• Journal of Convergence for Information Technology
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• v.8 no.5
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• pp.95-100
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• 2018

The metal oxide/graphene nanocomposites are promising functional materials for high capacitive electrode material of secondary batteries, and high sensitive material of high performance gas sensors. In this study, vanadium dioxide($VO_2$) nanostructrures were grown on CVD graphene which was synthesized on Cu foil by thermal CVD, and exfoliated graphene which was exfoliated from highly oriented pyrolytic graphite(HOPG) using a vapor transport method. As results, $VO_2$ nanostructures on CVD graphene were grown preferential growth on abundant functional groups of graphene grain boundaries. The functional groups are served to nucleation site of $VO_2$ nanostructures. On the other hand, 2D & 3D $VO_2$ nanostructures were grown on exfoliated graphene due to uniformly distributed functional groups on exfoliated graphene surface. The characteristics of morphology controlled growth of $VO_2$/graphene nanocomposites would be applied to fabrication process for high capacitive electrode materials of secondary batteries, and high sensitive materials of gas sensors.

• Applied Chemistry for Engineering
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• v.23 no.2
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• pp.195-203
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• 2012

Recycling method of waste LCD glass is the essential process for developing the total recycling process of LCD pannel. Pulverizing of LCD glass, determination of proper carbonacious foaming agent, the properties of residue from the recovery of valuable materials through an acid leaching process and the feasibility for the foaming of the residue obtained from leaching for indium and tin recovery were investigated for the developing of recycling method of waste LCD glass as industrial feed materials, such as heat insulation materials, sound absorbing materials, carrier of water treatment. Waste LCD glass could be pulverized finely for foaming process. Natural graphite was proper agent for foaming of the residue and the foaming technology of LCD glass would be effective recycling alternatives.

• Applied Chemistry for Engineering
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• v.9 no.7
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• pp.1059-1064
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• 1998

We have investigated various kind of graphite and MCMB6-28 to develop carbon negative electrode for lithium ion secondary battery. The interlayer length of them was $3.358{\sim}3.363{\AA}$ and the BET specific surface area was $2.95{\sim}26.15m^2/g$. From this study, When the interlayer of them was large and the BET specific surface area was high, the electrochemical characteristics of them was very excellent. Adding 0, 3, 5, wt% of KJ-Black as conducting agent to various graphitic carbon active materials, interface resistance of electrode and electrolyte was less, but rechargeability was better at 3 wt%. At constant current charge and discharge test, discharge capacity was small according to large current.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.10a
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• pp.40.2-40.2
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• 2011

초경합금은 경도가 높은 재료를 말하며 일반적으로는 탄화텅스텐(WC)계 재료를 말한다. 국내 현재 초경합금 동향은 반도체 산업, 내마모성 공구, 절삭공구, 금형 등 많은 분야에 사용되어지고 있다. 또한 최근 들어 FSW (Friction Stir Welding, FSW)기술이 발전함에 따라 접합기술개발이 다양화되면서 FSW Tool의 고성능의 초경 재료가 요구되어지며 장수명의 Tool개발이 되어야 한다. 국내에서는 초경 합금 재료로 사용되어지고 있는 텅스텐 카바이드(WC)와 코발트(Co)를 이용하여 많은 연구가 진행되었다. 본 실험에서는 텅스텐 카바이드와 코발트 및 몰르브덴 카바이드를 혼합하여 소결체를 제조하였다. 실험에 사용된 텅스텐 카바이드는 높은 경도를 가지고 강한 취성을 나타내며, 소결에 어려운 단점이 있다. 이러한 단점을 코발트와 몰리브덴 카바이드를 첨가하여 소결온도를 낮춰주는 역할과 액상 소결시 텅스텐카바이드 입자사이에 침투하여 액상소결에 의한 치밀화가 가능하게 해주며 인성이 향상되어 고인성 재료를 만들 수 있었다. 본 실험에서는 합성과 치밀화가 동시에 진행되는 SPS (Spark Plasma Sintering:SPS) 장비를 이용하여 실험을 진행하였다. 이 방법은 방전플라즈마 소결 공법으로, 기존의 연소법과 열간 가압기술(Hot-press, HIP)을 결합한 방식으로 단 시간, 단일공정으로 치밀한 소결체를 얻을 수 있는 장점이 있다. 본 연구에서는 $WC-5Mo_2C$-5wt%Co 소결체 제조를 위해 원소 분말을 Horizontal ball milling 혼합하였다. 균일하게 혼합된 분말을 흑연다이에 충진하여 펄스전류와 기계적 압력을 동시에 가하여 $WC-5Mo_2C-5Co$ 복합재료를 제조하고 소결체의 밀도, 순도, 상변태, 미세조직 등을 분석 및 평가하였다. SPS공정 조건은 고진공하에서 $1,200^{\circ}C$-60MPa, 펄스비 12:1 조건으로 수행하였으며, 얻어진 $WC-5Mo_2C-5Co$ 소결체의 상대 밀도는 98%이상 이였다. 또한, 결정립 크기는 약 400 nm였으며, 경도는 $2,453kg/mm^2$를 나타내었다.

