• Bulletin of the Korean Chemical Society
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• 제33권1호
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• pp.159-166
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• 2012

We have introduced the Pickering emulsion systems to generate novel confining geometries for the selforganization of monodisperse polymer microspheres using nanoparticle-stabilized emulsion droplets encapsulating the building block particles. Then, through the slow evaporation of emulsion phases by heating, these microspheres were packed into regular polyhedral colloidal clusters covered with nanoparticle-stabilizers made of silica. Furthermore, polymer composite colloidal clusters were burnt out leaving nonspherical hollow micro-particles, in which the configurations of the cluster structure were preserved during calcination. The selfassembled porous architectures in this study will be potentially useful in various applications such as novel building block particles or supporting materials for catalysis or gas adsorption.

• Particle and aerosol research
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• 제9권3호
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• pp.173-185
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• 2013

Oxidations of metal generate large quantity of thermal and light energies but no toxic pollutants, so that metals with high calorific values, such as beryllium, boron, aluminum, magnesium, and lithium, are possible to be used as clean fuels instead of fossil fuels. However, they are so explosive due to very high oxidation rates that they should be stabilized by their surface passivation with oxides, organics and inorganics. For reasonable use of energetic metal particles as solid fuel, therefore, some detail information, such as thermal properties, preparation and passivation methods, and application area, of the energetic metals is introduced in this manuscript.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part2
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• pp.1225-1226
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• 2006

Particles of high strength material when coated with silver offer a means of obtaining desirable electrical properties and high strength. The coating process employed aqueous ammoniacal silver-nitrate electrolytes with a formaldehyde solution as the reductant. Modifying additives were also applied. The reduction and subsequent deposition of silver occurred selectively on the surface of the tungsten particles. The morphologies of the coated particles were assessed by SEM imaging. The silver was uniformed coated on tungsten powder and its thickness was estimated to be approximately 100nm on the basis of a mass account.

• Journal of Powder Materials
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• 제8권1호
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• pp.13-19
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• 2001

Ni and NiO particles were made by a combustion synthesis process. The characteristics of synthesized powders were investigated with various kinds and amounts of fuels such as urea, citric acid and glycine. Ni phase particles without NiO phase were obtained through combustion synthesis process in air atmosphere with-out further calcinations process, when the content of glycine was 2.44 times of the stoichiometric ratio in the precursor solution. Primary particle sizes of synthesized Ni and NiO particles were about 20∼30 nm.

• Korean Journal of Materials Research
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• 제24권11호
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• pp.591-598
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• 2014

In this research, magnesium powder was prepared by gas atomizing. Refinement behaviors of magnesium powder produced under different conditions were investigated using a mechanical milling (attrition milling) process. Analyses were performed to assess the characterization and comparison of milled powder with different steel ball sizes and milling times. The powders were analyzed by field emission scanning electron microscope, apparent density and powder fluidity. The particle morphology of the Mg powders changed from spherical particles of feed metals to irregular oval particles, then plate type particles, with an increasing milling time. Because of the HCP structure, deformation occurs due to the existence of the easily breakable C-axis perpendicular to the base, which results in producing plate-type powders. An increase in ball size and the impact energy of the magnesium powder maximizes the effect of refinement. Furthermore, it is possible to improve the apparent density and fluidity according to the smoothness of the surface of the initial powder.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
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• pp.518-519
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• 2006

A connection between pulse-periodical laser radiation power and stability of liquid-metal contacts between powder particles during selective laser sintering (SLS) is determined based on analysis solving the problem of stability of liquid column in the gravity and capillary forces field. On the grounds of obtained relationships the optimization of pulse-periodical laser radiation power and SLS-process duration is realized, that allows to produce voluminous powder porous materials with pre-determined physical and mechanical properties and surface geometry. Results of metallographic investigations of powder porous materials of titanium powder produced with technological regimes calculated by means of obtained relationships are given in the work

• Bulletin of the Korean Chemical Society
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• 제33권4호
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• pp.1141-1146
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• 2012

