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Formation Characteristics of Precipitated Calcium Carbonate by Carbonation Process
Chiho Kim,Mingwang Seok,Yangdo Kim 한국재료학회 2021 한국재료학회지 Vol.31 No.1
The characteristics and morphology of precipitated calcium carbonate (PCC) particles produced by carbonation process with various experimental conditions are investigated in this study. The crystal structures of PCC formed by carbonation process are calcite and aragonite. The crystal structure of PCC particles synthesized without adipic acid additive is calcite only, regardless of the reaction temperature. Needle-like shape aragonite phase started to form at reactor temperature of 80°C with the adipic acid additive. Particle size of the single phase calcite PCC synthesized without adipic acid additive is about 1 ~ 3 μm, with homogenous distribution. The aragonite PCC also shows uniform size distribution. The reaction temperature and concentration of adipic acid additive do not show any significant effects on the particle size distribution. Aragonite phase grown to a large aspect ratio of needle-like shape showed relatively improved whiteness. The measured whiteness value of single calcite phase is about 95.95, while that of the mixture of calcite and aragonite is about 99.11.
탄소나노튜브로 표면처리 된 탄소섬유/에폭시 수지 복합재료의 기계적 특성 연구
홍은미(Eunmi Hong),이규환(Kyuhwan Lee),김양도(Yangdo Kim),임동찬(Dongchan Lim) 한국표면공학회 2013 한국표면공학회지 Vol.46 No.5
In this work, the grow of carbon nanotube (CNT) on carbon fiber was introduced on PAN-based carbon fibers for the enhancement of mechanical interfacial strength of carbon fibers-reinforced composites. The surface properties of carbon fibers were determined by scanning electron microscopy (SEM) and mechanical interfacial properties of the composites were studied by interlaminar shear strength (ILSS). From the results, it was found that the mechanical interfacial properties of CNT-carbon fibers-reinforced composites (CNTCFRPs) enhanced with decreasing the CNT content. The excessive CNT content can lead the failure due to the interfacial separation between fibers and matrices in this system. In conclusion, the optimum CNT content on carbon fiber surfaces can be a key factor to determine the mechanical interfacial properties of the CNT-CFRPs.
Plasma-Enhanced Atomic-Layer Deposition of a HfO2 Gate Dielectric
Sungwoo Choi,전형탁,Jaehyoung Koo,Yangdo Kim 한국물리학회 2004 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.44 No.1
Hafnium oxide (HfO2) lms deposited by using both the conventional atomic-layer deposition (ALD) and the plasma-enhanced ALD (PEALD) techniques using Hf(NEt2)4 were investigated as a potential replacement for SiO2 gate dielectrics. HfO2 lms deposited with oxygen plasma showed lower impurity contents than those of lms deposited with oxygen gas. HfO2 lms showed a randomly oriented polycrystalline structure with the relatively smooth amorphous characteristics of an interfacial layer. The interfacial layer of the HfO2 lms deposited with oxygen plasma showed silicate (or SiOx) characteristics. HfO2 lms showed almost negligible hysteresis with a positive at band shift. They also showed a leakage current of about 10..9 A/cm2. Post annealing signicantly changed the characteristic of the HfO2 lms. HfO2 lms deposited with oxygen plasma showed generally improved lm qualities compared to the lms deposited with oxygen gas.
Jaehyoung Koo,전형탁,Sangmin Jeon,Seokhoon Kim,Yangdo Kim,Youngdo Won 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.48 No.I
Al2O3 thin films were deposited by using the plasma-enhanced atomic-layer deposition (PEALD) method and then investigated as a replacement for SiO2 gate dielectric films. Two different precursors, dimethylaluminum isopropoxide [DMAI, (CH3)2AlOCH(CH3)2] and trimethylaluminum [TMA, Al(CH3)3], were used to deposit the Al2O3. An oxygen plasma was used as the reactant gas. The process window of the Al2O3 films deposited using the DMAI precursor was wider than that of the Al2O3 films deposited using the TMA precursor. A linear relationship between film thickness and the number of process cycles was observed after the initial 50 cycles of Al2O3 deposition. The linear film growth rates were 0.14 nm/cycle and 0.12 nm/cycle using TMA and DMAI, respectively. Both Al2O3 films showed an amorphous structure with an Al silicate phase. The leakage currents of as-deposited Al2O3 with TMA and DMAI were approximately 7.9 × 10.9 and 3.3 × 10.9 A/cm2 with calculated EOT values of approximately 3.2 and 3.3 nm, respectively. In particular, the Al2O3 films deposited using the newly synthesized DMAI precursor, which is non-pyrophoric and safe, had comparable electrical properties to those of the Al2O3 films deposited using the TMA precursor.e
Effect of Nonionic Surfactants on F-Gases (HFC-134a and SF<sub>6</sub>) Hydrate Formation
Lee, Hyunju,Lee, Ju Dong,Kim, Yangdo American Chemical Society 2018 INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH - Vol.57 No.39
