• 한국분말재료학회지
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• 제10권2호
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• pp.83-88
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• 2003

Nanocrystalline materials of Ni and Ni-Cu alloy have been synthesized by the pulsed wire evaporation (PWE) method and these abnormal magnetic properties in the magnetic ordered state have been characterized using both VSM and SQUID in the range of high and low magnetic fields. Ni and Ni-Cu particles with an average size of 20 to 80 nm were found to influence magnetic hysterisis behavior and the results of powder neutron diffraction patterns and saturation magnetization curves are shown to indicate the absence of the NiO phase. The shifted hysterisis loop and irreversibility of the magnetization curve in the high field region were observed in the magnetic-ordered state of both Ni and Ni-Cu. The virgin magnetization curve for Ni slightly spillover on the limited hysterisis loop ($\pm$20kOe). This irreversibility in the high field of 50 kOe can be explained by non-col-linear behavior and the existence of the metastable states of the magnetization at the surface layer (or core) of the particle in the applied magnetic field. Immiscible alloy of Cu-Ni was also found to show irreversibility having two different magnetic phases.

• 대한화학회지
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• 제23권4호
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• pp.206-209
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• 1979

Empirical force-field method를 단결정 회절방법으로 구조가 연구된 여덟개의 1,6-anhydropyranose 분자구조$^{13{\sim}21}$에 적용하였다. 이론적 계산에서도 분자들간의 pyranose고리 conformation의 $^1C_4$와 $E_0$ 사이간의 차이는 실험치와 비슷하게 얻어졌다. Five-membered anhydro 고리의 분자들간의 작은 conformation 차이는 잘 예측되지 않았다. C-C결합 길이의 계산치는 실험치와 0.012${\AA}$내에서, C-O결합 길이는 0.027${\AA}$내에서, non-hydrogen atom의 결합각은 1.9$^{\circ}$이내에서 일치되고 있다

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2006년도 춘계학술대회 논문집
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• pp.395-398
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• 2006

Forging is applied for many industrial fields. Also, it is applied to hose nipple. Stress and metal analysis is finding method of forging possibility and we predict this possibility by finite element forging analysis. But there are also many manufacturing procedure after forging, and metal texture is varied by additional heat treatment or coating. So this research is focused on the measuring and analysis of plastic residual stress distribution at overall manufacturing procedure. From raw material to final product we measured real residual stress at each manufacturing procedure by X ray diffract meter, and simulated another procedure except forging by nonlinear finite element analysis. Also we showed how Zn-Ni coating is more contributable to metal strength than Zn coating. By this research we make final conclusion that process analysis must be observed from raw material to final manufacturing state for robust design.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1994년도 하계학술대회 논문집 C
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• pp.1333-1335
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• 1994

The nitrification of pure iron powders is found to occur even at room temperature by high energy ball milling in $NH_3$ gas atmosphere. The powders of metastable iron nitrides ($0<at.%N{\le}23.3$) thus produced are identified as the super-saturated bee structure for the N content below 14.9 at.%N and the high temperature phase of the hcp structure above 19.4 at.%N. The atomic volume of Fe in the bcc phase is found to be smaller than that of the N-martensite reported in the literature. Magnetization at room temperature gradually decreases with increasing the N concentration in contrast to the enhancement reported for the bet nitrides. Neutron diffraction experiment also provide detailed information about the local structure surrounding the nitrogen atom. The coordination number of Fe atom around a nitrogen atom for the iron nitride containing 9.5 at.%N turns out to be 3.9 atoms.

• 보존과학연구
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• 통권20호
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• pp.91-120
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• 1999

This paper presents the results of investigation on crystal, firing temperature and trace elements analysis of fragments 4~8 centriesexcavated from Kyong ju historical sites such as Wang kyong,Walsung, Hwangnam great tomb by application of optical microscope, neutron activation analysis and X-ray diffraction. Temper analysis of clay for identification of local or foreign production; Trace elements is not presented a unique chemical composition. That’s data have to be treated a statistical process in order to normalize. The results followed ;(1) Firing temperature could be estimated $700^{\circ}C$ on some softness pottery at Walsung and most of hardness others are $1,000^{\circ}C$ to $1,200^{\circ}C$.(2) Crystal structures are divided into three kinds of mineralogical composition(Quartz, Mullite, Feldspar).(3) Considering of the results of statistical data, chemical composition of Walsung is more similarly Wang kyong than Hwangnam great tomb.

• 대한금속재료학회지
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• 제50권10호
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• pp.703-710
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• 2012

The effects of the ordering reaction on high temperature mechanical behavior is investigated by tensile tests at $2{\times}10^{-2}/s-3.3{\times}10^{-5}/s$ up to $745^{\circ}C$. The tensile deformed region is examined by differential scanning calorimeter (DSC), TEM, and high resolution neutron diffraction (HRPD). The results showed that a plateau of tensile strength appeared at $150-500^{\circ}C$ whereas the elongation minimum occurred at about $600^{\circ}C$. This suggests that the occurrence of a plateau does not cause the elongation minimum. The temperature of the elongation minimum decreases with the strain rate. HRPD results show a lattice contraction in the tensile deformed specimen at the temperature of the plateau occurring region. The plateau of tensile strength, the lattice contraction, and the occurrence of serration appeared in the same temperature region.

