• 분석과학
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• 제19권5호
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• pp.422-432
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• 2006

VOC는 대기오염의 주원인으로서 인식되어왔다. 촉매산화는 저온에서 높은 효율을 나타내기 때문에 VOCs 제거를 위한 가장 중요한 처리기술중 하나이다. 이 연구에서는 ${\gamma}-Al_2O_3$ 담체에 Pt, Pt-Ru 그리고 Pt-Ir을 담시지켜 촉매를 제조하였다. 반응물로서 Xylene, toluene 그리고 MEK를 사용하였다. 단일 또는 두 가지 이상의 촉매들은 함침법에 의해 준비하였고, XRD, XPS, TEM, BET 분석을 통하여 특성화하였다. 그 결과 Pt-Ru, Pt-Ir 촉매는 Pt 촉매에 비해 더 높은 전환율을 나타내었다. ${\gamma}-Al_2O_3$ 담체상에서 Pt-Ir 촉매가 가장 높은 전환율을 보인다. VOCs산화에서, Pt-Ru, Pt-Ir 촉매는 다양한 활성점을 나타내었고 그것은 Pt의 metal 영역를 강화시켰다. 따라서 두 가지 금속으로 이루어진 촉매가 단일 금속으로 이루어진 촉매에 비해 VOCs 전환율이 더 높았다. 이 연구에서 Pt에 소량의 Ru, Ir 첨가는 VOCs의 산화반응을 증진시켰다.

• Advances in materials Research
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• 제13권3호
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• pp.161-171
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• 2024

This study aimed to investigate the effect of physicochemical properties and mix ratios of iron ore (oxide feed): coke (reductant) on the carbothermic reductions of iron ore. Coke size was fixed at ≤63 ㎛ while iron ore size varied between 150-63 ㎛ and ≤63 ㎛ respectively. Mix ratios were changed from 100:0 (reference) to 80:20 and 60:40 while the temperature, heating rate and soaking duration in muffle furnace were fixed at 1100 ℃, 10 ℃/min and 1 hour. Particle size analyzer, XRF, CHNS and XRD analyses were used for determination of raw feed characteristics. The occurrence of phase transformations from various forms of iron oxides to iron during the carbothermal reductions were identified through XRD profiles and supported with weight loss (%). XRF analysis proved that iron ore is of high grade with 93.4% of Fe₂O₃ content. Other oxides present in minor amounts are 2% Al₂O₃ and 1.8% SiO₂ with negligible amounts of other compounds such as MnO, K₂O and CuO. Composite pellet with finer size iron particles (≤63 ㎛) and higher carbon content of 60:40 exhibited 45.13% weight lost compared to 32.30% and 3.88% respectively for 80:20 and 100:0 ratios. It is evident that reduction reactions can only occur with the presence of coke, the carbon supply. The small weight loss of 3.88% at 100:0 ratio occurs due to the removal of moisture and volatiles and oxidations of iron ore. Higher carbon supply at 60:40 leads into better heat and mass transfer and diffusivity during carbothermic reductions. Overall, finer particle size and higher carbon supply improves reactivity and gas-solid interactions resulting in increased reductions and phase transformations.

• 한국재료학회지
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• 제22권11호
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• pp.591-597
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• 2012

For heat exchanger applications, 2-ply clad materials were fabricated by rolling of aluminum (Al) and mild steel sheets. Effects of annealing temperature on interface properties, especially on inter-layer formation and softening of strain hardened mild-steel, for Al/mild steel clad materials, were investigated. To obtain optimum annealing conditions for the Al/mild steel clad materials, annealing temperature was varied from room temperature to $600^{\circ}C$. At the annealing temperature about $450^{\circ}C$, an inter-layer was formed in an island-shape at the interface of the Al/mild steel clad materials; this island expanded along the interface at higher temperature. By analyzing the X-ray diffraction (XRD) peaks and the energy dispersive X-ray spectroscopy (EDX) results, it was determined that the exact chemical stoichiometry for the inter-layer was that of $Fe_2Al_5$. In some samples, an X-layer was formed between the Al and the inter-layer of $Fe_2Al_5$ at high annealing temperature of around $550^{\circ}C$. The existence of an X-layer enhanced the growth of the inter-layer, which resulted in the delamination of the Al/mild-steel clad materials. Hardness tests were also performed to examine the influence of the annealing temperature on the cold deformability, which is a very important property for the deep drawing process of clad materials. The hardness value of mild steel gradually decreased with increasing annealing temperature. Especially, the value of hardness sharply decreased in the temperature range between $525^{\circ}C$ and $550^{\circ}C$. From these results, we can conclude that the optimum annealing temperature is around $550^{\circ}C$ under condition of there being no X-layer creation.

