• 한국결정성장학회지
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• 제14권3호
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• pp.83-89
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• 2004

본 연구에서는 우수한 생체적합성과 높은 기계적 성질을 갖는 아파타이트 생체세라믹스를 제조하기 위하여 수산화아파타이트(HA, $Ca_{10}(PO_4)_6(OH)_2/TiO_2$ 생체복합분말을 제조하였다. HA/$TiO_2$ 생체복합분말은 침전법과 졸겔법으로 각각 제조된 $TiO_2$ 분말과 수열합성법으로 제조된 HA 분말을 1:1의 무게분율로 혼합하여 제조하였다. HA/$TiO_2$ 생체복합분말은 $TiO_2$와 HA 입자의 크기와 모양에 따라 미세구조의 차이를 나타냈으며, $TiO_2$와 HA의 입자 크기가 서로 다른 복합분말의 경우, 작은 입자는 큰 입자의 표면에 둘러싸고 있었으나, $TiO_2$와 HA의 입자 크기가 비슷한 복합분말의 경우, $TiO_2$와 HA 입자가 서로 분산되어 균일한 미세구조를 가지고 있었다 균질한 미세구조를 갖는 복합분말은 소결체 제조 시 높은-소결밀도와 우수한 기계적 특성을 나타내었다.

• 한국자기학회지
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• 제17권2호
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• pp.71-75
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• 2007

계면활성제를 첨가한 음향화학적 침전법으로 두 가지 크기의 아연페라이트 나노입자를 합성하였다. 열분석장치(TGA/DSC)를 이용하여 열적 특성 및 결정화 온도를 조사하였고, 결정구조 확인을 위하여 X선 회절실험을 실시하였다. 제조된 입자는 $240^{\circ}C$ 부근에서 결정생성이 시작되었으며, 결정구조는 전형적인 스피넬 구조를 나타내었다. Scherrer식에 의해 측정된 입자의 크기는 11.2nm와 13.4nm이었다. SQUID를 통하여 자기적 성질을 분석한 결과, 작은 크기의 입자에 대한 방해온도 $T_B$(Blocking temperature)가 큰 입자의 경우보다 더 높게 나타났다.

• 한국환경과학회지
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• 제26권1호
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• pp.67-78
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• 2017

Combustion of ethanol (EtOH) at low temperatures has been studied using titania- and silica-supported platinum nanocrystallites with different sizes in a wide range of 1~25 nm, to see if EtOH can be used as a clean, alternative fuel, i.e., one that does not emit sulfur oxides, fine particulates and nitrogen oxides, and if the combustion flue gas can be used for directly heating the interior of greenhouses. The results of $H_2-N_2O$ titration on the supported Pt catalysts with no calcination indicate a metal dispersion of $0.97{\pm}0.1$, corresponding to ca. 1.2 nm, while the calcination of 0.65% $Pt/SiO_2$ at 600 and $900^{\circ}C$ gives the respective sizes of 13.7 and 24.6 nm when using X-ray diffraction technique, as expected. A comparison of EtOH combustion using $Pt/TiO_2$ and $Pt/SiO_2$ catalysts with the same metal content, dispersion and nanoparticle size discloses that the former is better at all temperatures up to $200^{\circ}C$, suggesting that some acid sites can play a role for the combustion. There is a noticeable difference in the combustion characteristics of EtOH at $80{\sim}200^{\circ}C$ between samples of 0.65% $Pt/SiO_2$ consisting of different metal particle sizes; the catalyst with larger platinum nanoparticles shows higher intrinsic activity. Besides the formation of $CO_2$, low-temperature combustion of EtOH can lead to many other pathways that generate undesired byproducts, such as formaldehyde, acetaldehyde, acetic acid, diethyl ether, and ethylene, depending strongly on the catalyst and reaction conditions. A 0.65% $Pt/SiO_2$ catalyst with a Pt crystallite size of 24.6 nm shows stable performances in EtOH combustion at $120^{\circ}C$ even for 12 h, regardless of the space velocity allowed.

• 한국자기학회지
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• 제16권3호
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• pp.163-167
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• 2006

초음파 조사 및 계면활성제 첨가에 따른 입자의 변화를 연구하기 위하여 침전법, 음향화학적 침전법 그리고 게면활성제를 첨가한 음향화학적 침전법으로 나노 입자를 합성하였고, X-선 회절실험을 통하여 마그네타이트가 합성된 것을 확인하였다. 침전법, 음향화학적 침전법으로 합성한 입자의 크기는 계면활성제를 첨가한 음향화학적 침전법으로 합성한 입자보다 크게 얻어졌고, 초음파 출력이 증가 할수록 크기는 증가하였다. 계면활성제로 올레인 산을 첨가한 음향화학적 기법에서는 게면활성제의 농도에 따라 입자 크기를 선택적으로 조절하여 합성할 수 있었고, 단순 침전법이나 음향화학적 기법에서 보다 생성되는 입자의 크기 분포가 좁게 나타났다. 마그네타이트 나노 입자들의 자기적 특성을 SQUID를 통하여 분석한 결과, 실온에서 모두 초상자성 거동을 보이는 것으로 나타났다.

