• 한국분말재료학회지
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• 제23권6호
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• pp.453-457
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• 2016

In this work, we synthesize brilliant yellow color ${\alpha}$-FeOOH by controlling the rod length and core-shell structure. The characteristics of ${\alpha}$-FeOOH nanorods are controlled by the reaction conditions. In particular, the length of the ${\alpha}$-FeOOH rods depends on the concentration of the raw materials, such as the alkali solution. The length of the nanorods is adjusted from 68 nm to 1435 nm. Their yellowness gradually increases, with the highest $b^*$ value of 57 based on the International Commission on Illumination (CIE) Lab system, by controlling the nanorod length. A high quality yellow color is obtained after formation of a silica coating on the ${\alpha}$-FeOOH structure. The morphology and the coloration of the nal products are investigated in detail by X-ray diffraction, scanning electron microscopy, UV-vis spectroscopy, and the CIE Lab color parameter measurements.

• 청정기술
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• 제8권4호
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• pp.173-180
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• 2002

본 연구에서는 MLCC의 원료인 $BaTiO_3$ 분말에 첨가제를 코팅한 core-shell 구조의 복합분말을 제조하였다. 이러한 복합분말은 MLCC 제조공정에서 VOC의 배출을 억제할 뿐만 아니라, MLCC의 초고용량화 및 신뢰성 향상을 목적으로 한다. 첨가제의 성분 및 함량은 국내 MLCC 제조기업으로부터 조사하였으며, 본 연구에서는 $Y_2O_3$와 $MnCO_3$ 두 성분에 대하여 연구하였다. 두 성분의 염은 $70^{\circ}C$이상의 반응온도에서 요소분해반응을 통해서 $BaTiO_3$분말의 표면에 동시에 그리고 균일하게 코팅될 수 있음이 확인되었다. 원소분석 결과, 코팅성분의 함량은 초기에 설정한 값과 근접하게 유지됨을 알 수 있었다. 본 연구실험 결과, 첨가제의 균일코팅을 위해서는 PVP 등의 분산제 역할이 크지 않은 반면, 반응온도 및 반응시간의 최적상태 유지가 매우 중요함이 확인되었다.

• 한국결정성장학회지
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• 제18권4호
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• pp.155-159
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• 2008

본 연구에서는 금속 Zn 팰렛을 원료 물질로 이용하여 열화학기상증착법으로 마이크로 크기의 프리스탠딩 ZnO/Zn 코어셀 다면체 구조물을 합성하였다. 마이크로 크기로 성장된 ZnO/Zn 코어셀 다면체의 형태와 구조적인 특성을 분석하기 위해서 주사전자현미경과 투과전자현미경을 이용하였다. 성장된 마이크로 크기의 다면체는 단결정 ZnO 나노막대 배열에 의해 둘러싸인 단결정 금속 Zn로 구성되어 있음을 확인할 수 있었다. 마이크로 크기의 단결정 Zn는 육방정 결정구조로 이루어져 있으며, 표면을 구성하고 있는 c-축 배향된 ZnO 나노막대가 10 nm와 100 nm 이하의 직경과 높이를 각각 가지며 육방정 결정구조의 단결정임을 확인하였다.

• Nano
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• 제13권12호
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• pp.1850148.1-1850148.9
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• 2018

The interconnected three-dimensional Ni-Co-S nanosheets were successfully deposited on ZnO nanorods by a one-step potentiostatic electrodeposition. The Ni-Co-S nanosheets provide a large electrode/electrolyte interfacial area which has adequate electroactive sites for redox reactions. Electrochemical characterization of the ZnO@Ni-Co-S core-shell nanorods presents high specifc capacitance (1302.5 F/g and 1085 F/g at a current density of 1 A/g and 20 A/g), excellent rate capabilities (83.3% retention at 20 A/g) and great cycling stability (65% retention after 5000 cycles at a current density of 30 A/g). The outstanding electrochemical performance of the as-prepared electrode material also can be ascribed to these reasons that the special structure improved electrical conductivity and allowed the fast diffusion of electrolyte ions.

• Korean Chemical Engineering Research
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• 제46권1호
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• pp.99-105
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• 2008

본 연구에서는 MLCC용 $BaTiO_3$에 첨가되는 $Cr_2O_3$와 $Mn_2O_3$의 나노코팅에 의한 core-shell 구조의 $BaTiO_3$ 분말을 제조하였다. 예비실험을 통해서 $KMnO_4$ 및 $K_2Cr_2O_4$ 그리고 sulfur를 사용하는 최적의 액상반응조건이 확립되었다. 본 연구에서는 두 첨가제 분말을 합성하였고 동일한 반응조건으로 두 첨가제를 $BaTiO_3$ 분말표면에 코팅하였다. 코팅은 one-step과 two-step의 두 방법으로 구분하여 시행하였고 그 결과를 분석 비교하였다. 결론적으로 말해서, $Cr_2O_3$와 $Mn_2O_3$의 두 첨가제는 용이한 반응조건에서 높은 수율로 우수한 품질의 코팅막을 형성하므로써, 첨가제 함량과 코팅막 특성의 정밀한 조절이 용이함을 보여주었다.