• 대한환경공학회지
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• 제32권10호
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• pp.986-993
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• 2010

본 연구에서는 열처리한 활성알루미나의 불소흡착특성을 분석하였다. 이를 위하여 평형 및 동적 흡착실험을 수행하였고, 용액 pH의 영향과 음이온의 존재에 따른 흡착 특성을 살펴보았다. 또한, 열처리한 활성알루미나의 여재특성을 분석하기 위하여, 전계방출주사현미경(field-emission scanning electron microscope), energy-dispersive spectrometry, X선 회절(X-ray Diffractometer, XRD)분석, 그리고 Brunauer-Emmett-Teller (BET) 비표면적 분석을 수행하였다. 다양한 온도(100, 300, 500, $700^{\circ}C$) 에서 열처리한 활성알루미나의 흡착능을 비교한 결과, 높은 불소 농도(50, 100, 200 mg/L)에서 열처리 온도가 높아짐에 따라서 활성알루미나의 흡착량이 증가하는 것으로 나타났다. 특히, 불소 초기농도 200 mg/L에서는 $700^{\circ}C$에서 고온처리한 활성알루미나(AA700)의 흡착량이 열처리하지 않은 활성알루미나(UAA)보다 3.67배 큰 것으로 나타났다. AA700과 UAA의 BET분석 결과, UAA의 단위질량당 비표면적이 AA700의 비표면적보다 약 2배 큼을 알 수 있었다. XRD 분석결과에 의하면, AA700의 결정구조는 Al2O3인 반면, UAA는 boehmite (AlOOH)와 bayerite ($Al(OH)_3$)가 혼합된 형태로 구성되어 있었다. 열처리에 의하여 비표면적이 감소하였음에도 불구하고, AA700의 불소 흡착능이 UAA에 비하여 증가한 이유는 결정구조의 변화 때문으로 판단된다. AA700의 동역학적 흡착실험결과, 불소의 흡착은 24 h 경과 후에 평형에 도달하였다. 또한, 평형 흡착실험결과에 의하면, 여재 당 불소의 최대 흡착량은 5.70 mg/g으로 나타났다. 용액 pH의 영향을 분석한 결과, pH 7에서 불소 흡착이 가장 높았으며, 산성과 알칼리성에서는 불소 흡착이 감소하는 것으로 나타났다. 음이온의 영향을 분석한 결과, 인산염, 질산염, 중탄산염은 불소 흡착을 감소시키는 것으로 나타났다. 본 연구에 의하면, 상용화된 활성알루미나를 이용하여 불소를 제거할 경우, 고온처리를 통하여 활성알루미나의 흡착능을 증가시킬 수 있을 것으로 판단된다.

• 한국재료학회지
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• 제22권4호
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• pp.190-194
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• 2012

The formation of high-quality polycrystalline silicon (poly-Si) on relatively low cost substrate has been an important issue in the development of thin film solar cells. Poly-Si seed layers were fabricated by an inverse aluminum-induced crystallization (I-AIC) process and the properties of the resulting layer were characterized. The I-AIC process has an advantage of being able to continue the epitaxial growth without an Al layer removing process. An amorphous Si precursor layer was deposited on Corning glass substrates by RF magnetron sputtering system with Ar plasma. Then, Al thin film was deposited by thermal evaporation. An $SiO_2$ diffusion barrier layer was formed between Si and Al layers to control the surface orientation of seed layer. The crystallinity of the poly-Si seed layer was analyzed by Raman spectroscopy and x-ray diffraction (XRD). The grain size and orientation of the poly-Si seed layer were determined by electron back scattering diffraction (EBSD) method. The prepared poly-Si seed layer showed high volume fraction of crystalline Si and <100> orientation. The diffusion barrier layer and processing temperature significantly affected the grain size and orientation of the poly Si seed layer. The shorter oxidation time and lower processing temperature led to a better orientation of the poly-Si seed layer. This study presents the formation mechanism of a poly seed layer by inverse aluminum-induced crystallization.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2010년도 추계학술대회 초록집
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• pp.55.1-55.1
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• 2010

Cost efficient and large area deposition of superior quality $Al_2O_3$ doped zinc oxide (AZO) films is instrumental in many of its applications including solar cell fabrication due to its numerous advantages over ITO films. In this study, AZO films were prepared by a highly efficient rotating cylindrical dc magnetron sputtering system using AZO target, which has a target material utilization above 80%, on glass substrates in argon ambient. A detailed analysis on the electrical, optical and structural characteristics of AZO thin films was carried out for solar cell application. The properties of films were found to critically depend on deposition parameters such as sputtering power, substrate temperature, working pressure, and thickness of the films. A low resistivity of ${\sim}5.5{\times}10-4{\Omega}-cm$ was obtained for films deposited at 2kW, keeping the pressure and substrate temperature constant at 3 mtorr and $230^{\circ}C$ respectively, mainly due to an increase in carrier mobility and large grain size which would reduce the grain boundary scattering. The increase in carrier mobility with power can be attributed to the columnar growth of AZO film with (002) preferred orientation as revealed by XRD analysis. The AZO films showed a high transparency of>87% in the visible wavelength region irrespective of deposition conditions. Our results offers a cost-efficient AZO film deposition method which can fabricate films with significant low resistivity and high transmittance that can find application in thin-film solar cells.