• Korean Journal of Crystallography
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• v.7 no.1
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• pp.36-43
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• 1996

The crystal structure Tris(ethylenediamine)nickel(II)Dichromate has been determined by X-ray crystallography. Crystal data: a=8.268(2), b=13.865(2), c=14.921(2)Å, γ=102.04(2)°, V=1672.9(5)Å3, Z=4, Monocline, P21/b (space group No.=14), Dcalc=1.806 gcm-3, μ=24.05 cm-0.1. The intensity data were collected with Mo-Kα radiation(λ=0.7107Å) on an automatic four-circle diffractometer with a graphite monochromator. The structure was solved by Patterson method and refined by full matrix least-square methods using unit weights. The final R and S values were R=0.045, Rw=0.051, Rall=0.059 and S=2.171for 2248 observed reflections. The two carbon atoms of a ring of Ni(en)-ion were split into crossed four atoms. In consideration of α- and β-angles of two rings of a disordered ethylenediamine of Nien3-ion and the hydrogen bonds between Ni(en)3-cation and Cr2O7-anion, the configuration of Ni(en)3-ion is assumed to be disordered with Λδδδ and Λδδλ.

• Journal of the Korean Electrochemical Society
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• v.24 no.4
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• pp.77-92
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• 2021

The energy density of lithium-ion batteries (LIBs) determines the mileage of electric vehicles. For increasing the energy density of LIBs, it is necessary to develop high-capacity active materials that can store more lithium ions within constrained weight. The rapid progress made in cathode technology has realized the utilization of the near-theoretical capacity of cathode materials. In contrast, commercial LIBs have still exploited graphite as active material in anodes since the 1990s. The most promising way to increase anodes' capacity is to mix high-capacity and long-cycle-life silicon oxides (SiOx) with graphite. However, the low initial Coulombic efficiency (ICE) of SiOx limits its content below 15 wt%, impeding the capacity increase in anodes. To address this issue, various prelithiation techniques have been proposed, which can improve the ICE of high-capacity anode materials. In this review paper, we introduce the principles and expected effects of prelithiation techniques reported so far. According to the reaction mechanisms, the strategies are categorized. Mainly, we focus on the recent progress of solution-based chemical prelithiation methods with commercial viability, of which lithiation reaction occurs homogeneously at liquid-solid interfaces. We believe that developing a cost-effective and mass-scalable prelithiation process holds the key to dominating the anode market for next-generation LIBs.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.23 no.1
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• pp.51-57
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• 2013

We have applied mechanical alloying (MA) to produce Heusler $Fe_2VAl$ thermoelectric alloy using a mixture of elemental $Fe_{50}V_{25}Al_{25}$ powders. An optimal milling and heat treatment conditions to obtain the single phase of Fe2VAl compound with fine microstructure were investigated by X-ray diffraction and differential scanning calorimetry (DSC) measurement. The $Fe_{50}V_{25}Al_{25}$ MA sample ball-milled for 60 hours exhibits a bcc ${\alpha}$-(Fe,V,Al) solid solution. Single phase of Heusler $Fe_2VAl$ compound can be obtained by MA of $Fe_{50}V_{25}Al_{25}$ mixture for 60 hours and subsequently heated up to $700^{\circ}C$. Sintering of the MA powders was performed in a spark plasma sintering (SPS) machine using graphite dies at $900{\sim}1000^{\circ}C$ under 60 MPa. The Vickers hardness of bulk sample sintered at $1000^{\circ}C$ was high value of Hv 870. All compact bodies have a high relative density above 90 % with metallic glare on the surface.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.17 no.3
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• pp.121-127
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• 2007

