• Journal of the Korean Applied Science and Technology
• /
• v.23 no.3
• /
• pp.207-214
• /
• 2006

$Y_{2-x}Gd_xO_3:Eu$, phosphors for plasma display panel(PDP), were prepared by Pechini method which use yttriun chloride, gadolinium chloride, and europium oxide as starting materials. This method is a different way to the synthesis of europium(Eu)-doped phosphors, and it consists of the formation of a polymeric resin obtained by polyesterification between metal chelate compounds and a polyfunctional alcohol. This needs lower temperature than solid-state synthetic method. The prepared $Y_{2-x}Gd_xO_3:Eu$ phosphor particles had spherical shape and coherence. The luminescence intensity of $Y_{2-x}Gd_xO_3:Eu$ phosphor particles increased according to the increase of gadolinium(Gd) content(to 0.8mol%), and $Y_{1.2}Gd_{0.8}O_3:Eu$ phosphors had the highest luminescence intensity under vacuum ultra violet(VUV) excitation. The optimum concentration of Eu in the phosphor and optimum calcination temperature was 3wt% and $1100^{\circ}C$. The prepared phosphors were consist of particle, and its size was between 100nm and 150nm. Among the different polyfunctional alcohols, diethylene glycol(DEG) improved the luminescence intensities of phosphors more than other additives. The Pechini method proved that it is demonstrated to be suitable for the synthesis of phosphors used in PDP.

• Journal of the Korean Ceramic Society
• /
• v.42 no.9 s.280
• /
• pp.602-606
• /
• 2005

[ $LiCoO_{2}$ ] is the most common cathode electrode materials in Lithium-ion batteries. $LiCo_{0.97}Mg_{0.03}O_2$ was synthesized by the solid-state reaction method. We investigated crystal structures, electrical conductivities and electrochemical properties. The crystal structure of $LiCo_{0.97}Mg_{0.03}O_2$ was analyzed by X-ray powder diffraction and Rietveld refinement. The material showed a single phase of a layered structure with the space group R-3m. The lattice parameter(a, c) of $LiCo_{0.97}Mg_{0.03}O_2$ was larger than that of $LiCoO_2$. The electrical conductivity of sintered samples was measured by the Van der Pauw method. The electrical conductivities of $LiCoO_2$ and $LiCo_{0.97}Mg_{0.03}O_2$ were $2.11{\times}10^{-4}\;S/cm$ and $2.41{\times}10^{-1}\;S/cm$ at room temperature, respectively. On the basis of the Hall effect analysis, the increase in electrical conductivities of $LiCo_{0.97}Mg_{0.03}O_2$ is believed due to the increased carrier concentrations, while the carrier mobility was almost invariant. The electrochemical performance was investigated by coin cell test. $LiCo_{0.97}Mg_{0.03}O_2$ showed improved cycling performance as compared with $LiCoO_2$.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.8 no.1
• /
• pp.145-150
• /
• 1998

The electrical and mechanical properties of the 8 mol% yittria-stabilized zirconia and alumina composites have been examined as a function of the alumina content. The 3-point bending strength and fracture toughness of the composites increased with increasing alumina content up to 20 wt%. The average grain size of the composites decreased with increasing alumina content up to 20 wt%. The composite with 5 wt% $Al_2O_3$ showed a 3-point bending strength of 310 MPa and fracture toughness about $7.8MPa\cdot\textrm m^{1/2}$. The electrical conductivity of the composites at $1000^{\circ}C$ increased slightly with increasing alumina content up to 10 wt% and decreased monotonically with alumina content. The conductivity of the TZ-8YS with 5 wt% alumina was 0.4 S/cm at $1000^{\circ}C$.

