• Advances in materials Research
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• v.2 no.2
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• pp.111-118
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• 2013

The changes of plastic plateau in the stress-strain curves of annealed polypropylene (PP) films during stretching under room temperature were followed and the corresponding melting properties and microstructure were characterized by differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). It was found that during stretching the plastic plateau disappeared progressively with the increase of drawing ratio. At the same time, the endotherm plateau in DSC curves also disappeared progressively. The presence of the plastic plateau was attributed to the stretching of unstable crystalline part which was formed by tie chains around initial row-nucleated lamellae structure during annealing. During stretching, the unstable part was stretched and converted to bridges connecting separated lamellae. There was direct relationship between the disappearance of plastic plateau and pore formation.

• Progress in Superconductivity and Cryogenics
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• v.24 no.3
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• pp.52-56
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• 2022

Single-grain (c-normal or c-parallel) and multi-grain YBCO superconductors were prepared by a melt growth process with/without seeding. The magnetic levitation force and trapped magnetic field at liquid N₂ temperature (77 K) of the YBCO superconductors were investigated. Samples for the levitation force measurement were zero-field cooled (ZFC) to 77 K, and samples for trapped field measurement were field-cooled (FC) using Nd magnets. As for the magnetic levitation force, the c-normal, single grain sample showed the largest value, whereas the multi-grain sample showed the lowest value. The trapped magnetic field of the c-normal and c-parallel single-grain samples was 4-5 times that of the multi-grain sample. In addition, as the external magnetic field (the number of magnets) increased, the both properties increased proportionally. These results were explained in terms of the orientation dependence of the levitation forces and the magnetic field trapping capability of the YBCO superconductor.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.644-651
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• 2002

The formation and stability of stationary laser weld keyholes are investigated using a numerical simulation. The effect of multiple reflections in the keyhole is estimated using the ray tracing method, and the free surface profile, flow velocity and temperature distribution are calculated numerically. In the simulation, the keyhole is formed by the displacement of the melt induced by evaporation recoil pressure, while surface tension and hydrostatic pressure oppose cavity formation. At laser powers of 500W and greater, the protrusion occurs on the keyhole wall, which results in keyhole collapse and void formation at the bottom. Initiation of the protrusion is caused mainly by collision of upward and downward flows due to the pressure components.

• Bulletin of the Korean Chemical Society
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• v.34 no.9
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• pp.2573-2576
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• 2013

Rate capability and cyclability of $LiMn_2O_4$ should be improved in order to use it as a cathode material of lithium-ion batteries for hybrid-electric-vehicles (HEV). To enhance the rate capability and cyclability of $LiMn_2O_4$, it was coated with $MnV_2O_6$ by a sol-gel method. A $V_2O_5$ sol was prepared by a melt-quenching method and the $LiMn_2O_4$ coated with the sol was heat-treated to obtain the $MnV_2O_6$ coating layer. Crystal structure and morphology of the samples were examined by X-ray diffraction, SEM and TEM. The electrochemical performances, including cyclability at $60^{\circ}C$, and rate capability of the bare and the coated $LiMn_2O_4$ were measured and compared. Overall, $MnV_2O_6$ coating on $LiMn_2O_4$ improves the cyclability at high temperature and rate capability at room temperature at the cost of discharge capacity. The improvement in cyclability at high temperature and the enhanced rate capability is believed to come from the reduced contact between the electrode, and electrolyte and higher electric conductivity of the coating layer. However, a dramatic decrease in discharge capacity would make it impractical to increase the coating amount above 3 wt %.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.12 no.5
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• pp.234-239
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• 2002

The spinel was calcined at temperatures in the range of $1000^{\circ}C$ to $1300^{\circ}C$ with $100^{\circ}C$ interval to evaluate the effect of calcination temperature on mechanical properties of spinel-glass dental composites. Although the average particle size of spinel calcined at temperatures from $1000^{\circ}C$ to $1200^{\circ}C$ was within 2.8~3.0 $\mu\textrm{m}$, the spinel calcined at $1300^{\circ}C$ was 4.66 $\mu\textrm{m}$ due to abnormal grain growth. Shrinkage and pore size of the spinel preform decreased and increased, respectively, as calcination temperature increased, indicating that the calcination temperature was significant to the powder compaction and the densification of the composites as a result of particle size and distribution. The optimum strength and the fracture toughness of the composite calcined at $1200^{\circ}C$ were 284$\pm$40 MPa, 2.5$\pm$0.1 MPaㆍ$m^{1/2}$ respectively. Optical experimental results showed that transmittance of the spinel-glass composite in the visible region was twice higher than that of the alumina-glass composite, suggesting that the spinel-glass composites possessed better aesthetic properties for all-ceramic dental crown application.