• Current Photovoltaic Research
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• 제2권3호
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• pp.103-109
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• 2014

Highly efficient hydrogenated nanocrystalline silicon (nc-Si:H) thin-film solar cells were prepared on flexible stainless steel substrates using plasma-enhanced chemical vapor deposition. To enhance the performance of solar cells, material properties of back reflectors, n-doped seed layers and wide bandgap nc-SiC:H window layers were optimized. The light scattering efficiency of Ag back reflectors was improved by increasing the surface roughness of the films deposited at elevated substrate temperatures. Using the n-doped seed layers with high crystallinity, the initial crystal growth of intrinsic nc-Si:H absorber layers was improved, resulting in the elimination of the defect-dense amorphous regions at the n/i interfaces. The nc-SiC:H window layers with high bandgap over 2.2 eV were deposited under high hydrogen dilution conditions. The vertical current flow of the films was enhanced by the formation of Si nanocrystallites in the amorphous SiC:H matrix. Under optimized conditions, a high conversion efficiency of 9.13% ($V_{oc}=0.52$, $J_{sc}=25.45mA/cm^2$, FF = 0.69) was achieved for the flexible nc-Si:H thin-film solar cells.

• Advances in nano research
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• 제3권2호
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• pp.97-109
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• 2015

Citrate ion is a commonly used reductant in metal colloid synthesis, undergoes strong surface interaction with silver nanocrystallites. The slow crystal growth observed as a result of the interaction between the silver surface and the citrate ion makes this reduction process unique compared to other chemical and radiolytic synthetic methods. The antimicrobial effects of silver (Ag) ion or salts are well known, but the effects of citrate coated Ag nanoparticles (CAgNPs) are scant. Herein, we have isolated biofilm causative bacteria and fungi from drinking water PVC pipe lines. Stable CAgNPs were prepared and the formation of CAgNPs was confirmed by UV-visible spectroscopic analysis and recorded the localized surface plasmon resonance of CAgNPs at 430 nm. Fourier transform infrared spectroscopic analysis revealed C=O and O-H bending vibrations due to organic capping of silver responsible for the reduction and stabilization of the CAgNPs. X-ray diffraction micrograph indicated the face centered cubic structure of the formed CAgNPs, and morphological studies including size (average size 50 nm) were carried out using transmission electron microscopy. The hydrodynamic diameter (60.7 nm) and zeta potential (-27.6 mV) were measured using the dynamic light scattering technique. The antimicrobial activity of CAgNPs was evaluated (in vitro) against the isolated fungi, Gram-negative and Gram-positive bacteria using disc diffusion method and results revealed that CAgNPs with 170ppm concentration are having significant antimicrobial effects against an array of microbes tested.

• 한국세라믹학회지
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• 제48권5호
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• pp.439-446
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• 2011

Yttria stabilized zirconia (YSZ) coating was formed on AA1050 Al alloys by aerosol deposition (AD), and its electrochemical corrosion properties were investigated in 3.5 wt% NaCl and 0.5M $H_2SO_4$ solutions. The crack-free, dense, and ~5 ${\mu}m$ thick YSZ coating was successfully obtained by AD. The as-deposited coating was composed of cubic-YSZ nanocrystallites of ~10 nm size. The potentiodynamic test indicated that the YSZ coated Al alloy had much lower corrosion current densities (2 nA/$cm^2$) by comparison to uncoated sample and exhibited a passive behavior in anodic branch. Particularly, a pitting breakdown potential could not be identified in $H_2SO_4$. EIS tests revealed that the impedance of YSZ coated sample was ${\sim}10^6{\Omega}cm^2$ in NaCl and ${\sim}10^7{\Omega}cm^2$ in $H_2SO_4$, which was about 3 or 4 orders of magnitude higher than that of uncoated sample. Consequently, the corrosion resistance of Al alloy had been significantly enhanced by the YSZ coating.

• 한국표면공학회지
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• 제38권3호
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• pp.100-105
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• 2005

Cr-Si-C-N coatings were deposited on steel substrate (SKD 11) by a hybrid system of arc ion plating (AIP) and sputtering techniques. From XRD, XPS, and HRTEM analyses, it was found that Cr-Si-C-N had a fine composite microstructure comprising nano-sized crystallites of Cr(C, N) well distributed in the amorphous phase of $Si_3N_4/SiC$ mixture. Microhardness of Cr(C, N) coatings and Cr-Si-N coatings were reported about $\~22 GPa$ and $\~35 GPa$, respectively. As the Si was incorporated into Cr(C, N) coatings, The Cr-Si-C-N coatings having a Si content of $9.2 at.\%$ showed the maximum hardness value. As increased beyond Si content of $9.2 at.\%$, the interaction between nanocrystallites and amorphous phase was gone, the hardness was reduced as dependent on amorphous phase of $Si_3N_4/SiC$. In addition, the average coefficient of Cr-Si-C-N coatings largely decreased compared with Cr(C, N) coatings.

• 한국표면공학회지
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• 제56권1호
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• pp.62-68
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• 2023

Silicon (Si) is considered as a promising substitute for the conventional graphite due to its high theoretical specific capacity (3579 mAh/g, Li₁₅Si₄) and proper working voltage (~0.3V vs Li⁺/Li). However, the large volume change of Si during (de)lithiation brings about severe degradation of battery performances, rendering it difficult to be applied in the practical battery directly. As a one feasible candidate of industrial Si anode, silicon monoxide (SiO_x) demonstrates great electrochemical stability with its specialized strategy, downsized Si nanocrystallites surrounded by Li⁺ inactive buffer phase (Li₂O and Li₄SiO₄). Nevertheless, SiO_x inherently has the initial irreversible capacity and poor electrical conductivity. To overcome those issues, conformal carbon coating has been performed on SiO_x utilizing ethylbenzene as the carbon precursor of chemical vapor deposition (CVD). Through various characterizations, it is confirmed that the carbon is homogeneously coated on the surface of SiO_x. Accordingly, the carbon-coated SiOx from CVD using ethylbenzene demonstrates 73% of the first cycle efficiency and great cycle life (88.1% capacity retention at 50th cycle). This work provides a promising synthetic route of the uniform and scalable carbon coating on Si anode for high-energy density.