• Journal of the Korean Ceramic Society
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• v.51 no.5
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• pp.498-504
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• 2014

Particulate nitride composites have been fabricated by sintering the compacted powder of AlN and 5 - 64.3 mol% $Al_2O_3$, with a small addition of $Y_2O_3$ ($Y_2O_3$/AlN, 1 wt%), in 1-atm nitrogen gas at $1650-1900^{\circ}C$. The composites were characterized in terms of sintering behavior, phase relations, microstructure and thermal shock resistance. AlN, 27R AlN pseudopolytype, and alminium oxynitride (AlON, $5AlN{\cdot}9Al_2O_3$) were found to existin the sintered material. Regardless of batch composition, the AlN-$Al_2O_3$ powder compacts exhibited similar sintering behavior; however, the degree of shrinkage commonly increased with increasing $Al_2O_3$ content, consequently giving high sintered bulk density. By increasing the $Al_2O_3$ addition up to ${\geq}50 mol%$, the matrix phase in the sintered material was converted from AlN or 27R to AlON. Above $1850^{\circ}C$, a liquid phase was formed by the reaction of $Al_2O_3$ with AlN, aided by $Y_2O_3$ and mainly existed at the grain boundaries of AlON. Thermal shock resistance was superior in the sintered composite consisting of AlON with dispersed AlN or AlN matrix phase.

• Journal of Powder Materials
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• v.12 no.6 s.53
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• pp.413-421
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• 2005

Copper is able to work as a current collector under wide range of hydrocarbon fuels without coking in Solid oxide fuel cells (SOFCs). The application of copper in SOFC is limited due to its low melting point, which result in coarsening the copper particle. This work focuses on the sintering of copper powder with ceria coating layer. Ceria-coated powder was prepared by thermal decomposition of urea in $Ce(NO_3)_3\cdot6H_2O$ solution, which containing CuO core particles. The ceria-coated powder was characterized by XRD, ICP, and SEM. The thermal stability of the ceria-coated copper in fuel atmosphere $(H_2)$ was observed by SEM. It was found that the ceria coating layer could effectively hinder the grain growth of the copper particles.

• Journal of the Korean Ceramic Society
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• v.44 no.12
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• pp.733-739
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• 2007

NiO-YSZ anode-supported single cell was prepared by spin-coating YSZ and LSM slurries as electrolyte and cathode, respectively. Dense YSZ electrolyte film was successfully prepared on the porous NiO-YSZ anode substrate by tuning pre-sintering temperature of NiO-YSZ and co-firing temperature. The thickness of YSZ film was controlled by the solid content of slurry and coating cycles. The experimental conditions affecting on the thickness of YSZ film was discussed. Single cells with the active electrode area ${\sim}0.8\;cm^2$ were prepared by spin-coating the cathode layers of LSM-YSZ mixture and LSM consequently as well. The effects of the pre-sintering temperature and thus the microstructure of NiO-YSZ substrate on the current-voltage characteristics of co-fired cell were investigated.

• Transactions on Electrical and Electronic Materials
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• v.16 no.4
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• pp.194-197
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• 2015

La_9.33(Si₅V₁)O₂₆ ceramics were fabricated by the mixed oxide method for solid oxide electrolytes. La_9.33(Si₅V₁)O₂₆ specimens showed the hexagonal, space group P63 or P63/m, and the unit cell volume increased when the sintering temperature increased. The specimen sintered at 1,400℃ showed the X-ray patterns of the homogeneous apatite single phase without the second phase, such as La₂SiO₅ and SiO₂. The specimen sintered at 1,400℃ showed the maximum sintered density of 4.93 g/cm³. When the sintering temperature increased, the electrical conductivities increased, the activation energy decreased and the values were 7.83×10⁻⁴ S/cm, 1.61 eV at 600℃, respectively.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.25 no.5
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• pp.392-397
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• 2012

