• 한국초전도ㆍ저온공학회논문지
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• 제19권1호
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• pp.36-41
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• 2017

The effects of $MgB_4$ addition on the superconducting properties and the microstructure of in situ processed $MgB_2$ bulk superconductors were studied. $MgB_4$ powder of 1-20 wt.% was mixed with (Mg + 2B) powder and then pressed into pellets. The pellets of (Mg + 2B + $xMgB_4$) were heat-treated at $650^{\circ}C$ for 1 h in flowing argon. The powder X-ray diffraction (XRD) analysis for the heat-treated samples showed that the major formed phase in all samples was $MgB_2$ and the minor phases were $MgB_4$ and MgO. The full width at half maximum (FWHM) values showed that the grain size of $MgB_2$ decreased as the amount of $MgB_4$ addition increased. $MgB_4$ particles included in a $MgB_2$ matrix is considered to suppress the grain growth of $MgB_2$. The onset temperatures ($T_{c,onset}$) of $MgB_2$ with $MgB_4$ addition (0-10 wt.%) was between 37-38 K. The 20 wt.% $MgB_4$ addition slightly reduced the $T_{c,onset}$ of $MgB_2$ to 36.5 K. This result indicates that $MgB_4$ addition did not influence the superconducting transition temperature ($T_c$) of $MgB_2$ significantly. On the other hand, the small additions of 1-5 wt.% $MgB_4$ increased the critical current density ($J_c$) of $MgB_2$. The $J_c$ enhancement by $MgB_4$ addition is attributed not only to the grain size refinement but also to the possible flux pinning of $MgB_4$ particles dispersed in a $MgB_2$ matrix.

• 한국재료학회지
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• 제4권1호
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• pp.9-23
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• 1994

Multitarget bias cosputter deposition(MBCD)에 의해 저온($200^{\circ}C$)에서 NaCI(100)상에 정합$CoSi_2$를 성장시켰다. X-선회절과 투과전자현미경에 의해 증착온도와 기판 bias전압에 따른 각각 silicide의 상전이와 결정성을 관찰하였다. Metal induced crystallization(MIC) 과 self bias 효과에 의해 $200^{\circ}C$에서 기판전압을 인가하지 않은 경우에도 결정질 Si이 성장하였다. MIC현상을 이론 및 실험적으로 고찰하였다. 관찰된 상전이는 $Co_2Si \to CoSi \to Cosi_2$로서 유효생성열법칙에 의해 예측된 상전이와 일치하였다. 기판 bias전압 인가시 발생한 이온충돌에 의한 충돌연쇄혼합(collisional cascade mixing), 성장박막 표면의 in situ cleaning, 핵생성처(nucleation site)이 증가로 인하여 상전이, CoSi(111)우선방위, 결정성은 증착온도에 비해 기판bias전압에 더 큰 영향을 받았다. $200^{\circ}C$에서 기판 bias전압을 증가시킴에 따라 이온충돌에 의한 결정입성장이 관찰되었으며, 이를 이온충독파괴(ion bombardment dissociation)모델에 의해 해석하였다. $200^{\circ}C$에서의 기판 bias전압증가에 따른 결정성변화를 정량적으로 고찰하기 위해 Langmuir탐침을 이용하여 $E_{Ar},\; \alpha(V_s)$를 계산하였다.

• 폴리머
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• 제31권6호
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• pp.518-525
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• 2007

내열성 유기화 점토를 사용하여 얻은 폴리(에틸렌 테레프탈레이트)(PET) 나노복합체 섬유들의 열적, 기계적 성질 및 모폴로지를 서로 비교하였다. PET 나노복합체 섬유에는 도데실트리페닐포스포늄-마이카($C_{12}PPh-Mica$)와 1-헥사데칸벤즈이미다졸-마이카($C_{16}BIMD-Mica$) 등의 유기화 점토가 사용되었다. In-situ 중합법을 이용하여 PET에 다양한 농도의 유기화 점토가 나노 크기로 분산된 복합재료를 합성하였다. PET 나노복합체 섬유의 열적-기계적 성질을 측정하기 위해 시차 주사 열분석기(DSC)와 열 중량 분석기(TGA), 넓은 각 X-선 회절 분석기(WAXD), 전자현미경(SEM과 TEM) 그리고 만능 인장 시험기(UTM)를 이용하였다. 전자현미경으로 관찰된 나노복합체 섬유 중 점토의 일부는 나노 크기로 잘 분산되었으나 한편으로는 뭉쳐진 형태도 보였다. 본 연구로부터 소량의 유기화 점토의 첨가가 나노복합체 섬유의 열 안정성과 기계적 성질을 증가시키는데 크게 기여하였음을 알았고, 5 wt% 이하의 소량의 유기화 점토를 이용한 복합재료의 열적 기계적 성질은 순수한 PET 섬유보다도 더 높은 값을 보여주었다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2010년도 제39회 하계학술대회 초록집
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• pp.243-243
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• 2010

