• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2002년도 춘계학술대회 논문집 초전도 자성체
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• pp.37-40
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• 2002

Superconductor wire fabricated by electrophoresis showed its critical current density depended on parameters such as applied voltage and deposition time. Substrate and suspension solutions. and its properties are also important parameters. When same optimal parameter and condition was used, deposition density of superconductor film affect directly its critical current density. In this study, therefore, electrophoretic deposition technique was utilized for a densification of YBCO superconducting wire, and researches on electrophoretic suspension solutions and additive were experimentally performed for an improvement of the critical current density of fabricated electrophoretically superconducting wire. The samples fabricated in the solution with the additive, 8 vol.% of 1% PEG(1000), showed the highest critical current density.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
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• pp.555-556
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• 2006

The study examines hardness pattern of SH737-2Cu-.9C samples transient liquid phase sintered at different temperatures viz. $1120^{\circ}C$, $1180^{\circ}C$ and $1250^{\circ}C$, heat treated by various methods and then tempered at different temperatures. Sintered samples were characterized for density and densification parameter, and austenitized at $900^{\circ}C$, subsequently cooled by four different methods viz. annealing, normalizing, oil and brine quenching. Hardness pattern was found minimum for air cooled and maximum for brine quenched, and samples sintered at $1250^{\circ}C$ had relatively higher hardness. The O.Q and B.Q samples were then tempered at $200^{\circ}C$, $400^{\circ}C$, $600^{\circ}C$ and $700^{\circ}C$. Hardness pattern typically showed secondary hardness taking place, with maximum around $600^{\circ}C$.

• 한국전기전자재료학회논문지
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• 제22권1호
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• pp.22-28
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• 2009

We investigated the sintering and electric properties of ZnO-1.0 at% $TeO_2$ (ZT1) and 1.0 at% Mn-doped ZT1(ZT1M1) system. $TeO_2$ itself melts at $732^{\circ}C$ in air but forms the $ZnTeO_3$ or $Zn_2Te_3O_8$ phase with ZnO as increasing temperature and therefore retards the densification of ZnO to $1000^{\circ}C$. In ZT1M1 system, also, the densification of ZnO was retarded up to $1000^{\circ}C$ and then reached > 90% of theoretical density above $1100^{\circ}C$. It was found that a good varistor characteristics(nonlinear coefficient $a{\sim}60$) were developed in ZT1M1 system sintered at $1100^{\circ}C$ due to Mn which known as improving the nonlinearity of ZnO varistors. The results of C-V characteristics such as barrier height (${\Phi}_b$), donor density ($N_D$), depletion layer (W), and interface state density ($N_t$) in ZT1M1 ceramics were $1.8{\times}10^{17}cm^{-3}$, 1.6 V, 93 nm, and $1.7{\times}10^{12}cm^{-2}$, respectively. Also we measured the resistance and capacitance of grain boundaries with temperature using impedance and electric modulus spectroscopy. It will be discussed about the stability and homogeneity of grain boundaries using distribution parameter ($\alpha$) simulated with the Z(T)"-logf plots.

• 한국결정성장학회지
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• 제34권2호
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• pp.73-77
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• 2024

스피넬계 산화물 중 (Ni_x, Mn_y, Co_3-x-y)O₄(NMC)는 부온도계수 온도센서 소재로 활용되어 전기자동차용 배터리 관리 시스템을 포함한 다양한 산업적 응용이 가능하다. 일반적으로 NMC는 Ni, Mn, Co 화합물 분말을 이용하여 고상반응법을 통해 제조되는데 이 중 소결 공정을 통한 치밀화 과정이 온도센서 소재의 온도에 따른 전기적 특성을 결정하는 중요한 인자로 알려져 있다. 본 연구에서는 NMC 펠렛을 고상반응법을 통해 제조하고 결정구조 및 미세구조를 관찰하였다. 또한, 소결 과정 동안의 치밀화 거동 분석을 위한 활성화 에너지를 도출하였다. 분석 결과에 따르면, NMC 펠렛의 상온 저항은 10.03 Kohm이었으며 센서민 감도인 B-value는 3601.8 K로 다양한 산업군에 온도센서로 적용이 가능할 것으로 기대된다. 또한, 치밀화를 위한 활성화 에너지는 273.3 ± 0.4kJ/mol로 도출되었으며, 이는 소결 과정의 열역학적 특성을 이해하는데 중요한 정보를 제공할 것으로 기대된다.

