• 열처리공학회지
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• 제12권1호
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• pp.31-39
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• 1999

In the present study, oxidation behavior of 304 and 316 stainless steels was investigated. After solution treatment, specimens were polished up to $1{\mu}m$ $Al_2O_3$ grade and then subjected to oxidation treatment in dry air. The range of temperature was used for oxidation treatment at $300^{\circ}C{\sim}500^{\circ}C$ and TEM was used for analyzing the components and structure of oxide film. Also, these results were compared with the results of ESCA and TG. According to the results of TEM analysis, it was found that Cr oxide film was formed on top of the surface after room temperature oxidation but amorphous Fe oxide was formed on top of the surface and polycrystalline $(Cr,Fe)_2O_3$ was formed below the amorphous Fe oxide layer after $500^{\circ}C$ oxidation treatment. The oxidized specimens at $500^{\circ}C$ showed that 316 stainless steel resists more strongly to grain and grain boundary oxidation than 304 stainless steel. These results suggested that Mo component resolved in 316 stainless steel matrix suppressed the formation of Cr carbide which may results in local Cr deplete area.

• 한국분말재료학회지
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• 제20권4호
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• pp.275-279
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• 2013

Fe-based oxide dispersion strengthened (ODS) powders were produced by high energy ball milling, followed by spark plasma sintering (SPS) for consolidation. The mixed powders of 84Fe-14Cr-$2Y_2O_3$ (wt%) were mechanically milled for 10 and 90 mins, and then consolidated at different temperatures ($900{\sim}1100^{\circ}C$). Mechanically-Alloyed (MAed) particles were examined by means of cross-sectional images using scanning electron microscopy (SEM). Both mechanical alloying and sintering behavior was investigated by X-ray diffraction (XRD) and high resolution transmission electron microscopy (HR-TEM). To confirm the thermal behavior of $Y_2O_3$, a replica method was applied after the SPS process. From the SEM observation, MAed powders milled for 10 min showed a lamella structure consisting of rich regions of Fe and Cr, while both regions were fully alloyed after 90 min. The results of sintering behavior clearly indicate that as the SPS temperature increased, micro-sized defects decreased and the density of consolidated ODS alloys increased. TEM images revealed that precipitates smaller than 50 nm consisted of $YCrO_3$.

• 청정기술
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• 제18권3호
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• pp.259-264
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• 2012

페롭스카이트형 산화물을 능금산법으로 합성하여 TG/DTA, XRD, XPS, TEM 및 $H_2$-TPR 등에 의해 특성분석을 하였고, 벤젠의 연소반응에서의 활성을 조사하였다. 대부분의 촉매들은 페롭스카이트 결정구조를 잘 가지고 있었으며 15에서 70 nm의 크기를 나타내었다. $LaMnO_3$ 촉매가 가장 높은 활성을 보여주었고 $350^{\circ}C$에서 거의 100%의 전환율을 나타내었다. 반응활성을 증가시키기 위해 페롭스카이트 산화물의 A-와 B-위치에 다른 금속이온의 치환을 행하였다. $LaMnO_3$ 촉매의 A-위치에 Sr을 일부분 치환시키면 벤젠의 전환율이 증가하였다. 또한, B-위치에 Co 및 Cu 이온의 치환 역시 촉매 활성을 증가시켰고, $LaMn_{1-x}B_xO_3$ (B = Co, Fe, Cu)형 페롭스카이트에서 촉매활성은 Co > Cu > Fe의 순서로 감소하였다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2009년도 제38회 동계학술대회 초록집
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• pp.72-72
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• 2010

