• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제53권4호
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• pp.237-246
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• 2004

The advantages of the Magnetic Fluid Linear Pump(MFLP) is that this device could Pump the non-conductive. non-magnetic liquid such as Insulin or blood because of the segregation structure of the magnetic fluid and pumping liquid. In this device. the sequential currents are needed to Produce pumping forces so that Pumping Forces and Pumping speed mainly depend on the current Patterns. The excessive forces at Pumping moment could cause the medical shock, and weak forces at intermediate moment could cause the back flow or the pumping liquid. So the ripples of the pumping forces need to be reduced for the medical application. In this research, the driving characteristics in the MFLP by operating current is analysed. The change of magnetic fluid surface according to the driving currents could be obtained be magneto-hydrodynamic analysis so that Pumping fortes could be computed by integration of the surface moving to the pumping direction at each moment. The actual MFLP with 13mm diameter was made and tested for experiments. The effects of driving current and frequency on the pumping forces and pumping speed were analyzed and compared with experimental measurements.

• 한국표면공학회지
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• 제32권1호
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• pp.49-60
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• 1999

The protective oxide scales and coatings formed on high temperature materials must be preserved in high temperature atmosphere. And the thermal stresses induced by thermal cycling and the growth stresses by the formation of oxide scales can cause the loss of adherence and spalling of the oxide scales and coated layers. Among the coating processes Al diffusion coating is favored due to thermochemical stability and superior adherence in an hostile atmosphere. In this study, protective oxide forming element, Al was coated on Ni, Inconel 600 and 690 by diffusion coating process varying coating temperature and time. And the surface stability and adherence of oxide scales formed on those Al diffusion coated materials were evaluated by thermal cycling test. Al diffusion coated specimens showed superior cyclic oxidation resistance compared to bare ones and specimens coated for longer period had better cyclic oxidation resistance, due to the abundant amount of Al in the coated layer. Meanwhile Al diffusion coated Inconel 600 and 690 showed improved cyclic oxidation resistance by the effect of Al in the coated layer and Cr in the substrate. Comparing both Al diffusion coated Inconel 600 and 690, Al diffusion coated Inconel 690 maintained better adhesion between coated layer and substrate by virtue of the bridging effect resulting from the segregation of Cr in the interdiffusion zone.

• 폴리머
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• 제37권2호
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• pp.177-183
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• 2013

본 연구에서는 poly(ethylene terephthalate)(PET) 필름을 기재로 하여 분산코팅에 의해 형성된 poly(vinylidene fluoride)(PVDF)와 poly(methyl methacrylate)(PMMA) 블렌드 코팅의 표면 특성을 관찰하였다. 분산코팅의 특성상 저온에서 형성된 블렌드 코팅은 PVDF 입자의 형태와 결정구조가 그대로 유지되었으나 $120^{\circ}C$ 이상의 코팅온도에서 형성된 코팅의 경우 블렌드에 포함되어 있는 PVDF의 양에 따라 다양한 표면 특성을 나타내었다. 블렌드 중 PVDF의 양이 80 wt% 이상인 경우 PVDF의 ${\alpha}$-결정구조에 의한 특성이 확실히 관찰되는 반면에 PMMA의 양이 증가하면 표면 형태와 결정구조의 변화가 변화하는 것을 관찰하였다. 또한 코팅층의 최외각 표면에 대한 XPS 분석결과는 분산코팅에서도 PVDF의 표면 이행성이 나타남을 보여준다.

