• Korean Chemical Engineering Research
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• v.57 no.1
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• pp.11-16
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• 2019

$La_{0.6}Sr_{0.4}Ti_{0.3}Fe_{0.7}O_{3-{\delta}}$(LSTF) coated $Ba_{0.5}Sr_{0.5}Co_{0.8}Fe_{0.2}O_{3-{\delta}}$(BSCF) membranes which has properties of high oxygen permeability and stability to $CO_2$ were applied to a bench scale apparatus to conduct oxygen permeation experiments. Also, the membranes of the laboratory and the bench scale device were divided into three regions according to the temperature gradient in the membrane reactor for comparative analysis. While oxygen permeation experiment were conducted up to $900^{\circ}C$, temperature dependence of Cr deposition was investigated. As a result, it was confirmed that the oxygen permeability was $2.37ml/min{\cdot}cm^2$, which was significantly lower than $3.79ml/min{\cdot}cm^2$ measured in the laboratory apparatus. It was found through XRD and SEM/EDS analysis that the decrease in oxygen permeability was originated from the deposition of gaseous Cr on the membrane surface released from the alloy material of the housing. In particular, a large amount of Cr was found in the medium temperature region.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2021-2025
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• 2007

Performance of single cell at solid oxide fuel cell (SOFC) system is largely affected by electrocatalytic and thermal properties of cathode. Samarium-based perovskite oxide material is recently recognized as promising cathode material for intermediate temperature-operating SOFC due to its high electrocatalytic property. Perovskite structured $Sm_{0.5}Sr_{0.5}CoO_{3-\delta}$ and its composite material, $Sm_{0.5}Sr_{0.5}CoO_{3-\delta}/Sm_{0.2}Ce_{0.8}O_{1.9}$ were investigated in terms of area specific resistance (ASR), thermal expansion coefficient (TEC), thermal cycling and long term performance. $Sm_{0.2}Ce_{0.8}O_{1.9}$ was used as electrolyte material. Electrochemical ac impedance spectroscopy (EIS) and dilatometer were used to measure the cathodic properties. Composite cathode ($Sm_{0.5}Sr_{0.5}CoO_{3-\delta}$: $Sm_{0.2}Ce_{0.8}O_{1.9}$ = 6:4) showed a good ASR of 0.13${\Omega}$ $cm^2$ at 650$^{\circ}C$ and its TEC value was 12.3${\times}$10-6/K at 600$^{\circ}C$ which is similar to the value of ceria-based electrolyte of 11.9${\times}$10-6/K. Performance of composite cathode was maintained with no degradation even after 13 times thermal cycle test.

• Korean Journal of Materials Research
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• v.7 no.2
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• pp.157-161
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• 1997

The crystallographic site dependent substitution of $^{18}O$ for $^{16}O$ in $Bi_{2}Sr_{2}Ca_{0.8}Y_{0.2}Cu_{2}^{16}O_{8+\delta}$ has heen investigated. In the Kaman spectra of $Bi_{2}Sr_{2}Ca_{0.8}Y_{0.2}Cu_{2}^{16}O_{8+\delta}$ three prominent Raman bands are observed at 297. 464, and $623cm^{-1}$. As the $^{16}O$ arc replaced hy $^{18}O$, all the three bands shift to lower wavewnumbers. The rate of this isotopic shift is similar for the hands at 397 and $464cm^{-1}$. whereas it is quite slower for the hand at $623cm^{-1}$ '['his implys that the $^{16}O-^{18}O$ exchange reaction is crystallographic sites dependent. .Assuming a tetragonal symmetry, we assign the bands at 623. 464, and $297cm^{-1}$ to the vibrations of $O_{pl}(A_{g}),\;O_{ap}\;and\;O_{Bi}$ respectively.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.9 no.2
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• pp.137-140
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• 1999

Effects of annealing and impurities on the superconducting properties were investigated by the magnetization measurement in $Bi_2Sr_2CaCu_2O_{8+{\delta}}(Bi2212)$ single crystals grown by flux method. It has been found that the superconducting properties are affected by Mg and Al impurities remarkably. The transition temperature$(T_c)$ has been lowered by the impurity of Mg. However, the diamagnetism is remarkably increased in an annealed crystal grown in MgO crucible compared to that in $Al_2O_3$ crucible. The content of Mg impurity can not be considered as a principal parameter for the decay of superconducting properties probably because the diamagnetism is remarkably improved in annealed crystal containing Mg.

• Journal of the Korean Society of Propulsion Engineers
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• v.21 no.2
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• pp.111-118
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• 2017

In this paper, combustion tests were performed to investigate performance characteristics of a canted slit-type pintle injector engine which uses kerosene and liquid oxygen as propellants. The number of slits, slit angle and blockage factor were chosen as design variables of the pintle injector. ${\Delta}SR$ was newly defined as the difference of skip ratio caused by both sides of the tip of the canted slit. The experimental results showed that optimal combustion was performed when the blockage factor is about 1 and the difference is less than 0.26.

