• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.19 no.7
• /
• pp.673-679
• /
• 2006

A sublimation method using the SiC seed crystal and SiC powder as the source material is commonly adopted to grow SiC bulk single crystal. However, it has proved to be difficult to achieve the high quality crystal and the process reliability because SiC single crystal should be grown at very high temperature in closed system. In this study, SiC crystal boules were prepared with different angles in trapezoid-shaped graphite seed holders using sublimation physical vapor transport technique (PVT) and then their crystal quality was systematically investigated. The temperature distribution in the growth system and the crystal shape were varied with angles in trapezoid-shaped graphite seed holders, which was successfully simulated using 'Virtual Reactor'. The SiC polytype proved to be the n-type 6H-SiC from the typical absorption spectrum of SiC crystal. The micropipe densities of SiC wafers in this study were measured to be < $100/cm^2$. Consequently, SiC single crystal with large diameter was successfully achieved with changing angle in trapezoid-shaped graphite seed holders.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.23 no.3
• /
• pp.129-134
• /
• 2013

Sapphire wafers are used as an important substrate for the production of blue LED (light emitting diode) and the LED's performance largely depends on the quality of the sapphire single crystals. There are several crystal growth methods for sapphire crystals and Kyropoulos method is an efficient way to grow large diameter and high-quality sapphire single crystals with low dislocation density. During Kyropoulos growth, the convection of molten melt is largely influenced by the hot zone geometry such as crucible shape, heater and refractory arrangements. In this study, CFD (computational fluid dynamics) simulations were performed according to the bottom/side ratios (per unit of the crucible surface area) of heaters. And, based on the results of analysis, the molten alumina flows and remelting phenomena were analyzed.

• Journal of Technologic Dentistry
• /
• v.36 no.3
• /
• pp.149-158
• /
• 2014

Purpose: Dental casting Co-Cr-Mo based alloys of five kinds of ingot type and two kinds of shot type were analyzed the melting processes with heating time of high frequency induction centrifugal casting machine using infrared thermal image analyzer. Methods: When Co-Cr-Mo based alloys were put about 30g/charge in the ceramic crucible of high frequency induction centrifugal casting machine and heat, Infrared thermal image analyzer and IR thermometer indicated these alloys in the crucible were set and operated. Results: The melting temperatures of alloys measuring infrared thermal image analyzer were deviated ${\pm}10^{\circ}C$ compared to those of manufacturing company. On the other hand, the melting time of alloys were differently appeared with the shape of alloys(ingot and shot type). Conclusion: The melting temperatures of dental Co-Cr-Mo based alloys were measured the degree of $1,360{\sim}1410^{\circ}C$ and the heating time with the alloys of ingot and shot type were deviated ${\pm}10sec$.

• Proceedings of the Korean Powder Metallurgy Institute Conference
• /
• 2006.09b
• /
• pp.771-772
• /
• 2006

Mechanical properties of metal injection molded titanium and titanium alloy parts were investigated in this study. Material powders with low oxygen content and spherical shape were obtained by electrode induction-melting gas atomization which could melt and atomize titanium and titanium alloy bars with no touch on crucible or tundish. Tensile specimens were fabricated from obtained powders by metal injection molding process. Tensile strength of the specimens increases with increasing oxygen content. This result corresponds to a tendency of wrought metal.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
• /
• v.11 no.3
• /
• pp.199-206
• /
• 2013

Electrowinning process in pyroprocessing recovers U (uranium) and TRU (Trans Uranium) elements simultaneously from spent fuels using a liquid cadmium cathode (LCC). When the solubility limit of U deposits over 2.35wt% in Cd, U dendrites were formed on the LCC surface during the electrodeposition at $500^{\circ}C$. Due to the high surface area of dendritic U, the deposits were not submerged into the liquid cadmium pool but grow out of the LCC crucible. Since the U dendrites act as a solid cathode, it prevents the co-deposition of U and TRUs. In this study, the electrodeposition of U onto a LCC was carried out at 440 and $500^{\circ}C$ to compare the morphology and component of U deposits. The U deposits at $440^{\circ}C$ have a specific shape and were stacked regularly at the center of the LCC pool, while the U dendrites (i.e., ${\alpha}$-phase) at $500^{\circ}C$ were grow out of the LCC crucible. Through the microscopic observation and XRD analysis, the electrodeposits at $440^{\circ}C$, which have a round shape, were identified as an intermetallic compound such as $UCd_{11}$. It can be concluded that the LCC electrowinning operation at $440^{\circ}C$ achieves the co-recovery of U and TRU without the formation of U dendrites.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.21 no.5
• /
• pp.193-198
• /
• 2011

