• Journal of the Korean Ceramic Society
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• v.38 no.1
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• pp.93-99
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• 2001

(La,Sr)MnO$_3$(LSM)-YSZ 복합체 양극에 있어서 소결온도 및 전극두께와 cathodic potential이 전극 특성에 미치는 영향을 고찰하였다. 양극의 소결은 삼상계면의 양을 결정하는 중요한 변수로 LSM 단미 양극과 YSZ가 40 wt% 포함된 LSM-YSZ 복합체 양극 모두 120$0^{\circ}C$에 소결했을 때 가장 낮은 분극저항을 나타내었다. 또한 양극 후막의 두께가 얇아지면 양극의 in-plane 저항이 증가하여 ohmic 저항이 증가하였는데, LSM-YSZ 복합체 양극의 경우 약 30$mu extrm{m}$ 정도의 전극두께가 가장 효과적인 전극 특성을 나타내었다. 한편, LSM-YSZ 복합체 양극에 -0.5 V의 cathodic potential을 인가함에 따라 양극에서 일어나는 산소환원반응의 활성이 증가하였는데, 1가 산소이온의 표면확산반응의 분극저항은 감소하였으나, 고주파수 영역에서 나타나는 산소이온전달반응의 저항은 거의 변화하지 않았다. 이것은 Mn의 환원에 의한 양극표면에 생성된 산소공공에 기인한다.

• Journal of the Korean Ceramic Society
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• v.38 no.1
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• pp.84-92
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• 2001

(La,Sr)MnO$_3$(LSM)-YSZ 복합체 양극의 산소환원 반응기구에 대해 고찰하였다. YSZ를 첨가함에 따라 복합체 양극의 ohmic 저항이 증가하고, 분극 저항은 YSZ를 40 wt%~50 wt% 혼합하였을 때 최소값을 나타내었다. 또한 LSM-YSZ 복합체 양극의 산소환원 반응기구는 1가 산소이온의 표면확산과 산소이온전달반응에 의해서 지배됨을 알 수 있었다. 임피던스 분석 결과에 따르면 고주파수 영역에서 나타나는 반원은 산소이온전달반응으로 산소분압 의존성이 거의 없고, YSZ가 40 wt% 첨가되었을 때 최소값을 나타내었다. 중간주파수 영역에서 나타나는 반원은 1가 산소이온의 표면확산반응으로 산소분압 의존성은 약 1/4이고, YSZ가 40~50 wt% 첨가되었을 때 최소값을 나타냈다. 한편, 저주파수 영역에 나타나는 반원은 가스확산반응으로 산소분압 의존성이 1이고, 온도에 따른 의존성이 거의 없었다.

• Journal of Sensor Science and Technology
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• v.4 no.4
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• pp.70-74
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• 1995

We have observed anisotropic anodisation process for porous silicon formation. The starting material was (100) silicon $n/n^{+}/n$ wafer structured by $n^{+}$-diffusion on n-type substrate and by subsequent n-epitaxial growth. After the top n-silicon epitaxial layer was etched to open the porous silicon layer(PSL) anodisation window, anodisation takes place only to $n^{+}$-buried layer. The process of porous silicon formation on (100) sample was anisotropic, which was evident from that the shapes of the reacted porous silicon layer was all squarelike regardless of the shapes of reaction windows. The experimental results show that the PSL anodisation process does not depend on chemical reaction but does on electrical conduction property, which is hole mobility depending on the crystal direction.

• Journal of Sensor Science and Technology
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• v.4 no.1
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• pp.64-71
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• 1995

We have developed a silicon etching method by which highly doped layers are selectively etched using stain etching technique. Current supply to the backside contact of silicon wafer and special reactor are not required in this method. Therefore this method is much simpler than anodic reaction method and could be applied to standard VLSI process. In addition, highly doped layers of several wafer structures, including the structures where conventional anodic reaction method cannot be used, could be preferentially etched by this technique. We have also fabricated micromechanical structures such as cantilevers and air-bridges on the $n/n^{+}/n$ wafer and air-bridges on the $p/p^{+}$ wafer using this stain etching technique.

• Journal of Sensor Science and Technology
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• v.1 no.2
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• pp.183-194
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• 1992

Some silicon micromechanical structures useful in sensors and actuators have been fabricated by electropolishing or porous silicon formation technique by anodic reaction in HF solution. The microstructures were lightly doped single crystal silicon and the formation was isotropic independent of crystal directions. Porous silicon layer(PSL) was formed selectively in $n^{+}$ region of $n^{+}/n$ silicon structure by anodic reaction in concentrated HF(20-48%) solution. Characteristics of the formed PSL were investigated along with change of the reaction voltage, HF concentration and the reaction time. PSL was formed only in $n^{+}$ region. The porosity of the PSL was decreased with the increase of HF concentration and independent of reaction voltage. For the case of $n/n^{+}/n$ structures, the etched surface of silicon was fairly smooth and a cusp was not found. The thickness of the microstructures was the same as that of the epitaxial n-Si layer and good uniformity. We have fabricated acceleration sensors by anodic reaction in HF solution(5 wt%) and planar technology. The process was compatible with conventional It fabrication technique. Various micromechanical structures, such as rotors of motor, gears and linear actuator, were also fabricated by the technique and examined by SEM photographs.

