• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2005년도 춘계 학술발표회 논문집
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• pp.627-632
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• 2005

In this study, a series of large-scale oedometer tests was performed to investigate the compressibility of rock fill materials. The testing samples were prepared to have three different grain size distributions and for each distribution, exist in two different states(dried and saturated). The test results indicated that particle breakages occurred mainly for the particles larger than 4.75mm in size and increased with increasing grain sizes. Also, it was found that, for a dry sample as it became well-graged, its compressibility decreased and accordingly, its tangent constrained modulus increased. A comparion between the samples in dry and saturated states revealed that compressibility of the materials increases with increasing water content. The values of tangent constrained modulus calculated for the tested dry samples were larger by about 10 to 20%, on average, than those for the saturated samples.

• 한국재료학회지
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• 제17권11호
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• pp.618-621
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• 2007

Chromium nitride (CrN) films were deposited on silicon substrate by RF magnetron sputtering assisted by inductive coupled nitrogen plasma without intentional substrate heating. Films were deposited with different levels of bombarding energy by nitrogen ions $(N^+)$ to investigate the influence of substrate bias voltage $(V_b)$ on the growth of CrN thin films. XRD spectra showed that the crystallographic structure of CrN films was strongly affected by substrate bias voltage. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) results showed that surface roughness and grain size of the CrN films varied significantly with bias voltage. For - 80 $V_b$ depositions, the CrN films showed bigger grain sizes than those of other bias voltage conditions. The lowest surface roughness of 0.15 nm was obtained from the CrN films deposited at .130 $V_b$.

• 한국재료학회지
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• 제4권5호
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• pp.581-589
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• 1994

인가자장하에서 성장한 $Co_{83}Cr_{17}$ 박막의 자가적 특성 및 미세구조를 조사하였고, 인가자장을 가하지 않은 경우에 성장한 박막과 그 특성 및 미세구조를 비교 하였다. 인가자장은 박막의 포화자화와 수평방향 보자력에는 아무런 영향을 주지 못하였지만, 수직보자력과 유효수직이방성자계를 감소시켰다. 또한 천이층의 결정립경과 두께는 인가자장에 의해 영향을 받지 않았지만, C축배향성은 약간 악화되었다. 또한 TEM사진은 인가자장의 유무에 관계없이 박막의 두께가 두꺼워질수록 (002)방위의 결정립 등이 우선적으로 성장함을 보여주었다.

• 한국분말재료학회지
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• 제9권1호
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• pp.25-31
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• 2002

The efects of mechanical aloying conditions and the type of reducing agent on the solid state reductionof haematite $Fe_2O_3$ have been investigated at room temperature. Aluminium titanium zinc and copper were used as reducing agent. Nanocomposites of metal-oxide in which oxide particles with nano size were dispersed in Fe matrix were obtained by mechanical alloying of $Fe_2O_3$ with aluminium and titanium respectively However the reduction of $Fe_2O_3$ by coppe was not occurred Composite materials of iron with $Al_2O_3$ and $TiO_2$ were obtained from the system of $Fe_2O_3-Al$ and $Fe_2O_3-Ti$ after ball milling for 20 hrs and 30 hrs respectively. And the system of $Fe_2O_3-Zn$ resulted in the formationof FeO with ZnO after ball milling of 120 hrs. The final grain sizes of iron estimated by X-ray diffraction line-width measurement were in the ranges of 24~33 nm.

• Nuclear Engineering and Technology
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• 제32권1호
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• pp.77-87
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• 2000

It is reported that the toughness and safety margins of the SA106 Gr.C main steam line piping steel is reduced due to dynamic strain aging (DSA) at the reactor operating temperature for Leak-Before-Break (LBB) application. In this study, intercritical annealing in two-phase ($\alpha$+${\gamma}$）region was performed to investigate the possibility of improving the toughness and reducing DSA susceptibility. The manifestations of DSA were still observed in the tensile tests of the annealed specimens. However, the ductility loss caused by DSA was smaller than that in the as-received material. Furthermore, the intercritical annealing was able to increase the Charpy impact toughness by 1.5 times compared to as-received. With the heat treatment, we could obtain microstructural changes such as the cleaner retained ferrite, increased ferrite content and somewhat finer grain size. It is considered that the reduced DSA was induced by cleaner retained ferrite, which in turn resulted in higher impact toughness in addition to the general toughening due to finer grain sizes and increased ferrite content.

