Flake Particles Research Articles

Mechanical and microstructural properties of recycling granite residual soil reinforced with glass fiber and liquid-modified polyvinyl alcohol polymer

Glass fiber and liquid-modified polyvinyl alcohol polymer (SH Polymer) are used to reinforce granite residual soil. In this paper, scanning electron microscopy (SEM) tests and drop-weight tests were used to study the microscopic interaction mechanism and impact resistance of granite residual soil specimens reinforced by glass fiber and SH Polymer. Combined with the equivalent confining pressure theory, Mohr-Coulomb intensity lines were used to quantitatively analyze the reinforcement effect of glass fiber. The SEM results showed that the granite residual soil solidified by a 3.5 % SH polymer had a tighter bond between the flake clay particles. In addition, with the incorporation of glass fiber, these flake clay particles were cemented on the glass fiber along the long axis, forming a cementing system of flake clay particles and glass fiber. When the glass fiber content was 3.0 %, the impact resistance of the specimen reached its maximum, 32.16 kN. Using the equivalent confining pressure theory, the reinforcement effect of glass fiber on soil could be quantified by Δσ3.

Mineral Layer Fillers for the Production of Functional Materials.

An original method based on the use of technogenic waste from the processing of mineral-layered materials, in particular phlogopite for obtaining highly efficient functional compositions of the “mica-TiO2”, has been developed. The composition core is a nanosized mica flake coated with mesoporous titanium dioxide of an anatase or rutile structure. Energy-saving and environmentally friendly technological methods are based on the splitting of the mica followed by heterogeneous electrohydrolysis of a mixture of titanium (IV) sulfate solution and flake particles. No destruction of the mica surface, which provided the obtained uniform coatings, has been observed. Such coatings are used in photocatalysis processes and possess a self-cleaning capability. Core–shell compositions are more economically attractive compared with titanium dioxide, in particular TiO2 grade P25 (Degusse). The core of the transparent flake and the shell of the rutile titanium dioxide endows the final product with a pearlescent optical effect. This type of material is widely used in the manufacturing of paints and varnishes, printing inks, cosmetics, etc. The use of technogenic waste could significantly reduce the cost of the final product, which would ensure its widespread use in various industries.

Growth and aggregation micromorphology of natural gas hydrate particles near gas-liquid interface under stirring condition

To investigate the morphological evolution of the whole growth and aggregation processes of hydrate crystals near the gas–liquid interface, we used a high-pressure visual reactor with high-speed camera to capture the micromorphology of hydrate particles in a natural gas + pure water system with pressure from 2.6 to 3.6 MPa and sub-cooling from 4.7 to 6.23 °C. The results showed that under low sub-cooling conditions, the amount and size of particles increased first and then decreased in the range of 0–330 μm, and the small particles always dominated. These particles can be roughly classified into two categories: planar flake particles and polyhedral solid particles. Then, the concept of maximum growth dominant particle size was proposed to distinguish the morphological boundary of growth and aggregation. In addition, the micro model was established to better reflect the effects of particle formation process and evolution mechanism near the gas–liquid interface under stirring condition. The results of this study can provide a guidance for flow assurance in multiphase pipeline.

The effect of Al3+ doping on the infrared radiation and thermophysical properties of SrZrO3 perovskites as potential low thermal infrared material

A series of Al3+-doped SrZrO3 perovskite powders with low infrared emissivity were prepared. The doping-effect of Al3+ on infrared radiation ability and thermophysical properties was investigated in detail by theoretical and experimental methods. As a result, Al3+-doped SrZrO3 perovskite's infrared emissivity is related to its electronic structure and particle morphology. It can be adjusted by the Al3+-doped concentration. The SrZr0.86Al0.14O2.935 powder with stronger electronic conductivity and flake particles has the lowest infrared emissivity with 0.256 in 3-5 μm waveband at 590 °C and 0.383 in 8-14 μm waveband at 550 °C. Al3+-doped SrZrO3 perovskites still maintain ideal thermal stability and low thermal conductivity above 800 °C. Base on both low infrared emissivity and thermal conductivity, Al3+-doped SrZrO3 tablets exhibited weaker thermal radiation intensity in the high-temperature condition and might be the potential low thermal infrared materials servicing under extreme temperature in the future.

