• 폴리머
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• 제24권3호
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• pp.399-406
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• 2000

히드로퀴논과 p-히드록시 벤조산, 그리고 1,6-디브로모헥산을 이용하여 유연한 알킬기를 주사슬에 가지는 열방성 액정 고분자(TLCP)를 얻었다. TLCP의 녹음 전이온도 이상에서 도데실 암모니움-몬모릴로나이트(C$_{12}$-MMT)를 첨가하여 나노복합재료를 만들었다. $C_{12}$-MMT를 TLCP에 대해 1 wt%만 섞어도 액정성은 파괴되었으며, 그 이상의 $C_{12}$-MMT양에 대해서도 마찬가지였다. 첨가된 $C_{12}$-MMT중 일부는 TLCP에 잘 분산되었으나, 일부는 뭉쳐진 형태로 존재하였다. 합성된 나노복합재료의 열적 성질과 몰폴로지는 시차주사 열분석기 (DSC), 열중량 분석기 (TGA), 편광 현미경, 그리고 전자 현미경 (SEM, TEM) 등을 이용하여 분석하였다.다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제45회 하계 정기학술대회 초록집
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• pp.190.2-190.2
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• 2013

Vanadium dioxide ($VO_2$) has been widely attracted for academic research and industrial applications due to its metal-insulator transition (MIT) temperature close to room temperature. We synthesized VOx film on (0001) sapphire substrate with vanadium target (purity: 99.9%) using DC magnetron sputtering in Ar ambience at a pressure of $10^{-3}$ Torr at $400{\sim}700^{\circ}C$. The VOx film subsequently was annealed at difference temperatures in ambience of Ar and $O_2$ gas mixture at $60{\sim}800^{\circ}C$. The structural properties of the films were investigated using scanning electron microscopic (SEM), x-ray diffraction (XRD) and x-ray absorption fine structure (XAFS) measurements. SEM reveal that small grains formed on the substrates with a roughness surface. XRD shows oriented $VO_2$(020) crystals was deposited on the $Al_2O_3$(006) substrate. From I-V measurements, the electric resistance near its MIT temperature were dramatically changed by ${\sim}10^4$ during heating and cooling the films. We will also discuss the temperature-dependent local structural changes around vanadium atoms using XAFS measurements.

• 한국재료학회지
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• 제18권1호
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• pp.22-25
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• 2008

In this study, calcium titanate $(CaTiO_3)$ gel was prepared by mixing calcium nitrate and titanium isopropoxide in 2-methoxy-ethanol. $CaTiO_3$ gel was single-layer coated on Ti-6Al-4V using a sol-gel dip-coating technique. The coating was calcined at $750^{\circ}C$ in air by utilizing a very slow heating rate of $2^{\circ}C/min$. The crystalline phases of the coating were characterized by x-ray diffraction using a slow scan rate of $1^{\circ}/min$. The morphology of the coating was analyzed by scanning electron microscopy. The corrosion behavior of Ti-6Al-4V samples coated with $CaTiO_3$ films were tested in an artificial saliva solution by potentiodynamic polarization and were quantified by the Tafel extrapolation method. The electrochemical parameters showed a considerable increase in the corrosion resistance for the $CaTiO_3$-coated Ti-6Al-4V samples compared to bare substrates.

• 한국레이저가공학회지
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• 제18권1호
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• pp.12-17
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• 2015

This work performed numerical analysis of electromagnetic field and thermal phenomena occurring in femtosecond laser irradiation of silver nanowires. The local electric field enhancement was computed to calculate the optical energy dissipation as a Joule heating source and the thermal transport was analysed based on the two-temperature model (TTM). Electron temperature increased up to 1000K after 50fs and its spatial distribution became homogeneous after 80fs at the fluence of 100mJ/cm2. The result of this work is expected to contribute to revealing the photothermal effects on silver nanowires induced by femtosecond laser irradiation. Although the highest increase of lattice temperature was substantially below the melting point of silver, the experimental results showed resolidification and fragmentation of the silver nanowire into nanoparticles, which cannot be explained by the photothermal mechanism. Further studies are thus needed to clarify the physical mechanisms.

• 대한금속재료학회지
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• 제50권8호
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• pp.575-582
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• 2012

Medium carbon steel was aluminized by hot dipping into molten Al or Al-1 at% Si baths. After hot-dipping in these baths, a thin Al-rich topcoat and a thick alloy layer rich in $Al_5Fe_2$ formed on the surface. A small amount of FeAl and $Al_3Fe$ was incorporated in the alloy layer. Silicon from the Al-1 at% Si bath was uniformly distributed throughout the entire coating. The hot dipping increased the microhardness of the steel by about 8 times. Heating at $700-1000^{\circ}C$, however, decreased the microhardness through interdiffusion between the coating and the substrate. The oxidation at $700-1000^{\circ}C$ in air formed a thin protective ${\alpha}-Al_2O_3$ layer, which provided good oxidation resistance. Silicon was oxidized to amorphous silica, exhibiting a glassy oxide surface.

