• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2002.05a
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• pp.226-234
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• 2002

A systematic study of the role of transfer films on friction properties was performed with various temperatures in the brake system. An NAO friction material specimens containing 9 ingredients were tested using a pad-on-disk type friction tester A new method of measuring the transfer film thickness was developed by considering the electrical resistance of the transfer film using a 4-point probe technique. The properties of transfer film such as surface morphology and film distribution vaied according to the relative amount of graphite and magnesium oxide. By using SEM, it was possible to obtain information about the chemical composition of the transfer film. Results showed that there detected a threshold value of the relative amount of a two active materials to maintain a certiain thickness of a transfer film. Results also showed that formation of friction layer generated on the friction surface was strongly affected by chemical action of two ingredients during sliding due to chemical reaction of solid lubricants at different interface temperature. The results suggested that no apparent relationship between transfer film thickness and the average friction coefficient was founded and friction characteristics were affected more by the property of the solid lubricant and abrasive in the material.

• Journal of Korea Foundry Society
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• v.21 no.6
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• pp.350-358
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• 2001

The machinability of cast iron is closely related to its microstructural property. In this study, the effect of graphite mophology and matrix microstructure on machinability in several commercial cast irons(GC 25, GCD 45, GCD 50, GCD 70, GCD HSMo, GCMP) was investigated. To estimate the machinability, turning test was carried out under conditions of spindle speed 80m/min, depth of cut 0.25mm, feed 0.16mm/rev and cutting distance 1 km. Thrust force in turning test decreases in the order of GCMP, GCD 70, GCD 50, GC 25, GCD 45 and GCD HSMo. i.e. machinability increases in this order. The superior machinability of GC 25 is caused by flake type graphite which acts as chip braker and provides lubrication during machining. Consequently, soft ferritic cast irons exhibit superior machinability compared with pearlitic cast irons.

• Corrosion Science and Technology
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• v.19 no.1
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• pp.31-36
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• 2020

An efficient wet process approach to modifying natural graphite (NG) electrodes for Li-ion batteries is introduced in this paper. With homogeneous mixing and thermal decomposition of NG with diammonium phosphate ((NH₄)₂HPO₄), phosphorus and nitrogen were successfully incorporated into the surface layer of NG particles. Electron microscopy and X-ray photoelectron spectroscopy analyses demonstrated that the surface was well modified by this process. As a result, the treated NG electrodes exhibited much improved electrochemical performance over pristine NG at two different temperatures: 25 ℃ and 50 ℃. Excellent capacity retention of 95.6% was obtained after 100 cycles at 50 ℃. These enhanced properties were confirmed in a morphology analysis on the cross-sections of the NG electrodes after galvanostatic cycling. The improved cycle and thermal stabilities can be attributed to the surface treatment with phosphorus and nitrogen; the treatment formed a stable solid electrolyte interphase layer that performed well when undergoing Li insertion and extraction cycling.

• Journal of Korea Foundry Society
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• v.17 no.1
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• pp.51-57
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• 1997

Effects of the amount of flake type graphite, morphology and (V,Mo)carbides on the specific damping capacity of austenitic low thermal expansion cast irons were investigated. Specific damping capacity(SDC) of low thermal expansion cast irons increased with the increased amount of graphite. Specific damping capacity of low thermal expansion cast iron decreased with the increased Young's modulus. In the case of V and Mo addition, SDC decreased with the increased amount of carbides. Specific damping capacity increased about 2% by the movement of magenetic domains which appeared in ferromagnetic materials.

• Journal of the Korean Society for Precision Engineering
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• v.12 no.12
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• pp.130-138
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• 1995

Machined graphite/epoxy surfaces were studied by using SEM (Scanning Electron Microscopy), surface profilometry and its analysis to determine suitable surface describing parameters for machined unidirectional and multidirectional laminate composite. The surface roughness and profile are found to be highly depdndent on the fiber layup direction and the measurement direction. It was possible to machine 90 .deg. and -45 .deg. plies due to the adjacent plies, which were holding those plies. It was found that the microgeometrical variations in terms of roughness parameters $R_{a}$ without $D_{y}$(Maximum Damage Depth) region and $D_{y}$are better descriptors of the machined laminate composite surface than commonly used roughness parameters $R_{a}$and $R_{max}$ The characteristics of surface profiles in laminate composite are well represented in CPD (Cumulative Probability Distribution) plot and PPD (Percentage Probability Density) plot. Edge-trimmed multidirectional laminate surfaces are Gaussian and random for profiles measured along the tool movement direction, they are periodic and non-Gaussian in the direction perpendicular to the tool movement.t.ent.t.

