• 한국결정성장학회지
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• 제26권1호
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• pp.49-52
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• 2016

본 연구에서는 AlN 결정 성장시 중요한 공정변수 중의 하나인 성장 압력과 온도 조건에 따라 다르게 성장되는 AlN 결정상의 결과에 대하여 고찰하였다. AlN 결정 성장은 6H-SiC 종자 결정을 사용하여 PVT(Physical Vapor Transport)법을 적용하여 성장시켰다. 성장 압력과 온도에 따라 AlN 결정의 특성이 변화하였고, Raman 분석을 통해 다양한 방향을 갖는 AlN 결정이 SiC 종자 결정 위에 성장되는 것을 확인하였다.

• 한국결정성장학회:학술대회논문집
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• 한국결정성장학회 1997년도 Proceedings of the 13th KACG Technical Meeting `97 Industrial Crystallization Symposium(ICS)-Doosan Resort, Chunchon, October 30-31, 1997
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• pp.39-43
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• 1997

Mercurous chloride (Hg$_2$Cl$_2$) has many advantages in its applications to acousto-optic, and opto-electronic devices because it has the unique properties of a broad transmisson range, well into the far infra-red, a low acoustic velocity, a large birefringence, and a high acousto-optic figure of merit[1]. Hg$_2$Cl$_2$ has a high vapor pressure, hence single crystals are usually grown by physical vapor transport(PVT) method in closed silica glass ampoules. We discuss the application of the laser Doppler velocimetry to measure the flow field inside a closed ampoule. The experimental results, are discussed its relationship to computational model and compared to their expectations.

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 1996년도 춘계학술발표회논문집(2)
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• pp.241-246
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• 1996

An analytical model to calculate rate of vapor generation due to heterogeneous wall nucleation in flashing flow is developed. In the present model, an important parameter of the vapor generation term, i.e. nucleation site density is calculated by integrating its probability distribution function with respect to active cavity radius. The limits of integration are minimum and maximum active cavity radii, and these are formulated using an active cavity model for nucleate boiling. This formulation, therefore. can statistically account for the effect of surface specific thermo-physical and geometric conditions on the vapor generation rate and flashing inception. For verifying the adequacy of the present model, steady state two-fluid and the bubble transport equations are solved with applicable constitutive equations. The applicable region of the bubble transport equation is also extended to churn-turbulent flow regime to predict interfacial area concentration at high void fraction. Predicted results in terms of axial pressure and void fraction profiles along the channels are compared with experimental data of Super Moby Dick and BNL Reasonable agreements have been achieved and this shows the applicability of the present model to flashing flow analysis.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2009년도 9th International Meeting on Information Display
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• pp.700-702
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• 2009

We present the epitaxial growth of high-quality ZnO layers by chemical vapor transport (CVT) technique on (01-12) sapphire with a ZnO buffer layer growth by metal-organic chemical vapor deposition (MOCVD). The surface of the grown ZnO epitaxial layers has atomically flats and the RMS is 0.11 nm. PL spectrum of as-grown samples exhibits two emissions originated by interactions between photon and free excitons.

• 한국결정성장학회지
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• 제29권3호
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• pp.107-114
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• 2019

A computational analysis has been carried out to get a thorough and full understanding on the effects of convective process parameters on double-diffusive convection during the growth of mercurous bromide ($Hg_2Br_2$) crystals on earth and under ${\mu}g$ conditions. The dimensional maximum magnitude of velocity vector, ${\mid}U{\mid}_{max}$ decreases much drasticlly near Ar = 1, and, then since Ar = 2, decreases. The ${\mu}g$ conditions less than $10^{-2}g$ make the effect of double-diffusion convection much reduced so that adequate advective-diffusion mass transfer could be obtained.

• 한국결정성장학회지
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• 제17권6호
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• pp.231-237
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• 2007

For an aspect ratio (transport length-to-width) of 5, Pr=3.34, Le=0.078, Pe=4.16, Cv=1.01, $P_B=50$ Torr, only thermally buoyancy-driven convection ($Gr=4.83{\times}10^5$) is considered in this study in spite of the disparity in the molecular weights of the component A ($Hg_2Cl_2$) and B which would cause thermally and/or solutally buoyancy-driven convection. The crystal growth rate and the maximum velocity vector magnitude are decreased exponentially for $3{\le}Ar{\le}5$, for (1) adiabatic walls and (2) the linear temperature profile, with a fixed source temperature. This is related to the finding that the effects of side walls tend to stabilize convection in the growth reactor. The rate for the linear temperature profiles walls is slightly greater than for the adiabatic walls far varied temperature differences and aspect ratios. With the imposed thermal profile, a fixed source region, both the rate and the maximum velocity vector magnitude increase linearly with increasing the temperature difference for $10{\le}{\Delta}T{\le}50K$.

