• 한국결정성장학회지
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• 제3권2호
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• pp.99-106
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• 1993

열분석(DTA : Differential Thermal Analysis) 방법에 의한 퀴리온도$(T_c)$ 측정방법으로부터 48.50에서 49 $Li_2O$ mole %까지의 퀴리온도$(T_c)$와 $Li_2O$ mole %(C)의 관계식 $(T_c = -17.869C^2+1840.2C-46623)$을 구하였다.$LiTaO_3$ 단결정의 congruent 조성을 결정하기 위하여 48.60 부터 48.70 mole %까지의 영역에서 쵸크랄스키법으로 $LiTaO_3$ 단결정을 육성하고 Top과 Tail 결정에서의 퀴리온도 차이,${\Delta}{T_c} (T_{c(Top)}-T{_c(Tail)})$ 그리고 결정성장 초기와 말기의 융액과 결정의 조성비로부터 분배계수(k)를 구하였다. 이 결과로부터 결정된 congruent 조성은 48.65 mole %였으며 그때의 $(T_c)$ 값은 $610{\pm}1^{\circ}C$였다.

• 한국결정성장학회지
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• 제30권6호
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• pp.232-236
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• 2020

본 연구에서는 광 발광특성이 우수하여 각종 광장치에 사용되고 있는 CaF2-Al2O3-B2O3-TiO2(CABT) 계 유리의 열처리 조건 및 결정상 생성에 따른 광학적 특성을 연구하였다. CAB 유리의 핵형성 및 결정성장을 제어하기 위해 핵형성제 TiO2를 첨가하고, 발광 특성을 향상시키기 위해 희토류 이온 Eu2O3를 첨가하였다. 열처리 조건에 따른 결정 성장 특성을 확인하기 위해 DTA 분석을 수행하였으며, 이에 따른 나노 크기 결정상 변화에 대한 XRD 및 SEM 분석을 수행하였다. 분석 결과 100 nm 크기의 결정생성은 발광강도를 향상시키지만 그 이상의 큰 결정 입자생성은 오히려 발광 특성을 저하시켰다.

• 한국결정성장학회지
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• 제32권5호
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• pp.199-204
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• 2022

유연한 구조의 p-XBP4 리간드를 활용하여 새로운 3차원 구조의 Gd-MOF를 합성하고 단결정 회절 분석기를 활용하여 정확한 구조를 분석하였다. 중심 금속인 Gd는 6개의 p-XBP4와 1개의 물 분자에 의해 총 7배위 되어 있으며, W(CN)₈는 배위되지 않고 전하 균형을 맞추기 위해 구조체 내에 위치하고 있다. 중심 금속인 Gd는 배위된 p-XBP4에 의해 이웃한 Gd와 연결되어 3차원의 입체구조를 형성한다. 란탄 금속의 특성을 고려하여 직류 자화율 측정을 활용하여 자성 특성에 대한 연구를 진행하였다.

• Bulletin of the Korean Chemical Society
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• 제33권10호
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• pp.3397-3406
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• 2012

Three types of spherulitic morphologies have been investigated in dual substrate mode of Belousov-Zhabotinsky (BZ) type reaction system. Prior to growth of spherulites, three distinct patterning behaviors have been observed sequentially during the reaction process. Initial and the early-phase of reaction showed the emergence of concentric ring-like wave patterns. A colloidal-state of reaction consists of numerous fine solid particles, which forms primarily some nucleation centers of dendritic characters. The nucleation centers were found to grow in sizes and shapes with the progress of reaction. It leads to growth of dendritic-like spherulitic crystal patterns. The resultant spherulites showed transitions in their morphologies, including sea-weeds and rhythmic spherulitic crystal patterns, by the effects substituted organic substrate and in the higher concentration of bromate-initiator respectively. The branching mechanism and crystal ordering of spherulitic textures were studied with help of optical microscope (OPM) and scanning electron microscope (SEM). Characteristics of crystal phases were also evaluated using X-ray diffraction (XRD) and differential thermal analysis (DTA). Results indicated that the compositions of reactants and crystal orderings were interrelated with morphological transitions of spherulites as illustrated and described.

• Journal of Pharmaceutical Investigation
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• 제41권6호
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• pp.371-376
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• 2011

The objective of this work was to investigate the existence of new crystal forms of tulobuterol which is used to prevent morning asthma attacks by ${\beta}_2$ agonist and the transformation of crystal forms. Three crystal forms of tulobuterol have been isolated by recrystallization and Form 2 was transformed to Form 4 at 52% RH and 95% RH and these four crystal forms are characterized by differential scanning calorimetry (DSC), powder X-ray diffractometry (PXRD) and thermogravimetric analysis (TG). The DSC and PXRD patterns of four crystal forms of tulobuterol were different respectively. The dissolution patterns of these three crystal forms of tulobuterol were studied and they showed significant differences in the dissolution rate. After storage of 2 months at 0% RH (silica gel, $20^{\circ}C$), 52% RH (saturated solution of $Na_2Cr_2O_7{\cdot}2H_2O/20^{\circ}C$) and 95% RH (saturated solution of $Na_2HPO_4/20^{\circ}C$), Form 1 and Form 3 were not transformed. But Form 2 was transformed to Form 4 at 52% RH and 95% RH.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 1998년도 추계학술대회논문집:21세기에 대비한 지능형 통합항만관리
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• pp.183-188
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• 1998

