논문현황

INSTITUTE FOR ADVANCED ENGINEERING

신소재공정센터 플라즈마 전해산화법에 의해 형성된 알루미늄 합금의 양극산화피막 내마모특성에 관한 연구

· 저자

정우철, 진연호, 최진주, 양재교


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 and EDS. 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


신소재공정센터 Thermodynamics of fluoride-based molten fluxes for extraction of magnesium through the low temperature solid oxide membrane (LT-SOM) process

· 저자

Y. Lee, J.K. Yang and J.H. Park


The melt quenching experiments and thermodynamic calculations of phase diagrams were carried out to investigate potential additives for the low temperature solid oxide membrane (LT-SOM) magnesium extraction process. The solubility of MgO, which is a major source of magnesium extraction, was also measured in the molten fluoride fluxes. The solubility of MgO in the 46.5MgF2-46.5CaF2-7LiF and 45MgF2-45CaF2-10NaF (wt%) systems reached 3.4 and 1.9 wt% at 1473 K, respectively, and 1.5 wt% MgO in both fluxes at 1223 K. In addition, the 45MgF2-55CaF2 binary eutectic flux, which has been widely used in SOM process, could dissolve up to 2.3 wt% MgO at 1473 K. This value is significantly lower than the literature value, i.e. 10 wt% MgO. From the evaluation of the activity coefficient of MgO in the 46.5MgF2-46.5CaF2-7LiF and 45MgF2-45CaF2-10NaF fluxes under MgO saturation, it was confirmed that the stability of MgO in the 7LiF flux is greater than that in the 10NaF flux. Hence, the driving force of MgO dissolution into the 7LiF flux is higher than that into the 10NaF flux. The newly developed molten flux for magnesium extraction using the LT-SOM process with an operating temperature lower than 1273 K is the 46.5MgF2-46.5CaF2-7LiF system.


신소재공정센터 The oxygen-permeation property of doped-zirconia membrane at high temperature and in reduced condition

· 저자

Hee Jung Park, Jae-kyo Yang, Yun-Ho Jin, K.H. Lee


Doped zirconia with fast oxygen ionic conduction can be applied to an oxygen ion transport membrane for the deoxidation from metal melts and the production of metals from molten metal oxides. For the application, an oxygen-permeation study is required in low-oxygen partial pressure and high temperature. In this study, the electrical conductivity of the zirconia at high temperature (above 1200 °C) was estimated with a 4-probe DC method in order to estimate the theoretical oxygen-permeation flux. The oxygen permeation was investigated with two types of apparatus: a permeation concentration cell and a common permeation structure. As a result, the measured oxygen flux was much lower than the value expected from the electrical conductivity, indicating that the oxygen permeation was mostly limited by the surface-exchange kinetics in spite of the very high temperature. The rate-determining elementary step of the surface-exchange kinetics was the surface ionic diffusion and the charge transfer of minor charge carriers. To enhance the oxygen permeation of the zirconia, a surface-coating strategy using a double layer of ceria and lanthanum-chromate was applied with various coating thickness. The oxygen-permeation flux was maximized by the surface modification with optimal coating thickness.


신소재공정센터 Corrosion-Erosion Behavior of MgAl2O4 Spinel Refractory in Contact with High MnO Slag

· 저자

J. Jeon, Y. Kang, J.H. Park and Y. Chung


The corrosion and erosion behavior of spinel refractory of different compressive strength has been investigated for refractories in contact with a high MnO slag for producing manganese ferroalloys. The finger rotating test (FRT) was adopted to evaluate the degradation behavior at 1550 °C under a rotating condition of 150 rpm. The sample with higher compressive strength (Sample C1) showed higher corrosion resistance than Sample C2. In Sample C1, the refractory progressively corroded from the surface to the inner region by chemical corrosion, while mechanical erosion of the refractory suddenly occurred in Sample C2 as a result of the penetration of the slag within the refractory and the rotating energy.


신소재공정센터 지르코니아 전해질을 이용한 단실형 고체산화물 연료전지의 전기화학 특성

· 저자

박희정, 주종훈, 양재교, 진연호, 이규형


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 La0.8Sr0.2MnO3 (cathode) / Zr0.84Y0.16O2-x (electrolyte) / Ni-Zr0.84Y0.16O2-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 86 mW/cm2 at 800℃ and stable performance for 3 hs under 0.7 V.


신소재공정센터 Synthesis of Gd-doped CeO2 by ultrasonic spray pyrolysis with salt-assisted decomposition and its electrical and mechanical properties

· 저자

Hee Jung Park, G.B. Kim, S.J. Jung, Y.I. Lee, Jae-kyo Yang, Yun Ho Jin, and Y.H. Choa


Much attention has been paid to acceptor doped-ceria as a promising solid electrolyte for intermediate temperature solid oxide fuel cells (IT-SOFCs) due to its high oxygen-ion conductivity. However, poor sinterability leading to high grain boundary resistance and weak mechanical properties have limited its commercialization. In this work, ceria nanoparticles were synthesized via ultrasonic spray pyrolysis using salt-assisted decomposition (SA-USP) to enhance the sinterabililty of the ceria. The effects of the quantity of added salt on the nanoparticle-characteristics were examined. Highly dense ceria (relative density ~ 97.5%) was obtained by sintering the nanoparticles at a temperature as low as 1300 oC and its mechanical and electrical properties were investigated. The hardness and the oxygen-ion conductivity of the ceria with high density were reasonably good, ~ 14 GPa and above 10−3 S/cm at the IT-SOFC operating temperatures.