• Applied Chemistry for Engineering
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• v.16 no.1
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• pp.45-51
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• 2005

$K^+-{\beta}^{{\prime}{\prime}}-Al_2O_3$ in the $K_2O-Li_2O-Al_2O_3$ ternary system was synthesized using aluminum nitrate solution as a starting material. For the synthesis of pure $K^+-{\beta}^{{\prime}{\prime}}-Al_2O_3$, raw materials with chemical composition of $0.84K_2O{\cdot}0.082Li_2O{\cdot}5.2Al_2O_3$ were mixed in solution state. The effects of dispersant and solution-pH were investigated in minimizing the particle size and on the synthesis of pure $K^+-{\beta}^{{\prime}{\prime}}-Al_2O_3$. Ethanol was used for a dispersant, and $NH_4OH$ solution and nitric acid were added for pH adjustment. The solution pH was increased from 1.0 to 7.5 by 0.5 increments. Each sample was calcined at $1200^{\circ}C$ for 2 h and characterized with X-ray diffraction and particle size analyzer. The pH of solution significantly effected both particle size and phase formation, while the addition of ethanol only effected particle size. The synthesis of pure $K^+-{\beta}^{{\prime}{\prime}}-Al_2O_3$ was favored by addition of nitric acid (for pH control).

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.2 no.1
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• pp.10-19
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• 1992

Mn - Zn Ferrite has physical properties of the high initial permeability, saturation magnetic flux density, and low loss factor as a representative magnetic material of soft ferrites, in addition the mechanical property is excellent as a single crystal. Therefore it is important electronic components and used for VTR Head. Mn - Zn Ferrite single crystals with the diameter 8mm were grown in atmosphere mixed with $O_2$ and Ar gas by the Floating Zone(FZ) method that impurities can not be incorporated to the crystals because of not-using the crucible to put in the melt, and the sharp temperature gradient results from making a focus at one point utilizing the infrared ray emitted from the halogen lamp as a heat source. During the crystal growing, the highest temperature of melting area was maintained to be $1650^{\circ}C$, growth rate and rotation rate were 10 mm/hr, 20 rpm respectively. The phases and the growth directions of crystals were determined from the analysis of X RD patterns, Laue, TEM diffraction patterns and etch pit shapes were observed by the optical microscope through the chemical etching. The corelation of optimum conditions for acquiring the better crystals was found out with the growth rate, the length and diameter of melt at the interface according to the diameter of feed rod, and the patterns of growing interface also studied.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.21 no.4
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• pp.147-152
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• 2011

ZnO nanorods fabricated on a Zn substrate pre-coated with ZnO as a seed layer by the hydrothermal method were studied mainly as a function of ZnO precursor concentration. Characteristic features by using field-emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD) were investigated to define the changed micro-structure and crystalline phase of the ZnO nanorods according to the experimental conditions. The nanorod morphology strongly depended on the precursor concentration. For example, ZnO nanorods vertically aligned with a hexagonal (002) oriented structure with a diameter of 600~700 nm and length of $6.75{\mu}m$ were clearly observed at the highest concentration of 0.015 M. The strong hexagonal structure was believed to be associated with the highest photoluminescene (PL) intensity and a promising voltage value of ca. 6.069 V at $1000{\mu}A$.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.23 no.1
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• pp.37-43
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• 2013

Conductivity of LSGMC materials were affected by secondary phase segregation, composition and synthetic route. $La_{0.8}Sr_{0.2}Ga_{0.8}Mg_{0.1}Co_{0.1}O_{3-{\delta}}$ (LSGMC) powders were prepared using the glycine nitrate process to produce high surface area and compositionally homogeneous powders. The powders were synthesized with different 0.5, 1, 1.5, 2, 2.5 of glycine/cation molar ratios. A single perovskite phase from the synthesized powders was characterized with X-ray diffraction patterns. The obtained sintered pellets showed the dense grain microstructure. In case of 1.5 molar ratio, its density was higher than the others. The electrical conductivity measured at $800^{\circ}C$ was observed to be 0.131 $Scm^{-1}$. In addition, the linear thermal expansion behavior was indicated between $25^{\circ}C$ and $800^{\circ}C$.

