-load process of current sintering combined with high-pressure compression. When compacted at 1.2GPa, the relative density of the powder was increased by 80% with close stacking of the flake particles. Although the subsequent current heating was only briefly performed at a low temperature of 400°C to avoid decomposition, the compact was consolidated into a rigid bulk in which the particles were bonded at the atomic level. Finally, by using cyclic compaction, this process produced bulk magnets with a density of 92% that exhibited the highest maximum energy product (BH)max of 16.2MGOe, which surpasses that of conventional isotropic Sm–Fe–N bond magnets.

Analysis on Factors Influencing Flake Silver Particles Prepared by Chemical Reduction

Flake silver powder has attracted tremendous interesting due to its specially electrical and optical properties. Chemical reduction method with the advantages of reaction conditions easily controlled and mass production is widely used to prepare flake silver particles. In order to more easily prepare flake silver particles, the generation mechanism of flake silver particles is studied by analyzing the impacts of reaction conditions, such as pH value, kinds of silver seeds, kind of surfactant and concentration of raw material. The results show that flake silver particles can be prepared through controlling reaction conditions. Some problems existing in the preparation of flake silver particles are put forward, and future research directions are also proposed.

Properties of Hybrid-Reinforced Aluminum Matrix Composites for Precision Instruments

Hybrid-reinforcement SiC/Gr/Al composites were fabricated by squeeze-casting technology, to provide a novel solution to machinable materials for precision instruments. The effect of flake graphite particles on mechanical properties, machinability, dimensional stability and coefficient of thermal expansion was studied. With the addition of 5% graphite particles in the SiC/Al composites, the tool life during cutting is prolonged by 40% and the tensile strength, elastic modulus and specific modulus are 405 MPa, 150 GPa and 51 GPa cm3/g respectively. The micro-yield stress of SiC/5%Gr/Al composite is higher than 300 MPa and the linear CTE is 11.6 × 10−6 °C−1. The properties of SiC/Gr/Al composite were in contrast to conventional materials of precision instruments and the advantages in application are discussed.

Mechanism Study on Forming Flake Silver Tin-Oxide Composite Powder

Silver powder and silver-tin oxide composite powder were synthesized by hydrothermal method. The powders were characterized by XRD and SEM. The results show that there are macroscopic appearance and microscopic structure differences between two kinds of powders. Silver powder is gray and spherical particles with 3μm diameter, and silver-tin oxide composite powder is black ash and mainly flake particles about 0.3μm in thickness. Silver crystal in silver tin-oxide composite powder is preferentially oriented in the (111) crystal plane and its oriented index is 2.581. However oriented index of silver crystal in silver powder is 1.048 which shows the crystal isn’t preferentially oriented in the (111) crystal plane. That crystal lattice parameter of silver crystal in silver tin oxide composite powder is 0.409 34 nm larger than 0.408 68 nm of silver powder. The mechanism analysis shows that the hydrogen bonds among Sn(OH)62- and Ag(SO3)23- complexes are inhere factor which result in the formation of flake silver tin-oxide composite powder.

Effect of shape of Sendust particles on their electromagnetic properties within 0.1–18 GHz range

The microwave permeability dispersion behaviors and microwave-absorbing properties for different shapes of Sendust particles prepared by vibrating ball milling at 35 vol% in paraffin wax matrix have been investigated. The dispersion spectrum of permeability was calculated by the Landau–Lifshitz–Gilbert equation and Bruggeman’s effective medium theory. The calculated results are in agreement with the experiment data. According to the calculation results, the value of ( μ 0−1) f r ( μ 0 is static permeability, and f r is resonance frequency) for flake particle with larger aspect ratio reached 59.1 GHz and exceeded the Snoek’s limit. Considering the quarter-wavelength model and transmission line theory, the microwave absorption peak was discussed. At the frequency range, the flake particle with larger aspect ratio can make a thinner absorber. It provides a way to decrease layer thickness of magnetic absorber.

Fabrication and electromagnetic properties of flake ferrite particles based on diatomite

Hexagonal ferrite BaZn 1.1Co 0.9Fe 16O 27 coated surfaces of diatomite flakes of low density were synthesized by a sol–gel method. The phase structures, morphologies, particle size and chemical compositions of the composites were characterized by X-ray diffraction, scanning electron microscope and energy dispersive X-ray spectroscopy. The results show that hexagonal ferrite coated diatomite flakes can be achieved, and that the coating consisted of BaZn 1.1Co 0.9Fe 16O 27 nanoparticles. The vibranting sample magnetometer results reveal that the flake ferrite particles have static magnetic properties. The complex permeability and permittivity of the composites were measured in the frequency range of 1–18 GHz. The microwave absorption properties of these ferrite particles are discussed. The results indicate that the flake ferrites have the potential to be used as a lightweight broad band microwave absorber.

Preparation, Characterization and Infrared Emissivity Properties of Cu / Polyurethane Composite

By the addition of flake Cu particles to polyurethane the infrared emissivity of polymers can be decreased significantly. In this work, the flake copper particles were prepared by solution phase reduction method. The PU pre-polymer was prepared by a typical method which using polyether polyol N220 and tolylene diisocyanate (TDI). Cu/Polyurethane composite was prepared by using incorporation method. The structure and morphology of Cu particles and Cu/Polyurethane composite were characterized by Fourier transform infrared spectrum spectroscopy (FTIR), scanning electron microscope (SEM), X-ray diffraction (XRD) and Energy Dispersive X-ray Detector (EDS). Moreover, the effects of copper particles content on infrared emissivity properties of composite were studied too. The results show that the flake Cu particles were prepared and dispersed well in polyurethane matrix. The infrared emissivity of composite was decreased with increasing particles loading. The composites get lowest infrared emissivity 0.546 when the loading of fillers increased to 20%.

The Magnetic Properties of FeCuNbSiB Flake Particles Prepared by Milling the Annealed Ribbons

The amorphous FeCuNbSiB ribbons were first annealed at the temperature of 450 oC and 540 oC, respectively. Then, these annealed ribbons were milled into flake particles with the same condition. The different annealing temperature made the ribbons have the different crystallinities, which caused the milled particles have the different structures, morphologies, and magnetic properties. As for the flake particles by milling the ribbons annealed at 540 oC, they had higher crystallinity, smaller size, lower coercivity, and higher complex permeability compared with those by milling the annealed ribbons at 450 oC.

Effect of shape of Fe particles on their electromagnetic properties within 1–18 GHz range

Spherical magnetic iron particles were milled into different flake shapes, and their permittivity, permeability dispersion behaviors have been investigated within the frequency range of 1–8 GHz range. The results show that both permittivity and permeability values depend on the particle shapes. These flake particles also demonstrate better microwave absorption performances.

Analysis of conduction noise attenuation by magnetic composite sheets on a microstrip line by the finite element method

Conduction noise attenuation by magnetic composite sheets along a microstrip line has been analyzed by using an electromagnetic field simulator that employs the finite element method. The simulation model consists of a microstrip line with planar input/output ports and noise absorbing materials of large magnetic loss (magnetic composite sheets containing iron flake particles as absorbent fillers). The input port is excited by a TEM-mode wave with a characteristic impedance of 50 Ω. Reflection and transmission parameters (S11 and S21) and power loss are calculated as a function of frequency with variation of the sheet size and thickness. The simulated values are in good agreement with experimental results and the estimated size dependency of power absorption is consistent with transmission line theory. It is proposed that the simulation technique can be effectively used in the design and characterization of noise absorbing materials in high-frequency transmission lines.