• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11a
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• pp.255-258
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• 2005

Recently, demands for the reduction of noise generated by transformers have been increasing. Almost all the noise generated by a transformer is a result of magnetostrictive vibration in the core. The noise radiates into the atmosphere from the tank through the insulation oil. One method of reduction such a noise is to build a free-standing enclosure of concrete and steel plates around the transformer. However, this method has some disadvantages, for example, a large area is needed for equipment installation. In this paper, the vibration and noise effects which is transferred from reinforce channel to insulation panel generated by transformer have been identified for the several kinds of insulation panel shape and damping sheet experimentally.

• Korean Journal of Metals and Materials
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• v.50 no.11
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• pp.823-828
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• 2012

Direct reduction of $Ta_2O_5$ using liquid calcium was investigated. The experiment was conducted in a closed stainless steel chamber in an Ar atmosphere for 5-120 minutes. Most of $Ta_2O_5$ was reduced to ${\alpha}-Ta$ in 30 minutes above 1173 K and at a molar ratio of Ca and $Ta_2O_5$ above 10. The particles size increased with the reaction temperature, but it did not change much above 1223 K. The oxygen content of metal Ta was about 1 wt%.

• Journal of Powder Materials
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• v.20 no.1
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• pp.53-59
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• 2013

Fe-TiC composite powder was fabricated via two steps. The first step was a high-energy milling of FeO and carbon powders followed by heat treatment for reduction to obtain a (Fe+C) powder mixture. The optimal condition for high-energy milling was 500 rpm for 1h, which had been determined by a series of preliminary experiment. Reduction heat-treatment was carried out at $900^{\circ}C$ for 1h in flowing argon gas atmosphere. Reduced powder mixture was investigated by X-ray Diffraction (XRD), Field Emission-Scanning Electron Microscopy (FE-SEM) and Laser Particle Size Analyser (LPSA). The second step was a high-energy milling of (Fe+C) powder mixture and additional $TiH_2$ powder, and subsequent in-situ synthesis of TiC particulate in Fe matrix through a reaction of carbon and Ti. High-energy milling was carried out at 500 rpm for 1 h. Heat treatment for reaction synthesis was carried out at $1000{\sim}1200^{\circ}C$ for 1 h in flowing argon gas atmosphere. X-ray diffraction (XRD) results of the fabricated Fe-TiC composite powder showed that only TiC and Fe phases exist. Results from FE-SEM observation and Energy-Dispersive X-ray Spectros-copy (EDS) revealed that TiC phase exists uniformly dispersed in the Fe matrix in a form of particulate with a size of submicron.

• Journal of the Korean Ceramic Society
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• v.24 no.4
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• pp.349-356
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• 1987

${\beta}$-Sialon powder was synthesized by the simultaneous reduction and nitridation of Hadong kaolin at 1350$^{\circ}C$ in N2-H2 atmosphere, using graphite as a reducing agent. The synthesized ${\beta}$-Sialon powder was pressurelessly sintered over 1450-1850$^{\circ}C$ in nitrogen atmosphere. The average particle size of ${\beta}$-Sialon powder was about 4.5$\mu\textrm{m}$. The relative density, M.O.R., fracture toughness and micro-hardness of ${\beta}$-Sialon ceramics sintered at 1800$^{\circ}C$ for 1 hour were 92%, 36 kpsi, 2.8MN/㎥/2 and 13.3 GN/㎡, respectively. The critical temperature difference (ΔT) in water quench thermal shock behavior showed about 375$^{\circ}C$ for the synthesized ${\beta}$-Sialon ceramics.

• Journal of the Korean Society for Precision Engineering
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• v.17 no.6
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• pp.111-118
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• 2000

The design of reference trajectory with respect to drag acceleration is necessary to decelerate from hypersonic speed safely after atmosphere re-entry of space vehicle. The re-entry guidance design involves trajectory optimization, generation of a reference drag acceleration profile with the satisfaction of 6 trajectory constraints during the re-entry flight. This reference drag acceleration profile can be considered as the reference trajectory. The cost function is composed of the accumulated total heating on vehicle due to the reduction of weight. And a regularization is needed to prevent optimal drag profile from varying too fast and achieve realized trajectory. This paper shows the relations between velocity, drag acceleration and altitude in drag acceleration profile, and how to determine the reference trajectory.