• 한국표면공학회지
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• 제46권1호
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• pp.36-41
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• 2013

Friction stir welding (FSW) is a relatively new joining technique particularly for magnesium and aluminum alloys that are difficult to fusion weld. In this study, AZ31 Mg alloys were joined by FSW with shoulder diameter 11, 19 mm and rotating speed 900, 1200, 1500, 1800 rpm. The shoulder diameter and welding speed depended on the heat input during FSW process. As a result, the microstructures of stir zone were a fine grain by dynamic recrystallization. According to the larger shoulder diameter and the higher rotating speed, refined grain sizes of stir zone were grown by higher heat input, and the microhardness of stir zone was lower. The tensile strength at the shoulder diameter 19 mm, rotating speed 900 rpm was obtained maximum value. This value compared with the base metal was over 93%.

• 한국재료학회지
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• 제19권12호
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• pp.680-685
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• 2009

Using a polyurethane foam replica method, porous hydroxyapatite scaffolds (PHS) were fabricated using conventional and microwave sintering techniques. The microstructure and material properties of the PHS, such as pore size, grain size, relative density and compressive strength, were investigated at different sintering temperatures and holding times to determine the optimal sintering conditions. There were interconnected pores whose sizes ranged between about 300 ${\mu}m$ and 700 ${\mu}m$. At a conventional sintering temperature of 1100$^{\circ}C$, the scaffold had a porous microstructure, which became denser and saw the occurrence of grain growth when the temperature was increased up to 1300$^{\circ}C$. In the case of microwave sintering, even at low sintering temperature and short holding time the microstructure was much denser and had smaller grains. As the holding time of the microwave sintering was increased, higher densification was observed and also the relative density and compressive strength increased. The compressive strength values of PHS were 2.3MPa and 1.8MPa when conventional and microwave sintering was applied at 1300$^{\circ}C$, respectively.

• 한국식품과학회지
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• 제11권2호
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• pp.81-85
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• 1979

1. Gram Quality Analyzer로 측정한 단백질과 Kjeldahi치와는 곡종에 관계없이 고도의 상관(상관계수 $0.97{\sim}0.98$)을 나타내었으며 반복 측정시 의미있는 차이를 보이지 않았다. 2. 밀의 경우 경연질별로 큰 차이가 없었으나 보리의 경우 겉보리가 쌀보리보다 상관계수가 약간 낮았고 반복간 오차도 컸다. 3. 측정시료의 입자크기는 단백질 측정치에 직접 영향은 없었으나 입자크기가 작을수록 측정오차가 작았다. 4. 측정 cell에 충진하는 시료는 12 g 정도가 적합하였으며 시료를 많이 넣는 경우 적외선 reflectance가 많아 단백질 측정치는 다소 증가하였으며, 8 g 이하로 넣는 경우 오차가 컸다.

• 대한금속재료학회지
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• 제50권1호
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• pp.39-44
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• 2012

Nanopowders of TiCo were synthesized from Ti and Co by high energy ball milling. Highly dense nanostructured TiCo compounds were consolidated at low temperature by pulsed current activated sintering within 3 minutes from the mechanical synthesis of the powders (TiCo) and horizontal milled Ti+Co powders under 100 Mpa pressure. This process allows very quick densification to near theoretical density and prohibits grain growth in nanostructured materials. The grain sizes of the TiCo compounds were calculated. Finally, the average hardness values of the nanostructured TiCo compounds were investigated.

• Electronic Materials Letters
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• 제14권6호
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• pp.725-732
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• 2018

The thermoelectric and transport properties of Ti-doped FeVSb half-Heusler alloys were studied in this study. $FeV_{1-x}Ti_xSb$ (0.1 < x < 0.5) half-Heusler alloys were synthesized by mechanical alloying process and subsequent vacuum hot pressing. After vacuum hot pressing, a near singe phase with a small fraction of second phase was obtained in this experiment. Investigation of microstructure revealed that both grain and particle sizes were decreased on doping which would influence on thermal conductivity. No foreign elements pick up from the vial was seen during milling process. Thermoelectric properties were investigated as a function of temperature and doping level. The absolute value of Seebeck coefficient showed transition from negative to positive with increasing doping concentrations ($x{\geq}0.3$). Electrical conductivity, Seebeck coefficient and power factor increased with the increasing amount of Ti contents. The lattice thermal conductivity decreased considerably, possibly due to the mass disorder and grain boundary scattering. All of these turned out to increase in power factor significantly. As a result, the thermoelectric figure of merit increased comprehensively with Ti doping for this experiment, resulting in maximum thermoelectric figure of merit for $FeV_{0.7}Ti_{0.3}Sb$ at 658 K.