• 한국해양공학회지
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• 제3권2호
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• pp.125-137
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• 1989

To check technical improvement in the soundness and strength of 12% Cr steel rotor, a 25 tons of rotor with 65 tons of ingot was made in real size and was cut to pieces to take test samples, and the various mechanical tests such as impact, tensile, creep, and fatigue were carried out. The strengths are compared with those of 1% Cr-Mo-V rotor of same size. Microstructures of the samples are examined and reviewed. The results can be summarized as follows. 1) Fracture appearance transition temperatures are 80.deg. C at the center part and 60.deg. C near surface of 12% Cr rotor, and 8.deg. C near surface of 1% Cr-Mo-V rotor. 2) Comparative rapid softening occurs at higher temperatures above 600.deg. C for 12% Cr steel and 550.deg. C for 1% Cr-Mo-V steel in tension tests. 3) Fatigue crack propagation rate of 12% Cr steel is almost same as that of 1% Cr-Mo-V steel at the same corresponding surface part of the rotors. The crack growth rate of center part of 12% Cr rotor is faster than near surface part of the rotor, and the crack growth rate at the load condition of R=0.04 is slower than that of the load condition of R=0.5 for both 12% Cr steel and 1% Cr-Mo-V steel. 4) Crack growth rate of radial direction near surface of 12% Cr rotor is faster than that of transverse direction at the same part because of the difference in residual stresses. 5) Both creep and fatigue strengths of 12% Cr steel are superior to those of 1% Cr-Mo-V steel and the difference is thought the effect of climb and glide controlled creep by solid solution of alloying elements and dispersion of carbides.

• 한국해양공학회지
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• 제3권2호
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• pp.625-625
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• 1989

To check technical improvement in the soundness and strength of 12% Cr steel rotor, a 25 tons of rotor with 65 tons of ingot was made in real size and was cut to pieces to take test samples, and the various mechanical tests such as impact, tensile, creep, and fatigue were carried out. The strengths are compared with those of 1% Cr-Mo-V rotor of same size. Microstructures of the samples are examined and reviewed. The results can be summarized as follows. 1) Fracture appearance transition temperatures are 80.deg. C at the center part and 60.deg. C near surface of 12% Cr rotor, and 8.deg. C near surface of 1% Cr-Mo-V rotor. 2) Comparative rapid softening occurs at higher temperatures above 600.deg. C for 12% Cr steel and 550.deg. C for 1% Cr-Mo-V steel in tension tests. 3) Fatigue crack propagation rate of 12% Cr steel is almost same as that of 1% Cr-Mo-V steel at the same corresponding surface part of the rotors. The crack growth rate of center part of 12% Cr rotor is faster than near surface part of the rotor, and the crack growth rate at the load condition of R=0.04 is slower than that of the load condition of R=0.5 for both 12% Cr steel and 1% Cr-Mo-V steel. 4) Crack growth rate of radial direction near surface of 12% Cr rotor is faster than that of transverse direction at the same part because of the difference in residual stresses. 5) Both creep and fatigue strengths of 12% Cr steel are superior to those of 1% Cr-Mo-V steel and the difference is thought the effect of climb and glide controlled creep by solid solution of alloying elements and dispersion of carbides.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2009년도 추계학술대회 논문집
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• pp.383-383
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• 2009

Silicon is commercially prepared by the reaction of high-purity silica with wood, charcoal, and coal, in an electric arc furnace using carbon electrodes, so called the metallurgical refining process, which produces ~98% pure Si (MG-Si). This can be further purified to solar grade silicon (SoG-Si) by various techniques. The most problematic impurity elements are B and P because of their high segregation coefficients. In this study, we explored the possibility of the using Cat-CVD for Si purification. The existing hot-wire CVD was modified to accommodate the catalyzer and the heating source. Mo boat (1.5 cm ${\times}$ 1 cm ${\times}$ 0.2 cm) was used as a heating source. Commercially available Si was purchased from Nilaco corporation (~99% pure). This powder was kept in the Mo-boat and heated to the purification temperature. In addition to the purification by cat-CVD technique, other methods such as thermal CVD, plasma enhanced CVD, vacuum annealing was also tried. It is found that the impurities are reduced to a great extent when treated with cat-CVD method.

