탄산리튬 분말 제조에 있어서 탄산화 반응에 관한 연구

양재교,진연호,양대훈,김대원,Yang, Jae-Kyo,Jin, Yun-Ho,Yang, Dae-Hoon,Kim, Dae-Weon 한국결정성장학회 2019 한국결정성장학회지 Vol.29 No.5

In this study, we carried out the experiment to prepare lithium carbonate powder through gas-liquid reactions with a lithium-containing solution and $CO_2$ gas using lithium hydroxide, lithium chloride, and lithium sulfate. Thermodynamically, the carbonation reaction of a lithium-containing solution showed that aqueous reaction of lithium hydroxide occurs spontaneously, but aqueous reactions of lithium chloride and lithium sulfate does not occur spontaneously. In the case of lithium hydroxide solution, the recovery rate of lithium carbonate was 69.8 % at room temperature ($25^{\circ}C$), and increased to 89.4 % at $60^{\circ}C$. In the case of lithium chloride and lithium sulfate solution, lithium carbonate could be prepared using sodium hydroxide as an additive, but the recovery rates were 19.2 % and 16.7 %, respectively. 본 연구는 수산화리튬, 염화리튬, 그리고 황산리튬을 이용한 리튬 함유 용액과 $CO_2$ 가스와의 기상-액상 반응을 통하여 탄산리튬 분말을 제조하는 실험을 실시하였다. 열역학적으로 리튬 함유 용액의 탄산화 반응에서 수산화리튬은 자발적으로 일어나지만, 염화리튬과 황산리튬은 비자발적이었다. 수산화리튬의 경우, $25^{\circ}C$의 반응온도에서 탄산리튬의 회수율이 69.8 %였으며, $60^{\circ}C$에서는 89.4 %로 증가하였다. 염화리튬과 황산리튬의 경우, 수산화나트륨을 첨가제로 사용하여 탄산리튬을 제조할 수 있었으나, 회수율은 각각 19.2 %와 16.7 %로 비효율적임을 알 수 있었다.

탄소나노튜브가 분산된 Al₂O₃ 나노복합분말의 치밀화 및 특성

유승화,양재교,오승탁,강계명,강성군,좌용호,Yoo Seung-Hwa,Yang Jae-Kyo,Oh Sung-Tag,Kang Kae-Myung,Kang Sung-Goon,Choa Yong-Ho 한국분말야금학회 2005 한국분말재료학회지 (KPMI) Vol.12 No.6

In-situ processing route was adopted to disperse carbon nanotubes (CNTs) into $Al_2O_3$ powders homogeneously. The $Al_2O_3$ composite powders with homogeneous dispersion of CNTs could be synthesized by a catalytic route for in-situ formation of CNTs on nano-sized Fe dispersed $Al_2O_3$ powders. CNTs/Fe/$Al_2O_3$ nanopowders were densified by spark plasma sintering (SPS). The hardness and bending strength as well as electrical conductivity increased with increasing sintering temperature. However, the electrical conductivity of the composites sintered at above $1500^{\circ}C$ showed decreased value with increasing sintering temperature due to the oxidation of CNTs.

극청정 가스필터용 다공성 니켈 멤브레인의 제조

송한복,양재교,성기훈,서동문,강두홍,좌용호,Song, Han-Bok,Yang, Jae-Kyo,Seong, Ki-Hun,Seo, Dong-Moon,Kang, Du-Hong,Choa, Yong-Ho 한국결정성장학회 2007 한국결정성장학회지 Vol.17 No.5

