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Kang B.-K.,Kyungpook National University | Lee H.-C.,Kyungpook National University | Heo Y.-W.,Kyungpook National University | Kim J.-J.,Kyungpook National University | And 2 more authors.
Ceramics International | Year: 2013

In this study, the thermal expansion behavior of the BSCF (Ba 0.5Sr0.5Co0.8Fe0.2O 3-δ) and La-doped BSCF, i.e., (Ba0.5Sr 0.5)0.7La0.3Co0.8Fe 0.2O3-δ (BSLCF30) was systematically examined. The thermal expansion rate of the sintered body increased rapidly at around 500° C. It was found from the TG analysis that the oxygen vacancies formed around this temperature. When La is doped in the A-site of BSCF, more weight loss was observed over 500 °C compared to BSCF, which shows that La doping induces oxygen vacancies. Consequently, chemical expansion of the B-site cations occurred. Therefore, the thermal expansion coefficient (TEC) of BSLCF was much bigger than that of the BSCF. When the samples were heated and cooled in an Ar atmosphere, hysteresis of TEC was observed since re-oxidation cannot occur during cooling. © 2013 Elsevier Ltd and Techna Group S.r.l.

Lee H.-C.,Kyungpook National University | Kang B.-K.,Kyungpook National University | Lee J.-H.,Kyungpook National University | Heo Y.-W.,Kyungpook National University | And 2 more authors.
Ceramics International | Year: 2013

Because of the different densification characteristics of a La 0.8Ca0.2Cr0.9Co0.1O 3-δ (LCCC) interconnector and a NiO added yttrium-stabilized zirconia (YSZ) anode, complete adhesion between the two layers is hardly obtainable. In this study, we have investigated the sintering behavior of LCCC with the addition of YSZ. As the amount of YSZ increases, densification of the LCCC is inhibited and the initial temperature of the densification increases. However, when the LCCC-YSZ composite layer is screen printed on the NiO-YSZ substrates, the density of the composite layer increases and the layer is firmly attached to the substrates. It is proposed that tensile stress is decreased on the composite layer due to the relatively delayed densification of the LCCC-YSZ composite, compared to the densification of the NiO-YSZ substrate. © 2013 Elsevier Ltd and Techna Group S.r.l.

Yoo C.-Y.,Korea Institute of Energy Research | Yun D.S.,Korea Institute of Energy Research | Park S.-Y.,Korea Institute of Energy Research | Park S.-Y.,SsangYong Materials Corporation | And 5 more authors.
Electrocatalysis | Year: 2016

Abstract: The electrochemical properties of La0.6Sr0.4Co0.2Fe0.8O3-δ-based cathodes are studied as model electrodes for proton ceramic fuel cells. The electrochemical performance of symmetric cells with porous cathodes (La0.6Sr0.4Co0.2Fe0.8O3-δ, La0.6Sr0.4Co0.2Fe0.8O3-δ–BaCe0.9Y0.1O3-δ, and La0.6Sr0.4Co0.2Fe0.8O3-δ–BaZr0.8Y0.2O3-δ), investigated as a function of oxygen and water partial pressures, follows the order La0.6Sr0.4Co0.2Fe0.8O3-δ–BaCe0.9Y0.1O3-δ ≥ La0.6Sr0.4Co0.2Fe0.8O3-δ >> La0.6Sr0.4Co0.2Fe0.8O3-δ–BaZr0.8Y0.2O3-δ. The results indicate that the cathode performance of La0.6Sr0.4Co0.2Fe0.8O3-δ–BaCe0.9Y0.1O3-δ is enhanced mainly due to the extension of the effective triple phase boundary, whereas that of La0.6Sr0.4Co0.2Fe0.8O3-δ–BaZr0.8Y0.2O3-δ is lowered due to the poor proton conductivity along the percolated BaZr0.8Y0.2O3-δ particles. From the observed oxygen partial pressure dependence, the rate-determining step of the above cathode polarization reaction is principally ascribed to the oxygen reduction reaction. [Figure not available: see fulltext.] © 2016, Springer Science+Business Media New York.

Park J.-H.,Dong - Eui University | Yang W.-S.,Dong - Eui University | Jung J.-Y.,Dong - Eui University | Lee S.-I.,Dong - Eui University | And 5 more authors.
Journal of the Korean Ceramic Society | Year: 2011

The effect of slurry composition and wafer flatness on a material removal rate (MRR) and resulting surface roughness which are evaluation parameters to determine the CMP characteristics of the on-axis 6H-SiC substrate were systematically investigated. 2-inch SiC wafers were fabricated from the ingot grown by a conventional physical vapor transport (PVT) method were used for this study. The SiC substrate after the CMP process using slurry added oxidizers into slurry consisted of KOH-based colloidal silica and nano-size diamond particle exhibited the significant MRR value and a fine surface without any surface damages. SiC wafers with high bow value after the CMP process exhibited large variation in surface roughness value compared to wafer with low bow value. The CMP-processed SiC wafer having a low bow value of 1ìm was observed to result in the Root-mean-square height (RMS) value of 2.747 Å and the mean height (Ra) value of 2.147 Å.