• 한국결정성장학회지
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• 제12권6호
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• pp.272-282
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• 2002

Mercurous bromide ($Hg_{2}0Br_{2}$) crystals hold promise for many acousto-optic and opto-electronic applications. This material is prepared in closed ampoules by the physical vapor transport (PVT) growth method. Due to the temperature gradient between the source and the growing crystal region, the buoyancy-driven convection may occur. The effects of thermal convection on the crystal growth rate was investigated in this study in a horizontal configuration for conditions ranging from typical laboratory conditions to conditions achievable only in a low gravity environment. The results showed that the growth rate increases linearly with Grashof number, and for 0.2 $\leq$ Ar (transport length-to-height, L/H)$\leq$1.0 sharply for Ar=5 and $\Delta$T=30 K. We have also shown that the magnitude of convection decreases with the Ar. For gravity levels of less than $10^{-2}$g the non-uniformity of interfacial distribution is negligible.

• 한국재료학회지
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• 제28권10호
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• pp.590-594
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• 2018

ZnO micro/nanocrystals are formed by a vapor transport method. Mixtures of ZnO and TiO powders are used as the source materials. The TiO powder acts as a reducing agent to reduce the ZnO to Zn and plays an important role in the formation of ZnO micro/nanocrystals. The vapor transport process is carried out in air at atmospheric pressure. When the weight ratios of TiO to ZnO in the source material are lower than 1:2, no ZnO micro/nanocrystals are formed. However, when the ratios of TiO to ZnO in the source material are greater than 1:1, the ZnO crystals with one-dimensional wire morphology are formed. In the room temperature cathodoluminescence spectra of all the products, a strong ultraviolet emission centered at 380 nm is observed. As the ratio of TiO to ZnO in the source material increases from 1:2 to 1:1, the intensity ratio of ultraviolet to visible emission increases, suggesting that the crystallinity of the ZnO crystals is improved. Only the ultraviolet emission is observed for the ZnO crystals prepared using the source material with a TiO/ZnO ratio of 2:1.

• 한국지역사회생활과학회지
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• 제27권2호
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• pp.295-304
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• 2016

This study was conducted to evaluate and compare the waterproofness and water vapor transport properties of 30 waterproof and breathable textiles in the market. MVTR upright cup test with water, MVTR inverted cup test with potassium acetate, and sweating hot plate test method were used for measuring the breathability of fabric samples. The waterproofness of all fabric samples and evaporative resistance of garment ensembles made with 5 selected waterproof and breathable textiles out of 30 samples were tested. The results of this study were as follows. The base fabrics of the most samples were basic weave structure with either polyester or nylon fiber. The waterproofness was over $5000mmH_2O$ for all the samples except densely woven fabrics. The evaporative resistance of garments that were made out of 5 fabric samples with a range of low to high breathability ranged $39.9{\sim}56.7m^2{\cdot}P{\cdot}W^{-1}$. The data of the water vapor transport properties of fabric samples varied with different test methods. Overall the bicomponent film fabrics showed better breathability and less standard deviation regardless of test methods. It is expected the breathability data without the information of test conditions used for marketing would confuse the consumers and the apparel manufacturers.

• 한국결정성장학회지
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• 제19권4호
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• pp.172-183
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• 2009

For the effects of the nonlinear temperature profiles and reduced-gravity conditions we conduct a two-dimensional numerical modeling and simulations on the physical vapor transport processes of $Hg_2Cl_2-Xe$ system in the horizontal orientation position. Our results reveal that: (1) A decrease in aspect ratio from 5 to 2 leads to an increasingly nonuniform interfacial distribution and enhances the growth rate by one-order magnitude for normal gravity and linear wall temperature conditions. (2) Increasing the molecular weight of component B, Xenon results in a reduction in the effect of solutal convection. (3) The effect of aspect ratio affects the interfacial growth rates significantly under normal gravity condition rather than under reduced gravitational environments. (4) The transition from the convection-dominated regime to the diffusion-dominated regime ranges arises near at 0.1g$_0$ for operation conditions under consideration in this study.