• Journal of the Korean Ceramic Society
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• v.39 no.2
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• pp.204-209
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• 2002

In this study, $UO_4{\cdot}2NH_4F$, the precipitates which has low solubility, was obtained by chemical precipitation method to recover and reuse the trace uranium from the liquid waste producing in AUC process and for this compound it was characterized by means of chemical analysis, TG-DTA, XRD and FT-IR analyses. This compound was analyzed as $UO_4{\cdot}2NH_4F$ and shape of this precipitate was hexagonal type, having the size of 2∼3 ${\mu}m$. Also, the intermediates were obtained as $UO_4F,\;UO_4,\;UO_3,\;and\;U_3O_8$ by the thermal decomposition over the temperature of 220, 310, 515 and 640$^{\circ}C$, respectively. It is concluded that under the condition of a constant heating rate of 5$^{\circ}C$/min in air atmosphere range of between room temperature and 800$^{\circ}C$, thermal decomposition reaction mechanism of $UO_4{\cdot}2NH_4F$ is as follow; $UO_4{\cdot}2NH_4F{\rightarrow}UO_4F{\rightarrow}UO_4{\rightarrow}UO_3{\rightarrow}U_3O_8$.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.9
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• pp.1663-1670
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• 2006

Single crystal Fe thin films were grown directly onto n-Si(111) substrates by pulsed electrodeposition. Cyclic Voltammogram(CV) indicated that the $Fe^{2+}/n-Si(111)$ interface shows a good diode behavior by forming a Schottky barrier. From Mott-Schottky (MS) relation, it is found that the flat-band potential of n-Si(111) substrate and equilibrium redox potential of $Fet^{2+}$ ions are -0.526V and -0.316V, respectively. The nucleation and growth kinetics at the initial reaction stages of Fe/n-Si(111) substraste was studied by current transients. Current transients measurements have indicated that the deposition process starts via instantaneous nucleation and 3D diffusion limited growth. After the more deposition, the deposition flux of Fe ions was saturated with increase of deposition time. from the as-deposited sample obtained using the potential pulse of 1.4V and 300Hz, it is found that Fe nuclei grows to three dimensional(3D) islands with the average size of about 100nm in early deposition stages. As the deposition time increases, the sizes of Fe nuclei increases progressively and by a coalescence of the nuclei, a continuous Fe films grow on the Si surface. In this case, the Fe films show a highly oriented columnar structure and x-ray diffraction patterns reveal that the phase ${\alpha}-Fe$ grows on the n-Si(111) substrates.

• Journal of the Korea Concrete Institute
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• v.28 no.3
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• pp.317-328
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• 2016

This research intends to understand the impact of super-absorbent polymer (SAP) as an internal curing agent in Ultra-High Performance Concrete (UHPC). Two different types of SAPs of acrylic acid (SAP_AA) and acrylic acid-co-acrylamide (SAP_AM) were examined with UHPC formulation. Isothermal calorimetry and x-ray diffraction experiments revealed the impact of polymers with the different chemical bonds on cement hydration. To test its feasibility as a shrinkage reducing admixture for UHPC, a series of experiments including flowability, compressive strength, rapid chloride permeability and autogenous shrinkage profile was performed. While both SAPs showed a reduction in autogenous shrinkage, it has been concluded that the SAP size and chemical form significantly affect the performance as an internal curing agent in UHPC by controlling cement hydration and porosity modification. Between the tested SAPs, SAP_AM which absorbs more water in UHPC than SAP_AA, shows better mechanical and durability performance.

• Applied Chemistry for Engineering
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• v.3 no.1
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• pp.53-63
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• 1992

M/BM -series catalysts, $MoO_3$ supported on ${\alpha}-Bi_2Mo_3O_{12}$ were also prepared by impregnation method. BM/M-series catalysts, ${\alpha}-Bi_2Mo_3O_{12}$ supported on $MoO_3$ were also prepared by coprecipitation. Structure and catalytic properties of the two phase catalysts were studied by means of using nitrogen adsorption, X-ray diffraction, and scanning electron microscopy. The reaction test for the selective oxidation of propylene to acrolein over Bi-molybdate catalysts was studied using a fixed-bed reactor system. In M/BM-series catalysts, $MoO_3$ was dispersed on ${\alpha}-Bi_2Mo_3O_{12}$, and the crystal structure of ${\alpha}-Bi_2Mo_3O_{12}$ remains unchanged by the presence of excess $MoO_3$. However the surface morphology and bulk structure of BM/M-series catalysts were altered probably because the precipitated $Bi(OH)_3$ reacted with $MoO_3$ during the calcination to form ${\alpha}-Bi_2Mo_3O_{12}$ phase. The results of propylene oxidation on both series catalysts showed that the reaction took place over the surface of ${\alpha}-Bi_2Mo_3O_{12}$ particle and the role of excess $MoO_3$ was to supply oxygen to ${\alpha}-Bi_2Mo_3O_{12}$. These increasing effects on activity were also observed in the mechanical mixtures of ${\alpha}-Bi_2Mo_3O_{12}$ and $MoO_3$.