Simulation of BNNSs Dielectrophoretic Motion under a Nanosecond Pulsed Electric Field

Using a nanosecond pulsed electric field to induce orientation and arrangement of insulating flake particles is a novel efficient strategy, but the specific mechanism remains unclear. In this study, the dielectrophoretic motion of boron nitride nanosheets (BNNSs) in ultrapure water under a nanosecond pulsed electric field is simulated for the first time. First, the simulation theory is proposed. When the relaxation polarization time of the dielectric is much shorter than the pulse voltage width, the pulse voltage high level can be considered a short-term DC voltage. On this basis, the Arbitrary Lagrangian–Euler (ALE) method is used in the model, considering the mutual ultrapure water–BNNS particles-nanosecond pulsed electric field dielectrophoretic interaction, to study the influence of different BNNSs self-angle α and relative angle β on local orientation and global arrangement. The particles are moved by the dielectrophoretic force during the pulse voltage high level and move with the ultrapure water flow at the zero level, without their movement direction changing during this period, so the orientation angle and distance changes show step-like and wave-like curves, respectively. The model explains the basic mechanism of dielectrophoretic motion of BNNSs under a pulsed electric field and summarizes the motion law of BNNSs, providing a reference for subsequent research.

Large-scale ceramic–metal joining by nano-grained Ag particles paste sintering in low-temperature pressure-less conditions

This paper proposes a method to prepare aluminum nitride (AlN) ceramic–metal joints by nano-grained Ag flake particle sintering under low temperate pressure-free conditions. A robust shear strength larger than 25 MPa was achieved at 280 °C sintering for 3 mm × 3 mm joints. Moreover, large chip (5 mm × 5 mm, 10 mm × 10 mm) bonding confirmed that the technology was not influenced by the size and can be applied to large-scale ceramic–metal joining. Further investigation confirmed that nano-grained Ag micro flake particles were easily necked together, and the AlN/Ag interface could be tightly bound at a low temperature of 180°C. This study provides a new method for low-temperature pressure-less conditions for bonding ceramic-metal structure materials on a large-scale.

Structure and mechanical properties of powders obtained by electrodisperging cobalt-chromium alloy

The work presents the results of attestation of powders that were obtained from the KHMS "Cellite" alloy (Co-63%, Cr-27%, Mo-5%, Ni-2%, Fe-2%) by electroerosive dispersion under various technological conditions (voltage from 100V to 220V, the capacitance of condenser from 15mF to 50mF, pulse frequency from 100Hz to 200Hz), and with using working fluids of different chemical composition and properties (water, kerosene, butyl alcohol). The study of the dispersion of the obtained powders, based on the results, established: the range of particle sizes is from 20mm to 110mm depending on the production modes. The results show various particle sizes, both a few nanometers and hundreds of microns. Depending on the technological modes of production, various mechanisms of the formation of powder particles can occur. Flake particles ranging in size from a few nanometers to (as a rule) one micron are obtained by the crystallization of the material vapor. They usually form agglomerates or stick to larger particles. Spherical and elliptical particles with a diameter from tens of nanometers to hundreds of microns were formed in crystallized material upon melting. The result of thermal and mechanical action during electroerosive dispersion was fragmentation grains with an average size from units to hundreds of microns. To meet the requirements for powders used in additive machines, it is necessary to select modes that exclude brittle destruction of the particles of the powder material and ensure the production of spherical or elliptical particles in the required particle size ranges. As a result of the experiment during the study of the phase composition of powders, using various technological modes and the composition of working fluids, the following phases were revealed: Cobalt (Co) with a cubic crystal lattice, a=b=c=3.561079 Å; Chromium (Cr) with a hexagonal crystal lattice a=b=2.738459 Å, c=4.55078 Å; Nickel (Ni) with a hexagonal crystal lattice, a=b=2.652590 Å, c=4.380519 Å; SIGMA-Cr7Co3 (Cr7Co3 with a tetragonal crystal lattice, a=b=8.656172 Å, c=4.484030 Å; Cobalt Iron (CoFe), with a cubic crystal lattice, a=b=c=2.846754 Å; Chromium Carbide (Cr3C2) with an orthorhombic crystal lattice: a=2.821Å, b=5.53Å and c=11.47Å; Iron (Fe) with a cubic crystal lattice, a=b=c=3.604293 Å; Cobalt Carbide (Co3C), with an orthorhombic crystal lattice, a=b=4.455931 Å, c=6.86598Å; Cobalt Oxide (CoO) with a cubic crystal lattice a=b=c=4.563279 Å; Magnetite (Fe3O4) with a cubic crystal lattice a=b=c=8.4774342 Å.