• 한국분말재료학회지
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• 제18권2호
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• pp.112-121
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• 2011

This study investigated the effect of solvent on the fabrication of Ni-free Fe-based alloy nano powders by employing the PWE (pulsed wire evaporation) in liquid and compared the alloy particles fabricated by three different methods (PWE in liquid, PWE in Ar, plasma arc discharge), for high temperature oxidation-resistant metallic porous body for high temperature soot filter system. Three different solvents (ethanol, acetone, distilled water) of liquid were adapted in PWE in liquid process, while X-ray diffraction (XRD), field emission scanning microscope (FE-SEM), and transmission electron microscope (TEM) were used to investigate the characteristics of the Fe-Cr-Al nano powders. The alloy powder synthesized by PWE in ethanol has good particle size and no surface oxidation compared to that of distilled water. Since the Fe-based alloy powders, which were fabricated by PWE in Ar and PAD process, showed surface oxidation by TEM analysis, the PWE in ethanol is the best way to fabricate Fe-based alloy nano powder.

• 한국분말재료학회지
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• 제18권2호
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• pp.105-111
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• 2011

This study investigated the effect of wire diameter and applied voltage on the fabrication of Ni-free Fe-based alloy nano powders by employing the PWE (pulsed wire evaporation) in liquid, for high temperature oxidation-resistant metallic porous body for high temperature particulate matter (or soot) filter system. Three different diameter (0.1, 0.2, and 0.3 mm) of alloy wire and various applied voltages from 0.5 to 3.0 kV were main variables in PWE process, while X-ray diffraction (XRD), field emission scanning microscope (FE-SEM), and transmission electron microscope (TEM) were used to investigate the characteristics of the Fe-Cr-Al nano powders. It was controlled the number of explosion events, since evaporated and condensed nano-particles were coalesced to micron-sized secondary particles, when exceeded to the specific number of explosion events, which were not suitable for metallic porous body preparation. As the diameter of alloy wire increased, the voltage for electrical explosion increased and the size of primary particle decreased.

• 한국주조공학회지
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• 제30권2호
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• pp.60-65
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• 2010

In this study, we investigate the effects of austempering heat treatment on the processing window and mechanical properties in cast and hot-rolled Fe-0.7 C-2.3 Si-0.3 Mn steel. Each specimens were austenitised at $900^{\circ}C$ for 7 min, and austempered at $260^{\circ}C,\;320^{\circ}C$, and $380^{\circ}C$ for the various periods of time from 2 min to 240 min. After heat treatment, the evaluation of stage I and stage II as performed by optical metallography, XRD, hardness test. Both cast and hot rolled specimens had similar processing window. So grain size effect is not important to the austempered high carbon high silicon cast steel. When the austempering temperature was $260^{\circ}C$, the microstructure consisted of the lower ausferrite while the upper ausferrite structure was formed at $380^{\circ}C$. As the austempering temperature increases from 260 to $380^{\circ}C$, the strength and hardness decreased, elongaton and volume fraction of austenite increased. In addition, there was no change of mechanical properties between cast and hot-rolled specimens.

• 한국수소및신에너지학회논문집
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• 제20권5호
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• pp.432-438
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• 2009

In this paper, we synthesized LSG powder by Modified-GNP method. Lanthanum, strontium and gallium (LSG) were selected in the preparation of an oxygen-electrode (anode) for High Temperature Steam Electrolysis system (HTSE). The used amount and concentration of nitric acid were varied to find out an appropriate composition for oxygen-electrode (anode). In order to optimize the molar ratio of La and Sr, ratio of La to Sr was varied that 2:8, 5:5 and 8:2. The combined LSGs were calcined for 2 hours at $700^{\circ}C$ and were sintered in a furnace for 4 hours at $1200^{\circ}C$. The phase and crystallinity of LSG powder were determined by XRD. The surface morphology was observed through SEM photograph, and the specific surface area was investigated with BET. The thermochemical property was determined by TG/DTA. The synthesized preparation was obtained of $La_{0.8}Sr_{0.2}GaO_{3}$ formula for 3M nitric acid, which was the best perovskite phase.