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LiF-NdF<sub>3</sub>-Nd<sub>2</sub>O<sub>3</sub> 용융염에서 질화물계 세라믹재료의 고온안정성
권숙철,이영준,류홍열,이고기,조성구,이종현,Kwon, Sukcheol,Lee, Young-Jun,Ryu, Hong-Youl,Lee, Go Gi,Jo, Sung Koo,Lee, Jong-Hyeon 한국재료학회 2015 한국재료학회지 Vol.25 No.12
Nd-Fe-B permanent magnets have been used in a wide variety of applications because of their high magnetic flux density. So, demand for neodymium has been increasing in worldwide. In this study, an electrowinning process was performed in $LiF-NdF_3-Nd_2O_3$ high temperature molten salts. However, a corrosion resistant material for use in the molten salt must be found for stable operation because of the harsh corrosion environment of the electrowinning process. Therefore, for this paper, boron nitride(BN), aluminum nitride(AlN), and silicon nitride($Si_3N_4$) were selected as protective and structural materials in the high temperature electrolyte. To investigate the characteristics of BN, AlN, and $Si_3N_4$, in molten salts, materials were immersed in the molten salts for 24, 72, 120, and 192 hours. Also, surface condition and stability were investigated by SEM and EDS and corrosion products were calculated by HSC chemistry. As a result, among BN, AlN, and $Si_3N_4$, AlN was found to show the best protective material properties.
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CaCl<sub>2</sub>-CaF<sub>2</sub>-CaO 용융염에서 YSZ 세라믹의 고온 안정성에 미치는 성형공정의 영향
김완배,권숙철,조수행,이종현,Kim, Wan-Bae,Kwon, Suk-Cheol,Cho, Soo-Haeng,Lee, Jong-Hyeon 한국재료학회 2020 한국재료학회지 Vol.30 No.4
The high-temperature stability of YSZ specimens fabricated by die pressure and cold isostatic press (CIP) is investigated in CaCl<sub>2</sub>-CaF<sub>2</sub>-CaO molten salt at 1,150 ℃. The experimental results are as follows: green density 46.7 % and 50.9 %; sintering density 93.3 % and 99.3 % for die press and CIP, respectively. YSZ foremd by CIP exhibits higher stability than YSZ formed by die press due to denseness dependency after high-temperature stability test. YSZ shows peaks mainly attributed to CaZrO<sub>3</sub>, with a small t-ZrO<sub>2</sub> peak, unlike the high-intensity tetragonal-ZrO<sub>2</sub> (t-ZrO<sub>2</sub>) peak observed for the asreceived specimen. The t-ZrO<sub>2</sub> phase of YSZ is likely stabilized by Y<sub>2</sub>O<sub>3</sub>, and the leaching of Y<sub>2</sub>O<sub>3</sub> results in phase transformation from t-ZrO<sub>2</sub> to m-ZrO<sub>2</sub>. CaZrO<sub>3</sub> likely forms from the reaction between CaO and m-ZrO<sub>2</sub>. As the exposure time increases, more CaZrO<sub>3</sub> is observed in the internal region of YSZ, which could be attributed to the inward diffusion of molten salt and outward diffusion of the stabilizer (Y<sub>2</sub>O<sub>3</sub>) through the pores. This results in greater susceptibility to phase transformation and CaZrO<sub>3</sub> formation. To use SOM anodes for the electroreduction of various metals, YSZ stability must be improved by adjusting the high-density in the forming process.