Kim E.-H.,Hongik University | Jung H.-J.,Hongik University | An K.-S.,Korea Research Institute of Chemical Technology | Park J.-Y.,Ssangyong Materials Corporation | And 6 more authors.
Ceramics International | Year: 2014

Aluminum oxide was deposited into the porous cathode compartment of the (Sc,Al)-doped ZrO2 electrolyte cell through atomic layer deposition involving trimethyl aluminum and water as aluminum and oxygen sources, respectively. The deposited aluminum oxide had a detrimental effect on the cell performance of the zirconia-based SOFC unit cells in terms of the output power but did not change the open-cell voltage. Based on impedance spectroscopy, the open-cell voltage, and the output performance, the resultant degradation is attributed to the geometrical blockade of functional triple phase boundaries in La0.6Sr0.4CoO3 (LSCo)-based cathode materials of mixed ionic electronic conduction, indicating that there is a disruption at the interface between the charge collector and cathode that is proportional to the amount of deposited Al2O3. © 2014 Elsevier Ltd and Techna Group S.r.l.

Kang Y.-M.,Samsung | Kwon Y.-H.,Samsung | Kim M.-H.,SsangYong Materials Corporation | Lee D.-Y.,SsangYong Materials Corporation
Journal of Magnetism and Magnetic Materials | Year: 2015

We report the magnetic properties of Mn-Zn substituted M-type Sr-hexaferrites (SrM), SrFe12-2xMnxZnxO19, and compare them with those of non-substituted SrM and La-Zn substituted SrM. The highest saturation magnetization (MS) of 75.6 emu/g was obtained at a Mn-Zn substitution of x=0.1 (SrFe11.8Mn0.1Zn0.1O19), which is higher than those of the non-substituted SrM and La-Zn substituted SrM by 2.6% and 1.7%, respectively. The enhanced MS can be attributed to the selective substitution of Zn2+ and Mn4+ into the down-spin site of Fe3+ (4f1 or 4f2). Sintered anisotropic magnets fabricated with the optimal Mn-Zn doping level of x=0.1 exhibited a remanent magnetic induction (Br) over 4300 G and maximum energy product (BH)max of ~4.6 MGOe (36.6 kJ/m3). © 2015 Elsevier B.V. All rights reserved.

A ferrite magnetic material comprising a primary phase of a magnetoplumbite-type hexagonal ferrite, the primary phase having a composition represented by formula (I), can provide improved magnetic properties in terms of the residual magnetic flux density (Br), intrinsic coercive force (iHc), squareness (Hk/iHc), and maximum energy product (B.Hmax). Therefore, a segment-type permanent magnet derived therefrom can be used in the manufacture of small type motors for automobiles, motors for electric equipments as well as for home appliances, and other devices.

Lee H.-C.,Kyungpook National University | Kang B.-K.,Kyungpook National University | Lee J.-H.,Kyungpook National University | Heo Y.-W.,Kyungpook National University | And 2 more authors.
Journal of the Korean Ceramic Society | Year: 2012

In this study, in order to improve densification of La 0.8Ca 0.2Cr 0.9Co0.1O 3-σ (LCCC), which is known for one of the most proper candidate interconnector materials in the solid oxide fuel cells, CaCrO 4 was prepared via solid oxide synthesis route and added to the LCCC with different amount and particle sizes. As the amount of the CaCrO 4 increased, porosity of the sintered samples increased, and the pore size was proportional to the particle size of the CaCrO 4. This supports the fact that the CaCrO 4 phase forms liquid during sintering and permeate into the matrix leaving behind large pores. Then the liquid reacts with the matrix through the solid solution. However, when the samples were sintered with a slow ramp up rates, the porosity decreased. This is thought to be caused by the progressive solid solution of CaCrO 4 before the temperature reach to the melting temperature and forms a fluent amount of liquids. The sintering behavior of the LCCC with the addition of CaCrO 4 was analyzed through the transient liquid phase sintering on the basis of the microstructure observation and phase identification by x-ray diffraction.

Park J.,KAIST | Bae J.,KAIST | Kim J.-Y.,Ssangyong Materials Corporation
Renewable Energy | Year: 2012

Fuel cells convert the chemical energy present in fuel (e.g., hydrogen) into electrical energy with high efficiency, low pollution and low noise. Of the various types of fuel cells, the solid oxide fuel cell (SOFC) was developed specifically for power plants and residual power systems. SOFCs are classified into three categories based on their shape: planar, cylindrical and flat-tube. The flat-tube SOFC (FT-SOFC) exhibits the advantages of ease in sealing, low stack volume and low current-collecting resistance. However, due to its weak strength, the FT-SOFC may get deformed or break during the manufacturing process. To improve the cell strength, the cell support must be thickened. However, as the support thickness is increased, the electrons must travel a longer distance, which leads to an increase in the electrical resistance. In another method, the hydrogen channel diameter can be reduced for the strong strength. But, it may lead to a corresponding decrease in the hydrogen mass transfer rate. In this manuscript, we study the performance of several FT-SOFC designs and suggest the better design. The numerical analysis for the FT-SOFC incorporates several physical phenomena such as gas flow, heat transfer and electrochemical reactions. The governing equations (i.e., mass, momentum, energy and species balance equations) are calculated for heat and mass transfer. The open circuit voltage, activation polarization, ohmic polarization and contact resistance are simulated simultaneously. The experimental results are compared with the numerical data for the purposes of code validation. The current density and temperature distribution are then investigated on the SOFC surface. The average current density decreases by 14.6% if the hydrogen channel diameter is narrowed by 50%, and by 10.2% if the support thickness is increased by 50%. Based on these results, we present a design for a stack of FT-SOFCs. © 2011 Elsevier Ltd.

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