극청정 가스필터용 다공성 멤브레인을 제조하기 위해 금속산화물 분말의 in-situ한 환원/소결 공정을 이용하였다. 또한 기공도의 향상을 위해 solid pore forming agent로써 구형의 폴리머 입자를 첨가하여 금속 섬유를 사용한 멤브레인과 비슷한 52%의 기공도를 가지는 니켈 멤브레인을 제조하였다. 제조된 니켈 멤브레인은 폴리머의 첨가에 따라 평균기공크기와 기공도가 증가하였다. 한편 환원/소결 온도가 $800^{\circ}C$에서 $1000^{\circ}C$로 상승함에 따라 평균기공크기와 기공도는 감소하였다. 이는 환원/소결 온도가 상승함에 따라 격자확산 및 입계확산이 진행되어 멤브레인의 수축률 증가를 일으켰기 때문이다. Porous nickel membrane far high precision gas filter was prepared by in-situ reduced/sintered process of NiO with an addition of polymer(PMMA; polymethyl methacrylate). It showed that the porosity of Ni membrane was approximately 52%. It is similar to metal membrane which prepared using metal fiber as raw materials. The average pore diameter and porosity of Ni membrane increased as content of added polymer and decreased as elevating reduced/sintered temperature from $800^{\circ}C$ to $1000^{\circ}C$. Increase of porosity at $800^{\circ}C$ was associated with surface diffusion mechanism that leads to initial sintering, while decrease of porosity at $1000^{\circ}C$ was associated with lattice diffusion and grain boundary diffusion.

기계화학공정을 이용한 Perovskite 구조의 (Pb, La)$TiO_3$ 나노 분말 합성 및 특성

임보라미,양재교,이동석,노태형,서정혜,이연승,김희택,좌용호,Lim, Bo-Ra-Mi,Yang, Jae-Kyo,Lee, Dong-Suk,Noh, Tae-Hyung,Seo, Jung-Hye,Lee, Youn-Seoung,Kim, Hee-Taik,Choa, Yong-Ho 한국결정성장학회 2008 한국결정성장학회지 Vol.18 No.5

기계화학공정(MCP; Mechano Chemical Process)은 원료 분말이 기계적인 에너지로 인해 상 형성이 활성화되기 때문에 기존의 볼밀링을 이용한 고상반응에서 필수적인 높은 온도에서의 하소 공정이 필요하지 않다. 본 연구에서는 고 에너지 MCP 방법을 이용하여 perovskite 구조를 가지는 PLT 나노 분말을 제조하였다. 특히, 일반적으로 출발물질로 염을 이용하는 것과 달리 산화물을 원료 분말로 사용하여 어떠한 열처리 공정 없이 PLT 나노 분말을 합성하였다. 또한 건식으로 밀링을 하여 분말 건조 공정이 필요 없어서 공정이 간단하다. MCP 밀링은 시간 별로 12시간까지 진행하였으며, 제조된 분말의 상 분석과 결정면 분석 결과 3시간 이후에는 perovskite 구조의 순수한 PLT 상을 형성하였다. 또한 마이크로 크기의 원료 분말이 밀링 3시간이 지나자 약 20 nm 크기의 균일한 나노 입자가 생성되었다. Mechano Chemical Process (MCP) skips the calcinations steps at an intermediate temperature that is always required in the conventional solid-state reaction because forming phase from raw powder is activated by mechanical energy. In this study, we prepared (Pb, La)$TiO_3$ nanopowder with perovskite structure by only high energy MCP. Especially, the PLT nanopowder was synthesized without any thermal treatment using oxides, not salts as raw powder. This process is also very simple due to dry milling method, unnecessary to dry of powder. The oxide powder was milled up to 12 hr at intervals of an hour using MCP and the pure PLT phase of perovskite structure was formed after milling time of 3 hr. And the average particle size was 20 nm with narrow distribution after milling time of 3 hr from raw powder of several $\mu m$ with inhomogeneous distribution.