• 한국재료학회지
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• 제13권2호
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• pp.120-125
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• 2003

A low melting borosilicate glass frit was used as an adhesion promoter, which enables $MnWO_4$to be sintered with in a reasonable sintering temperature range ($800∼1000^{\circ}C$). The glass was evaluated for glass transition temperature ($Τ_{g}$ X) and thermal expansion coefficient($\alpha$). Mechanical property (Vickers hardness), grain growth, the comparison of lattice parameter and pore distribution of sintered $MnWO_4$ with the frit were methodically discussed. As sintering temperature increased, a typical liquid phase sintering showed the rapid grain growth and high densification of X$MnWO_4$grain, improvement of hardness (until $920^{\circ}C$) and different pore size distribution. Resistance of sintered $MnWO_4$varied from 450k$\Omega$ to 8.8M$\Omega$ under the measuring humidify ranging from 30 to 90%. Thus, the results will contribute to the application of glass frit containing sensor materials and their future use.

• 한국세라믹학회지
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• 제53권6호
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• pp.628-634
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• 2016

The 8 wt% yttria($Y_2O_3$) stabilized zirconia ($ZrO_2$), 8YSZ, a typical thermal barrier coating (TBC) for turbine systems, was fabricated under different starting powder conditions and coating parameters by atmospheric plasma spray (APS) coating process. Four different starting powders were prepared by conventional spray dry method with different additive and process parameter conditions. As a result, large- and small-size spherical-type particles and Donut-type particles were obtained. Dense structure of 8YSZ coating was produced when small size spherical-type or Donut-type particles were used. On the other hand, 8YSZ coating with a porous structure was formed from large-size spherical-type particles. Furthermore, a segmented coating structure with vertical cracks was observed after post heat treatment on the surface of dense structured coating by argon plasma flame at an appropriate gun distance and power condition.

• 콘크리트학회논문집
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• 제21권3호
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• pp.255-264
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• 2009

콘크리트의 투수계수는 콘크리트 구조물의 내구성능 및 미세구조의 밀실성을 판단할 수 있는 핵심적인 재료 매개변수이다. 투수계수를 산정하기 위한 많은 연구들이 있었으나, 시멘트페이스트 및 골재 각각이 콘크리트의 투수성능에 미치는 영향을 다룬 연구는 드물다. 더우기, 탄산화가 염소이온의 확산계수에 큰 영향을 미칠 수 있음에도 불구하고, 탄산화된 콘크리트에 대한 확산계수를 다룬 연구는 매우 드문 실정이다. 본 연구의 목적은 탄산화 및 비탄산화된 콘크리트의 투수계수를 추정할 수 있는 기초적 접근방법을 개발하는 것이다. 본 연구에서는 미세구조 모델 및 시멘트의 경화특성을 기초로 투수계수를 산정할 수 있는 해석적 기법이 개발되었는데, 시간단계별로 변화하는 투수계수의 해석과 탄산화된 콘크리트의 투수계수를 계산할 수 있다. 탄산화된 콘크리트에서 감소된 공극량이 계산되었으며 이는 투수계수의 산정에 이용되었다. 해석 결과는 실험적 결과를 얻어서 상호비교하여 검증하였다.

