• 한국세라믹학회지
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• 제33권3호
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• pp.327-331
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• 1996

$\delta$-FeOOH was prepared by rapid oxidation method of Fe(OH)2 using H2O2. The effects of reaction temperature and mole ratio ([OH-]/[Fe2+])의 몰비를 제조 변수로 하여 최종 생성된 $\delta$-FeOOH의 입자크기 입자형태, 자기특성을 조사하였다. Fe(OH)2 의 반응온도 및 [OH-]/[Fe2+] 비가 $\delta$-FeOOH의 입자크기 및 형상에 많은 영향을 미침을 알수 있었으며 입자 크기는 이 두인자에 비례하여 증가하였다 Fe(OH)2 의 반응온도가 4$0^{\circ}C$ [OH-]/[Fe2+]=5 Fe(OH)2 숙성 시간 2시간에서 제조된 $\delta$-FeOOH를 TEM, VSM으로 입자의 크기 및 자기특성을 조사한결과 평균 입경이 630$\AA$ 정도이고 입도 분포가 양호하였으며 포화자화 및 보자력은 각각 20.8emu/g 210 Oe였다.

• 대한화학회지
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• 제46권5호
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• pp.419-437
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• 2002

산성조건에서 $H_2O_2$에 의한 $Fe^{2+}$ 이온의 산화($Fe^{2+}{\to}Fe^{3+}$)반응과 $Fe^{3+}$이온과 $SCN^-$이온이 결합하여 붉은색 Fe$(SCN)^{3-x}_x$ 이온을 형성하는 착화반응을 도입한 흐름주입분석기법을 사용하여 $Fe^{2+}$이온과 $Fe^{2+}$이온이 공존하는 시료용액 중 각 이온들의 동시정량을 위한 분석법을 개발하였다. 이 분석법은 개별 이온들에 대한 정량단계에 앞서 혼합시료의 전처리($Fe^{2+}$이온의 예비산화 혹은 $Fe^{2+}$이온의 예비환원)단계를 거쳐야 하는 기존의 분석법들과는 달리 두가지 단계들을 동시에 수행할 수있다는 장점을 가진다. 이 분석법의 측정한계는 [$Fe^{2+}$]=6.00${\times}10^{-7}$M 이었다.

• 한국표면공학회지
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• 제43권5호
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• pp.243-247
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• 2010

The micro Vickers hardness and internal stress of Ni-Fe metal thin film synthesized by electrodeposition method at $25^{\circ}C$ were studied as a function of bath composition, and surface microstructure and atomic compositions of thin films were investigated by SEM and EDS. And the shape change of $200\;{\AA}$ Ni-Fe nanowires made using anodic aluminum oxide(AAO) templates by electrodeposition method were observed by SEM as a function of ultrasonic treatment time and bath composition. The Fe deposition contents on the substrate non-linearly increased with Fe ion concentration over total metal ion concentration. In case of low Fe contents film, the grain size is smaller and denser than high Fe contents deposited films, and the micro Vickers hardness increased with Fe contents of electrodeposited films. These results affected the shape change of nanowire after ultrasonic treatments.

• 산업기술연구
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• 제36권
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• pp.77-81
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• 2016

Superparamagnetic $Fe_3O_4$ nanoparticles with particle size from 10 to 20 nm were synthesized by coprecipitation method. Subsequently, the $Fe_3O_4$ nanoparticles were used to fabricate $Fe_3O_4/SiO_2$ core-shell nanoparticles by sol-gel method. The $Fe_3O_4/SiO_2$ nanoparticles synthesized by sol-gel method exhibit the high uniformities of particle size and shape. We also investigated the heating characteristics of $Fe_3O_4$ and $Fe_3O_4/SiO_2$ nanoparticles for biomedical applications. The $Fe_3O_4$ nanoparticles show the faster temperature increase and the higher specific loss power(SLP) value than the $Fe_3O_4/SiO_2$ nanoparticles.

• Structural Engineering and Mechanics
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• 제30권4호
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• pp.467-480
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• 2008

An aggregation multigrid method (AMM) is a leading iterative solver in solid mechanics. Recently, AMM is applied for solving Schur Complement system in the FE analysis of shell structures. In this work, an extended application of AMM for solving Schur Complement system in the FE analysis of continuum elements is presented. Further, the performance of the proposed AMM in multiple load cases, which is a challenging problem for an iterative solver, is studied. The proposed method is developed by combining the substructuring and the multigrid methods. The substructuring method avoids factorizing the full-size matrix of an original system and the multigrid method gives near-optimal convergence. This method is demonstrated for the FE analysis of several elastostatic problems. The numerical results show better performance by the proposed method as compared to the preconditioned conjugate gradient method. The smaller computational cost for the iterative procedure of the proposed method gives a good alternative to a direct solver in large systems with multiple load cases.