열 CVD법에 의한 CNTs/Metal/Al₂O₃ 나노복합분말의 합성 및 특성

좌용호,유승화,양재교,오승탁,강성군,Choa Yong-Ho,Yoo Seung-Hwa,Yang Jae-Kyo,Oh Sung-Tag,Kang Sung-Goon 한국분말야금학회 2005 한국분말재료학회지 (KPMI) Vol.12 No.2

An optimum route to synthesize $Al_2O_3$-based composite powders with homogeneous dispersion of carbon nanotubes (CNTs) was investigated. CNTs/Metal/$Al_2O_3$ nanocomposite powders were fabricated by thermal chemical vapor deposition of $C_2H_2$ gas over metal/$Al_2O_3$ nanocomposite catalyst prepared by selective reduction of metal oxide/$Al_2O_3$ powders. The FT-Raman spectroscopy analysis revealed that the CNTs have single- and multi-walled structure. The CNTs with the diameter of 25-43 nm were homogeneously distributed in the metal/$Al_2O_3$ powders, and their characteristics were strongly affected by a kind of metal catalyst and catalyst size. The experimental results show that the composite powder with required size and dispersion of CNTs can be realized by control of synthesis condition.

방전 플라즈마 소결법을 이용한 8YSZ-$Al_2O_3$ 고체 산화물 연료전지 전해질 제조

김재광,최봉근,양재교,좌용호,심광보,Kim Jae Kwang,Choi Bong Geun,Yang Jae Kyo,Choa Yong Ho,Shim Kwang Bo 한국결정성장학회 2005 한국결정성장학회지 Vol.15 No.1

고체 산화물 연료전지 전해질 재료인 8YSZ(yttria stabilized zirconia)세라믹 소재의 전기 전도도와 기계적 특성을 동시에 향상시키기 위하여 첨가제로서 Al₂O₃를 사용하고, 방전 플라즈마 소결법을 적용하였다. 제조된 소결체는 1200℃의 소결 온도에서 96% 이상의 밀도를 보이며, 1 ㎛ 이하의 균일한 크기의 결정립들로 구성된 미세구조를 보여주고 있다. 첨가된 Al₂O₃는 순수한 8YSZ의 결정립성장을 억제하여 파괴인성 및 굽힘강도 등 기계적 물성을 향상시키고, 또한 결정립 내부 전도도는 일정하게 유지한 채, 결정립계 전도도를 향상시켜 전체 이온 전도도를 증가시킴을 확인하였다. 이는 방전플라즈마 소결법이 비교적 낮은 온도에서 소결이 가능하여 기존의 소결 방법에서 문제시 되었던 8YSZ내로 Al₂O₃가 용해되는 것이 억제 되었을 뿐 아니라, 결정립계에 존재하는 SiO₂가 Al₂O₃와 반응하여 Al/sub 2-x/Si/sub l-y/O/sub 5/상으로 결정화되면서 결정립계 전도도를 향상시킨 결과로 사료된다. In order to improve electrical conductivity and mechanical properties of 8YSZ SOFC electrolyte material, we used Al₂O₃ as an additive and applied the spark plasma sintering (SPS) method. The sintered bodies were densified above 96 % of theoretical density at 1200℃ and possessed microstructures composed of homogeneous grains less than 1 ㎛ in size. The addition of Al₂O₃ improved fracture toughness and bending strength by inhibiting grain growth of 8YSZ and increased total ionic conductivity because grain interior conductivity appeared to remain constant and grain boundary conductivity increased. It was assumed that the dissolution of Al₂O₃ into 8YSZ which was inevitable problem at commercial sintering method was effectively prohibited by the SPS technique with a relatively low sintering temperature and the reaction between Al₂O₃ and SiO₂ present at grain boundary to produce the crystalline Al/sub 2-x/Si/sub l-y/O/sub 5/ phase, resulting in the increase of grain boundary conductivity.

