• Korean Journal of Materials Research
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• v.22 no.9
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• pp.470-475
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• 2012

$La_{1-x}Sr_xMnO_3$(LSM,$0{\leq}x{\leq}0.5$) powders as the air electrode for solid oxide fuel cell were synthesized by a glycine-nitrate combustion process. The powders were then examined by X-ray diffraction(XRD) and scanning electron microscopy (SEM). The as-formed powders were composed of very fine ash particles linked together in chains. X-ray maps of the LSM powders milled for 1.5 h showed that the metallic elements are homogeneously distributed inside each grain and in the different grains. The powder XRD patterns of the LSM with x < 0.3 showed a rhombohedral phase; the phase changes to the cubic phase at higher compositions($x{\geq}0.3$) calcined in air at $1200^{\circ}C$ for 4 h. Also, the SEM micrographs showed that the average grain size decreases as Sr content increases. Composite air electrodes made of 50/50 vol% of the resulting LSM powders and yttria stabilized zirconia(YSZ) powders were prepared by colloidal deposition technique. The electrodes were studied by ac impedance spectroscopy in order to improve the performance of a solid oxide fuel cell(SOFC). Reproducible impedance spectra were confirmed using the improved cell, which consisted of LSM-YSZ/YSZ. The composite electrode of LSM and YSZ was found to yield a lower cathodic resistivity than that of the non-composite one. Also, the addition of YSZ to the $La_{1-x}Sr_xMnO_3$ ($0.1{\leq}x{\leq}0.2$) electrode led to a pronounced, large decrease in the cathodic resistivity of the LSM-YSZ composite electrodes.

• Journal of Powder Materials
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• v.18 no.5
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• pp.430-436
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• 2011

Joining of NiO-YSZ to 316 stainless steel was carried out with B-Ni2 brazing alloy (3 wt% Fe, 4.5 wt% Si, 3.2 wt% B, 7 wt% Cr, Ni-balance, m.p. 971-$999^{\circ}C$) to seal the NiO-YSZ anode/316 stainless steel interconnect structure in a SOFC. In the present research, interfacial (chemical) reactions during brazing at the NiO-YSZ/316 stainless steel interconnect were enhanced by the two processing methods, a) addition of an electroless nickel plate to NiO-YSZ as a coating or b) deposition of titanium layer onto NiO-YSZ by magnetron plasma sputtering method, with process variables and procedures optimized during the pre-processing. Brazing was performed in a cold-wall vacuum furnace at $1080^{\circ}C$. Post-brazing interfacial morphologies between NiO-YSZ and 316 stainless steel were examined by SEM and EDS methods. The results indicate that B-Ni2 brazing filler alloy was fused fully during brazing and continuous interfacial layer formation depended on the method of pre-coating NiO-YSZ. The inter-diffusion of elements was promoted by titanium-deposition: the diffusion reaction thickness of the interfacial area was reduced to less than 5 ${\mu}m$ compared to 100 ${\mu}m$ for electroless nickel-deposited NiO-YSZ cermet.

• Journal of the Korean Ceramic Society
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• v.43 no.12 s.295
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• pp.823-828
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• 2006

One of the main issues of Solid Oxide Fuel Cells (SOFCs) is to reduce the operating temperature to $750^{\circ}C$ or less. It has advantages of improving the life of component parts and the long-term stability of a system, so the production cost could be decreased. In order to achieve that, the ohmic and polarization loss of a single cell should be minimized first. This paper presents.to fabricate anode-supported single cells with controlling microstructure as a function of particle size and volume of graphite and NiO-YSZ weight ratio. By means of optimizing the manufactural condition through microstructure analysis and performance evaluation, the single cell which had NiO-YSZ=6:4, graphite volume of 24% and graphite size of $75{\mu}m$ as the anode composition showed a distinguished power density of $510mW/cm^2$ at $650^{\circ}C$ and $810mW/cm^2$ at $700^{\circ}C$, respectively.