In the $(La_{0.8}Ca_{0.2})(Cr_{0.9}Co_{0.1})O_3$ (LCCC), which has been using as interconnector materials in SOFC, Al ions were substituted for Co because ionic radius of Al is similar to that of Co. Because of the almost identical ionic radius of Al and Co, the substitution was not thought to be affect the tolerance factor of LCCC, and the densification behavior, high temperature electrical conductivity and thermal expansion coefficient were examined as a function of Al concentration. In the cases of the x= 0 and x= 0.02 in $(La_{0.8}Ca_{0.2})(Cr_{0.9}Co_{0.1-x}Al_x)O_3$ (x= 0~0.1), the samples showed the relative densities above ${\geq}95%$ when those were sintered at ${\geq}1,350^{\circ}C$. In the case of the $x{\geq}0.06$ the sintered density deteriorated greatly at lower sintering temperatures. High temperature electrical conductivity of the samples decreased as the content of Al increased. Since the valence state of Al ion is unchangeable, while Cr or Co ions contribute to the electrical conduction by changing those valence states, Al substitution resulted in the decreased electrical conductivity. Al doping of LCCC was an effective way of decreasing the thermal expansion coefficient (TEC).

• Electrical & Electronic Materials
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• v.10 no.2
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• pp.141-149
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• 1997

L $a_{0.7}$S $r_{0.3}$Mn $O_{3}$ powders were prepared by both GNP(Glycine-Nitrate Process) and solid state reaction method in various of calcination temperature(800-1000.deg. C) and time in air. Also, L $a_{0.7}$S $r_{0.3}$Mn $O_{3}$ cathode contacts on YSZ(Yttria-Stabilized Zirconia) substrate were prepared by screen printing and sintering method as a function of sintering temperature(1100-1450.deg. C) in air. Sintering behaviors have been investigated by SEM(Scanning Electron Microscope) and porosity measurement. Compositional and structural characterization were carried out by X-ray diffractometer and ICP AES(Inductively Coupled Plasma-Atomic Emission Spectrometry) analysis. Electrical characterization was carried out by the electrical conductivity with linear 4 point probe method. As the calcination period increased in solid state reaction method, L $a_{0.7}$S $r_{0.3}$Mn $O_{3}$ phase increased. Although L $a_{0.7}$S $r_{0.3}$Mn $O_{3}$ single phase was obtained only for 48hrs at 1000.deg. C, in GNP method it was easy to get single and ultra-fine L $a_{0.7}$S $r_{0.3}$Mn $O_{3}$ powders with submicron particle size at 650.deg. C for 30min. The particle size and thickness of L $a_{0.7}$S $r_{0.3}$Mn $O_{3}$ cathode contact by solid state reaction method did not change during the heat treatment, while those by GNP method showed good sintering characteristics because initial powder size fabricated from GNP method is smaller than that fabricated from solid state reaction method. Based on enthalpy change from thermodynamic data and ICP-AES analysis, it was suggested to make cathode contact in composition of (L $a_{0.7}$S $r_{0.3}$)$_{0.91}$ Mn $O_{3}$ which have little second phase (L $a_{2}$Z $r_{2}$ $O_{7}$) for high efficient solid oxide fuel cells applications. As (L $a_{0.7}$S $r_{0.3}$)$_{0.91}$Mn $O_{3}$ cathode contact on YSZ substrate was sintering at 1250.deg. C the temperature that liquid phase sintering did not occur. It was possible to obtain proper cathode contacts with electrical conductivity of 150(S/cm) and porosity content of 30-40%.m) and porosity content of 30-40%.

• Korean Journal of Materials Research
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• v.18 no.9
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• pp.470-474
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• 2008

Composites of gadolinium-doped ceria/magnesia(CGO/MgO) were synthesized and characterized for the electrolytes of intermediate temperature solid oxide fuel cells. XRD and SEM results revealed that composite electrolytes consisted of their own phases after sintering at $1400^{\circ}C$ without noticeable solid solution of Mg into CGO. As the MgO content increased, the total electrical conductivity decreased, which might be attributed to the decrease of grain boundary conductivity, possibly due to the lowering of the continuity of the CGO grains and blocking effects of the insulating MgO phase. The space charge effect may not be a significant factor to affect the electrical conductivity of the CGO/MgO composites.