• 한국세라믹학회지
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• 제27권2호
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• pp.201-210
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• 1990

The mullite-15v/o ZrO2 composites were prepared by dispersing ZrO2-3m/o Y2O3 powders into the mullite matrix in order to improve the mechanical properties of the mullite. The densification and retention of t-ZrO2 in the matrix of synthetic mullite were also investigated. From IR spectroscopic analysis, the obtained amorphous SiO2-Al2O3 powder was observed to have Si-O-Al chemical bond in its structure which might result in the homogeneous mullite composition. The lattice parameter of the mullite powder calcined above 130$0^{\circ}C$ (a0=7.5468$\AA$) is nearly close to the value of stoichiometric mullite (71.8wt% Al2O3, a0=7.5456$\AA$). The sintering behavior, microstructure, flexural strength and fracture toughness of the mullite and mullite-15v/o ZrO2 composites have been studied. The mullite-15v/o ZrO2(+3m/o Y2O3) ceramics with relative densities of 96% were obtained when sintered at 1$600^{\circ}C$. The flexural strength and fractrue toughness of the composites sintered at 1$600^{\circ}C$(calcination temperature of mullite powders ; 125$0^{\circ}C$) had maximum values of 307MPa and 2.50MPa.m1/2, respectively. The fracture toughness improvement in the mullite-ZrO2 cmoposite is assumed to be resulted from the combined effect of the stress-induced phase transformation of tetragonal ZrO2 and the crack deflection due to microcracking by the monoclinic ZrO2 formation.

• Advanced Composite Materials
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• 제17권3호
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• pp.259-275
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• 2008

This study aims to optimize the mechanical and electrical properties of electrically conductive polymer composites (CPCs) for use as a material of bipolar plates for PEM fuel cells. The thin CPCs consisting of conductive fillers and polymer resin were fabricated by a preform molding technique. Expanded graphite (EG), flake-type graphite (FG) and carbon fiber (CF) were used as conductive fillers. This study tested two types of CPCs, EG/FG filled CPCs and EG/CF filled CPCs, to optimize the material properties. First, the characteristics of EG/FG filled CPCs were investigated according to the FG ratio for 7 and $100{\mu}m$ sized FG. CPCs using $100{\mu}m$ FG showed optimal material properties at 60 wt% FG ratio, which were an electrical conductivity of 390 S/cm and flexural strength of 51 MPa. The particle size was an important parameter to change the mechanical and electrical behaviors. The flexural strength was sensitive to the particle size due to the different levels of densification. The electrical conductivity also showed size-dependent behavior because of the different contributions to the conductive network. Meanwhile, the material properties of EG/CF filled CPCs was also optimized according to the CF ratio, and the optimized electrical conductivity and flexural strength were 290 S/cm and 58 MPa, respectively. The electrical conductivity of this case decreased similarly to the EG/FG filled case. On the other hand, the behavior of the flexural strength was more complicated than the EG/FG filled case, and the reason was attributed to the interaction between the strengthening effect of CF and the deterioration of voids.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 춘계 학술발표회 제20권1호
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• pp.1053-1056
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• 2008

콘크리트의 투수계수는 콘크리트 구조물의 내구성능 및 미세구조의 밀실성을 판단하는 핵심적인 재료 매개변수이다. 투수계수를 산정하기 위한 많은 연구들이 있었으나, 시멘트 페이스트 및 골재 각각이 콘크리트의 투수성능에 미치는 영향을 다룬 연구는 드물다. 더우기, 탄산화가 염소이온의 확산계수에 큰 영향을 미칠 수 있음에도 불구하고, 탄산화된 콘크리트에 대한 확산계수를 다룬 연구는 더욱 드문 실정이다. 본 연구의 목적은 탄산화 및 비탄산화된 콘크리트의 투수계수를 추정할 수 있는 기초적 접근방법을 개발하는 것이다. 본 연구에서는 미세구조 모델 및 시멘트의 경화특성을 기초로 투수계수를 산정할 수 있는 해석적 기법이 개발되었다. 본 연구에서는 시간단계별로 변화하는 투수계수의 해석과 중성화된 콘크리트의 투수계수이다. 탄산화된 콘크리트에서 감소된 공극량이 계산되었으며 이는 투수계수의 산정에 이용되었다. 본 연구결과는 실험적 결과를 얻어서 상호 비교하여 검증하였다.