We have applied mechanical alloying (MA) to get $Mg_2Si$ thermoelectric material with nano-sized grains. An optimal milling and heat treatment conditions to obtain the single phase of $Mg_2Si$ compound with fine microstructure were investigated by X-ray diffraction and differential scanning calorimetry (DSC) measurement. The $Mg_{66.7}Si_{33.3}$ MA samples ball-milled for $20{\sim}180\;hrs$ exhibit two broad exothermic heat releases around $220^{\circ}C$ and $570^{\circ}C$. On the other hand, MA sample ball-milled far 260 hrs exhibits only a sharp exothermic peak at $230^{\circ}C$ Single phase Mg2Si powder can be obtained by MA of $Mg_{66.7}Si_{33.3}$ mixture for 60 hours and subsequently heated up to $620^{\circ}C$. Sintering of the MA powders was performed in a spark plasma sintering (SPS) machine using graphite dies at $800{\sim}900^{\circ}C$ under 50 MPa. The shrinkage of sintering sample during SPS was significant at about $200^{\circ}C$. All compact bodies have a high relative density above 94% with metallic glare on the surface.

• Korean Journal of Materials Research
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• v.5 no.7
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• pp.835-841
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• 1995

The deposition properties of Si$_3$N$_4$ deposited by low pressure chemical vapor deposition were studied to evaluate Si$_3$N$_4$as part of multi-layer coatings for anti-oxidation and anti-wear coating of graphite in the propellant-burning environment. Si$_3$N$_4$was deposited on the pack-SiC coated graphite and the tendencies of deposition rate and surface morphology changes with temperatures and reaction gas ratios were investigated. In low deposition temperatures the deposition rate increased tilth increasing temperature but in high temperatures the deposition rate decreased with increasing temperature. The grain size of Si$_3$N$_4$decreased with increasing temperature. In condition that the range of reaction gas ratios is 20$\leq$NH$_3$/SiH$_4$$\leq$40, the deposition rate and surface morphology did not change. The Si$_3$N$_4$deposited at 800~130$0^{\circ}C$ was amorphous, and by post-annealing at 130$0^{\circ}C$ in a $N_2$ambient, the Si$_3$N$_4$crystalized.

• Journal of the Korean Chemical Society
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• v.38 no.4
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• pp.283-287
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• 1994

The crystal stucture of bithional surfoxide, $C_{12}H_6Cl_4O_3S$, has been determined from 2295 independent reflections collected on an automated CAD-4 diffractometer with a graphite-monochromated $Mo-K\alpha$ radiation. The crystal belongs to the monoclinic, space group P2$_1$/n, with a unit cell dimensions a = 12.448(4), b = 9.740(1), c = $11.815(2)\AA$, $\beta$ = $100.06^{\circ}$, $\mu$ = 9.02 cm$^{-1}$, Dm = 1.76 g/cm$^3$, Dc = 1.75 g/cm$^3$, F(000) = 744, and Z = 4. The structure was solved by the direct method and refined by the least-squares method. The final R values was 0.037 for 2295 independent reflections. Overall conformation of the molecule is folded with respect to central surfur atom. Comparing with the molecular conformation of bithional, one of phenyl rings was swinged with about $180^{\circ}.$ This conformational change in the molecule results in the existance of intramolecular-hydrogen bond of S-O(3)---H-O(1) type and its steric hindrance between this moiety and the other phenyl ring. The two best planes of the phenyl rings have a maximum deviation of 0.009 $\AA$ for C(1) atom. The dihedral angle between two phenyl rings is $99.22^{\circ}.$ In the crystal structure, the molecules are packed with intermolecular-hydrogen bond of O(3)---H-O(2).