• Journal of Powder Materials
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• v.21 no.5
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• pp.371-376
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• 2014

In this study, modified catalytic chemical vapor deposition (CCVD) method was applied to control the CNTs (carbon nanotubes) growth. Since titanium (Ti) substrate and iron (Fe) catalysts react one another and form a new phase ($Fe_2TiO_5$) above $700^{\circ}C$, the decrease of CNT yield above $800^{\circ}C$ where methane gas decomposes is inevitable under common CCVD method. Therefore, we synthesized CNTs on the Ti substrate by dividing the tube furnace into two sections (left and right) and heating them to different temperatures each. The reactant gas flew through from the end of the right tube furnace while the Ti substrate was placed in the center of the left tube furnace. When the CNT growth temperature was set $700/950^{\circ}C$ (left/right), CNTs with high yield were observed. Also, by examining the micro-structure of CNTs of $700/950^{\circ}C$, it was confirmed that CNTs show the bamboo-like structure.

• Progress in Superconductivity and Cryogenics
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• v.23 no.4
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• pp.14-18
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• 2021

The Mg-Powder-Compaction (MPC) process is proposed to fabricate the MgB₂ superconducting wires. Mg powder wall, similar to the Mg metal tube, inside the Nb outer sheath has been made and the stochiometric B powder was inserted into the wall. Even though the very high MgB₂ core density of 2.53 g/cm³ is obtained, the superconducting area fraction of MgB₂ is not high enough for the applications. In this work, an advanced MPC process was adopted by adding Mg powder into B powder. The Mg powder wall in the initial wire was fabricated by controlling the wall thickness while maintaining a constant density, and the mixture of B and Mg powder was filled into the Mg powder wall with the same filling density. It is found that the reduction in the area of the Mg powder wall proceeds similar to the wire, and the Mg powder wall is well maintained at the final wire diameter, which is advantage for the fabrication of long wires. With the advanced MPC process, as the added Mg is increased the densities of MgB₂ core is decreased and the porous structure is formed, it is found that the area fraction of superconducting MgB₂ increase up to the 37.7 % with the improved high critical current density (J_c) and the engineering critical current density (J_e).

• Journal of the Korean Society of Safety
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• v.25 no.4
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• pp.19-24
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• 2010

A large amount of electrostatic charges is often generated on polymer powders in fluidized bed and thereby may lead to electrostatic problems. In this study, to evaluate electrostatic hazards of powder in fluidized bed, the electric field(E[v/m]) and the charge amount(q[c/g]) during fluidizing were monitored. We also investigated the Minimum Ignition Energy(MIE [J]) of sample powder used in fluidized bed with the Hartman vertical-tube apparatus. The batch-type fluidized bed system and 2kg as Polypropylene(PP) resin powders were used in the experiments. The following results were obtained: (1) Even when a safe margin of several times was considered, the values of E obtained with PP powder in this paper did not exceed 3 to 5kV/cm, at which an incendiary electrostatic discharge could occur. (2) the ave. q was -0.26${\mu}$C/g during fluidizing. This value was high enough to cause electrostatic agglomeration and adhesion. (3) the entrained PP powder in upper column due to fluidizing could be ignited by electrostatic discharges of 71mJ.

• Tribology and Lubricants
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• v.23 no.3
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• pp.89-94
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• 2007

The stress and displacement behavior analysis of an aluminum tube for an organic photo conductor drum has been presented using a finite element analysis technique by non-linear FEM program. The maximum displacement in the radial direction of OPC drum may directly affect to the quality of printed matter. Thus, the deformed profile of the aluminum tubes should be limited depending on the toner powder size and the contact rolling forces between an OPC drum and a paper. This paper recommends the critical loading of 400 Pa for the provided toner size, $8{\mu}m$ for excellent printed matters and long life of the toner cartridge.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2001.02a
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• pp.25-28
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• 2001

Bi-2212 HTS tube was fabricated by centrifugal forming process(CFP). As a variation of melt casting process(MCP) or centrifugal casting technique, the centrifugal forming process is a flexible method for manufacturing Bi-2212 bulk tubes and has been optimized to achieve smooth surface and uniform thickness. At this process, the slurry was prepared in the mixing ratio of 10:1 between Bi-2212 powder and binder and initially charged into the rotating mold under the speed of 300~450 rpm Heat-treatment was performed at the temperature ranges of 860 ~ $890^{\circ}C$ in air for partial melting. The HTS tube fabricated by centrifugal forming process at $890^{\circ}C$ under the rotating speed of 450 rpm was highly densified and the plate-like grains with more than 20$\mu$m were well oriented along the rotating axis. The measured Tc and Jc at 10K were around 85K and 3,000A/cm2 respectively.

