• 한국세라믹학회지
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• 제46권1호
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• pp.74-80
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• 2009

Electrospinning process is the useful and unique method to produce nanofibers from metal precursor and polymer solution by controlled viscosity. In this study, the NiZn ferrite nanofibers were prepared by electrospinning with a aqueous metal salts/polymer solution that contained polyvinyl pyrrolidone and Fe (III) chloride, Ni (II) acetate tetrahydrate and zinc acetate dihydrate in N,N-dimethylformamide. The applied electric field and spurting rate for spinning conditions were 10 kV, 2 ml/h, respectively. The obtained fibers were treated at $250^{\circ}C$ for 1 h to remove the polymer. Finally, the NiZn ferrite fibers were calcined at $600^{\circ}C$ for 3 h and annealed at $900{\sim}1200^{\circ}C$ in air. By tuning the viscosity of batch solution before electrospinning, we were able to control the microstructure of NiZn ferrite fiber in the range of $150{\sim}500\;nm$ at 770 cP. The primary particle size in $600^{\circ}C$ calcined ferrite fiber was about 10 nm. The properties of those NiZn ferrite fibers were determined from X-ray diffraction analysis, electron microscopy, energy dispersive spectroscopy, Fourier transform infrared spectroscopy, thermal analysis, and magnetic measurement.

• 자원환경지질
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• 제28권1호
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• pp.43-51
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• 1995

The Jangsan Quartzite is a basal unit of the Cambro-Odovician sequence, in Socheon-Myeon, Bonghwa-Gun, Gyeongsangbug-Do, South Korea, was petrologically and geochemically investigated. The quartzite consists mainly of quartz and muscovite, assosiated with tourmaline and graphite. The quartzite shows white and/or gray color and various green color in hand specimens. The white and gray colored rocks have very low vanadium contents, but a dark green colored rock contains 8960 ppm vanadium. The muscovites in the quartzite show colorless and green color, of which green ones range from pale blue green to pale green. The dark green colored muscovites have above 8 wt. % vanadium and pale green ones have 1-3 wt. % vanadium. Vanadium contents in moscovite increase with decreasing $Al^{v1}$ contents. It suggests that vanadium substitutes for octahedral aluminium in moscovite. In general, it tends to large volumes of muscovite (up to 14 modal %) in deep green colored rocks, and high vanadium contents in their muscovites. Most of the moscovite flakes occur along the quartz boundaries and some are enclosed by quartz grain. The moscovite grains intergrowth each other in the former. The mouscovite aggragates are divided into two types on the basis of their intergrowth(cut) times. Two cut times and one cut time are named T type and D type, respectively. The T type is mainly distributed at western part (near of the Chunyang granite), whereas the D type is distributed from middle to estern part(near the Janggunbong) of the formation. The boundary is consistent with metamorphic isograd between andalusite and sillimanite zone by Ahn et. al. (1993).

• Advances in materials Research
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• 제3권2호
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• pp.105-116
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• 2014

The microwave dielectric properties of $CeO_2$ nanoparticles (0.5, 1.0 & 1.5wt%) doped $Mg_2TiO_4$ (MTO) ceramics have been investigated at cryogenic temperatures. The XRD patterns of the samples were refined using the full proof program reveal the inverse spinel structure without any secondary phases. The addition of $CeO_2$ nanoparticles lowered the sintering temperature with enhancement in density and grain size as compared to pure MTO ceramics. This is attributed to the higher sintering velocity of the fine particles. Further, the microwave dielectric properties of the MTO ceramics were measured at cryogenic temperatures in the temperature range of 6.5-295 K. It is observed that the loss tangent ($tan{\delta}$) of all the samples increased with temperature. However, the $CeO_2$ nanoparticles doped MTO ceramics manifested lower loss tangents as compared to the pure MTO ceramics. The loss tangents of the pure and MTO ceramics doped with 1.5 wt% of $CeO_2$ nanoparticles measured at 6.5K are found to be $6.6{\times}10^{-5}$ and $5.4{\times}10^{-5}$, respectively. The addition of $CeO_2$ nanoparticles did not cause any changes on the temperature stability of the MTO ceramics at cryogenic temperatures. On the other hand, the temperature coefficient of the permittivity increased with rise in temperature and with the wt% of $CeO_2$ nanoparticles. The obtained lower loss tangent values at cryogenic temperatures can be attributed to the decrease in both intrinsic and extrinsic losses in the MTO ceramics.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2002년도 하계학술대회 논문집 Vol.3 No.2
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• pp.625-628
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• 2002