• Journal of the Korean Ceramic Society
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• v.38 no.9
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• pp.787-793
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• 2001

$La_{0.6}Sr_{0.4}Co_{0.2}Fe_{0.8}O_{3-{\delta}}$ membranes were fabricated by solid-state reaction. We investigated sintering behavior and oxygen permeation flux as a function of time-on-stream, temperature and upstream oxygen partial pressure. The oxygen was permeated at temperatures form 750$^{\circ}$C to 950$^{\circ}$C by mixed conducting through oxygen vacancy diffusion in the dense membrane. The oxygen permeation flux through the membrane were about 0.1ml/$cm^3{\cdot}$min at 850$^{\circ}$C. A constant time was required for reaching stable oxygen flux, and oxygen partial pressure affected the oxygen permeation fluxes.

• 한국신재생에너지학회:학술대회논문집
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• 2007.06a
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• pp.133-136
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• 2007

Perovskite-structured samarium strontium cobaltite (SSC), which is mixed ionic electronic conductor (MIEC), is considered as a promising cathode material for intermediate temperature-operating solid oxide fuel cell (SOFC) due to its high electrocatalytic property. Cathode material containing cobalt (Co) is unstable at high temperature and has a relatively high thermal expansion property. In this paper, Sm-Sr-(Co,Fe,Ni)-O system with perovskite and spinel structures was investigated in terms of electrochemical property and thermal expansion property, respectively. Area specific resistance (ASR) was measured by ac impedance spectroscopy to investigate the electrochemical property of cathode, and thermal expansion coefficient (TEC) was measured by using dilatometer. Micro structure of cathode was observed by scanning electron microscopy. Perovskite-structured $Sm_{0.5}Sr_{0.5}CoO_{3-\delta}$ showed the ASR of $0.87{\Omega}/cm^{2}$, and $Sm_{0.5}Sr_{0.5}NiO_{3-\delta}$, which actually has a spinel structure, showed the lowest TEC value of $13.3{\times}10^{-6}/K$.

• Journal of Environmental Science International
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• v.26 no.6
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• pp.719-728
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• 2017

In order to investigate the adsorption characteristics for Sr ion using the Na-X zeolite synthesized from coal fly ash, batch tests and response surface analyses were carried out. The adsorption kinetic data for Sr ions, using Na-X zeolite, fitted well with the pseudo-second-order model. The uptake of Sr ions followed the Langmuir isotherm model, with a maximum adsorption capacity of 196.46 mg/g. Thermodynamic studies were conducted at different reaction temperatures, with the results indicating that Sr ion adsorption by Na-X zeolite was an endothermic (${\Delta}H^o$>0) and spontaneous (${\Delta}G^o$<0) process. Using the response surface methodology of the Box-Behnken method, initial Sr ion concentration ($X_1$), initial temperature ($X_2$), and initial pH ($X_3$) were selected as the independent variables, while the adsorption of Sr ions by Na-X zeolite was selected as the dependent variable. The experimental data fitted well with a second-order polynomial equation by multiple regression analysis. The value of the determination coefficient ($R^2=0.9937$) and the adjusted determination coefficient (adjusted $R^2=0.9823$) was close to 1, indicating high significance of the model. Statistical results showed the order of Sr removal based on experimental factors to be initial pH > initial concentration > temperature.

• Journal of Environmental Science International
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• v.25 no.12
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• pp.1623-1632
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• 2016

Zeolite (FZ) prepared using coal fly ash from an Ulsan industrial complex was immobilized with polysulfone (PS) to fabricate PS-FZ beads. The prepared PS-FZ beads were characterized by scanning electron microscopy and Fourier transform infrared spectroscopy. The optimum ratio for preparing PS-FZ beads was 1 g of PS to 2 g of FZ. The removal efficiencies of Sr and Cu ions by the PS-FZ beads increased as the solution pH increased and nearly reached a plateau at pH 4. A pseudo-second-order model morel fit the adsorption kinetics of both ions by the PS-FZ beads better than a pseudo-first-order model. The Langmuir isotherm model fit the equilibrium data well. The maximum adsorption capacities calculated from the Langmuir isotherm model were 46.73 mg/g and 62.54 mg/g for the Sr and Cu ions, respectively. Additionally, the values of thermodynamic parameters such as free energy (${\Delta}G^{\circ}$), enthalpy (${\Delta}H^{\circ}$) and entropy (${\Delta}S^{\circ}$) were determined. The results implied that the prepared PS-FZ beads could be interesting an alternative material for Sr and Cu ion removal.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.07a
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• pp.697-700
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• 2001

In this paper, the structural and electrical properties of the Sr$_{1-x}$ Ca$_{x}$TiO$_3$ (0$\leq$x$\leq$0.2) (0$\leq$r$\leq$0.2)-based grain boundary layer ceramics were investigated by X-ray, SEM and V-I system. Increasing the Ca content, the average grain size and the lattice constant were decreased. The relative density of all specimens was >96%. The 2nd phase formed by thermal diffusing from the surface lead to a very excellent electrical properties, that is, $\varepsilon$$_{r}$>50000, tan$\delta$<0.05, $\Delta$C< $\pm$ 10%.\pm$ 10%.%.