• Journal of the Korean Ceramic Society
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• v.38 no.5
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• pp.466-473
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• 2001

Ni-YSZ 음극의 미세구조와 임피던스특성에 미치는 YSZ 입자크기 및 소결온도의 영향을 고찰하였다. 0.3~0.6$\mu\textrm{m}$의 미세한 NiO 분말을 사용할 경우에는 NiO 분말과 크기가 비슷한 미세한 YSZ 분말(TZ8Y, 0.3$\mu\textrm{m}$)을 첨가했을 때 NiO의 입성장을 억제하는 효과가 가장 크고 환원후 Ni의 입자크기를 미세하게 유지할 수 있는 미세구조를 형성하였다. 또한 미세한 YSZ 분말 (TZ8Y, 0.3$\mu\textrm{m}$)과 조대한 YSZ 분말(FYT13.0, 2$\mu\textrm{m}$)의 혼합비를 달리하여 후막을 제조하였을 때에 TZ8Y 분말만 첨가한 조성이 가장 낮은 분극 저항을 나타내었다. 한편 소결온도는 삼상계면의 양과 분극저항에 영향을 주었으며, 140$0^{\circ}C$에서 소결한 시편의 분극저항이 가장 낮은 값을 나타내었다.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.28 no.5
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• pp.295-299
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• 2015

In this paper to improve the ionic conduction properties, lanthanum silicate apatite $La_{9.33}(SiO_4)_6O_2$ ceramic, which substituted by V ions at Si-site, were fabricated by the mixed-oxide method. And we investigated the structural and electrical properties of $La_{9.33}(Si_{6-x}V_x)O_{26}$ specimens with variation of dopants for the application of solid oxide fuel cells. The sintering temperature of $La_{9.33}(Si_{6-x}V_x)O_{26}$ specimens decreased from $1,600^{\circ}C$ to $1,400^{\circ}C$. As results of X-ray diffraction patterns, all $La_{9.33}(Si_{6-x}V_x)O_{26}$ specimens showed the formation of a complete solid solution in a apatite polycrystallin structure. But the specimens doped with more than 1.5mol% showed the second phase, $La_2SiO_5$ and $SiO_2$. The specimen dopants with 1.0 mol% showed the maximum ion conductivity. Ion conducting and activation energy of the $La_{9.33}(Si_5V_1)O_26$ specimens were about $7.8{\times}10^{-4}S/cm$ 1.62 eV at $600^{\circ}C$, respectively.

• Proceedings of the KIEE Conference
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• 1998.07d
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• pp.1303-1305
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• 1998

In order to reduce or avoid oxidation problem at operation the interconnects in SOFCs have so far mostly been made of ceramic material. It has high chemical stability both under cathode and anode condition, relatively thermal expansion coefficient that matchs that of electrolyte material YSZ. But this material shown rather weak in the low oxygen atmosphere and thermal shock, and it has lower mechanical strength than alloys. To avoid these problems one may consider to use metals or alloys as materials for interconnects. Metallic interconnects are advantageous because of their high thermal and electronic conductivities. But it has some problems, Those are high thermal expansion and oxidation at high temperature in air. To solve these problems in the interconnection material in this study, $LaCrO_3$-dispersed Cr alloys for metallic interconnector of SOFC have been investigated as a fuction of $LaCrO_3$ content in the range of 5 to 25 vol.%. The Cr alloy were prepared by mixing Cr and $LaCrO_3$ powders in high-energy ball mill for 48h and by sintering under Ar atmosphere with 5vol.% $H_2$ for 10h at $1500^{\circ}C$. The alloys had a relative density of 95% and above. The Cr alloys in composed of two kind of small $LaCrO_3$ and large Cr particles. As the $LaCrO_3$ content increased, the Cr particle size decreased but the $LaCrO_3$ particle size remained contant. Also the oxidation tests show that the $LaCrO_3$-dispersed Cr is very resistant to oxidation in air. These results means that $LaCrO_3$-dispersed Cr is a useful material for metallic interconnect of planar SOFC.