The electrical properties of the praseodymium-based ZnO varistor ceramics, which are composed of Zn-Pr-Co-Cr-Dy oxides were investigated with $Dy_2O_3$ amount. The average grain size of varistor ceramics was greatly decreased from 18.2 to 4.6 pm with increasing $Dy_2O_3$ amount. The calculated nonlinear exponent$({\alpha})$ in varistor ceramics without $DY_2O_3$ was only 4.9, whereas the a value of the varistors with $DY_2O_3$ was abruptly increased in the range of 48.8 to 58.6. In particular, the maximum value of a was obtained by doping of 1.0 mol% $DY_2O_3$, reaching 58.6. The measured leakage current$(I_l)$ value in varistors without $DY_2O_3$ was $85.45{\mu}A$, whereas the $I_{\ell}$ value of the varistors with $DY_2O_3$ was very abruptly decreased in the range of 1.10 to $0.12{\mu}A$. In particular, the minimum value of $I_{\ell}$ was obtained by doping of 0.5 mol% $DY_2O_3$, reaching $0.12{\mu}A$. The tan $\delta$ varied in V-shape, with minimum 2.28% at 0.5 mol% $DY_2O_3$. The donor concentration and the density of interface states were decreased in the range of $(4.66{\sim}0.25){\times}10^{18}cm^3$ and $(5.70{\sim}1.39){\times}10^{12}/cm^2$, respectively, as $DY_2O_3$ amount is increased.

• 소성∙가공
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• 제27권4호
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• pp.250-256
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• 2018

Oxygen-free copper (OFC) was prepared as a 90 mm cube and then processed with Multi-Axial Diagonal Forging - Initialization of Prior manufacturing History (MADF). The MADF process has been newly developed as a severe plastic deformation method. The MADF process consists of upset forging with a thickness reduction of 30% and diagonal forging with a diagonal angle of $135^{\circ}$. 1 cycle process consists of a 12 passes forging process. In order to analyze the characteristic changes according to the number of iterations, 1, 2, and 3 cycles of the MADF process were performed. The OFC specimens were MADF processed without surface cracks up to 3 cycles. The microstructure, hardness and tensile test of processed materials were analyzed to study the change of material properties according to the amount of MADF process. The results showed that the MADF process effectively refined the microstructure and increased the strength of OFC. In the case of specimens processed for more than 2 cycles, the grains of all measurement regions were refined to be less than $7{\mu}m$ of grain size. The 1 cycle MADF processed OFC showed the highest mechanical properties with the hardness of 132 HV and tensile strength of 395 MPa. Hardness and strength seemed to be saturated when processed over 2 cycles.

• 한국전기전자재료학회논문지
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• 제15권8호
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• pp.664-670
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• 2002

The electrical characteristics of $ZnO-Pr_6O_{11}-CoO-Cr_2O_3-Y_2O_3$(ZPCCY)-based varistors were investigated with $Y_2O_3$ content in the range of 0.0~4.0 mol%. As $Y_2O_3$ content is increased, the average grain size was markedly decreased in the range of 18.6~3.2 $\mu m$ and the density of the ceramic was decreased in the range of 5.53 ~3.74 $g/\textrm{cm}^3$. While, the varistor voltage was increased in the range of 39.4~748.1 V/mm and the nonlinear exponent was in the range of 4.5~51.2 with increasing $Y_2O_3$ content. The addition of $Y_2O_3$ greatly enhanced the nonlinear properties of varistors, compared with the varistor without $Y_2O_3$. In particular, the varistors with $Y_2O_3$content of 0.5 mol% exhibited the highest nonlinearity, in which the nonlinear exponent is 51.2 and the leakage current is 1.3 $\mu A$. The donor concentration and the density of interface states were decreased in the range of (4.19~0.14) $\times$10$^{18}$ /㎤ and (5.38~1.15)${\times}10^{18}/\textrm{cm}^3$, respectively, with increasing $Y_2O_3$ content.

• 한국재료학회지
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• 제12권4호
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• pp.269-273
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• 2002

The NASICON solid electrolyte films, $Na_{1+x}Zr_2Si_xP_{3-x}O_{12}$(1.5< x < 2.3), was prepared from ceramic slurry by modified doctor-blade process. The NASICON solid electrolyte and fabricated sensors, Pt-electrode/NASICON/Carbonate$(Na_2CO_3-K_2CO_3CaCO_3\; system)$ electrode, were investigated to measure phase, microstructure and e.m.f variation for sensing $CO_2$ concentration. The uniform grain size of $2-4{\mu}m$ and major phase of sodium zirconium silicon phosphate phase, $Na_{1+x}Zr_2Si_xP_{3-x}O_{12}$was identified with X-ray diffraction patterns and scanning electron microscopy, respectively. The Nernst's slope of 84 mV/decade for $CO_2$ concentration from 500 to 8000 ppm was obtained at operating temperature of $400^{\circ}C$.