• 한국초전도학회:학술대회논문집
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• v.11
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• pp.58-58
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• 2001

• Journal of Powder Materials
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• v.3 no.4
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• pp.227-232
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• 1996

(i) The development of a metallurgical bond during the spray forming of clad products has offered the possibility of manufacturing large rolls, including those used in hot and cold strip mills. Small rolls are already being produced in Japan. (ii) Technical developments, including the use-of-multi-atomizers have resulted in the elimination of porosity from the internal bore of a sprayed tube. Bimetallic tubing can also be manufactured and the installation of a 4.5 ton tube plant in the USA should provide low operation costs. (iii) Spray forming offers a potentially low cost manufacturing route for superalloy ring/casing components in high strength superalloys. (iv) A large pilot plant has been built for the spray forming of ultra-clean superalloys for turbine disc applications. (v) Using twin-atomizing technology, special steel billets have been spray formed up to 400mm diameter with deposition yields in excess of 90%. (vi) Al/Si alloy extrusion billets with excellent dimensional tolerances are being manufactured for large scale automotive applications. Several new aluminum alloys have also been developed, including high strength, low density and low cocfficient of expansion materials. (vii) New copper alloys have been developed and pilot plants are in operation to produce these alloys once markets have become established.

• Proceedings of the KIEE Conference
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• 1993.11a
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• pp.213-215
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• 1993

Silver-sheathed Bi-Pb-Sr-Ca-Cu-O wires by the powder-in-tube method were preparated to study on the superconducting properties with cooling conditions. Superconducting wires were cooled down in the furnace, air and liquid $N_2$ after sintering at $840^{\circ}C$. Critical current density of sample cooled in the furnace is $5.1{\times}10^3\;A/cm^2$ at 77K, zero magnetic field and Jc of sample cooled in the air is very low. 2223 high-Tc superconducting phase of sample cooled in the air was distroyed. Therefore, we knew that superconducting wire need to cool slowly to get the high critical current density.

• Proceedings of the Korean Institute of Industrial Safety Conference
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• 1998.11a
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• pp.179-182
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• 1998

It is widely recognized that conventional means for determining the minimum ignition energy(MIE) of powder are time-consuming and require operational skill. As a variety of new fine powders are being produced day by day in industry, there is an urgent need to a quicker and more economical means to measure MIE. To meet this requirement, we have developed a measurement system which employs a novel method to create an air/dust mixture in a miniature combustion box. In this system, the powder to be tested input into a hopper made of metal mesh, and successively fed downward to form a thin, curtain-like dust/air mixture by vibration. With this new apparatus, three type of powders -Lycopodium, Anthraquinone, and Polyacrylonitrile-were tested and the MIE data were compared with those taken with a conventional apparatus(the Hartmann tube). Two of them agreed satisfactory, but the other, anthraquinone, showed quite different values supposedly due to the agglomeration of the powder particles by static-charge.

• Transactions of Materials Processing
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• v.13 no.1
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• pp.78-83
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• 2004

High-temperature superconduction materials(Bi2223) possess electrical/electronic and magnetic properties. Because high-temperature superconduction materials is a ceramic powder, that cannot be produced singlehandedly. So Ag sheathed Bi-2223 wire was produced by drawing process using powder-in-tube(PIT) method. This superconductor has many difficulties to produce. The main difficulty is that the mechanical properties of the ceramic powder are very different from those of the Ag sheath. And by these properties, Bi2223 high-temperature superconductor, which has a single filament drawing process and multi-filament drawing process, has a defect like sausaging and bursting at a center. This study analyzed multi-filament drawing process by FEM, and a defect generated during multi-filament drawing was studied by FEH. Specially, in order to prevent a bursting at a center, this study presented a method that inserts a pure Ag at a center of multi-filament wire