• 산업경영시스템학회지
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• 제46권3호
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• pp.15-22
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• 2023

BNKT Ceramics, one of the representative Pb free based piezoelectric ceramics, constitutes a perovskite(ABO3) structure. At this time, the perovskite structure (ABO3) is in the form where the corners of the octahedrons are connected, and in the unit cell, two ions, A and B, are cations, A ion is located at the body center, B ion is located at each corner, and an anion O is located at the center of each side. Since Bi, Na, and K sources constituting the A site are highly volatile at a sintering temperature of 1100℃ or higher, it is difficult to maintain uniformity of the composition. In order to solve this problem, there should be suppression of volatilization of the A site material or additional compensation of the volatilized. In this study, the basic composition of BNKT Ceramics was set to Bi_0.5(Na_0.78K_0.22)_0.5TiO₃ (= BNKT), and volatile site (Bi, Na, and K sources) were coated in the form of a shell to compensate additionally for the A site ions. In addition, the physical and electrical properties of BNKT and its coated with shell additives(= @BNK) were compared and analyzed, respectively. As a result of analyzing the crystal structure through XRD, both BNKT(Core) and @BNK(Shell) had perovskite phases, and the crystallinity was almost similar. Although the Curie temperature of the two sintered bodies was almost the same (TC = 290 ~ 300 ℃), it was confirmed that the d33 (piezoelectric coefficient) and Pr (residual polarization) values were different. The experimental results indicated that the additional compensation for a shell additive causes the coarsening, resulting in a decrease in sintering density and Pr(remanent polarization). However, coating shell additives to compensate for A site ion is an effective way to suppress volatilization. Based on these experimental results, it would be the biggest advantage to develop an eco-friendly material (Lead-free) that replaced lead (Pb), which is harmful to the human body. This lead-free piezoelectric material can be applied to a biomedical device or products(ex. earphones (hearing aids), heart rate monitors, ultrasonic vibrators, etc.) and skin beauty improvement products (mask packs for whitening and wrinkle improvement).

• 한국섬유공학회:학술대회논문집
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• 한국섬유공학회 2003년도 The Korea-Japan Joint Symposium
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• pp.88-89
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• 2003

A series of novel spinning acrylic polymer containing silk protein were synthesized by copolymerization of acrylonitrile (AN) and silk fibroin peptide (SFP) modified by acryloyl chloride (AC) with vinyl groups. The viscosity values of these copolymers showed that the copolymers have good spinnability, which are synthesized under the condition of putting a micro amount of metal ions into synthesizing solvent. The fiber based on the poly (AN-co-SFP) was prepared and characterized by SEM, FTIR measurement of its shell and core flakes, and moisture absorption. The fiber appeared a smooth surface and could be assumed to have excellent adhesive between SFP and PAN. Furthermore, these fibers showed a shell-core structure and excellent moisture absorption.

• Bulletin of the Korean Chemical Society
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• 제33권11호
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• pp.3576-3580
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• 2012

Larva-like GaS nanostructures synthesized by the thermal evaporation of Ga metals and S powders were coated with $SiO_2$ by the sputtering technique. Transmission electron microscopy and X-ray diffraction analyses revealed that the cores and shells of the GaS-core/$SiO_2$-shell larva-like nanostructures were single crystal wurtzite-type hexagonal structured-GaS and amorphous $SiO_2$, respectively. Photoluminescence (PL) measurements at room temperature showed that the passivation of the larva-like GaS nanostructures was successfully achieved with $SiO_2$ without nearly harming the major emission from the wires. However, subsequent thermal annealing treatment was found to be undesirable owing to the degradation of their emission in intensity.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
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• pp.420-421
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• 2006

In the present study, ultrafined Zr-V-Fe based alloy powder prepared by a plasma arc discharge process with changing process parameters. The chemical composition of synthesized powder was strongly influenced by the process parameters, especially the hydrogen volume fraction in the powder synthesis atmosphere. The synthesized powder had an average particle size of 50 nm. The synthesized Zr-V-Fe based particles had a shell-core structure composed of metal in the core and oxidse in the shell.

• Applied Microscopy
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• 제36권spc1호
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• pp.47-56
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• 2006

Improvements are made to existing primitive cell volume measurement method to provide a real-time analysis capability for the phase analysis of nanocrystalline materials. Simplification is introduced in the primitive cell volume calculation leading to fast and reliable method for nano-phase identification and is applied to the phase analysis of Mo-Si-N nanocoating layer. In addition, comparison is made between real-time and film measurements for their accuracy of calculated primitive cell volume values and factors governing the accuracy of the method are determined. About 5% accuracy in primitive cell determination is obtained from camera length calibration and this technique is used to investigate the cell volume variation in WC-TiC core-shell microstructure. In addition to chemical compositional variation in core-shell type structure, primitive cell volume variation reveals additional information on lattice coherency strain across the interface.