• Applied Microscopy
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• 제43권4호
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• pp.164-172
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• 2013

In this work, microstructural and hardness evolution of the X20 steel upon short-term creep test ($550^{\circ}C$ to $650^{\circ}C$, $180^{\circ}C$ to 60 MPa) was studied by using scanning electron microscope, electron backscattered diffraction, and transmission electron microscope, microhardness tester. After creep rupture, gauge and grip part of the specimens were microstructurally analyzed. Creep at the $650^{\circ}C$/60 MPa resulted in a rupture at 1,460 hours with growth of lath width from 1.31 to $2.87{\mu}m$ and a grain growth with a more equiaxed feature. There is a close relationship between Microhardness and lath width. The formation and coarsening of Laves phase, which was observed up to $600^{\circ}C$ of creep temperature, was accelerated by the applied stress. Slight coarsening of the $M_{23}C_6$ was observed in the $550^{\circ}C$ and $600^{\circ}C$ crept or aged specimens. The coarsening of $M_{23}C_6$ depended on the temperature, where specimens crept at $650^{\circ}C$ showed higher growth rate. The microstructural evolution of X20 after short-term creep test was extensively discussed in relation to the long-term creep/aging test reported in literatures.

• 한국작물학회지
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• 제34권1호
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• pp.1-6
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• 1989

추대두형품종을 조파 또는 적파 재배하여 개체당 생육량을 증대시키면서 건실한 생육을 유동하기 위하여 생장조절제를 처리하였을 때 이들이 콩의 생육 및 수량형질에 영향하는 바를 조사한 결과를 요약하면 다음과 같다. 1. 조파할 경우 적파에 비하여 주경절수, 분기수, 협수, 100립량 등의 형질들이 증가되는 경향을 보였으며 10a당 수량도 8% 증가했다. 2. TIBA 또는 ABA 처리는 경장단축, 경직경증대 및 도복경감 등 건실한 생육을 유도하는데 효과적이었으며 결협률 주당입수를 증대시켜 종실수량이 6% 이상 증가하였다. 특히 TIBA 처리에 의해서는 12%의 수량이 증대되었다. 3. 생장조절제 처리횟수에 있어서는 6엽기에서부터 5일 간격으로 2∼3회 처리하는 것이 건실한 생육을 유도하여 수량이 증대되었으며 3회 처리구에서는 도복경감, 결협률 및 천립량 증대효과가 크게 나타나 16%의 수량이 증대되었다. 4. 본 실험에 사용한 생장조절제 중에서느 TIBA의 효과가 가장 좋아서 조파구나 적파구에서 모두 TIBA 3회 처리구에서 20% 이상의 수량이 증대되었다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.384-384
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• 2013

본 연구에서는 e-beam 증착을 이용하여 Al, Mg 단일 금속으로 다층형 Al-Mg 코팅층을 제조하여 특성 분석 및 내식성을 평가하였다. Al-Mg 코팅층은 99.99%의 Al, 99.9%의 Mg grain을 사용하여 E-Beam 가열을 통해 냉연강판 위에 코팅하였다. 증발물질과 기판과의 거리는 48 cm이며, 기판은 세척을 실시한 후 진공 챔버에 장착하고 ~10-5 Torr 까지 진공배기를 실시하였다. 진공챔버가 기본 압력까지 배기되면 아르곤 가스를 주입하고 기판홀더에 800 V의 직류 전압을 인가하여 약 30분간 글로우 방전 청정을 실시하였다. 기판의 청정이 끝나면 아르곤 가스를 차단하고 코팅층의 구성형태에 따라 Al 또는 Mg을 코팅하였다. 다층형 Al-Mg 코팅층은 2층에서 최대 6층까지 제조하였으며 $3{\mu}m$의 두께를 기준으로 Al과 Mg 코팅층의 두께비가 각각 1:1 과 2:1이 되도록 코팅하였다. 6층 이상에서는 코팅층의 두께 제어가 쉽지 않기 때문에 층수는 6층으로 제한하였다.다층형 Al-Mg 코팅층을 주사전자현미경으로 관찰한 결과, Al-Mg 코팅층간의 계면을 관찰할 수 있었다. 또한 글로우방전분광기로 Al-Mg 코팅층을 관찰한 결과, Al과 Mg 코팅층이 균일한 다층 구조를 형성하고 있는 것을 확인할 수 있었다. 다층의 Al-Mg가 코팅된 강판을 염수분무시험을 통해서 내부식 특성을 확인하였다. Al-Mg 코팅 강판의 염수분무시험 결과, Al-Mg 코팅층의 층수가 증가할 수록 내부식 특성이 향상되는 것을 확인할 수 있었으며, 이러한 현상은 Al-Mg 코팅층이 다층으로 형성되어 있어 부식 생성물을 효과적으로 차단하여 강판의 부식을 방지한 것으로 판단된다.