탄소나노튜브(carbon nanotubes : CNTs)는 뛰어난 전기적, 물리적인 특성을 가지고 있기 때문에 다양한 분야에서 이를 활용하려는 노력들이 활발히 이루어지고 있다. CNTs의 전기적인 특성은 직경에 의해 결정되므로, 직경을 균일하게 제어하는 일이 CNTs를 기반으로 한 전자소자 응용에 가장 중요한 사항이라 할 수 있다. 일반적으로 화학기상증착법(chemical vapor deposition, CVD)으로 합성된 CNTs의 직경은 촉매의 크기에 의존하기 때문에, 촉매의 크기를 제어하기 위한 다양한 연구들이 활발히 진행되고 있다[1-3]. 하지만 CNTs의 성장온도 근처에서 촉매 입자는 표면 확산(surface diffusion)에 의해 응집(agglomeration)되기 때문에 작고 균일한 크기의 촉매를 얻기 어렵다. 본 연구에서는 Si(001) 기판 위에 지지층(supporting layer)인 Al의 두께를 변화시켜 증착하고, 열적산화과정을 통해 $Al_2O_3$ 층을 형성한 후 Fe을 증착하여 CNTs를 합성하였다. $Al_2O_3$ 지지층과 Fe 촉매입자의 구조와 화학적 상태를 원자힘현미경 (atomic force microscopy, AFM), 주사전자현미경 (scanning electron microscopy, SEM), 투과전자현미경 (transmission electron microscopy, TEM), X-선 광전자 분광기(X-ray photoelectron spectroscopy)를 통해 분석하였고, 성장된 CNTs는 SEM, TEM, 라만 분광법 (Raman spectroscopy)을 통해 분석하였다. 그 결과, $Al_2O_3$ 층은 두께에 따라 각기 다른 표면 거칠기(RMS roughness)와 결정립(grain)의 크기를 갖게 되며, 이러한 표면구조가 Fe 촉매입자의 표면확산에 의한 응집에 관여하여 CNTs의 직경에 영향을 미치는 것을 확인하였다. 또한 $Al_2O_3$ 지지층의 두께가 15 nm인 경우, Fe의 응집현상이 억제되어 좁은 직경분포를 지닌 고순도 단일벽 탄소나노튜브(Single-walled CNTs)가 성장되는 것을 확인하였다.

• Composites Research
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• 제21권2호
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• pp.31-35
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• 2008

자성 금속 코팅을 위해 폴리스티렌 submicron 입자를 제조하였다. 니켈과 철 코팅을 위해 무전해 도금을 적용하였고 열처리를 통해 폴리스티렌을 탄화 시켜 중공형 구조를 형성하였다. 이러한 중공형 자성 입자는 가볍고 효율이 우수한 전자파 흡수체 제조에 적용될 수 있다. 코팅 층의 두께, 성분 및 표면 형상은 SEM/EDS/TEM 으로 관찰하였고, 중공 자성 입자의 전자파 특성 비교를 위해 고분자 복합재료를 제조하였다. 복합재료의 투자율 측정 결과, 중공형 철이 니켈에 비해 우수하였으며 바륨 페라이트 (Barium ferrite)와 같은 기존의 자성 재료보다 우수하였다.

• Composites Research
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• 제20권5호
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• pp.43-48
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• 2007

전자기파의 흡수와 간섭 문제는 상업적, 군사적 용도에서 중요한 문제로 다루어져 왔다. 스텔스 기술은 전자기파 흡수 기술의 가장 전형적인 적용 방법 중에 하나이다. 본 연구는 유전성 및 자성 손실을 함유한 복합성의 필러를 개발하고자 시작되었다. 전도성 나노 소재인 탄소나노섬유 (CNFs)에 자성을 부여하기 위해 두 가지의 니켈-인과 니켈-철을 무전해 도금을 적용하여 각각 코팅하는 실험에 성공하였다. 제작된 복합 소재의 미세 구조를 SEM/TEM을 통해 관찰하였고, 이들의 성분 분석(EDS/ELLS)을 수행하였다. 코팅 층의 평균 두께는 약 $50\;{\sim}\;100\;nm$의 결과를 나타내었으며, 코팅 층의 성분은 Ni-6wt%P와 Ni-70wt%Fe의 결과를 각각 나타내었다.

