• 한국응용과학기술학회지
• /
• 제31권4호
• /
• pp.679-687
• /
• 2014

본 연구에서는 캐비테이션에 의한 부식에 강한 도료를 개발하기 위하여 고탄성의 우레탄 수지에 내마모 성능을 향상시키기 위한 첨가제로서 Multi wall과 Single wall type의 Carbon nano tube(CNT)와 Spherical과 Fiber type의 Graphite 나노 입자를 첨가하여 물성과 캐비테이션에 대한 저항성, 작업성 등을 비교 평가하였다. 나노 입자로서 Graphite에서는 캐비테이션 저항성($t_{50}$)이 Spherical type($t_{50}$ 182min)보다는 Fiber type($t_{50}$ 292min)이 높은 캐비테이션 저항성을 갖는 것으로 관찰되었다. 또한 CNT에서는 Single wall type의 캐비테이션 저항성($t_{50}$ 286min)이 Multi wall보다는 더 높은 것으로 관찰되었다. 나노 입자중에서 가격 및 캐비테이션 저항성을 감안하면 가장 최적의 나노 입자는 Fiber type의 Graphite로 관찰되었다. 도료의 작업성 평가에서 수동 작업에 의해 제작된 표면은 매끈한 표면을 가지고 있으나 Spray 작업에 의해 제작된 표면은 표면이 균일하지 않으며 Spray시 발생된 Dust가 표면에 고착된 형태로 관찰되었다.

• Nuclear Engineering and Technology
• /
• 제53권5호
• /
• pp.1569-1579
• /
• 2021

This study aims to provide microstructural characterization for the matrix graphite which molten salt reactors (MSRs) use, and improve resistance to molten salt infiltration of the matrix graphite for fuel elements. Mesocarbon microbeads (MCMB) densified matrix graphite A3-3 (MDG) was prepared by a quasi-isostatic pressure process. After densification by MCMBs with average particle sizes of 2, 10, and 16 ㎛, the pore diameter of A3-3 decreased from 924 nm to 484 nm, 532 nm, and 778 nm, respectively. Through scanning electron microscopy, the cross-section energy spectrum and time-of-flight secondary ion mass spectrometry, resistance levels of the matrix graphite to molten salt infiltration were analyzed. The results demonstrate that adding a certain proportion of MCMB powders can improve the anti-infiltration ability of A3-3. Meanwhile, the closer the particle size of MCMB is to the pore diameter of A3-3, the smaller the average pore diameter of MDG and the greater the densification. As a matrix graphite of fuel elements in MSR was involved, the thermal and mechanical properties of matrix graphite MDG were also studied. When densified by the MCMB matrix graphite, MDGs can meet the molten salt anti-infiltration requirements for MSR operation.

• 한국분말재료학회지
• /
• 제20권2호
• /
• pp.100-106
• /
• 2013

Ultra-fine zirconium carbide (ZrC) powder with nano-sized primary particles was synthesized by the carbothermal reduction method by using nano-sized $ZrO_2$ and nano-sized graphite powders mixture. The synthesized ZrC powder was well dispersed after simple milling process. After heat-treatment at $1500^{\circ}C$ for 2 h under vacuum, ultra-fine ZrC powder agglomerates (average size, $4.2{\mu}m$) were facilely obtained with rounded particle shape and particle size of ~200 nm. Ultra-fine ZrC powder with an average particle size of 316 nm was obtained after ball milling process in a planetary mill for 30 minutes from the agglomerated ZrC powder.

• The Korean Journal of Ceramics
• /
• 제2권4호
• /
• pp.226-230
• /
• 1996

A small amount of fine particle graphite was added to $\alpha$-SiC and $\beta$-SiC having certain particle distributions, and they were mixed clay and frit. After forming, they were sintered at 140$0^{\circ}C$ for 3 hours. Tribological properties of sintered $\alpha$-SiC-$\beta$-SiC-graphite-clay (frit) system showed that kinetic friction coefficient was 0.108, specific wear rate was 1.3${\times}10^-8\;mm^2$.$kgf^1$, and torque was 0.01kgf.cm at the wrench torque of 100 kgf.cm.

• 동력기계공학회지
• /
• 제18권6호
• /
• pp.7-12
• /
• 2014

The effect of various synthesis conditions in the fabrication of graphene using the exfoliation methods has been investigated. Graphite oxide and graphene fabricated by various synthesis conditions were identified by SEM and XRD. Graphite oxide was made from graphite by the chemical oxidation, and graphene was manufactured from graphite oxide by thermal exfoliation method. As a result, it is confirmed that graphite oxide was well formed from graphite, and the graphene could be obtained from graphite oxide. And it was found that the interlayer spacing between the graphene layers depended on the reaction time and particle size, regardless of the reaction temperature from $5^{\circ}C$ to $25^{\circ}C$.