• Progress in Superconductivity
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• 제14권1호
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• pp.11-16
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• 2012

본 연구에서는 자체일관적인 DFT+DMFT 계산을 통해 철의 3d 전자의 상관관계가 LiFeAs와 NaFeAs의 전자구조와 페르미 면 겹싸기 등에 미치는 영향을 알아보았다. 이들은 모두 철계 초전도체의 초전도성 형성에 매우 중요한 역할을 가지고 있다. DFT+DMFT 계산에서 얻어진 LiFeAs의 스펙트럼은, DFT에서 얻어진 띠 구조에 비해 매우 약한 페르미 면 겹싸기 현상을 보이며, NaFeAs 의 경우 DMFT 에서도 페르미 면 겹싸기 현상이 어느 정도 남아있는 것을 확인하였다. 그리고 이는 실험에서 보고된 ARPES 결과와 일치함을 확인했다.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1995년도 춘계학술대회 논문집
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• pp.603-607
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• 1995

Static and dynamic response of a mechanical system can be easily and readily obtained using an approximate method such as the Finite Element Method. However, FE solution cannot be totally trusted, since there are many numerical uncertainies inherent in an FE analysis. FE solution error can be estimated based on FE analysis result. Error estimator shows the quality of the FE solution, and helps FE users to enhance the accuracy of the FE solution.

• 동력기계공학회지
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• 제18권6호
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• pp.64-69
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• 2014

A circular plate is one of the important structures in many industrial fields. In static analysis of a circular plate, we may obtain an exact solution by analytical method, but it is limited to a simple circular plate. Thus, many researchers and designers have used numerical methods such as the finite element method. The authors of this paper developed the finite element-transfer stiffness coefficient method (FE-TSCM) for static and dynamic analyses of various structures. FE-TSCM is the combination of the modeling technique of the finite element method (FEM) and the transfer technique of the transfer stiffness coefficient method (TSCM). FE-TSCM has the advantages of both FEM and FE-TSCM. In this paper, the authors formulate the computational algorithm for the static analysis of axisymmetric circular plates under lateral loading using FE-TSCM. The computational results for three computational models obtained by FE-TSCM are compared with those obtained by FEM in order to confirm the accuracy of FE-TSCM.

• Nuclear Engineering and Technology
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• 제49권3호
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• pp.576-580
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• 2017

A dynamic nanoindentation method was applied to study an Fe-18 at.% Gd alloy as a neutron-absorbing material prepared by vacuum arc-melting and cast in a mold. The Fe-18 at.% Gd cast alloy had a microstructure with matrix phases and an Fe-rich primary dendrite of $Fe_9Gd$. Rietveld refinement of the X-ray spectra showed that the Fe-18 at.% Gd cast alloy consisted of 35.84 at.% $Fe_3Gd$, 6.58 at.% $Fe_5Gd$, 16.22 at.% $Fe_9Gd$, 1.87 at.% $Fe_2Gd$, and 39.49 at.% ${\beta}-Fe_{17}Gd_2$. The average nanohardness of the primary dendrite phase and the matrix phases were 8.7 GPa and 9.3 GPa, respectively. The fatigue limit of the matrix phase was approximately 37% higher than that of the primary dendrite phase. The dynamic nanoindentation method is useful for identifying local phases and for analyzing local mechanical properties.

• Bulletin of the Korean Chemical Society
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• 제30권8호
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• pp.1738-1742
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• 2009

Nanocrystalline Zn$Fe_2O_4$ oxide-semiconductor with spinel structure was synthesized by the polymerized complex (PC) method and investigated for its photocatalytic and photoelectric properties. The observation of a highly pure phase and a lower crystallization temperature in Zn$Fe_2O_4$ made by PC method is in total contrast to that was observed in Zn$Fe_2O_4$ prepared by the conventional solid-state reaction (SSR) method. The band gap of the nanocrystalline Zn$Fe_2O_4$ determined by UV-DRS was 1.90 eV (653 nm). The photocatalytic activity of Zn$Fe_2O_4$ prepared by PC method as investigated by the photo-decomposition of isopropyl alcohol (IPA) under visible light (${\geq}$ 420 nm) was much higher than that of the Zn$Fe_2O_4$ prepared by SSR as well as Ti$O_{2-x}N_x$. High photocatalytic activity of Zn$Fe_2O_4$ prepared by PC method was mainly due to its surface area, crystallinity and the dispersity of platinum metal over Zn$Fe_2O_4$.