• 한국기계가공학회지
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• 제16권2호
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• pp.149-154
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• 2017

Numerous studies of the dynamic behavior of powders have been performed by Discrete Element Method (DEM). The behavior of powders can be analyzed using the DEM assuming that the powder is composed of spherical particles. Moreover, the assumption of spherical particle reduces the computing time significantly. However, the biggest problem with this assumption is the real shape of the particles. Some types of particles, such as calcium carbonate and colloidal copper, are needle shaped. Thus, analysis based on spherical particles can produce errors because of the incorrect assumption. In this research, we developed a new model to simulate needle-shaped particles using the DEM. In the model, a series of particles are connected and regarded as a rod. There is no relative motion among the particles. Thus, the behavior of the rod is rigid motion. To validate the developed model, we carried out the drop-and-bounce test with different initial angles. The results showed negligible error of less than 2%.

• 한국주조공학회지
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• 제15권5호
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• pp.483-493
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• 1995

The microstructural changes during semi-solid state processing of hypereutectic Al-Si alloy has been investigated in the present study. Stirring of semi-solid slurry results in the morphological changes of the primary Si particles, i.e. from angular rod shape to near-spherical shape. Besides the spherodization of primary Si particles, the average particle size increases, especially, at much higher rate in the final stage than that in the early stage of stirring. Various microstructure characterization techniques, such as anisotropic etching, SEM imaging and ECP analysis, reveal that the spherodization of primary Si particles occurs by the combinations of the mechanisms of coalescence, fracture, and wear of the individual particles. Isothermal shearing of hypereutectic Al-Si at $580^{\circ}C$ shows that spherical ${\alpha}-Al$ particles are formed by the dissociation of Al-Si eutectic structure at the early stage of isothermal shearing. The spherical ${\alpha}-Al$ particles gradually grow by the mechanisms of Ostwald ripening and coalescence of the particles.

• 한국세라믹학회지
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• 제28권10호
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• pp.831-837
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• 1991

Spherical TiO2 particles are prepared from TiCl4 aqueous solution by the spray pyrolysis method using ultrasonic atomization technique. The formation mechanism of TiO2 particles from atomized droplets it studied by varying the concentration of the source solution, reaction temperature, and the solvent. spherical TiO2 powders with almost the same normalized particle size distribution can be made reproducibly by changing the concentration of the source solution, and their mean sizes are in the range of 0.2~1.4${\mu}{\textrm}{m}$.

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 1995년도 추계학술발표회논문집(2)
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• pp.623-629
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• 1995

To investigate the effects of powder shape on U loading density of fuel meat, two kinds of fuel meats were prepared with atomized and comminuted U$_3$Si$_2$ powders by extrusion or rolling process. Extruded fuel meats with atomized spherical U$_3$Si$_2$ powder appeared to have much less porosity than those with comminuted irregular U$_3$Si$_2$ powder at higher U$_3$Si$_2$ fraction- The U$_3$Si$_2$ particles with spherical shape are less fractured in extrusion than in rolling. Most of atomized particles on the whole maintained to have spherical shapes in the extrusion. It has been shown that atomized spherical particles are expected to approach similar upper loading limits comparing with comminuted particles in rolled plates, but exceed comminuted powder loading limits in extruded rods.

• 한국세라믹학회지
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• 제53권6호
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• pp.628-634
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• 2016

The 8 wt% yttria($Y_2O_3$) stabilized zirconia ($ZrO_2$), 8YSZ, a typical thermal barrier coating (TBC) for turbine systems, was fabricated under different starting powder conditions and coating parameters by atmospheric plasma spray (APS) coating process. Four different starting powders were prepared by conventional spray dry method with different additive and process parameter conditions. As a result, large- and small-size spherical-type particles and Donut-type particles were obtained. Dense structure of 8YSZ coating was produced when small size spherical-type or Donut-type particles were used. On the other hand, 8YSZ coating with a porous structure was formed from large-size spherical-type particles. Furthermore, a segmented coating structure with vertical cracks was observed after post heat treatment on the surface of dense structured coating by argon plasma flame at an appropriate gun distance and power condition.