Wet milling synthesis of NH4CoPO4·H2O platelets: Formation reaction, growth mechanism, and conversion into high-voltage LiCoPO4 cathode for Li-ion batteries

A ball milling process not only affords particle size reduction by grinding but also particle synthesis induced by mechanical actions at ambient temperature. However, in traditional mechanical synthesis, it is difficult to control the particle morphology, including the size and shape, because of collision with the balls. This study shows that platelet-like NH4CoPO4·H2O particles are synthesized via wet planetary ball milling and converted into a high-voltage LiCoPO4 cathode for Li-ion battery. The NH4CoPO4·H2O platelets formed by the dissolution–precipitation reaction are repeatedly ground, dissolved into a solution, and recrystallized to afford crystal growth during the milling treatment. The converted LiCoPO4 cathodes retain the precursor morphologies, exhibiting high discharge capacities for flake particles and better cyclabilities for large platelet particles. The mechanical-assisted particle synthesis in solution is a simple method for the large-scale production of morphology-controlled nanomaterials.

Microwave absorption performance of FeCoNiAlCr0.9 alloy powders by adjusting the amount of process control agent

Different amounts of absolute ethanol (0−50 mL) are used as process control agents (PCA) to prepare FeCoNiAlCr0.9 high entropy alloy (HEA) powders via 90 h ball milling. The results show that the increased amount of PCA plays an active role in the crystallinity of powders, and regulate the thickness and size distribution of flake particles. As the volume of PCA increases, the real and imaginary parts (ε′ and ε″) of complex permittivity get increased by the enhancement of the interface polarization and surface polarization, while the increase in the real and imaginary parts (μ′ and μ″) of complex permeability arises from the increased anisotropic energy. The addition of PCA not only promotes the reflection loss but also extends the effective bandwidth (up to 4.28 GHz). Here, the performance adjustment of HEA electromagnetic absorber is realized by forthrightly changing the process parameters of ball milling.

Influence of fillers on mechanical behaviour of carbon fiber/vinyl ester hybrid composites

In this experimental work, vinyl ester resin was reinforced with high strength carbon fiber (CV) and the mechanical properties were further improved by incorporating SiC/graphite particles. Overall, the enhancements of both the hardness and strengths of CV composites with SiC/graphite were successfully achieved by fabricating composites using hand lay-up stacking followed by hot pressing. Mechanical tests demonstrate that, the tensile and flexural strengths/moduli of CV improved by increasing SiC/graphite from 2 to 6 wt%. The mechanical performances of CV/graphite hybrid composites were found to be supreme with the incorporation of 6 wt% of graphite particles. Meantime, the use of higher surface area and rigid flake kind graphite particles considerably showed improvement in the overall mechanical performance of CV hybrid composites. Furthermore, the CV/SiC hybrid composites show superior hardness. The utmost increment of hardness was found for the CV composite with 6 wt% SiC. The information bestowed during this paper is accustomed to develop load bearing hybrid composites for structural applications.

Effects of Needle Flake Particles on Splitting Experiment of Asphalt Mixture: An Experimental and Numerical Investigation

The purpose of this work is to study the influence of the content and shape of needle flake particles on the meso-scale splitting test performance of asphalt mixture, a three-dimensional laser scanning method is used to build the needle and flake particle model, and then the particle model is put into the numerical simulation software EDEM to establish the splitting experimental model. The influence of loading speed and model parameters on the experimental results is revealed by assigning macro and micro parameters to different particles. With calibrating the parameters by Marshall experiment, the simulation experiment results after parameter adjustment are in good agreement with the experimental results in laboratory. The results show that the splitting experimental model can be established intuitively by means of using 3D discrete element modeling technology, and the stress of each particle size in the loading process can be observed directly. The loading speed, the content of needle flake particles, the size of needle flake particles and the distance from the loading area all have a great influence on the experimental results.

Rapid synthesis of scaly SiO2 coating on flake carbonyl iron powders by plasma electrolysis

The scaly SiO2 coating was rapidly synthesized on the flake carbonyl iron powders by plasma electrolysis to solve the poor corrosion resistance. The effect of the processing numbers on the microstructure and corrosion resistance was systematically investigated. A fully covered and dense thin film was formed, excepted for the processing number of two and three times, where several typically smooth uncoated flake particles were observed. The corrosion test during immersion in NaCl solution for 60 days evidenced the greatly improved corrosion resistance with the one-time powders showed the best. The initial oxidation temperatures of the coated powders were increased by 50–85 °C with the one-time best, again revealing the effective protection of the film. The formation mechanism was also discussed mainly based on the electrochemical process and the plasma effects. We believe the plasma electrolysis will find a wide range of applications in the surface modification of metal powders.