• Bulletin of the Korean Chemical Society
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• 제31권5호
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• pp.1128-1134
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• 2010

Nanocarbon supported Fe/$TiO_2$ composite catalysts were prepared using CNTs (carbon nanotubes) and $C_{60}$ (fullerene) as nanocarbon sources by a modified sol-gel method. The Fe/$TiO_2$-nanocarbon composites were characterized by the BET surface area, scanning electron microscope (SEM), Transmission Electron Microscope (TEM), X-ray diffraction (XRD), energy dispersive X-ray (EDX) and UV-vis spectra. In comparison with non-nanocarbon doped Fe/$TiO_2$ composites, the nanocarbon supported Fe/$TiO_2$ composites had higher absorption ability with a larger specific surface area, and showed higher photocatalytic activity during the degradation of methylene blue (MB) under visible light. The reasons for the obvious increase of photocatalytic activity indicated that the photoactivity not only benefits from nanocarbon introduced, but also relates to the cooperative effect of the Fe as a dopant.

• Advances in materials Research
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• 제3권4호
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• pp.233-242
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• 2014

Magnetic and conducting aniline sulfide resin cross-linked (ASC-Fe3O4) nanocomposite has been prepared in the presence of aniline sulfide resin (ASR), aniline, $Fe_3O_4$ coated by polyethylene glycol (PEG) and initiator. The magnetic properties of the resulting composites showed ferromagnetic behavior, such as high-saturated magnetization (Ms= 41 emu/g), and coercive force (Hc=1.5 Oe). The saturated magnetization was increased by increasing of $Fe_3O_4$ content and decreased by increasing aniline ratio. The transmission electron micrograph (TEM) and X-ray diffraction proved that nanometer-sized about 20-30 nm $Fe_3O_4$ in the composite. The average size of ASC-$Fe_3O_4$ nanocomposite with core-shell structure was about 50-60 nm, and polydisperse. This approach may also be extended to the synthesis and modification of other polymers. Electrical conductivity of aniline sulfide resin cross-linked (ASC) nanocomposite has been studied by four-point probe method and produced $3.3{\times}10^{-4}S/cm$ conductivity for it. The conductivity of the composites at room temperature depended on the $Fe_3O_4$, aniline ratio and doping degree. The thermogravimetry analysis (TGA) results showed that this resin is thermal resistance near of $500^{\circ}C$. So, It can be used for resistance thermal coating for military applications. $Fe_3O_4$-PASC nanocomposite has been flexible structure with electrical and magnetic properties.

• 한국재료학회지
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• 제14권7호
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• pp.511-515
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• 2004

Fe nano powders were synthesized by plasma arc discharge (PAD) process and studied by means of X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM) and X-ray Photoelectron Spectroscopy (XPS). Pure Fe rod($99.9\%$) was used as a source of metallic vapor under argon and hydrogen mixed atmosphere. The synthesized Fe nano powders had nearly spherical shapes and core-shell type structures. The influence of process parameters on the structure and size was investigated. The powder size increased with increasing of the chamber pressure and input current. High hydrogen gas ratio in chamber atmosphere affected the particle size and amount of Fe nanopowder.

• 한국분말재료학회지
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• 제11권6호
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• pp.472-476
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• 2004

The Fe-Ni compact bodies were fabricated using Fe-Ni mixed powders with 50 nm in diameter by injection molding process. The relationship between microstructure and material properties was characterized with respect to the volume ratio of powder/binder and sintering temperature with SEM and TEM. In the compact body having the volume percent ratio of 45(Fe-Ni) : 55(binder), which was sintered at $900^{\circ}C$ the values of relative density and hardness were low about 97.7% and 277.1 Hv, respectively. Using the composition of 50(Fe Ni) : 50(binder) and sintered at $900^{\circ}C$, the values of relative density and hardness were 98.5%, 294.4 Hv, respec-tively. The grain size of sintered bodies strongly depended on the sintering temperature. In both samples sintered at $600^{\circ}C$ and $900^{\circ}C$, the average grain sizes were about 150 nm and 500 nm in diameter, respectively.