A quartz crystal analyzer is utilized to monitor the cmsion process of an aluminum surface of a quartz crystal by sea water. A quartz crystal having 2000${\AA}$ of aluminum layer is installed in a spedally designed cell and is in contact with an electrolyte solution. While a constant potential is applied to the cell, the resonant frequency and resonant resistance are simultaneously measured using the quartz crystal analyzer. In addition, surface topographs are taken with an atomic force microscope(AFM) and the element analysis of the surface is conducted using an energy dispersive X-ray spectrornetedEDX). The simultaneous measurement of resonant frequency and resonant resistance during the corrosion process explains the change of surface structure caused by the corrosion. The variation of resonant frequency addresses the amount surface metal dissolution. As a conclusion, it is found that a simple measurement using the quartz crystal analyzer can replace the complex monitoring employing large equipments in the investigation of a corrosion process of metal surface.

• 한국결정성장학회지
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• 제27권1호
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• pp.57-63
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• 2017

High-purity ${\beta}-SiC$ powders for SiC single-crystal growth were synthesized by direct carbonization. The use of high-purity raw materials to improve the quality of a SiC single crystal is important. To grow SiC single crystals by the PVT method, both the particle size and the packing density of the SiC powder are crucial factors that determine the sublimation rate. In this study, we tried to produce high-purity ${\beta}-SiC$ powder with large particle sizes and containing low silicon by introducing a milling step during the direct carbonization process. Controlled heating improved the purity of the ${\beta}-SiC$ powders to more than 99 % and increased the particle size to as much as ${\sim}100{\mu}m$. The ${\beta}-SiC$ powders were characterized by SEM, XRD, PSA, and chemical analysis to assess their purity. Then, we conducted single-crystal growth experiments, and the grown 4H-SiC crystals showed high structural perfection with a FWHM of about 25-48 arcsec.

• 대한전자공학회논문지TE
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• 제42권1호
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• pp.7-12
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• 2005

유한요소해석 프로그램인 ANSYS를 이용하여 수정진동자의 진동 및 주파수특성을 해석하였다. 수정진동자의 직경을 고정하고 두께를 변화시키면서 주파수특성을 조사하였다. 전극박막을 금, 은, 알루미늄으로 적층하였을 경우, 금속의 종류에 따른 공진주파수를 구하였다. 그 결과 유한요소법을 이용하여 수정진동자의 최적조건을 예측할 수 있었다. 또 수정편 두께가 0.2mm 보다 작은 영역에서의 주공진주파수는 8.102 MHz이상의 고주파를 얻을 수 있는 것을 확인하였다. 전극박막으로 사용한 금속의 종류에 따른 수정진동자의 주공진주파수 변화를 조사한 결과, 금이나 은에 비해 알루미늄이 우수한 주파수특성을 나타내었다.

• Coupled systems mechanics
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• 제5권4호
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• pp.341-353
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• 2016

Manufactures of multi-crystalline silicon ingots by means of the directional solidification system (DSS) is important to the solar photovoltaic (PV) cell industry. The quality of the ingots, including the grain size and morphology, is highly related to the shape of the crystal-melt interface during the crystal growth process. We performed numerical simulations to analyze the thermo-fluid field and the shape of the crystal-melt interface both for steady conditions and transient processes. The steady simulations are first validated and then applied to improve the hot zone design in the furnace. The numerical results reveal that, an additional guiding plate weakens the strength of vortex and improves the desired profile of the crystal-melt interface. Based on the steady solutions at an early stage, detailed transient processes of crystal growth can be simulated. Accuracy of the results is supported by comparing the evolutions of crystal heights with the experimental measurements. The excellent agreements demonstrate the applicability of the present numerical methods in simulating a practical and complex system of directional solidification system.

• 한국결정학회:학술대회논문집
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• 한국결정학회 2003년도 춘계학술연구발표회
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• pp.15-15
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• 2003

To discover new drugs more quickly and more efficiently, pharmaceutical companies and biotechnology firms are increasingly turning to the genomics and the structural proteomics technologies. Structural-proteomics can provide a foundation for this through the determination and analysis for protein structure on a genomics scale. Among many structures determined by CGI, we will present with the representative examples drawn from our work on novel structures or complex structures of the disease-related proteins. The alpha subunit of Hypoxia-inducible factor (HIF) is targeted for degradation under normoxic conditions by an ubiquitin-ligase complex that recognizes a hydroxylated proline residue in HIF. Hydroxylation is catalysed by HIF prolyl 4-hydroxylases (HIFPH) which are fe(II) and 2-oxoglutarate (2-OG) dependent oxygenases. Here, we discuss the first crystal structure of the catalytic domain of HIFPH in complexes, with the Fe(II)/2-OG at 1.8Å. These structures suggest that the Ll region (residues 236-253), which is also conserved in mammals, form a 'lid' that closes over the active site. The structural and mutagenesis analyses allow us to provide a focus for understanding cellular responses to hypoxia and a target for the therapeutic manipulation.