• Korean Journal of Materials Research
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• v.21 no.3
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• pp.156-160
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• 2011

FePt nanoparticles suspension was synthesized by reduction of platinum acetylacetonate and decomposition of iron pentacarbonyl in the presence of oleic acid and oleyl amine. FePt nanoparticles were coated on a substrate by convective assembly from the suspension. To prevent the coalescence during the annealing of FePt nanoparticles double convective coatings were tried. First convective coating was for silica particle assembly on a silicon substrate and second one was for FePt nanoparticles on the previously coated silica layers. It was observed by scanning electron microscopy (SEM) that FePt nanoparticles were dispersed on the silica particle surface. After annealing at $700^{\circ}C$ for 30 minutes under nitrogen atmosphere, FePt nanoparticles on silica particles were maintained in a dispersed state with slight increase of particle size. On the contrary, FePt nanoparticles that were directly coated on silicon substrate showed severe particle growth after annealing due to the close-packing of nanoparticles during assembly. The size variation during annealing was also verified by X-ray diffractometer (XRD). It was suggested that pre-coating, which offered solvent flux oppose to the capillary force between FePt nanoparticles, was an effective method to prevent coalescence of nano-sized particles under high temperature annealing.

• Computers and Concrete
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• v.22 no.4
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• pp.373-381
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• 2018

Hollow center cracked disc (HCCD) in Brazilian test was modelled numerically to study the crack propagation in the pre-cracked disc. The pre-existing edge cracks in the disc models were considered to investigate the crack propagation and coalescence paths within the modelled samples. The effect of particle size on the hollow center cracked disc (HCCD) in Brazilian test were considered too. The results shows that Failure pattern is constant by increasing the ball diameter. Tensile cracks are dominant mode of failure. These crack initiates from notch tip, propagate parallel to loading axis and coalescence with upper model boundary. Number of cracks increase by decreasing the ball diameter. Also, tensile fracture toughness was decreased with increasing the particle size. In this research, it is tried to improve the understanding of the crack propagation and crack coalescence phenomena in brittle materials which is of paramount importance in the stability analyses of rock and concrete structures, such as the underground openings, rock slopes and tunnel construction.

• Structural Engineering and Mechanics
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• v.68 no.4
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• pp.497-505
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• 2018

Three points bending flexural test was modeled numerically to study the crack propagation in the pre-cracked beams. The pre-existing edge cracks in the beam models were considered to investigate the crack propagation and coalescence paths within the modeled samples. The effects of particle size on the single edge-notched round bar in bending test were considered too. The results show that Failure pattern is constant by increasing the ball diameter. Tensile cracks are dominant mode of failure. These crack initiates from notch tip, propagate parallel to loading axis and coalescence with upper model boundary. Number of cracks increase by decreasing the ball diameter. Also, tensile fracture toughness was decreased with increasing the particle size. In the present study, the influences of particles sizes on the cracks propagations and coalescences in the brittle materials such as rocks and concretes are numerically analyzed by using a three dimensional particle flow code (PFC3D). These analyses improve the understanding of the stability of rocks and concretes structures such as rock slopes, tunnel constructions and underground openings.

• Smart Structures and Systems
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• v.22 no.6
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• pp.663-673
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• 2018

In this study, the effect of particle size on the cracks propagation and coalescence or cracking pattern of the edge notched disc specimens are investigated. Firstly, calibration of PFC3D was performed using Brazilian experimental test output. Then micro parameters were used to build edge notched disc specimen. The horizontal wall of the assembly is let to move downward with a standard low speed of 0.016 m/s. The numerical results show that the tensile cracks are dominant failure pattern for the modeled discs. These tensile cracks initiate from the pre-existing notch tip and propagate parallel to the loading direction then interact with the upper boundary of the modeled specimen. As the size of the balls (ball diameter) decrease the number of tensile cracks increase. The tensile fracture toughness of the samples also decreases as the particle size increases. Understanding the crack propagation and crack coalescence phenomena in brittle materials such as concretes and rocks is of paramount importance in the stability analyses for engineering structures such as rock slopes, underground structures and tunneling.

• Composites Research
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• v.21 no.6
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• pp.15-22
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• 2008

Reversed plane bending fatigue tests were conducted on SiC particle aluminum composite. The initiation and growth behaviors of small surface fatigue cracks were continuously monitored by the replica technique and investigated in detail. The fatigue life of MMC is shorter than that of matrix because there exists interface debonding of SiC particles and matrix on the whole face of the notch part in the casting metal matrix composite(MMC). The coalescence of micro-cracks was observed in the tests conducted at high stress levels. Due to the coalescence, a higher crack growth rate of small cracks rather than those of long cracks was recognized in da/dn-$K_{max}$ relationship.