• Bulletin of the Korean Chemical Society
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• 제18권9호
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• pp.929-933
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• 1997

Morphological studies in the micro-end-to-end (m-E-E) and micro-side-by-side (m-S-S) aggregations were conducted by using of scanning electron microscope (SEM) for the samples precipitated by heating of the end-products of the transition of FormⅡ (left-handed helix, three peptides per turn, 31) Form Ⅰ (right-handed helix, 3.3 peptides per turn, 103) in poly(L-proline) (PLP) in acetic acid(water)-propanol (1:9 v/v) solvent. The observed morphology for the solide state shows a rope (or super helical) type and pebbles type aggregate for the (m-E-E) and (m-S-S) aggregate respectively. The viscosities were also measured during the heat-precipitation in order to elucidate the process of formation of the rope- and pebbles-type aggregates. The result for the (m-E-E) aggregations exhibit two steps, i.e., at first, the viscosity increases with time (step 1), thereafter it decrease until attain the last value (step 2). But the (m-S-S) aggregations show only one step in the decreases in viscosity. On the bases of all experimental results it is possible to propose a reasonable mechanism for the formation of the two types of aggregates of the (m-E-E) and (m-S-S).

• 한국태양에너지학회 논문집
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• 제35권1호
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• pp.89-96
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• 2015

n-octadecnae based shape stabilized phase change material (SSPCM) was prepared by using vacuum impregnation method. And an exfoliated graphite nanoplate (xGnP) which has high thermal conductivity properties is used as a PCM container. And then we made heat storage concretes which contains SSPCM for reducing heating and cooling load in buildings. In the prepararion process, the SSPCM was mixed to a concrete as 10, 20 and 30wt% of cement weight. The thermal properties and chemical properties of heat storage concrete were analyzed from Scanning electron microscope (SEM), Fourier transformation infrared spectrophotometer (FT-IR), Deferential scanning calorimeter (DSC), Thermogravimetric analysis (TGA) and TCi thermal conductivity analyzer. And we conducted surface temperature analysis of SSPCM and xGnP by using heat plate and insulation mold.

• 대한금속재료학회지
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• 제48권2호
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• pp.180-186
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• 2010

For the application of field emission display (FED), it is essential to develop a carbon nanotube (CNT) cathode with high emission current density. In this study, we developed and demonstrated a post-heat treatment (PHT) process to improve field emission properties of CNT cathodes. Since the PHT is intended to burn out organic materials covering the CNTs, the PHT was carried out by heating samples at a high temperature in an atmosphere. The PHT process is applied for samples processed by surface treatment with an adhesive tape. Compared to samples prior to the PHT, samples after the PHT at $360^{\circ}C$ showed about 17% improvement in emission current density. The major reason for the increased current density is mainly the increased aspect ratio of the CNTs because of the removal of the adhesive organic residues covering the CNTs, which were attached on the CNT surfaces during the surface treatment using the adhesive taping method.

• Journal of the Korean Physical Society
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• 제73권9호
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• pp.1334-1339
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• 2018

Spherical nickel ferrite nanoparticles were synthesized using the thermal decomposition method and coated with cetyl trimethyl ammonium bromide (CTAB) after the synthesis. Transmission electron microscopy images showed that the average diameter of the particles was 9.40 nm. The status of the CTAB-coating on the surface of the particles was checked using Fourier-transform infrared spectroscopy. Their hysteresis curve showed that the particles exhibited a superparamagnetic behavior. The $T_1$ and the $T_2$ relaxations of the nuclear spins were observed in aqueous solutions of the particles with different particles concentrations by using a magnetic resonance imaging (MRI) scanner, which showed that the $T_1$ and the $T_2$ relaxivities of the particles in water were $0.57mM^{-1}{\cdot}s^{-1}$ and $10.42mM^{-1}{\cdot}s^{-1}$, respectively. In addition, using an induction heating system, we evaluated their potentials for magnetic hyperthermia applications. The aqueous solution of the particles with a moderate concentration (smaller than 6.5 mg/mL) showed a saturation temperature larger than the hyperthermia target temperature of $42^{\circ}C$. These findings show that the CTAB-coated nickel ferrite particles are suitable for applications as $T_2$ contrast agents in MRI and heat generators in magnetic hyperthermia.

• 한국분말재료학회지
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• 제29권6호
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• pp.485-491
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• 2022

Lithium lanthanum titanium oxide (LLTO) is a promising ceramic electrolyte because of its high ionic conductivity at room temperature, low electrical conductivity, and outstanding physical properties. Several routes for the synthesis of bulk LLTO are known, in particular, solid-state synthesis and sol-gel method. However, the extremely low ionic conductivity of LLTO at grain boundaries is one of the major problems for practical applications. To diminish the grain boundary effect, the structure of LLTO is tuned to nanoscale morphology with structures of different dimensionalities (0D spheres, and 1D tubes and wires); this strategy has great potential to enhance the ion conduction by intensifying Li diffusion and minimizing the grain boundary resistance. Therefore, in this work, 0D spherical LLTO is synthesized using ultrasonic spray pyrolysis (USP). The USP method primarily yields spherical particles from the droplets generated by ultrasonic waves passed through several heating zones. LLTO is synthesized using USP, and the effects of each precursor and their mechanisms as well as synthesis parameters are analyzed and discussed to optimize the synthesis. The phase structure of the obtained materials is analyzed using X-ray diffraction, and their morphology and particle size are analyzed using field-emission scanning electron microscopy.