• Journal of the Korean Ceramic Society
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• v.38 no.9
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• pp.853-859
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• 2001

The dispersion stability of nano $Y_2O_3-CeO_2$ system was investigated using colloid surface chemistry. Green body of $Y_2O_3$ doped $CeO_2$ was prepared by slip casting in and aqueous system. The dispersion stability of suspension between powders and organic additive was accomplished through electrokinetic behavior of suspension, which was done by ESA apparatus. The dynamic mobility of particles was enhanced when the anionic dispersant of the amount of 1wt% was added. The dissolution of $Y^{3+}$ ion in suspension occurred in the acidic region so that pH value in slurries did not move to below 7.0. In the $CeO_2-Y_2O_3$ system, optimal preparation of suspension was made after adding the anionic dispersant as the amount of 1wt% and pH value of 11.0, and then slip-cast and sintered at 1400$^{\circ}$C, 2 hrs. It appeared relative density of >98% and homogeneous distribution of Y element in depth direction as well as in the microstructure of surface.

• Journal of Energy Engineering
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• v.25 no.4
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• pp.251-258
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• 2016

This article reports current status of micro fuel cell-combined heat and power (${\mu}FC$-CHP) systems which utilize both power and heat generated by fuel cells. There are several options for constructing CHP systems and among them, fuel cells are the most useful and their total energy efficiency combining heat and power can reach up to about 90%. Fuel cells are classified as five types based on the electrolyte, but the most suitable fuel cell types for the ${\mu}FC$-CHP system are proton exchange membrane fuel cells (PEMFCs) and solid oxide fuel cells (SOFCs). ${\mu}FC$-CHP systems have several advantages such as decrease of the transmission-distribution loss, reduced costs of electricity due to distributed power generation, and environmental-friendliness owing to zero emission. The main drawback of the ${\mu}FC$-CHP systems is the high initial investment, however, it keeps decreasing as the technology development reduces production costs. Currently, Japan is the most leading country of the ${\mu}FC$-CHP market, however, Korea tries to expand the market by planning the deployment of 1 million units of ${\mu}FC$-CHP systems and governmental subsidiary supporting of half of the install price. In this report, integration technologies for connecting FC and CHP, and technology trends of leading countries are presented as well.

• Journal of the Korean Ceramic Society
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• v.39 no.4
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• pp.352-358
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• 2002

The variations of the properties of Sr and Mg added $LaGaO_3$ system electrolyte with the amount of the additive and the sintering condition were studied. Main phase was (La$_{1-x}Sr_x)(Ga_{1-y}Mg_y)O_{3-\delta}$ phase for each compositions and the single phases $(La_{0.85}Sr_{0.15})(Ga_{0.85}Mg_{0.15})O_{3-\delta},(La_{0.85}Sr_{0.15})(Ga_{0.8}Mg_{0.2})O_{3-\delta}$ and $(La_{0.8}Sr_{0.2})(Ga_{0.8}Mg_{0.2})O{3-\delta}$ were obtained with the decrease in the sintering temperature and Mg addition. Thermal expansion coefficient of the $(La_{0.8}Sr_{0.2})(Ga_{0.8}Mg_{0.2})O_{3-\delta}$ decreased with the increase in the sintering temperature. Electric conductivity of electrolyte sintered at $1500^{circ}C$ for 1h was 0.14 S/cm at $800^{circ}C$ with 1 mA.

• Applied Chemistry for Engineering
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• v.16 no.1
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• pp.45-51
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• 2005

$K^+-{\beta}^{{\prime}{\prime}}-Al_2O_3$ in the $K_2O-Li_2O-Al_2O_3$ ternary system was synthesized using aluminum nitrate solution as a starting material. For the synthesis of pure $K^+-{\beta}^{{\prime}{\prime}}-Al_2O_3$, raw materials with chemical composition of $0.84K_2O{\cdot}0.082Li_2O{\cdot}5.2Al_2O_3$ were mixed in solution state. The effects of dispersant and solution-pH were investigated in minimizing the particle size and on the synthesis of pure $K^+-{\beta}^{{\prime}{\prime}}-Al_2O_3$. Ethanol was used for a dispersant, and $NH_4OH$ solution and nitric acid were added for pH adjustment. The solution pH was increased from 1.0 to 7.5 by 0.5 increments. Each sample was calcined at $1200^{\circ}C$ for 2 h and characterized with X-ray diffraction and particle size analyzer. The pH of solution significantly effected both particle size and phase formation, while the addition of ethanol only effected particle size. The synthesis of pure $K^+-{\beta}^{{\prime}{\prime}}-Al_2O_3$ was favored by addition of nitric acid (for pH control).