Recently sapphire crystals are used in LED applications. The Czochralski (CZ) growth process is one of the most important techniques for growing high quality sapphire single crystal. A successful growth of perfect single crystals requires the control of heat and mass transport phenomena in the CZ growth furnace. In this study, the growth processes of the sapphire crystal in an inductively heated CZ furnace have been analyzed numerically using finite element method. The results shown that the high temperature positions moved from the crucible surface to inside the melt and the crystal-melt interface changed to the flat shape when the rpm was increased. Also the crystal-melt interface shape has been influenced by the shoulder shape of the grown crystal during the initial stage.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.8 no.1
• /
• pp.1-9
• /
• 1998

In this study, we have investigated the preparation conditions of 45$\times$45$\times$20(mm) square cross-section sapphire single crystal by the modified heat exchanger method using water as a coolant. Melting and solidification processes were optimized by the systematic change of the chamber pressure with the heater temperature. As a results, solidification temperature was between 1960 and $1970^{\circ}C$. The crucible was formed by handling. Therefore its shape should had the 'spiral type' ear at edge of its side. Heat exchanger affected to the temperature distribution and gradient of molten alumina. Heat flux and unmelted seed were controlled by volume of heat exchanger. Voids were controlled by the cooling rate of the heater below $0.2^{\circ}C$/min.

• Progress in Superconductivity
• /
• v.10 no.2
• /
• pp.103-107
• /
• 2009

$Bi_2Sr_2Ca_1Cu_2O_x$(BSCCO 2212) superconductors for current lead were fabricated by centrifugal melting process(CMP). BSCCO 2212 powder was melted at $1200^{\circ}\C$ in a resistance furnace using a Pt crucible and poured in a rotating cylindrical mold preheated at $550^{\circ}\C$ for 2 hour. The solidified BSCCO-2212 samples were heat-treated by partial melting process in oxygen atmosphere. The current-voltage curves at 77 K of the samples were obtained by transport measurement, and the microstructure was investigated by scanning electron microscope. The $J_c$ values at 77 K of the tubes partially melted at $840^{\circ}C,\;860^{\circ}C\;and\;880^{\circ}C$ were 492, 430 and 398 $A/cm^2$, respectively. It was observed that the plate-like grains in BSCCO 2212 tube was more developed in the sample heat-treated at $840^{\circ}C$. It was found that the critical current of the BSCCO 2212 samples was dependent on the partial melting schedule regarding the grain shape and size of the BSCCO 2212.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.10 no.3
• /
• pp.177-184
• /
• 2000

The effect of the buyancy and thermocapillarity for differnent aspect ratio of flow field on melt motion and mass transfer has been numerically investigated in magnetic Czochralski crystal growth of silicon. During the process of crystal growth, the melt depth of crucible reduces so the aspect ratio of flow field also reduces. Therefore the shape of magnetic field of the flow field changes and the flow pattern also changes significantly. Together with the melt flow which forms the Marangoni convection (or thermocapillary flow) that comes from the inside the flow field, a flow circulation is observed near the corner close both to the crucible wall and the free surface. Due to this circulation, buoyancy effect has been turned out to be local rather than global. As the aspect ratio decreases, the radial component of the magnetic field prevails compared with the axial component in the flow field. Under the influence of this magnetic field, the melt flow and the temperature distribution in a meridional plane tend to depend on the radial position. As the aspect ratio decreases, the temperature gradient near the edge of the crystal decreases yielding smaller thermocapillarity, and the oxygen concentration near the crystal and the oxygen incorporation rate also decrease.

• Journal of Korea Foundry Society
• /
• v.33 no.2
• /
• pp.69-74
• /
• 2013

Silicon (Si) wafer was grown by using direct growth from Si melt and contaminations of wafer during the process were investigated. In our process, BN was coated inside of all graphite parts including crucible in system to prevent carbon contamination. In addition, coated BN layer enhance the wettability, which ensures the favorable shape of grown wafer by proper flow of Si melt in casting mold. As a result, polycrystalline silicon wafer with dimension of $156{\times}156$ mm and thickness of $300{\pm}20$ um was successively obtained. There were, however, severe contaminations such as BN and SiC on surface of the as-grown wafer. While BN powders were easily removed by brushing surface, SiC could not be eliminated. As a result of BN analysis, C source for SiC was from binder contained in BN slurry. Therefore, to eliminate those C sources, additional flushing process was carried out before Si was melted. By adding 3-times flushing processes, SiC was not detected on the surface of as-grown Si wafer. Polycrystalline Si wafer directly grown from Si melt in this study can be applied for the cost-effective Si solar cells.