• Korea-Australia Rheology Journal
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• 제13권1호
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• pp.19-27
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• 2001

In this symposium paper, the migration and hydrodynamic diffusion of non-colloidal, spherical particles suspended in polymer solutions are considered under Poiseuille or torsional flows. The migration phenomena in polymer solutions are compared with those in Newtonian fluids and the effect of fluid elasticity is discussed. The experimental results on particle migration in dilute polymer solution reveal that even a slight change in the rheological property of the dispersing medium can induce drastic differences in flow behavior and migration of particles, especially in dilute and semi-concentrated suspensions.

• 한국세라믹학회지
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• 제53권1호
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• pp.13-17
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• 2016

It is highlighted that increasing the adsorbent surface area on volumetric basis is very important in providing an easy access for gas molecules. Fine particles around $3{\mu}m$ of soft-burned dolomite kiln dust (SB-DKD) were hydrated to wet slurry samples by ball mill process and then placed in a chamber to use spray dryer method. Spherical granules with particle size distribution of $50{\sim}60{\mu}m$ were prepared under the experimental condition with or without addition of a pore-forming agent. The relationship between bead size of the pore-forming agent and size of SB-DKD particles is the most significant factor in preparation of spherical granules with a high porosity. Whereas addition of smaller beads than SB-DKD resulted in almost no change in the surface porosity of spherical granules, addition of larger beads than SB-DKD contributed to obtaining of the particles with both 15 times larger average pore volume and 1 order of magnitude larger porosity. It is considered that spherical granules with improved $N_2$ gas adsorption ability may also be utilized for other atmospheric gas adsorption.

• 한국세라믹학회지
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• 제39권4호
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• pp.420-426
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• 2002

가열가수분해반응에 의하여 제조된 구형의 $ZrO_2$ 겔을 수열결정화시켜 순수한 $ZrO_2$ 분말과 $Y2_O_3$, CaO 등 상안정화제가 도핑된 $ZrO_2$ 분말을 합성하였다. 합성된 $ZrO_2$ 결정분말들은 평균 10nm 크기의 일차 입자들로 구성된 이차입자들이었다. 이차입자의 평균 크기는 $0.4{\mu}m$였고, 수열결정화과정에서 겔의 구형 형상이 그대로 유지되었으며 일차 입자들 사이에는 약한 응집으로 존재하였다. 입자모양, 크기, 상분율, 도핑된 분율 등을 SEM, TEM, XRD, ICP로 연구하였고 구형 겔의 수열결정화기구를 논의하였다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집D
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• pp.91-96
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• 2001

Ultrafine particles have been widely used in many high technology industrial areas. The spherical nonagglomerated and uniform nanometer-size $SiO_{2}$ particles are synthesized by the injection of TEOS vapor, ions and reaction gas in furnace. Ions were generated by Corona discharge electrode and these ions charge $SiO_{2}$ particles. As a result, spherical, nonagglomerated and ultrafine particles are generated in various conditions, it's morphology, charging portion and size distribution are examined by using TEM, ESP and SMPS. As the applied voltage of electrode changes from 0 kV to 5.0 kV, it is observed that the mean diameter of $SiO_{2}$ particle decreases from 94 nm to 42 nm.

• 한국세라믹학회지
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• 제28권10호
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• pp.757-766
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• 1991

These powder properties were investigated and prepared of ultrafine Mn-Zn ferrite powder by Direct-wet process from variation of oxidation condition. H2O2 oxidation the products were ultrafine spherical particles of about 400${\AA}$ in diameter and superparamagnetics. H2O2 and Air oxidation, Coexistance ultrafine spherical particles of about 400${\AA}$ and cubic particles of about 1000${\AA}$. The products were constructed of superparamagnetic and ferromagnetic particles, and Magnetization were about 30 emu/g. Air Oxidation, Above 6 hr Air 120 ι/hr and 4 hr of Air 180 ι/hr were uniform cubic particles of above 1000${\AA}$. The products were ferromagnetic particles and Magnetization of above 45 emu/g.