• Progress in Superconductivity
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• v.9 no.1
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• pp.115-118
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• 2007

This study investigated the effects of different kinds of seed crystals with miscut angles and pretreatment on the characteristics of a RE-123 superconductor processed by a top-seeded melt-growth (TSMG) method. When the seed crystal was heat-treated in an oxygen atmosphere, the surface structure was cleaned removing hydroxide. When the seed crystal had a miscut angle, in addition, the surface structure showed a well defined hill-and-valley structure after heat-treatment. A better microstructure, with a well-distributed small RE-123 phase, was obtained using a high miscut angle after heat-treatment in an oxygen atmosphere. As a result of the microstructure improvement, the magnetic characteristics also improved. The experimental result can be explained by reduction of nucleation activation energy.

• Journal of the Korean Ceramic Society
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• v.28 no.4
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• pp.269-278
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• 1991

Fine AlN powder was synthesized by carbothermal reduction and nitridation of alumimun hydroxide prepared from Al-isopropoxide. AlN ceramics with Y2O3 and CaO were prepared by hot-pressing under the pressure of 30 MPa at 180$0^{\circ}C$ for 1 h in N2 atmosphere. Grain boundary behavior and purification mechanism of AlN lattice were examined by heat treatment of AlN ceramics at 185$0^{\circ}C$ for 1-6 h in N2 atmosphere. AlN ceramics without sintering additives showed poor sinterability. However, Y2O3-doped and CaO-doped AlN ceramics were fully densified nearly to theoretical density. As the heat treatment time increased, c-axis lattice parameter increased. This is attributed to the removal of Al2O3 in AlN lattice. This purification effect of AlN attice depended upon the quantity of secondary oxide phase in the inintial stage of heat treatment and the heat treatment time.

• Journal of the Korean Ceramic Society
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• v.21 no.1
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• pp.11-18
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• 1984

$eta$-Sialon synthesis was investigated via the simultaneous reduction and nitridation of Hadong Pink Kaolin using the graphite as a reducing agent at 135$0^{\circ}C$ under 80% $N_2-20%H_2$ atmosphere. When Hadong Pink Kaolin-graphite-silicon nitride seed(molar ratio ; $SiO_2:C:Si_3N_4$=1;3.5:0.05) mixture was heated at 135$0^{\circ}C$ for as long as 20h in 80%$N_2-20%H_2$ atmosphere a homogeneous $eta$-Sialon$(Si_{3.5}Al_{2.5}O_{2.5}N_{2.5})$ was mainly formed together with a small amount of $\alpha$-$Si_3N_4$.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.9 no.4
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• pp.360-364
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• 1999

The growth of crystals with high melting point$t_{fus}$$\geq$$1600^{\circ}C$ faces the researcher with experimental problems, as the choice of materials that withstand such high t is rather limited. Many metallic construction materials are in this high t range already molten or exhibit at least a drastically reduced mechanical strength. The very few materials with$t_{fus}$$1600^{\circ}C$ as e.g. W, Mo, and partially even Ir are more or less sensitive against oxygen upon heating. Whenever possible, high t crystal growth is performed under inert atmosphere (noble gases). Unfortunately, many oxides are not thermodynamically stable under such conditions, as reduction takes place within such atmosphere. A thoroughly search for suitable growth conditions has to be performed, that are on the one side "oxidative enough" to keep the oxides stable and on the other side "reductive enough" to avoid destruction of constructive parts of the crystal growth assembly. The relevant parameters are t and the oxygen partial pressure${po}_{2}$. The paper discusses quantitatively relevant properties of interesting oxides and construction materials and wasy to forecast theri behavior under growth conditions.

• Transactions of Materials Processing
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• v.26 no.3
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• pp.150-155
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• 2017

To obtain the Goss texture, {110}<001>, IF steel sheets were asymmetrically rolled by 50-89% reduction in the thickness at room temperature and subsequently annealed at 200, 900, and $1200^{\circ}C$ in a box furnace under air atmosphere. The asymmetrically rolled specimens and annealed specimens show well-developed Goss texture, {110}<001>. After the IF steel sheets were asymmetrically rolled at room temperature and subsequently annealed at $900^{\circ}C$ for 1 h in a box furnace under air atmosphere, the intensity of the Goss texture, {110}<001> was high in the IF steel sheets.