• Transactions of the Korean hydrogen and new energy society
• /
• v.17 no.1
• /
• pp.62-68
• /
• 2006

High temperature electrolysis is a promising technology to produce massively hydrogen using renewable and nuclear energy. Solid oxide fuel cell materials are candidates as the components of steam electrolysers. However, the polarization characteristics of the typical electrode materials during the electrolysis have not been intensively investigated. In this study, NiO electrode was deposited on YSZ electrolyte by spin coat process and firing at $1300^{\circ}C$. Pt electrode was applied on the other side of the electrolyte to compare the polarization characteristics with those by NiO during electrolysis. The $H_2$ evolution rate was also monitored by measuring the electromotive force of Lambda probe and calculated by thermodynamic consideration. At low current density, Pt showed lower cathodic polarization and thus higher current efficiency than Ni, but the oxidation of Ni into NiO caused the increase of anodic resistance with increasing current density. High overpotential induced high power consumption to produce hydrogen by electrolysis.

• Transactions of the Korean hydrogen and new energy society
• /
• v.21 no.6
• /
• pp.533-539
• /
• 2010

Ni-YSZ supported button cells were prepared by spray-coating YSZ and screen-printing YSZ-LSM powder as an electrolyte and oxygen electrode on Ni-YSZ cermet disks. In order to identify the polarization loss mechanism in high temperature electrolysis current-voltage characteristics coupled with electrochemical impedance spectroscopy were investigated as a function of temperature, current load, and the humidity. The effects of the different current collectors of platinum and silver for oxygen electrodes were compared. With Ag current collector two polarization losses were distinguished. The high frequency component was attributed to the Ni-YSZ cermet which was less susceptible to temperature variation but increasing in loss with humidity. The lower frequency component was attributed to the LSM electrode. Platinum current collector led to a much lower polarization loss.

• Transactions of the Korean hydrogen and new energy society
• /
• v.25 no.3
• /
• pp.280-288
• /
• 2014

SDC (Samarium doped Ceria) electrolyte was developed for Intermediate temperature SOFC ($500^{\circ}C-800^{\circ}C$) which showed a good electrical conductivity. In this study, we used sintering aids to reduce the SDC sintering temperature down to $1000^{\circ}C$, especially which can help the SOFC scale-up. In order to reduce the SDC sintering temperature, $Li_2CO_3$ and $TiO_2$ were used as a sinering aids for decreasing sintering temperature. $Li_2CO_3$ and $TiO_2$ doped SDC sintered at $1000^{\circ}C$ showed 99% of the theoretical density and higher electrical conductivity than the pure SDC sintered at $1500^{\circ}C$. When measuring the OCV (Open circuit voltage) with the $Li_2CO_3$ and $TiO_2$ doped SDC electrolyte, however, the OCV values were lower than the theoretical OCV values which means that the modified SDC still had electronic conductivity.

• Journal of Advanced Marine Engineering and Technology
• /
• v.36 no.8
• /
• pp.1050-1060
• /
• 2012

As an approach to high-efficiency of SOFC system, SOFC/GT Hybrid system is effective. However, if the output size of the system belongs to the marine class of dozens MWs, the introduction of the cooling system of GT system, which is used as sub-system, makes its related devices complicated and also makes its control difficult. Accordingly, for the marine use, SOFC/GT (non-cooling)Hybrid system looks more suitable than SOFC/GT(cooling)Hybrid system. This study established the SOFC/GT (non-cooling)Hybrid system, and examined the operating temperature & current density of the stack for the system, pressure ratio of the gas turbine, the influence of TIT(Turbine Inlet Temperature) on system performance, etc. through the simulation process. Through this research process, this study was able to confirm that electrical efficiency rises in spite of the increase in the required power for the air compressor, and there exists a limited range of temperatures for operation in TIT.

• Journal of Energy Engineering
• /
• v.19 no.3
• /
• pp.188-194
• /
• 2010

Direct Carbon Fuel Cell(DCFC), unlike gas turbines or engines, is a kind of fuel cell which directly generates electricity by electrochemical reaction from a carbon fuel. The advantages of DCFC are higher efficiency and lower emission in comparison with existing power generation facilities. In this study, the effects of CO and $CO_2$ on theoretical potential are examined using the thermodynamic equilibrium method, and the dependence of product on operating temperature is examined via two dimensional CFD method. As a result, when the reaction of CO production (Boudouard reaction) considered, theoretical potential is higher than that in only $CO_2$ reactions, and its value increases as temperature increases. Two dimensional results of computational fluid dynamics(CFD) confirm that the Boudouard reaction becomes more important to be considered as temperature increases and inert gas affects the equilibrium composition of the Boudouard reaction.