• Nuclear Engineering and Technology
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• 제55권1호
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• pp.156-168
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• 2023

This study investigates the high temperature oxidation behaviour of a Ni-20Cr-1.2Si (wt.%) alloy in steam from 1200 ℃ to 1350 ℃ by Thermogravimetric Analysis (TGA), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDS) and X-ray Diffraction (XRD). The results demonstrate that exposed Ni-based alloy developed a thin oxide scale, consisted mainly of Cr₂O₃. The oxidation kinetics obtained from the experimental results was applied to evaluate the hydrogen generation considering a simplified reactor core model with different cladding alloys following an unmitigated Loss-Of-Coolant Accident (LOCA) scenario in a hypothetical Small Modular Reactor (SMR). Overall, experimental data and simulations results show that both Fe-based and Ni-based alloys may enhance cladding survivability, delaying its melting, as well as reducing hydrogen generation under accident conditions compared to Zr-based alloys. However, a substantial neutron absorption occurs when Ni-based alloys are used as cladding for current uranium-dioxide fuel systems, even when compared to Fe-based alloys.

• 대한화학회지
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• 제29권2호
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• pp.104-110
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• 1985

Empirical force-field 방법을 중성자 회절 방법으로 분자구조가 밝혀진 D-sorbitol, CH_2OH\;(CHOH)_4\;CH_2OH$에 적용하여 비교 연구하였다. C-C결합 길이는 계산값과 실험값이 0.009${\AA}$ 내에서 C-O 결합 길이는 0. 023${\AA}$내에서 일치하는 좋은 결과를 얻었다. C-C-C 와 C-C-O 결합 각도는 각각 $2.3^{\circ}$와 $1.9^{\circ}$이내에서 일치하였으나 crystal packing force의 영향을 많이 받고 있는 torsion angle은 상당한 차이가 있었다. C(1)-C(2)-C(3)-C(4) torsion angle을 규칙적으로 변화시키면서 steric 에너지를 연구한 결과 분자의 최저 에너지는 ${\phi}$=+$90^{\circ}$부근에서 나타나 회절법에 의한 결정 구조와는 다른 결과를 얻었다. 그러나 C-O, O-H, O-lone-pair dipole들 간의 상호작용을 무시하면 ${\phi}$=-$60^{\circ}$부근에서 최저에너지를 나타내어 결정구조와 일치 하였다. Empirical force-field 방법의 dipole 상호작용에 관한 에너지항을 개선하면 더 좋은 결과를 얻을 수 있을 것으로 예측 한다.

• Bulletin of the Korean Chemical Society
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• 제29권4호
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• pp.817-821
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• 2008

We have investigated the influence of the crystal structure on the chemical bonding nature and photocatalytic activity of cubic and hexagonal perovskite A[$Cr_{1/2}Ta_{1/2}$]O3 (A = Sr, Ba) compounds. According to neutron diffraction and field emission-scanning electron microscopy, the crystal structure and particle size of these compounds are strongly dependent on the nature of A-site cations. Also, it was found that the face-shared octahedra in the hexagonal phase are exclusively occupied by chromium ions, suggesting the presence of metallic (Cr-Cr) bonds. X-ray absorption and diffuse UV-vis spectroscopic analyses clearly demonstrated that, in comparison with cubic Sr[$Cr_{1/2}Ta_{1/2}$]$O_3$ phase, hexagonal Ba[$Cr_{1/2}Ta_{1/2}$]$O_3$ phase shows a decrease of Cr oxidation state as well as remarkable changes in interband Cr d-d transitions, which can be interpreted as a result of metallic (Cr-Cr) interactions. According to the test of photocatalytic activity, the present semiconducting materials have a distinct activity against the photodegradation of 4-chlorophenol. Also the Srbased compound was found to show a higher photocatalytic activity than the Ba-based one, which is attributable to its smaller particle size and its stronger absorption in visible light region.

• 한국결정학회:학술대회논문집
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• 한국결정학회 2003년도 춘계학술연구발표회
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• pp.8-8
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• 2003

Electron-phonon interaction plays a significant role in forming of colossal magnetoresistance effect (CMR). Polaron formation was observed by neutron diffraction and by extended X-ray absorption fine structure (EXAFS) analysis. Local probe as given by the EXAFS is a useful method to study the polaronic charge and its dependence on temperature and ions size. Here we present the EXAFS study of polaronic charge in La/sub 0.7/Ca/sub 0.3-X/Ba/sub X/MnO₃ compositions. The single phase La/sub 0.7/Ca/sub 0.3-X/Ba/sub X/MnO₃ manganites (x=0; 0.03; 0.06, ..., 0.3) were prepared by ceramic technology [1]. The Curie temperature was determined by extrapolation of the temperature dependence of the magnetization (down to zero magnetization). EXAFS experiments were carried out at the 7C EC beam line of the Pohang Light Source (PLS) in Korea. The atomic pair distribution functions (PDF) were obtained by re-regularization method [2] from filtered spectra. The PDF for the x=0.3 sample showed a single peak function and for x=0.0, 0.03, 0.06, 0.09, 0.12 compositions were asymmetric in agreement with a small Jahn-Teller elongation of two (short and long) bonds of the MnO/sub 6/ octahedron. Dispersion, σ/sub Min-O//sup 2/, and asymmetry, σ/sub Min-O//sup 3/, of the Mn-O bond distances varied significantly with x and showed a maximums at x=0.09. The maximum of σ/sub Min-O//sup 2/ is caused by increase of dynamic rms displacements of the Mn-O distances near the T/sub C/. The observed x dependence of σ/sub Min-O//sup 3/ reflects the reduction of charge carriers mobility at approaching to T/sub C/ from low as well as high temperatures.