Low-temperature grown (LTG) InGaAs epilayers were grown by MBE technique for studying a correlation between terahertz (THz) emission and the intrinsic defects. The 1.2-um-thick Be-compensated LTG-InGaAs epilayers were prepared on SI-InP:Fe substrate at $200-250^{\circ}C$, and subsequently in-situ annealed under As environment at $550^{\circ}C$ for 5-30 minutes. The carrier concentration/mobility and the crystalline structure were analyzed by the Hall effect and the x-ray diffraction (XRD), respectively, and the carrier lifetime were determined by the fs time-resolved pump-probe spectroscopy. THz generation from LTG-InGaAs was carried out by a Ti-sapphire laser (800 nm) of a pulse width of 190 fs at a repetition of 76 MHz. Figure shows the spectral amplitude of generated waves in the THz region. As the growth temperature of epilayer increases, the amplitude is enhanced. However, two samples grown at $200^{\circ}C$, as-grown and annealed, show almost no difference in the spectral amplitude. This suggests that the growth temperature is critical in the formation of defect states involved in THz emission. We are now investigating the correlations between the XRD band attributed to defects, the Hall parameter, and the spectral amplitude of generated THz wave.

• 한국산업융합학회 논문집
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• 제25권2_2호
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• pp.289-297
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• 2022

Deterioration in durability of structures due to the steel corrosion is difficult to determine whether or not corrosion is initiated and how much propagated, and moreover, repair and maintenance are not easy to deal with. Therefore, preventive treatments can be the best option to avoid the deterioration. Various methods for preventing corrosion of steel, such as electrochemical treatments, anti-corrosion agents and steel surface coatings, are being developed, but economic and environmental aspects make it difficult to apply them to in-situ field. Thus, the purpose of this study was to improve corrosion resistance by using CA-based clinker that are relatively simple and expected to be economically profitable Existing CA-based clinkers had problems such as flash setting and low strength development during the initial hydration process, but in order to solve this problem, CA clinker with low initial reactivity were used as binder in this study. The cement paste used in the experiments was replaced with CA₂ clinker for 0%, 10%, 20%, and 30% in OPC. And the mixture used in the chloride binding test for the extraction of water-soluble chloride was intermixed with Cl- 0.5%, 1%, 2%, and 3% by weight of binder content. To evaluate characteristic of hydration heat evolution, calorimetry analysis was performed and simultaneously chloride binding capacity and acid neutralization capacity were carried out. The identification of hydration products with curing ages was verified by X-ray diffraction analysis. The free chloride extraction test showed that the chlorine ion holding ability improved in order OC 10 > OC 30 > OC 20 > OC 0 and the pH drop resistance test showed that the resistance capability in pH 12 was OC 0 > OA 10 > OA 20 > OA 30. The XRD analyses showed that AFm phase, which can affect the ability to hold chlorine ions, tended to increase when CA₂ was mixed, and that in pH12 the content of calcium hydroxide (Ca(OH)₂), which indicates pH-low resistance, decreased as CA₂ was mixed

• 한국분말재료학회지
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• 제12권4호
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• pp.279-283
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• 2005

In this study, the ZnS composite powders for host material in phosphor was synthesized in situ by mechanical alloying. As the mechanical alloying time increases, particle size of ZnS decreases. ZnS powders of $1.85\;\mu{m}$ in a mean size was fabricated by mechanical alloying for 10h. The crystal structures of ZnS powders were investigated by X-ray diffraction and the photo-luminescence properties was evaluated with the optical spectra analyzer. The steady state condition of mechanically alloyed ZnS was obtained as a mean particle size of $2\;\mu{m}$ in 5h milling. The sphalerite and wurtize structures coexist in the ZnS mechanically alloyed for 5h. The ZnS powder mechanically alloyed for 10h grows to the sphalerite structure. And the strong emission peaks of ZnS are observed at 480 nm wave length at the powders of mechanically alloyed for 10h, but the sphalerite and wurtize structures in ZnS coexist and emission peaks are not appeared at the powders of mechanically alloyed for 10h.

• 한국진공학회지
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• 제2권4호
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• pp.439-454
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• 1993

The phase sequence of codeposited Co-Si alloy and Co/si multilayer thin film was investigated by differential scanning calormetry(DSC) and X-ray diffraction (XRD) analysis, The phase sequence in codeposition and codeposited amorphous Co-Si alloy thin film were CoSilongrightarrow Co2Si and those in Co/Si multilayer thin film were CoSilongrightarrowCo2Silongrightarrow and CoSilongrightarrowCo2Si longrightarrowCoSilongrightarrowCoSi2 with the atomic concentration ration of Co to Si layer being 2:1 and 1:2 respectively. The observed phase sequence was analyzed by the effectvie heat of formatin . The phase determining factor (PDF) considering structural facotr in addition to the effectvie heat of formation was used to explain the difference in the first crystalline phase between codeposition, codeposited amorphous Co-Si alloy thin film and Co/Si multilayer thin film. The crystallinity of Co-silicide deposited by multitarget bias cosputter deposition (MBCD) wasinvestigated as a funcion of deposition temperature and substrate bias voltage by transmission electron microscopy (TEM) and epitaxial CoSi2 layer was grown at $200^{\circ}C$ . Parameters, Ear, $\alpha$(As), were calculate dto quantitatively explain the low temperature epitaxial grpwth of CoSi2 layer. The phase sequence and crystallinity had a stronger dependence on the substrate bias voltage than on the deposition temperature due to the collisional daxcade mixing, in-situ cleannin g, and increase in the number of nucleation sites by ion bombardment of growing surface.