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바나듐 레독스 흐름 전지용 고순도 오산화바나듐 및 전해액 제조 연구
김선경,권숙철,홍혜진,서용재,장한권,전호석,박인수 한국자원공학회 2021 한국자원공학회지 Vol.58 No.1
We investigated the hydrolytic precipitation process with regard to purification of low-purity vanadium pentoxide (V2O5) to obtain high-purity vanadium electrolyte (VE) of a vanadium redox flow battery (VRFB). The lowest purities of VE and V2O5 for VRFB, which were reviewed through the purity analysis of commercial VE, were found to be 99.98% and 99.8%, respectively. The hydrolytic precipitation process applied to V2O5 powder with 99.7% and 98.3% purity resulted in V2O5 powder with a purity higher than 99.8%. However, the V2O5 powder contained impurities such as Fe and Ga. To further improve the purity, a two-step process comprising red cake precipitation was applied. However, this process exhibited a low vanadium recovery rate; therefore, development of a new single purification process with a high vanadium recovery rate is required. 본 연구에서는 VRFB의 고순도 바나듐 전해액을 제조하기 위해 저순도 오산화바나듐의 고순도화공정으로 가수분해 침전 공정을 적용하였다. 상용 바나듐 전해액 순도 분석을 통하여 검토한 VRFB 용 바나듐 전해액 및 오산화바나듐의 최저 순도는 각각 99.98% 및 99.8%로 확인되었다. 초기 순도가 99.7% 및 98.3%인 오산화바나듐에 가수분해 침전 공정을 적용할 경우 99.8% 이상의 고순도 오산화바나듐이 제조되었지만 Fe, Ga 성분이 불순물로 함유되었다. 추가적인 순도 향상을 위해 red cake 침전 단계를 포함하는 2단계 공정을 적용하였으나 바나듐 회수율이 감소하는 단점이 확인되었다. 따라서 향후 단일 공정으로 구성되어 높은 바나듐 회수율을 얻을 수 있는 고순도 바나듐 정제공정 개발이 필요하다.
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킬레이트제를 활용한 VRFB용 고순도 오산화바나듐 제조 연구
김선경,권숙철,김희서,서용재,유정현,장한권,전호석,박인수 한국자원리싸이클링학회 2022 資源 리싸이클링 Vol.31 No.2
This study implemented a chelating agent (Ethylenediaminetetraacetic acid, EDTA) in purification to obtain high-purity vanadium pentoxide (V2O5) for use in VRFB (Vanadium Redox Flow Battery). V2O5 (powder) was produced through the precipitation recovery of ammonium metavanadate (NH4VO3) from a vanadium solution, which was prepared using a low-purity vanadium raw material. The initial purity of the powder was estimated to be 99.7%. However, the use of a chelating agent improved its purity up to 99.9% or higher. It was conjectured that the added chelating agent reacted with the impurity ions to form a complex, stabilizing them. This improved the selectivity for vanadium in the recovery process. However, the prepared V2O5 powder exhibited higher contents of K, Mn, Fe, Na, and Al than those in the standard counterparts, thus necessitating additional research on its impurity separation. Furthermore, the vanadium electrolyte was prepared using the high-purity V2O5 powder in a newly developed direct electrolytic process. Its analytical properties were compared with those of commercial electrolytes. Owing to the high concentration of the K, Ca, Na, Al, Mg, and Si impurities in the produced vanadium electrolyte, the purity was analyzed to be 99.97%, lower than those (99.98%) of its commercial counterparts. Thus, further research on optimizing the high-purity V2O5 powder and electrolyte manufacturing processes may yield a process capable of commercialization. 본 연구에서는 VRFB용 고순도 오산화바나듐을 제조하기 위한 불순물 분리 정제 공정에서 킬레이트제(EDTA)의 영향을 조사하였다. 저순도 바나듐 원료를 이용하여 제조된 바나듐 용액으로부터 NH4VO3 을 침전 회수하여 제조된 최종 V2O5 분말의 순도는 99.7%로 분석되었지만 NH4VO3 침전 회수 공정에서 킬레이트제를 첨가한 경우 최종 V2O5 분말 순도가 99.9% 이상으로 향상되었다. 이러한 결과는 첨가된 킬레이트제가 불순물 이온과 반응하여 complex를 형성하고 불순물 이온이 안정화되기 때문에 침전 회수 공정에서 바나듐에 대한선택성이 향상된 것으로 판단된다. 하지만 제조된 V2O5 분말내에는 불순물 규격 대비 K, Mn, Fe, Na 및 Al 함유량이 높아 추가적인 불순물 정제 연구가 필요하였다. 고순도 V2O5 분말을 새롭게 개발된 직접 전해공정에 적용하여 바나듐 전해액을 제조하였고 이의 특성을 상용 전해액과 비교 분석하였다. 제조된 바나듐 전해액의 순도는 불순물 K, Ca, Na, Al, Mg 및 Si 성분의 높은 함량으로 인하여 상용 전해액의 순도 99.98%보다 낮은 99.97%로 분석되었다. 따라서 고순도 V2O5 분말 및 전해액 제조 공정의 불순물 분리 정제에 대한 추가적인 최적화 연구가 수행된다면 상용화가 가능한 공정이 개발될 것으로 기대된다.
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