• Proceedings of the Korean Vacuum Society Conference
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• 1999.07a
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• pp.58-58
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• 1999

The diamond films which can be applied to SOD (silicon-on-diamond) structure were deposited on Si(100) substrate using CO/H2 CH4/H2 source gases by microwave plasma chemical vapor deposition(MPCVD), and SOD structure have been fabricated by poly-silicon film deposited on the diamond/Si(100) structure y low pressure chemical vapor deposition(LPCVD). The phase of the diamond film, surface morpholog, and diamond/Si(100) interface were confirmed by X-ray diffraction(XRD), scanning electron microscopy(SEM), atomic force microscopy(AFM), and Raman spectroscopy. The dielectric constant, leakage current and resistivity as a function of temperature in films are investigated by C-V and I-V characteristics and four-point probe method. The high quality diamond films without amorphous carbon and non-diamond elements were formed on a Si(100), which could be obtained by CO/H2 and CH4/H2 concentration ratio of 15.3% and 1.5%, respectively. The (111) plane of diamond films was preferentially grown on the Si(100) substrate. The grain size of the films deposited by CO/H2 are gradually increased from 26nm to 36 nm as deposition times increased. The well developed cubo-octahedron 100 structure nd triangle shape 111 are mixed together and make smooth and even film surface. The surface roughness of the diamond films deposited by under the condition of CO/H2 and CH4/H2 concentration ratio of 15.3% and 1.5% were 1.86nm and 3.7 nm, respectively, and the diamond/Si(100) interface was uniform resistivity of the films deposited by CO/H2 concentration ratio of 15.3% are obtained 5.3, 1$\times$10-9 A/cm, 1 MV/cm2, and 7.2$\times$106 $\Omega$cm, respectively. In the case of the films deposited by CH4/H2 resistivity are 5.8, 1$\times$10-9 A/cm, 1 MV/cm, and 8.5$\times$106 $\Omega$cm, respectively. In this study, it is known that the diamond films deposited by using CO/H2 gas mixture as a carbon source are better thane these of CH4/H2 one.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.04b
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• pp.49-49
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• 2009

최근 범세계적인 그린에너지 정책에 관련해 화석연료를 대체할 수 있는 수소, 풍력, 태양광 등의 대체 에너지에 대한 관심이 고조되고 있다. 이러한 여러 대체에너지 중에서도 태양광을 전기에너지로 변환하는 태양전지에 관한 연구가 집중되고 있다. 태양전지는 구조적으로 단순하고 제조 공정도 비교적 간단하지만, 보다 널리 보급되기 위해서는 경제성 향상이라는 문제점을 해결해야 한다. 이를 위해서는 기존의 실리콘 태양전지를 대체할 수 있는 신물질에 대한 연구가 필요하며, 그 중에서도 반도체 기술을 이용한 박막형 태양전지는 기존의 실리콘 태양 전지가 가지고 있는 고비용이라는 문제점을 극복할 수 있을 것으로 기대를 모으고 있다. 박막형 태양전지의 박막 재료로는 CIGS, CdTe 등이 연구되어지고 있지만, 아직까지는 기존의 실리콘 태양전지에 비해 에너지변환효율이 낮은 이유로 인해 실용화가 많이 이루어지지 못하고 있는 것이 사실이다. 이러한 박막형 태양전지의 재료들 중에서도 CdTe는 이종접합 박막형 태양전지에 흡광층으로 사용되는 것으로 상온에서 1.45eV 정도의 밴드갭(band gap) 에너지를 갖는 II-VI족 화합물반도체로써 태양광 스펙트럼과 잘 맞는 이상적인 밴드랩 에너지와 높은 광흡수도 때문에 박막형 태양전지로 가장 주목을 받고 있다. CdTe 박막의 제조 방법으로는 진공증착법(vacuum evaporation), 전착법(electrodeposition), 스퍼터링법(sputtering) 등이 있지만 본 연구에서는 스퍼터링법을 이용하여 박막을 증착하였다. 이상과 같이 증착된 CdTe 박막을 화학적기계적연마(CMP, chemical mechanical polishing) 공정을 적용시킴으로써, 태양전지의 에너지변환효율에 직접적인 영향을 끼칠 수 있는 CdTe 박막의 물리적, 전기적 특성들의 변화를 연구하기 위한 선행 연구를 진행하였다. 특히 본 연구에서는 CdTe 박막의 화학적 기계적 연마 특성을 분석하여 정규화를 통한 모델링을 수행하였다. 또한 화학적기계적연마 공정 전과 후의 표면 특성을 관찰하기 위해 SEM(scanning electron microscopy)과 AFM(atomic forced microscope)를 이용하였으며, 구조적 특성 관찰을 XRD(X-ray diffraction)를 사용하여 실험을 수행하였다.