<P>Fluorinated gases (F-gases), such as 1,1,1,2-tetrafluoroethane (HFC-134a) and sulfur hexafluoride (SF<SUB>6</SUB>), are used widely in a variety of industrial processes but they are some of the most potent greenhouse gases. A clean process using the principle of gas hydrate formation can be a new alternative to the separation and recovery of these greenhouse gases. In this study, alcohol ethoxylate (AE), vegetable oil ethoxylate (VOE), and alkyl polymer (AP), which are known to be nonionic, less toxic, and readily biodegradable surfactants, were used as additives to improve the hydrate kinetics. All surfactants increased the kinetics of HFC-134a and SF<SUB>6</SUB> hydrate formation. In particular, the rates of HFC-134a and SF<SUB>6</SUB> hydrate formation was fastest when AP was added. In the case of AP addition, the inflection point at which the formation rates of SF<SUB>6</SUB> hydrate increased significantly was also found. The addition of AP not only improved the rates of HFC-134a and SF<SUB>6</SUB> hydrate formation but also reduced the hydrate nucleation time.</P> [FIG OMISSION]</BR>
탄화온도 및 재담금 처리에 따른 중공형 탄소다공체의 기공구조 및 특성
이은주,이창우,김양도,임영목,Yi, Eunju,Lee, Changwoo,Kim, Yangdo,Rhyim, Youngmok 한국재료학회 2013 한국재료학회지 Vol.23 No.1
Today, the modification of carbon foam for high performance remains a major issue in the environment and energy industries. One promising way to solve this problem is the optimization of the pore structure for desired properties as well as for efficient performance. In this study, using a sol-gel process followed by carbonization in an inert atmosphere, hollow spherical carbon foam was prepared using resorcinol and formaldehyde precursors catalyzed by 4-aminobenzoic acid; the effect of carbonization temperature and re-immersion treatment on the pore structure and characteristics of the hollow spherical carbon foam was investigated. As the carbonization temperature increased, the porosity and average pore diameter were found to decrease but the compression strength and electrical conductivity dramatically increased in the temperature range of this study ($700^{\circ}C$ to $850^{\circ}C$). The significant differences of X-ray diffraction patterns obtained from the carbon foams carbonized under different temperatures implied that the degree of crystallinity greatly affects the characteristics of the carbon form. Also, the number of re-impregnations of carbon form in the resorcinol-formaldehyde resin was varied from 1 to 10 times, followed by re-carbonization at $800^{\circ}C$ for 2 hours under argon gas flow. As the number of re-immersion treatments increased, the porosity decreased while the compression strength improved by about four times when re-impregnation was repeated 10 times. These results imply the possibility of customizing the characteristics of carbon foam by controlling the carbonization and re-immersion conditions.
김지혜(Ji-Hye Kim),이창래(Chang Rae Lee),정용수(Youngsoo Jeong),김양도(Yangdo Kim),김인배(In-Bae Kim) 한국표면공학회 2008 한국표면공학회지 Vol.41 No.3
The pyrolysized carbon xerogel and aerogels were prepared from the sol-gel polymerization of resorcinolformaldehyde(RF) followed by the dry process under ambient pressure and supercritical carbon dioxide condition respectively. The thermal behaviour of RF polymer xerogel was investigated with TGA analyzer to correspond with the pyrolysis process. The surface properties such as particle size, morphology and the point of zero charge of the pyrolysized porous carbon aerogels were studied for the precious metal catalyst supported media. It was found that the volume of the polymer aerogel decreased because of the significant linear shrinkage and weight loss of polymer gel during the carbonization. The point of zero charge of the carbon aerogel pyrolysized at 1050℃ under inert gas flow was about 10.
Moonhee Choi,Jihun Yu,Donghwan Kim,Inbae Kim,Yangdo Kim 한국자기학회 2011 Journal of Magnetics Vol.16 No.4
Nd2Fe14B permanent magnetic powders (iHc = 9.2 kOe, Br = 12.2 kG) were produced by HDDR process. Their coercivity was enhanced to 12.6 kOe through the grain boundary diffusion process with dysprosium hydride (DyHX). DyHX diffusion process was optimized through rotating diffusion process, resulting in distinct phases rich in Nd and Dy observable by field emission scanning microscopy and transmission electron microscopy. The mechanism of coercivity enhancement that resulted in restrain the coupling effect between Nd2Fe14B grains is also discussed.
Cyclic Voltammetry를 이용한 CuInSe<sub>2</sub> 박막의 전기화학적 전착 연구
홍순현,이현주,김양도,Hong, Soonhyun,Lee, Hyunju,Kim, Yangdo 한국재료학회 2013 한국재료학회지 Vol.23 No.11
Chalcopyrite $CuInSe_2$(CIS) is considered to be an effective light-absorbing material for thin film photovoltaic solar cells. CIS thin films have been electrodeposited onto Mo coated and ITO glass substrates in potentiostatic mode at room temperature. The deposition mechanism of CIS thin films has been studied using the cyclic voltammetry (CV) technique. A cyclic voltammetric study was performed in unitary Cu, In, and Se systems, binary Cu-Se and In-Se systems, and a ternary Cu-In-Se system. The reduction peaks of the ITO substrate were examined in separate $Cu^{2+}$, $In^{3+}$, and $Se^{4+}$ solutions. Electrodeposition experiments were conducted with varying deposition potentials and electrolyte bath conditions. The morphological and compositional properties of the CIS thin films were examined by field emission scanning electron microscopy (FE-SEM) and energy dispersive spectroscopy (EDS). The surface morphology of as-deposited CIS films exhibits spherical and large-sized clusters. The deposition potential has a significant effect on the film morphology and/or grain size, such that the structure tended to grow according to the increase of the deposition potential. A CIS layer deposited at -0.6 V nearly approached the stoichiometric ratio of $CuIn_{0.8}Se_{1.8}$. The growth potential plays an important role in controlling the stoichiometry of CIS films.