• Carbon letters
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• 제13권2호
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• pp.130-132
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• 2012

In this study, cobalt oxide ($Co_3O_4$)/graphene composites were synthesized through a simple chemical method at various calcination temperatures. We controlled the crystallinity, particle size and morphology of cobalt oxide on graphene materials by changing the annealing temperatures (200, 300, $400^{\circ}C$). The nanostructured $Co_3O_4$/graphene hybrid materials were studied to measure the electrochemical performance through cyclic voltammetry. The $Co_3O_4$/graphene sample obtained at $200^{\circ}C$ showed the highest capacitance of 396 $Fg^{-1}$ at 5 $mVs^{-1}$. The morphological structures of composites were also examined by scanning electron microscopy and transmission electron microscopy (TEM). Annealing $Co_3O_4$/graphene samples in air at different temperatures significantly changed the morphology of the composites. The flower-like cobalt oxides with higher crystallinity and larger particle size were generated on graphene according to the increase of calcination temperature. A TEM analysis of the composites at $200^{\circ}C$ revealed that nanoscale $Co_3O_4$ (~7 nm) particles were deposited on the surface of the graphene. The improved electrochemical performance was attributed to a combination effect of graphene and pseudocapacitive effect of $Co_3O_4$.

• 한국세라믹학회지
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• 제44권10호
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• pp.580-584
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• 2007

The ZrC layer instead of SiC layer is a critical and essential layer in TRISO coated fuel particles since it is a protective layer against diffusion of fission products and provides mechanical strength for the fuel particle. In this study, we carried out computational simulation before actual experiment. With these simulation results, Zirconium carbide (ZrC) films were chemically vapor deposited on $ZrO_2$ substrate using zirconium tetrachloride $(ZrCl_4),\;CH_4$ as a source and $H_2$ dilution gas, respectively. The change of input gas ratio was correlated with growth rate and morphology of deposited ZrC films. The growth rate of ZrC films increased as the input gas ratio decreased. The microstructure of ZrC films was changed with input gas ratio; small granular type grain structure was exhibited at the low input gas ratio. Angular type structure of increased grain size was observed at the high input gas ratio.

• 한국입자에어로졸학회지
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• 제15권4호
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• pp.183-190
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• 2019

Here, we introduce porous graphene balls (PGB) showing superior electrochemical properties as supercapacitor electrode materials. PGB was fabricated via activation of graphene oxides (GO) by H₂O₂ and aerosol spray drying in series. Effect of activation on the morphology, specific surface area, pore volume, and electrochemical properties were investigated. As-prepared PGB showed spherical morphology containing pores, which lead to the effective prevention of restacking in graphene sheets. It also exhibited a large surface area, unique porous structures, and high electrical conductivity. The electrochemical properties of the PGB as electrode materials of supercapacitor are investigated by using aqueous KOH under symmetric two-electrode system. The highest specific capacitance of PGB was 279 F/g at 0.1 A/g. In addition, the high rate capability (93.8% retention) and long-term cycling stability (92.2%) of the PGB were found due to the facilitated ion mobility between the porous graphene layers.

• 한국결정성장학회지
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• 제15권3호
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• pp.99-103
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• 2005

NaCl-KCl을 flux로 사용한 용융염 합성법을 이용하여 $Pb(Sc_{1/2}Ta_{1/2})O_3$, 분말을 제조하였다. $700^{\circ}C$에서 $800^{\circ}C$의 온도범위에서 상형성 및 분말 상태의 변화를 조사하였다. 용융염 합성법으로 $750^{\circ}C$ 2시간 하소하였을 때, 순수한 페로브스카이트 구조를 가진 $Pb(Sc_{1/2}Ta_{1/2})O_3$ 상이 형성되었으며, 평균 입자 크기는 $0.5\{mu}m$ 이하이고 입방체와 유사한 형상을 갖는 분말이 제조되었다. DIA, X-선 회절 분석, 미세구조 변화를 통해 합성된 분말의 특성을 고찰하였다.

• 한국입자에어로졸학회지
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• 제11권3호
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• pp.87-92
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• 2015

MCM-41 (Mobil Composition of Matter) and SBA-15 (Santa Barbara Amorphous) were used as a supported catalyst for ethylene polymerization due to their combination of large surface area and wide range of pore size distribution. The morphology of supports was used to control the morphology of the resulting polymer. Different molar ratios of Al/Ti were used for ethylene polymerization at $60^{\circ}C$ under atmospheric pressure. The effect of different mass ratios of MCM-41/SBA-15 and 1-hexene concentration on polymerization activity and polymer properties was investigated. The catalytic activity and the crystallinity reached the highest value at Al/Ti of 480. Upon incorporation of MCM-41 and SBA-15 into $MgCl_2/TiCl_4$ catalyst, the molecular weight and crystallinity of polyethylene were enhanced. The obtained polyethylene showed melting temperature between 130 and $135^{\circ}C$. The polyethylene with replication structure of support and bimodal MWD was expected.