• Journal of the Korean Ceramic Society
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• v.35 no.4
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• pp.364-370
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• 1998

Boron-phoshor-silicate glass was fabricated on Si substrates by FHD(Flame Hydrolysis Deposition) The microstructrue of silica soot deposited at various conditon such as composition and substrate temperature was analysed by SEM. After consolidation the refractive index and composition of the silica layer were in-vestigated. For refractive index control B, P and Ge were used as additive elements while B and Ge oxides are easily mixed into $SiO_2$, P oxide($B_2O_3$) doping is difficult because of the volatile property due to low melt-ing point. Boron-phosphorous-silicate glass (BPSG) layer were fabricated using bertical torch and optimized flame temperature substrate temperature and distance of torch and substrate. P concentration of BPSG lay-er measured 3.3 Wt% and the consolidation temperature was lower than $1180^{\circ}C$. The measured refractive index of BPSG silica layer in $1.55\;\mu\textrm{m}$ wavelength was $1.4480{\pm}1{\times}10^{-1}$ and the thickness was $22{\pm}1\;\mu\textrm{m}$.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.4
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• pp.1186-1191
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• 2010

Colored cubic zirconia specimen made by skull melt process were annealed in vacuum at the temperature of $1200^{\circ}C{\sim}1400^{\circ}C$ for 10~60 minutes to enhance the color. All the seven specimen become darker and eventually be black as annealing temperature and time increase. The black samples turned into original colors when we elevated the temperature with oxy-acetylene torch for around 10 minutes in the air. Finally, we could tune the colors of cubic zirconia either anneal in vacuum or the black samples in the air to obtain the proposed colors. Our proposed new process may be appropriate to fabricate the precious synthetic colored cubic zirconia to simulate the natural colored gem quality diamonds.

• Korean Chemical Engineering Research
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• v.46 no.2
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• pp.340-347
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• 2008

In the case of a melting process, the velocity of waste-gas has been measured to produce the melt of an equal condition and to analyze the combustion situation of the fuel which was inputted in a furnace. Recently, there are many kinds of measuring equipments of gas-velocity on the market. But, the waste-gas produced from a melting process is high temperature, the slow speed and includes much dust. Existent measuring equipments are not suited to these conditions. Therefore, we made the measuring equipment of new method which is enough detailed to react on the slow speed and sustains in high temperature. As shown in the result of field test, the manufactured measuring equipment is so sensitive as to react on a small change of velocity and senses temperature change rapidly, we expect that this equipment helps in temperature control of a melting furnace.

• Korean Journal of Materials Research
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• v.12 no.4
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• pp.259-263
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• 2002

Three different ribbons of amorphous $Til_{1-x}Be_x$ alloys such as $Ti_{0.59}Be_{0.41},\;Ti_{0.61}Be_{0.39}\;and\;Ti_{0.63}Be_{0.37}$ were made by melt-spinning method to be used as brazing filler metals for joining Zircaloy-4 nuclear fuel cladding tubes, and their crystallization behavior as well as microstructure of the brazed zone were examined. The crystallization behavior was investigated in teams of thermal stability, crystallization temperature and activation energy. The crystallization of the $Ti_{1-x}Be_x$ alloys proceeded in two steps by the formation of ${\alpha}$-Ti at a lower temperature and of TiBe at a higher temperature. The crystallization temperature and activation energy of $Ti_{1-x}Be_x$ alloys were higher and larger than those of $Zr_{1-x}Be_x$ alloys and PVD Be. Those resulted thinner joining layer with $Ti_{1-x}Be_x$ alloys, which kept sound thickness of Zircaloy-4 nuclear fuel cladding tubes after brazing. But in the brazed zones made by $Ti_{1-x}Be_x$ filler metals, a little solid-solution layers composed of Zr and Ti were formed toward the Zr cladding tube and Zr was detected in the brazed zones. Microstructure of brazed zone was changed from globular to dentrite with decreasing Be content in the $Ti_{1-x}Be_x$ filler metal.

• Journal of Korea Foundry Society
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• v.13 no.6
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• pp.532-539
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• 1993

The effect of casting variables for making pure Al and Al-5wt%Si alloy rods free from any surface and inside defects was studied by adopting the horizontal continuous casting method with heated mold. The rods were cast under the casting conditions such as the mold temperature of $670{\sim}690^{\circ}C$, water flow rate of $0.2{\sim}0.6{\ell}/min$, and rod diameter of $4{\sim}8mm$, when the melt temperature and mold to cooler distance was fixed at $700^{\circ}C$ and 20mm, respectively. The results represented that the casting speed for good quality rod increased as the water flow rate increased, whereas, the casting speed decreased as the rod diameter or mold temperature increased. The statistical analysis of $2^3$ factorial design was also applied and the results represented that the averaged optimum casting speed for pure Al(302mm/min) was higher than that of Al-5wt%Si alloy(273mm/min) resulting from the difference of superheat applied. The effect of rod diameter on the optimum casting speed was the highest for pure Al as well as Al-5wt%Si alloy. The effect of water flow rate and mold temperature on the optimum casting speed was in decreasing order.