• Corrosion Science and Technology
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• 제20권3호
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• pp.158-168
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• 2021

Austenitic 316 stainless steel was irradiated with protons accelerated by an energy of 2 MeV at 360 ℃, the various defects induced by this proton irradiation were characterized with microscopic equipment. In our observations irradiation defects such as dislocations and micro-voids were clearly revealed. The typical irradiation defects observed differed according to depth, indicating the evolution of irradiation defects follows the characteristics of radiation damage profiles that depend on depth. Surface oxidation tests were conducted under the simulated primary water conditions of a pressurized water reactor (PWR) to understand the role irradiation defects play in surface oxidation behavior and also to investigate the resultant irradiation assisted stress corrosion cracking (IASCC) susceptibility that occurs after exposure to PWR primary water. We found that Cr and Fe became depleted while Ni was enriched at the grain boundary beneath the surface oxidation layer both in the non-irradiated and proton-irradiated specimens. However, the degree of Cr/Fe depletion and Ni enrichment was much higher in the proton-irradiated sample than in the non-irradiated one owing to radiation-induced segregation and the irradiation defects. The microstructural and microchemical changes induced by proton irradiation all appear to significantly increase the susceptibility of austenitic 316 stainless steel to IASCC.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2001년도 추계학술대회(한국공작기계학회)
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• pp.319-323
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• 2001

In significant number of energy-related facilities for like thermal power plant or petro-chemical industry, CrMo steels are widely used energy conversion industries. However, these materials undergo precipitation of carbides or intermetallic compounds into grain boundary and change of internal microstructure such as coarsening of precipitation, decrease of solute elements and impurity segregation under more severe service conditions, which results in deterioration of inherent superior material characteristics. In this study, it was verified experimentally the feasibility of the aging degradation evaluation for degraded 2.25Cr-lMo steel specimens prepared by isothermal aging heat treatment at 63$0^{\circ}C$ by high frequency longitudinal ultrasonic and surface SH wave investigating the change of attenuation coefficient analyzed by spectral analysis. Attenuation coefficient had a tendency to increase as degradation proceeded.

• 한국세라믹학회지
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• 제26권2호
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• pp.210-220
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• 1989

The properties of the powder of Al2O3-15v/o ZrO2(＋3m/o Y2O3) system prepared by co-precipitation method at the pH values of 7, 9, 10 and 11 were investigated. Al2(SO4)3.18H2O, ZrOCl2.8H2O and YCl3.6H2O were used as starting materials and NH4OH as a precipitation agent. Zirconium hydroxide decreased the specific surface area of aluminum hydroxide of AlOOH type, while increased the specific surface area of aluminum hydroxide of Al(OH)3 type, and formed co-network structure of Al-O-Zr type with the aluminum hydroxides. The rate of transition to $\alpha$-Al2O3 from co-precipitated materials occurred in the order of 7≒10, 9 and 11 of pH values. Al2O3 and ZrO2 interacted to bring about coupled grain growth, and the growth of ZrO2 crystallite size rapidly occurred within $\theta$-Al2O3 matrix. Segregation did not occur in the system Al2O3-15v/o ZrO2(＋3m/o Y2O3) and Y2O3 acted as a stabilizer to ZrO2. The lattice strain of tetragonal ZrO2 was increased by the constraint effect of Al2O3 matrix.

• 한국재료학회지
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• 제13권8호
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• pp.503-508
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• 2003

The purpose of this study is to investigate the effect of $V_2$$O_{5}$ addition on the Ag and Cu precipitation in the NiCuZn ferrite layers of 7.7${\times}$4.5${\times}$1.0 mm sized multi-layer chip inductors prepared by the screen printing method using 0∼0.5 wt% $V_2$$O_{5}$ -doped ferrite pastes. With increasing the $V_2$$O_{5}$ content and sintering temperature, Ag and Cu oxide coprecipitated more and more at the polished surface of ferrite layers during re-annealing at $840^{\circ}C$. It was thought that during the sintering process, V dissolved in the NiCuZn ferrite lattice and the Ag-Cu liquid phase of low melting point was formed in the ferrite layers due to the Cu segregation from the ferrite lattice and Ag diffusion from the internal electrode. During re-annealing at $840^{\circ}C$, the Ag-Cu liquid phase came out the polished surface of ferrite layers, and was decomposed into the isolated Ag particles and the Cu oxide phase during the cooling process.