• Korean Chemical Engineering Research
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• v.46 no.5
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• pp.852-857
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• 2008

The immobilization technique is important to extend the application field of a photocatalyst. Titanium surface was changed into a $TiO_2$ thin film by the anodizing process. The anodized $TiO_2$ had photocatalytic activity, and showed sponge like shape. The photocatalytic degradation of gas phase acetaldehyde and VOCs by anodized titania has been studied in various initial concentrations, humidity and discharge potentials. The reactivity of anodized titania was increased with relative humidity, but excessive humidity led to a decrease of the reaction rate. The electric dark discharge that was combined with photocatalytic reaction enhanced the decomposition rate of the organic compounds. But excessively applied voltage caused corona discharge, which decreased the reaction rate. Optimum relative humidity was 40% and discharge potential was 5 kV under dark discharge region in photocatalytic reaction.

• Journal of Surface Science and Engineering
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• v.22 no.2
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• pp.88-92
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• 1989

양극산화 피막의 졀정구조에 관한 연구는 1960년대부터 반응 Mechanism의 연구와 병행하여 많은 논란이 되어왔다. 결정구조의 정확한 Model 이 아직까지 확립되어 있지 않은 상태에서, 여러 가지 접근방식으로 연구되고 있는 실정이다. 최근에는 HRTEM, NAS-NMR등의 고성밀 장비의 응용에 의한 결정구조의 분석에 활발히 진행이 되고 있으며, 이론 물리학의 응용 또한 이곳까지 확산되고 있는 상태이다. 본 고에서는 반응 Mechanism을 연구하는데 가장 밀접한 분야인 양극산화 피막 결정 구조에 관해 1950년대이후 어떻게 연구되고 설명되었는가를 조명하기로 한다.

• Journal of the KSME
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• v.29 no.2
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• pp.138-143
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• 1989

부식피로에 대한 몇 가지 이론 및 실제를 소개하였다. 그러나, 부식피로가 학문적으로 관심을 갖게되고 연구의 대상이 된 것은 1970년초 부터로서, 아직까지도 많은 부분이 연구대상으로 남 아있다. 특히, 균열선단에서의 부식반응의 역할이 좀 더 상세히 밝혀져야 하고, 자연 부식조건 에서의 양극반응과 음극반응이 각각 어떠한 역할을 하는가도 좀더 밝혀져야 할 것이다. Mode II 또는 Mode III 상태에서의 균열전파 특성이나, 균열전파에 있어서 반복응력의 주파수의 영 향도 좀더 상세히 밝혀져야 할 연구 대상이다. 이러한 연구들을 통해서 현재까지는 주로 부식의 측면에서만 고려되는 산업현장의 부식피로 문제에 대해 좀더 근본적이고 효과적인 해결 방법을 제시할 수 있을 것이다.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.13 no.3
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• pp.229-233
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• 2015

Developing novel anode materials to replace the Pt anode currently used in electrolytic reduction is an important issue on pyroprocessing. In this study, the electrochemical behavior of TiN was investigated as the conductive ceramic anode which evolves O₂ gas during the reaction. The feasibility and stability of the TiN anode was examined during the electrolytic reduction of UO₂. The TiN anode could electrochemically convert UO₂ to metallic U in a LiCl–Li₂O molten salt electrolyte. No oxidation of TiN was observed during the reaction; however, the formation of voids in the bulk section appeared to limit the lifetime of the TiN anode.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.9 no.3
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• pp.334-338
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• 1999

Porous silicon layers were fabricated with various conditions of HF concentration and current density. And their masses were measured. From these data, the porosity and fractal dimension were estimated and analyzed. We found that the porosity was proportional to the current density when the anodic reaction time was fixed and the constant values of fractal dimension could be estimated from a series of data with fixed HF concentration. The values of fractal dimension were decreased with increasing HF concentration. The obtained porosity and fractal dimension were compared with the 2-dimensional computer simulation based on diffusion limited deposition model. According to the simulation, the porosity was proportional to the diffusion length and the fractal dimension was inversely proportional to the diffusion length. Since, the diffusion length is proportional to current density and inversely proportional to base concentration, our experimental data qualitatively agreed with the results from the simulation. The porosity obtained by experiments, however, was not consistent with the results by simulation.