• Journal of the Korean institute of surface engineering
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• v.47 no.2
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• pp.75-80
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• 2014

Nanocrystalline diamond(NCD) films on steel(SKH51) has been investigated using SiC interlayer film. SiC was deposited on SKH51 or Si wafer by RF magnetron sputter. NCD was deposited on SiC at $600^{\circ}C$ for 0.5~4 h employing microwave plasma CVD. Film morphology was observed by FESEM and FIB. Film adherence was examined by Rockwell C adhesion test. The growth rate of NCD on SiC/Si substrate was much higher than that on SiC/SKH51. During particle coalescence, NCD growth rate was slow since overall rate was determined by the diffusion of carbon on SiC surface. After completion of particle coalescence, NCD growth became faster with the reaction of carbon on NCD film controlling the whole process. In the case of SiC/SKH51 substrate, a complete NCD film was not formed even after 4 h of deposition. The adhesion test of NCD/SiC/SKH51 samples revealed a delamination of film whereas that of SiC/SKH51 showed a good adhesion. Many voids of less than 0.1 ${\mu}m$ were detected on NCD/SiC interface. These voids were believed as the reason for the poor adhesion between NCD and SiC films. The origin of voids was due to the insufficient coalescence of diamond particles on SiC surface in the early stage of deposition.

• Particle and aerosol research
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• v.5 no.2
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• pp.83-90
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• 2009

This paper describes a condensation-evaporation method (CEM) to produce size-controlled spherical silver nanoparticles by perturbing coagulation and coalescence processes in the gas phase. Polydisperse silver nanoparticles generated by the CEM were first introduced into a differential mobility analyzer (DMA) to select a group of silver nanoparticles with same electrical mobility, which also enables to make a group of nanoparticles with elongated structures and same projected area. These silver nanoparticles selected by the DMA were then in-situ sintered at ${\sim}600^{\circ}C$, and then they were observed to turn into spherical shaped nanoparticles by the rapid coalescence process. With the assistance of modified converging-typed quartz reactor, we can also produce the 10 times higher number concentration of silver nanoparticles compared with a general quartz reactor with uniform diameter. Finally, the spherical silver nanoparticles with 30 nm were electrostatically deposited on the surface of silicon substrate with the coverage rate of ~4%/hr. This useful preparation method of size-controlled monodisperse silver nanoparticles developed in this work can be applied to the various studies for characterizing the physical, chemical, optical, and biological properties of nanoparticles as a function of their size.

• Journal of the Microelectronics and Packaging Society
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• v.19 no.2
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• pp.61-66
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• 2012

Bismuth(Bi) nanoparticles were synthesized at room temperature by a modified polyol process using bismuth(III) carbonate basic as precursor. In addition, some characteristics of the synthesis with respect to the exchange of a capping agent/surface stabilizer and solvent type were observed. When polyvinylpyrroldone was added, the finest Bi nanoparticles were synthesized in diethylene glycol(DEG), while the coarsest nanoparticles were formed in polyethylene glycol(PEG). The particle size immediately after synthesis was proportionate to final particle size which was determined by particle growth through coalescence and aggregation during drying. As a result, the finest Bi particles with the diameter range of several tens of nanometers - 300 nm were finally obtained in DEG. Regardless of the type of capping agent/surface stabilizer, extensive coalescence and aggregation behavior occurred in PEG, resulting in final products agglomerated with coarse particles.

• Food Science and Biotechnology
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• v.16 no.6
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• pp.999-1005
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• 2007

An oil-in-water (O/W) emulsion [20 wt% com oil, 0.5-6.0 wt% fish gelatin (FG), pH 3.0] was produced by high pressure homogenization, and the influence of pH, protein concentration, and homogenization condition on the formation of FG-stabilized emulsions was assessed by measuring particle size distribution, electrical charge, creaming stability, microstructure, and free FG concentration in the emulsions. Optical microscopy indicated that there were some large droplets ($d>10\;{\mu}m$) in all FG-emulsions, nevertheless, the amount of large droplets tended to decrease with increasing FG concentration. More than 90% of FG was present free in the continuous phase of the emulsions. To facilitate droplet disruption and prevent droplet coalescence within the homogenizer, homogenization time was adjusted in O/W emulsions stabilized by 2.0 or 4.0 wt% FG. However, the increase in the number of pass rather promoted droplet coalescence. This study has shown that the FG may have some limited use as a protein emulsifier in O/W emulsions.

• Journal of the Korean Society of Visualization
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• v.19 no.3
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• pp.39-45
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• 2021

An experiment to visualize fine dust captured by FOG droplet is conducted. Coal dust with 23.56 MMD (Mean Median Diameter) and water with 17.02 MMD is used as fine dust and FOG droplet. Long distance microscope and high-speed camera are used to capture the images of micro-scale particles sprinkled by acrylic duct. After measuring and comparing the size of the coal dust and FOG droplet to MMD, process to seize the coal dust with FOG droplet is recorded in 2 conditions: Fixed and Floated coal dust in the floated FOG droplet flow. In both conditions, a coal dust particle is collided and captured by a FOG droplet particle. A FOG droplet particle attached at the surface of the coal dust particle does not break and remains spherical shape due to surface tension. Combined particles are rotated by momentum of the particle and fallen.