지르코니아 전해질을 이용한 단실형 고체산화물 연료전지의 전기화학 특성

박희정,주종훈,양재교,진연호,이규형,Park, Hee Jung,Joo, Jong Hoon,Yang, Jae-Kyo,Jin, Yun Ho,Lee, Kyu Hyoung 한국전기전자재료학회 2016 전기전자재료학회논문지 Vol.29 No.8

Single-chamber solid oxide fuel cells (SC-SOFCs) consist of only one gas chamber, in which both the anode and the cathode are exposed to the same fuel-oxidant mixture. Thus, this configuration shows good thermal and mechanical resistance and allows rapid start-up and -down. In this study, the unit cell consisting of $La_{0.8}Sr_{0.2}MnO_3$ (cathode) / $Zr_{0.84}Y_{0.16}O_{2-x}$ (electrolyte) / $Ni-Zr_{0.84}Y_{0.16}O_{2-x}$ (anode) was fabricated and its electrochemical property was investigated as a function of temperature and the volume ratio of fuel and oxidant for SC-SOFCs. Impedance spectra were also investigated in order to figure out the electrical characteristics of the cell. As a result, the cell performance was governed by the polarization resistances of the electrodes. The cell exhibited an acceptable cell-performance of $86mW/cm^2$ at $800^{\circ}C$ and stable performance for 3 hs under 0.7 V.

급속소결에 의해 제조된 Al₂O₃/Fe-Ni 나노복합재료의 미세조직 및 기계적 특성

이영인,이근재,장대환,양재교,좌용호,Lee, Young-In,Lee, Kun-Jae,Jang, Dae-Hwan,Yang, Jae-Kyo,Cho, Yong-Ho 한국분말야금학회 2010 한국분말재료학회지 (KPMI) Vol.17 No.3

A new High Frequency Induction Heating (HFIH) process has been developed to fabricate dense $Al_2O_3$ reinforced with Fe-Ni magnetic metal dispersion particles. The process is based on the reduction of metal oxide particles immediately prior to sintering. The synthesized $Al_2O_3$/Fe-Ni nanocomposite powders were formed directly from the selective reduction of metal oxide powders, such as NiO and $Fe_2O_3$. Dense $Al_2O_3$/Fe-Ni nanocomposite was fabricated using the HFIH method with an extremely high heating rate of $2000^{\circ}C/min$. Phase identification and microstructure of nanocomposite powders and sintered specimens were determined by X-ray diffraction and SEM and TEM, respectively. Vickers hardness experiment were performed to investigate the mechanical properties of the $Al_2O_3$/Fe-Ni nanocomposite.

알루미늄 7075 합금의 PEO 처리 기술 및 첨가제 영향 분석

진연호(Yun-Ho Jin),양재교(Jae-Kyo Yang) 한국표면공학회 2020 한국표면공학회지 Vol.53 No.2

In this study, we developed plasma electrolytic oxidation (PEO) process for aluminum 7075 alloy to improve the corrosion and mechanical properties. The electrolyte consists of potassium hydroxide and sodium silicate. Additionally, sodium stannate was added into the electrolyte to investigate its effect on PEO film formation. Titanium was used as the counter electrode. Plasma generation voltage reduced from 300V to 150 V by adding 4 g/L of sodium stannate. The thin oxide films were observed by SEM(Scanning Electron Microscopy)/ EDS (Energy Dispersive Spectroscopy) for quantitative and qualitative analyses. XRD (X-ray diffraction) and XRF (X-ray Fluorescences) analyses were also carried out to identify oxide layer on aluminum 7075 surface. Vicker’s hardness test was performed on the PEO-treated aluminum 7075 surface.

플라즈마 전해산화법에 의해 형성된 알루미늄 합금의 양극산화피막 내마모 특성에 관한 연구

정우철,진연호,최진주,양재교,Jung, Woo-Chul,Jin, Yun-Ho,Choi, Jin-Ju,Yang, Jae-Kyo 한국표면공학회 2018 한국표면공학회지 Vol.51 No.6

In this study, plasma electrolytic oxidation (PEO) method was used to from anodic oxide films on Al alloy and their resistance and morphological characteristics were investigated as a function of film formation voltage and treatment time. Cross-sectional morphology and composition of the PEO films were analyzed by SEM (Scanning Electron Microscopy) and EDS (Energy Dispersive Spectroscopy). The PEO films showed increased surface roughness and thickness with of film formation voltage and treatment time. The wear resistance was found to be the best for the PEO film formed for 5 min at 500V which is attributed to be denser structure relatively and lower surface roughness.