Magnetic Comparison Between Experimental Flake Powder and Spherical Powder for Inductor Cores at High Frequency

This article is the first work to carefully investigate the characteristics of iron loss per weight and relative permeability between the flake and spherical powders with a sinusoidal excitation up to a high frequency of 3.5 MHz in experiments using three separate measurement systems. The composition of the considered powder samples contains 0.001 wt% C, 0.012 wt% Si, 0.09 wt% Mn, 0.0004 wt% P, 0.008 wt% S, and 0.06 wt% O. The flake particle has the preferred orientation that the easy axes are normal to the platelet face, and the water atomized iron powder was processed with ball milling with the lubrication. Key objectives of the utilization of the three independent measurement systems with different specialized equipment and probes are to cross-check and overcome unexpected measurement errors of the related devices in use for validating measured results thoroughly. Experimental results demonstrate the much better performances on the iron loss per weight and relative permeability of the flake powder than that of the spherical powder at high frequencies. Physics-based explanations for the measured results are also presented. Furthermore, two estimation functions based on a six-parameter Steinmetz equation for the measured iron loss of the powders are developed by using MATLAB.

One-step in situ preparation of flexible CuS/TiO2/polyvinylidene fluoride fibers with controlled surface morphology for visible light-driven photocatalysis

In this study, flexible CuS/TiO2/polyvinylidene fluoride (PVDF) fibers with controlled surface morphologies were successfully prepared in situ via one-step hydrothermal growth. The morphology was controlled based on the amounts of the Cu source and functional surfactant cetyltrimethylammonium bromide (CTAB) used in the preparation process. When the amount of CTAB was kept constant, the Cu source significantly affected the amount of CuS nanoflowers loaded on the TiO2/PVDF fibers as well as the morphology of the CuS. When the amount of Cu source was kept constant, the addition of CTAB had a key effect on the morphology of the CuS. By decreasing the amount of CTAB, the morphology of the CuS loaded on the TiO2/PVDF fibers gradually changed from dense nanoflowers into small flake particles. Under irradiation with visible light, experiments based on the photodegradation of levofloxacin hydrochloride (LFXH) showed that Cu1C0.01 (CuS/TiO2/PVDF fibers prepared with 1 mmol Cu(NO3)2·3H2O and 0.01 mmol CTAB) obtained the highest degradation efficiency. Due to the morphology of Cu1C0.01 comprising small flake particles, CuS could fully contact with the internal TiO2 and pollutants, thereby allowing photogenerated carriers to fully participate in the photodegradation reaction. Further analysis demonstrated that photogenerated holes (h+) played a key role in the photodegradation of LFXH.

Effects of size, volume fraction, and orientation of metallic flake particles on infrared radiation characteristics of Al/acrylic resin composite coatings

The composite functional coating containing micro-nano flake particles is a kind of classic thin-layer structural material, which has excellent photothermal properties. In this paper, a model of random distributed flake particles system is established, and then combining with the geometrical optics theory, the spectral radiation transfer model of the composite functional coating containing micro-nano flake particles is built by the Monte Carlo ray-tracing method (MCRT). After verifying the reliability of the model, the effect of the distribution characteristics, particle size parameters, volume fraction and other parameters of random distributed flake particles system on the spectral radiation characteristics of the coating in 8∼14 μm infrared window is investigated. The results indicate that the spectral emissivity of the coating enhances about 9 % at most when particle radius increases from 5 μm to 15 μm, decreases about 60 % at most when volume fraction of particle system increases from 10 % to 30 %, and goes up about 74.5 % when the flake particles change form horizontal arrangement to orientation range is 0°∼60°.

Study on the characteristics of natural gas hydrate crystal structures during decomposition process

Hydrate decomposition is inevitable in the process of hydrate formation, and has an important research significance. In order to study the crystal decomposition process, the formation and flow of hydrate particles in natural gas + pure water system were experimentally studied in a high-pressure visual autoclave. During the experiments, the high-speed digital camera was used to capture the micro-morphology and decomposition process of gas hydrate particles, and the high definition camera was used to capture the agglomeration state of nature gas hydrate at the visual window to connect macro-and micro-phenomena organically. By analyzing the data obtained from experiments, we find that the micro-morphology of hydrate particles can be roughly divided into two categories: planar flake particles and polyhedral solid particles. The planar flake particles are further refined into non-trunk snowflake particles and dendritic particles with trunk growth. When snowflake particles begin to decompose, they tend to decrease in area and have rounded edges. The decomposition time of dendritic particles is longer, and there is always trunk in the system. During the decomposition process, the number of particles gradually decreases to zero, but there will be a slightly increase. Meanwhile, it is found that the higher heating temperature and initial pressure will aggravate the fluctuation of particle number. Finally, according to the microscopic changes of hydrate particles in the decomposition process obtained by high-speed digital camera and other equipment, and based on the independent physical models of two types of hydrate particles, the physical model of hydrate particles decomposition is established.