• 한국초전도ㆍ저온공학회논문지
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• 제10권1호
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• pp.19-23
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• 2008

Spherical $MgB_2$ powders was synthesized with the ultrasonic spray pyrolysis(USP) process using aqueous solutions of boron and magnesium ion. The properties of synthesized $MgB_2$ powder were characterized by XRD, SEM and EDS. A small amount of MgO was detected as the secondary phase out of the synthesized powder and the ratios of $MgB_2$ to MgO increased with increasing furnace temperature. The particle size and morphology of $MgB_2$ powder were investigated with varying molar concentration of the boron and magnesium solution and furnace temperature between $600^{\circ}C$ and $1000^{\circ}C$ in $Ar/H_2$. The average particle size of $MgB_2$ showed narrow distribution ranging from 300nm to 400nm. The morphology of particles exhibited mostly spherical shapes and uniform distribution.

• Corrosion Science and Technology
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• 제23권1호
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• pp.54-63
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• 2024

This work investigated the influence of concentration and applied potential on the characteristics of zinc powder (purity, apparent density, morphology, particle size distribution, and particle zeta potential) produced by the electrochemical process from waste brass. High-purity zinc powder is obtained using selective leaching of industrial brass waste in acidic, neutral, and alkaline solutions. The free immersion method with and without voltage using linear polarization technique is used. In the electrochemical process, hydrochloric acid HCl in three different concentrations (0.1, 0.2, and 0.3) M is used. The time and the distance between the electrodes are set to be 30 min and 3 cm, respectively. It has been found that the percentage purity is 98%, 96%, and 94% for the acidic, neutral, and alkaline solutions, respectively. In addition, the morphology of zinc powder analyzed by SEM was dendritic and mossy. It has been recorded that the purity of zinc increases with the increase of the concentration and applied potential. The highest value of purity for zinc powder was %98.58 in 1000 mV and 0.3M concentration for graphite cathode.

• 항공우주시스템공학회지
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• 제13권2호
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• pp.34-42
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• 2019

열을 이용한 접합은 소재 간 열역학적 차이에 의한 열 변형 및 잔류응력 등 원하지 않은 결과를 야기한다. 폭발력 또는 전자기력을 이용한 고상 접합은 열이 사용되지 않아 열역학적 차이가 있는 소재접합에 이점이 있다. 이때, 해당 접합은 짧은 시간 내(${\mu}s$) 이루어지며, 접합면에서 고속 및 대 변형이 동반된다. 수치해석 모델은 고속 충돌 접합 메커니즘을 이해하는 데 중요한 역할을 수행한다. 하지만 고속 및 대 변형이 나타나는 해석에서 전통적인 라그랑지안 기법은 격자 얽힘이 발생해 결과의 신뢰성이 낮다. 본 연구는 무격자 수치해석 방식의 SPH(Smoothed Particle Hydrodynamics)를 이용하여 열역학적 차이가 있는 Cu와 CP-Ti의 고속 충돌 접합을 수행하였고 경계면 결합 형상이 발생함을 확인하였다. 해석의 결과로 경계면 결합 형상이 매개변수(충돌 속도, 충돌 각도)의 관계에 따라 형상의 정도(직선, 소용돌이), 주기, 길이 등이 다르게 나타나는 것을 확인 및 비교하였다.

• 한국수소및신에너지학회논문집
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• 제19권4호
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• pp.305-312
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• 2008

ZnO/Zn redox cycle is the one of the promising thermochemical cycles for hydrogen production via water splitting with high temperature heat source like a concentrated solar energy. This paper reports the particle size effect of Zinc on water splitting behavior. Water splitting reaction experiments were carried out at isothermal conditions of 350 and 400$^{\circ}C$ in TGA (Thermo Gravimetric Analyzer) using four commercial Zinc powders (nano, <10 ${\mu}m$, <150 ${\mu}m$ and $150{\sim}600\;{\mu}m$ particle sizes). Before the experiments, average particle size of Zinc powders was analyzed by PSA (Particle Size Analysis). After the experiments, XRD (X-Ray Diffraction) and SEM (Scanning Electron Microscope) analyses were conducted on the samples. The experimental results showed that particle size had a effect on the conversion of Zinc to ZnO. Zinc conversion was increased, as the particle size decreased. Especially, the nano size particles were aggregated and the particle's morphology changed on the surface during hydrolysis reaction.

• 폴리머
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• 제30권1호
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• pp.50-55
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• 2006

분산중합으로 제조된 폴리스티렌(PS) 시드 고분자 미립자에 가교단량체인 HDDA(1,6-hexanedioldiacrylate)를 one-step으로 흡수시키고 이를 중합하여 단분산 가교고분자 미립자를 제조할 시 1) 시드 고분자의 분자량, 2) 흡수된 가교단량체와 시드의 중량비, 3) 중합반응속도 등의 변화에 따른 가교고분자 입자의 표면 모폴로지 변화 등을 관찰하였다. 이번 연구를 통해 PS/HDDA계에서는 시드 고분자의 분자량 및 가교단량체 흡수비에 관계없이 가교고분자 입자표면에 분화구 형태의 모폴로지가 관찰되었으며, 이와 같은 표면 모폴로지는 중합반응속도를 조절함으로써 조절이 가능함을 알 수 있었다.