• 한국재료학회지
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• 제23권12호
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• pp.695-701
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• 2013

To understand how reactivity between reinforcing nanoparticles and aqueous solution affects electrodeposited Cu thin films, two types of commercialized cerium oxide (ceria, $CeO_2$) nanoparticles were used with copper sulfate electrolyte to form in-situ nanocomposite films. During this process, we observed variation in colors and pH of the electrolyte depending on the manufacturer. Ceria aqueous solution and nickel sulfate ($NiSO_4$) aqueous solutions were also used for comparison. We checked several parameters which could be key factors contributing to the changes, such as the oxidation number of Cu, chemical impurities of ceria nanoparticles, and so on. Oxidation number was checked by salt formation by chemical reaction between $CuSO_4$ solution and sodium hydroxide (NaOH) solution. We observed that the color changed when $H_2SO_4$ was added to the $CuSO_4$ solution. The same effect was obtained when $H_2SO_4$ was mixed with ceria solution; the color of ceria solution changed from white to yellow. However, the color of $NiSO_4$ solution did not show any significant changes. We did observe slight changes in the pH of the solutions in this study. We did not obtain firm evidence to explain the changes observed in this study, but changes in the color of the electrolyte might be caused by interaction of Cu ion and the by-product of ceria. The mechanical properties of the films were examined by nanoindentation, and reaction between ceria and electrolyte presumably affect the mechanical properties of electrodeposited copper films. We also examined their crystal structures and optical properties by X-ray diffraction (XRD) and UV-Vis spectroscopy.

• 방사성폐기물학회지
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• 제19권4호
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• pp.459-467
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• 2021

In the majority of countries, the upper limit of buffer temperature in a repository is set to below 100℃ due to the possible illitization. This smectite-to-illite transformation is expected to be detrimental to the swelling functions of the buffer. However, if the upper limit is increased while preventing illitization, the disposal density and cost-effectiveness for the repository will dramatically increase. Thus, understanding the characteristics and creating a database related to the buffer under the elevated temperature conditions is crucial. In this study, a strategy to investigate the bentonite found in Korea under the elevated temperatures from a mineral transformation and radionuclides retardation perspective was proposed. Certain long-term hydrothermal reactions generated the bentonite samples that were utilized for the investigation of their mineral transformation and radionuclide retardation characteristics. The bentonite samples are expected to be studied using in-situ synchrotron-based X-Ray Diffraction (XRD) technique to determine the smectite-to-illite transformation. Simultaneously, the 'high-temperature and high-pressure mineral alteration measurement system' based on the Diamond Anvil Cell (DAC) will control and provide the elevated temperature and pressure conditions during the measurements. The kinetic models, including the Huang and Cuadros model, are expected to predict the time and manner in which the illitization will become detrimental to the performance and safety of the repository. The sorption reactions planned for the bentonite samples to evaluate the effects on retardation will provide the information required to expand the current knowledge of repository optimization.

• 폴리머
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• 제34권2호
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• pp.144-149
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• 2010

Ag/polystyrene(PS) 나노복합체를 110 $^{\circ}C$의 가열법에 의하여 silver 2-ethylhexylcarbamate(Ag-CB) 복합체의 환원과 동시에 라디칼 중합을 진행하여 제조하였다. 또한, 이러한 전통적인 가열법과는 대조적으로 마이크로파를 조사하여 스티렌 단량체의 중합이 진행됨이 없이 은 나노입자가 잘 분산된 콜로이드 스티렌 용액을 제조할 수 있었다. 이렇게 단지 마이크로파를 조사하여 은 나노입자를 제조하는 방법은 반응기 내의 전체 용액 속에서 균일하고 빠르게 진행되어 매우 입자가 작고 균일한 은 나노콜로이드 용액을 제조할 수 있었다. 또한, 연속적으로 얻어진 은 나노입자를 포함하는 단량체 용액을 라디칼 중합시킴으로써 PS 고분자 매트릭스에 은 나노입자가 잘 분산된 Ag/PS 나노복합체를 얻을 수 있었다. Ag/PS(0.1/100) 나노복합체는 Ag/PS(4.0/100)를 마스터배치로 사용하여 용융-혼합 방법에 의하여 성공적으로 제조할 수 있었으며 그러한 나노복합체를 UV-VIS spectroscopy, TEM, 그리고 XRD를 이용하여 확인하였다.