Broadband and high-sensitivity permeability measurements on a single magnetic particle by transformer coupled permeameter

We have developed a system to measure permeability over a wide frequency range with high sensitivity, which we call the transformer coupled permeameter. In this system, the magnetic sample is sandwiched by two short-terminated coplanar waveguides that form a loosely coupled transformer. In this way, the stimulus signal acting as a background becomes smaller as the frequency decreases, thus significantly suppressing the deterioration of the signal-to-noise ratio (SNR) at low frequencies that most conventional permeameters suffer from. It has been demonstrated that this system can provide a sensitivity high enough to measure the permeability of a single ferromagnetic flake particle comprising a noise suppression sheet over 10 MHz–20 GHz with a high SNR.

Governing the Inclination Angle of Graphite Flakes in the Graphite Flake/Al Composites by Controlling the Al Particle Size via Flake Powder Metallurgy

The inclination angle of the flake particle has a significant impact on the in-plane thermal conductivity of composites. The graphite flake/Al composites (50 vol%) with different inclination angles were fabricated via flake powder metallurgy, and the results show that with increasing the size of Al particle from 25.6 to 50.7 μm, the inclination angle of graphite flake decreases from 7.3° to 4.4°, while the in-plane thermal conductivity of composites increases from 473 to 555 Wm−1 K−1. Based on the rules of mixture, an effective model was established to qualify and quantify the relation between the inclination angle and the in-plane thermal conductivity of the corresponding composites. This model can also be applied to other flake particle-reinforced composites.

The effect of titanium carbide particles on microstructure and mechanical properties of copper/graphite composites prepared by flake powder metallurgy route

The current study focuses on the effect of titanium carbide particles that are used as a reinforcement in Cu/graphite composite fabricated successfully through flake powder metallurgy technique. The reinforced titanium carbide particles were added in 1, 3 and 5% by weight in the Cu/5wt%Gr matrix. Microstructural analysis of the composites was conducted using scanning electron microscopy and optical microscopy. The mechanical properties such as hardness and density of the composites were assessed. SEM analysis shows formation of flake particles. The hardness is optimum for Cu-5Gr with 5 wt% TiC but the relative density reduces to 74.01% for 5 wt% TiC composite due to increase in porosity at higher percentages of TiC.

Micron-sized Ag flake particles direct die bonding on electroless Ni–P-finished DBC substrate: low-temperature pressure-free sintering, bonding mechanism and high-temperature aging reliability

Adoption of wide-bandgap semiconductors in power electronic systems enables these devices to operate at high switching speeds and at high temperatures (above 200 °C). Sinter Ag joining as an attractive die attach material received more and more attention. This study introduced a robust bonding of sinter Ag joining direct on an electroless Ni(P) surface-finished DBC (direct bonded copper) substrate with a low-cost micron-sized Ag flake particle. Die shear strength of sinter Ag joining increased from sintering temperature of 180 °C to 300 °C and achieved 43.6 MPa at 300 °C in air and without pressure during sintering. The shear strength decreased at the sintering temperature of 350 °C due to mass Ni oxide and dense voids generation. The bonding mechanism of sinter Ag joining direct on the Ni-plated structure was discussed via SEM, EDX, XRD and TEM analysis. There is not clear inter-diffusion between Ni and Ag element at the bonding interface. TEM observation reveals that many Ag nanoparticles with the size < 10 nm were self-generated and touched on the thin Ni oxide layer to form a robust interface bonding. In addition, the high-temperature aging test also was investigated for the sinter Ag joining at the aging temperature 250 °C for 1000 h. The die shear strength keeps 30 MPa after 500 h aging and down to 17.9 MPa after 1000 h, may mainly induce by the interface connection ratio decrease with the Ag grain coarsening during high-temperature aging. This work provided experimental and theoretical studies for high-strength connections between sinter Ag joining and Ni-finished substrate, which impacts the application of sinter Ag joining for die attach modules in high temperature.