• Korean Journal of Materials Research
• /
• v.20 no.4
• /
• pp.217-222
• /
• 2010

Zirconium diboride (ZrB2) and mixed diboride of (Zr0.7Ta0.3)B2 containing 30 vol.% silicon carbide (SiC) composites were prepared by hot-pressing at $1800^{\circ}C$. XRD analysis identified the high crystalline metal diboride-SiC composites at $1800^{\circ}C$. The TaB2 addition to ZrB2-SiC showed a slight peak shift to a higher angle of 2-theta of ZrB2, which confirmed the presence of a homogeneous solid solution. Elastic modulus, hardness and fracture toughness were slightly increased by addition of TaB2. A volatility diagram was calculated to understand the oxidation behavior. Oxidation behavior was investigated at $1500^{\circ}C$ under ambient and low oxygen partial pressure (pO2~10-8 Pa). In an ambient environment, the TaB2 addition to the ZrB2-SiC improved the oxidation resistance over entire range of evaluated temperatures by formation of a less porous oxide layer beneath the surface SiO2. Exposure of metal boride-SiC at low pO2 resulted in active oxidation of SiC due to the high vapor pressure of SiO (g), and, as a result, it produced a porous surface layer. The depth variations of the oxidized layer were measured by SEM. In the ZrB2-SiC composite, the thickness of the reaction layer linearly increased as a function of time and showed active oxidation kinetics. The TaB2 addition to the ZrB2-SiC composite showed improved oxidation resistance with slight deviation from the linearity in depth variation.

• Proceedings of the Materials Research Society of Korea Conference
• /
• 2003.11a
• /
• pp.214-214
• /
• 2003

고체 고분자 전해질에 대한 연구는 1979년 wright와 Armand에 처음 시작된 이래로 지난 20여년간 연구가 계속적으로 지속되고 있다. 전지의 적용되기 위해 전해질이 갖추어야 할 조건중에 이온전도도가 상온에서 10-4 S/cm 이상의 전도도를 나타내야 하지만 지금까지 연구되고 있는 여러 고체 고분자 전해질은 이런 조건을 만족시키지 못하고 있는 실정이다. 본 연구에서는 이런 상온에서의 이온 전도성을 향상시키기 위해 여러 종류의 실리카와 세라믹 계열의 첨가제를 첨가하여 이온전도성의 향상을 꾀하고자 하였다. 본 연구에서는 고체 고분자 전해질의 host polymer로써 분자량 400,000 의 Polyethylene oxide를 사용하였으며 Lithuim salt로는 Lithium (bisperfluroethylsulfonyl)imide(3M)를 기본적으로 사용하였다. 여기에 가소제의 역활로써 (3-cyanopropyl)methylsiloxane cyclics를 첨가하였고 표면그룹이 CH3와 OH기로 이루어진 기능성 나노 실리카를(<11nm)이용하여 함량별 전기 화학적 특성 및 기본 물성을 측정하였다. 기본적으로 이 네 가지 물질을 유기용매 Acetonitril에 잘 용해하여 Solid Casting방법으로 80-100 마이크로의 복합고분자 전해질을 제조하였다. Homogeneous하고 uniform한 필름 제조하기 위해 9$0^{\circ}C$에서 열처리를 24h 동안 실시하였다. 제조되어진 복합고분자전해질은 XRD를 통하여 결정성을 조사하였고 DSC를 이용하여 유리 전이온도 및 결정화도를 조사하였다. 복합고체고분자의 전기화학적 성질을 평가하기 위해 blocking electrode를 제작하여 임피던스 스펙트로 스코피를 이용하여 이온전도성을 측정하였다. 또한 복합 고분자 전해질의 온도의존성에 대해서도 조사하였다. 또한 실제 전지의 작동구간에서의 전해질의 안정성을 확인하기 위해 LSV를 측정하였고. Li metal을 사용하여 non-blocking electrode를 제작하여 복합고분자 전해질과의 계면저항을 측정하였다.