Ce-doped $Y_3Al_5O_{12}$ (YAG:Ce) phosphor powder was prepared using a ${NO_3}^-$-malonic acid-$NH_4NO_3-NH_3{\cdot}H_2O$ system. The YAG:Ce precursor was ignited at $240^{\circ}C$ and the resulting powder contained YAG:Ce crystallites (42%) - active in the visible region at 460 nm - amorphous particles (53%) - inactive at visible wavelengths - and less than 3% oxide (3%) crystallite impurities. The impurities transformed to acitive YAG:Ce crystallites at above $800^{\circ}C$. At above $1000^{\circ}C$, the amorphous phase became YAG phase and isolated $Ce_2O$ crystallites emerged. The powder particles comprised < $4{\mu}m$ secondary aggregates of 20 nm primary particles. The thermal dusting of the secondary particles coincided with the aggregation of the secondary particles at above $900^{\circ}C$.

• Journal of the Korean Ceramic Society
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• 제39권3호
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• pp.217-221
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• 2002

Si and ${\alpha}-Si_3N_4$ powder mixtures added with 3 wt% $Y_2O_3$ were reacted under 5 MPa nitrogen pressure. The reaction products contained ${\alpha}-Si_3N_4$ particles with elongated shapes. Length and width of the elongated grains were the maximum when the starting powder mixture of 50 wt% Si - 47 wt% ${\alpha}-Si_3N_4$ and 3 wt% $Y_2O_3$ was used. Aspect ratio of the elongated grains were between 4.4 and 5. When the starting powder mixture contained 70 wt% Si, large particles with irregular shapes appeared. Meanwhile, the reaction did not proceed when the starting powder mixture contained 30 wt% Si and less. The SHS product was easy to crush and the elongated particles obtained from the starting powder mixtures of 40 wt% Si - 57 wt% ${\alpha}-Si_3N_4$ - 3 wt% $Y_2O_3$ and 50 wt% Si - 47 wt% ${\alpha}-Si_3N_4$ - 3 wt% $Y_2O_3$ were good candidates for the seeds.

• Korean Journal of Materials Research
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• 제24권1호
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• pp.25-32
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• 2014

In this study, nano-sized cobalt oxide powder with an average particle size below 50 nm was prepared from a cobalt chloride solution by the spray pyrolysis process. The influences of reaction temperature on the properties of the generated powder were examined. The average particle size of the particles formed based on the spray pyrolysis process at a reaction temperature of $700^{\circ}C$ is roughly 20 nm. Moreover, most of these particles cannot appear with an independent type, thereby coexisting in a droplet type. When the reaction temperature increases to $800^{\circ}C$, the average particle size not only increases to roughly 40 nm but also shows a more dense structure while the ratio of particles which shows a polygonal form significantly increases. As the reaction temperature increases to $900^{\circ}C$, the distribution of the particles is from roughly 70 nm to 100 nm, while most of the particle surface is more intricately close and forms a polygonal shape. When the reaction temperature increases to $1000^{\circ}C$, the particle size distribution of the powder shows an existing form from 80 nm to at least 150 nm in an uneven form. As the reaction temperature increases, the XRD peak intensity gradually increases, yet the specific surface area gradually decreases.

• Journal of Ocean Engineering and Technology
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• 제33권1호
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• pp.42-49
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• 2019

Drilling mud was used once in the step of separating the gas and powder they were transported to a surge tank. At that time, the fine powder, such as dust that is not separated from the gas, is included in the gas that was separated from the mud. The fine particles of the powder are collected to increase the density of the powder and prevent air pollution. To remove particles from air or another gas, a cyclone-type separator generally can be used with the principles of vortex separation without using a filter system. In this study, we conducted numerical simulations of air-particle flow consisting of two components in a cyclone separator in a mud handling system to investigate the characteristics of turbulent vortical flow and to evaluate the collection efficiency using the commercial software, STAR-CCM+. First, the single-phase air flow was simulated and validated through the comparison with experiments (Boysan et al., 1983) and other CFD simulation results (Slack et al., 2000). Then, based on one-way coupling simulation for air and powder particles, the multi-phase flow was simulated, and the collection efficiency for various sizes of particles was compared with the experimental and theoretical results.