• Bulletin of the Korean Chemical Society
• /
• 제27권4호
• /
• pp.556-562
• /
• 2006

Studies on Ag nanoparticles grown on Highly Ordered Pyrolytic Graphite (HOPG) using HREELS provide different results for smaller and larger particle sizes corresponding to Ag coverages below and above 4 monolayers, respectively. For the larger particles, a positive frequency shift with decreasing particle size and a broadening of the plasmon resonance were observed with decreasing particle size, in line with previous studies on Ag on alumina. For the smaller particles, in contrast, a shift to lower energy with decreasing particle size, and a narrowing of the plasmon resonance with decreasing particle size can be found. The asymmetry of the Ag-features present for Ag coverages above 4 monolayers disappears for Ag coverages below 4 monolayers. The result for the smaller particles can be rationalized in terms of change of the particle growth mode with increasing particle size, which corroborates our STM data, as well as electronic effects due to the metal/support charge transfer.

• 연구논문집
• /
• 통권33호
• /
• pp.147-155
• /
• 2003

In order to fabricate porous materials having an anisotropic thermal conductivity by aligning plate-shaped pores structure, alumina powder (AM-21, mean particle size $4\mum$) and flake crystalline graphite was used. The aligned pore structure was realized using multi-pressing process. Degree of pore orientation increased with the number of pressing and thermal conductivity, parallel to the pressing direction, decreased with the number of pressing. Thermal conductivity decreased significantly to the addition of 30vol% crystalline graphite, however, in the case of 60vol%, thermal conductivity did not decrease significantly due to the breakage of crystalline graphite. An anisotropy of the thermal conductivity increased with the content of crystalline graphite up to 30vol%. Graded pore structure was fabricated by controlling the content and size of crystalline graphite, which provides, possibly, the enhancement in mechanical strength and thermal insulation properties of the insulating bricks.

• Bulletin of the Korean Chemical Society
• /
• 제29권10호
• /
• pp.1965-1968
• /
• 2008

The effects of carbon-coated silicon/graphite (Si/Gr.) composite anode on the electrochemical properties were investigated. The nanosized silicon particle shows a good cycling performance with a reasonable value of the first reversible capacity as compared with microsized silicon particle. The carbon-coated silicon/graphite composite powders have been prepared by pyrolysis method under argon/10 wt% propylene gas flow at $700{^{\circ}C}$ for 7 h. Transmission electron microscopy (TEM) analysis indicates that the carbon layer thickness of 5 nm was coated uniformly onto the surface silicon powder. It is confirmed that the insertion of lithium ions change the crystalline silicon phase into the amorphous phase by X-ray diffraction (XRD) analysis. The carbon-coated composite silicon/graphite anode shows excellent cycling performance with a reversible value of 700 mAh/g. The superior electrochemical characteristics are attributed to the enhanced electronic conductivity and low volume change of silicon powder during cycling by carbon coating.

• Carbon letters
• /
• 제8권4호
• /
• pp.326-334
• /
• 2007

In this study, graphite composites were fabricated by warm press molding method to realize commercialization of PEM fuel cells. Graphite composites have been considered as alternative economic materials for bipolar plate of PEM fuel cells. Graphite powder that enables to provide electrical conductivity was selected as the main substance. The graphite powder was mixed with phenolic resin and the mixture was pressed using a warm press method. First of all, the graphite powder was pulverized with a ball mill for the dense packing of composite. As the ball milling time increases, the average size of particles decreases and the size distribution becomes narrow. This allows for improvement of the uniformity of graphite composite. However, the surface electrical resistivity of graphite composite increases as the ball milling time increases. It is due to that graphite particles with amorphous phase are generated on the surface due to the friction and collision of particles during pulverizing. We found that the contact electrical resistivity of graphite particles increases as the particle size decreases. The contact electrical resistivity of graphite powders was reduced due to high molding pressure by warm press molding. This leads to improvement of the mechanical properties of graphite composite. Hydrogen gas impermeability was measured with the graphite composite, showing a possibility of the application for bipolar plate in fuel cell. And, I-V curves of the graphite composite bipolar plate exhibit a similar performance to the graphite bipolar plate.

• 한국세라믹학회지
• /
• 제26권4호
• /
• pp.583-587
• /
• 1989

Various $\alpha$-silicon carbied and colloidal graphite particles were sintered at 155$0^{\circ}C$ in vacuum atmosphere by reaction bonding sintering method, and the physical properties and microstructural analysis of specimen were investigated. With decreasing particle size, sintered density and 3-point bending strength of materials were increased and 3.2${\mu}{\textrm}{m}$ specimen showed high density and strength, 3.05g/㎤, 40kg/$\textrm{mm}^2$, respectively. The results of X-ray diffractometer and optical micrographs analysis showed that graphite and silicon melt reacted to convert to fine $\beta$-SiC particle and the body was changed to dense material.