• Korean Chemical Engineering Research
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• v.51 no.4
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• pp.411-417
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• 2013

To use as an anode material of lithium secondary battery, graphite-silicon composite powders are prepared by ball-milling with silicon nanoparticles (average diameter 100 nm, 0~50 wt%) and graphite powder (average diameter $15{\mu}m$) and their electrochemical properties are examined. As the silicon content increases, the graphite becomes smaller by the ball-milling and amorphous phase appears whereas the silicon do not suffer the change of nanocrystalline phases and embeds within the amorphous phase of graphite. Cyclic voltammetry at low scan rate reveals that typical oxidation peaks of graphite and silicon appear at 0.2~0.35 and 0.55~0.6 V, respectively, with higher reversibility for repeated cycles. In contrast, the high-scan-rate redox behavior is very irreversible for repeated cycles. High irreversible capacity is exhibited in the initial charging-discharging cycles, but it diminishes as the cycle number increases. The saturated discharge capacity achieves about 485 mAh $g^{-1}$ at 50th cycle for the composite of Si 20 wt%. This is due to the formation of amorphous graphite morphology by the adequate composition (C:Si=8:2 w/w), which efficiently buffers the volume change during alloying/dealloying between silicon and lithium.

• Nuclear Engineering and Technology
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• v.52 no.6
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• pp.1243-1251
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• 2020

Irradiation-induced damage of binderless nanoporous-isotropic graphite (NPIG) prepared by isostatic pressing of mesophase carbon microspheres for molten salt reactor was investigated by 3.0 MeV He⁺ irradiation at room temperature and high temperature of 600 ℃, and IG-110 was used as the comparation. SEM, TEM, X-ray diffraction and Raman spectrum are used to characterize the irradiation effect and the influence of temperature on graphite radiation damage. After irradiation at room temperature, the surface morphology is rougher, the increase of defect clusters makes atom flour bend, the layer spacing increases, and the catalytic graphitization phenomenon of NPIG is observed. However, the density of defects in high temperature environment decreases and other changes are not obvious. Mechanical properties also change due to changes in defects. In addition, SEM and Raman spectra of the cross section show that cracks appear in the depth range of the maximum irradiation dose, and the defect density increases with the increase of irradiation dose.

• Korean Chemical Engineering Research
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• v.48 no.6
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• pp.673-678
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• 2010

In the present study, mixed carbon-supported platinum(Pt) nanoparticles were prepared by a chemical reduction method of Pt precursor solution on two types of carbon materials such as activated carbons(ACs) and graphite nanofibers(GNFs). Average crystalline sizes and loading levels of Pt metal particles could be controlled by changing a content of GNFs. The highest electroactivity for methanol oxidation was obtained by preparing the carbon supports having 15 wt% GNFs. Furthermore, with an increase of GNFs content from 0% to 15%, an electrical conductivity was changed from $10^{-4}S/cm$ to $10^{-1}S/cm$. By an introduction of 10 wt% GNFs additive, the electroactivity of platinum particles was enhanced, but was saturated in the case of 15 wt% GNFs contents. This was related with the fact that the electroactivity change was dependent on the electrical conductivity of mixed carbon supports and Pt particle deposition content or deposition morphology.

• Journal of Adhesion and Interface
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• v.12 no.4
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• pp.133-137
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• 2011

Exfoliated graphite oxide (EGO) was prepared by graphite oxide in an aqueous solution of TMAOH. The hybrid graphene/Zn-Al LDH material was fabricated by the hydrothermal reduction of the solution of EGO, $Zn(NO_3)_2{\cdot}6H_2O$, $Al(NO_3)_3{\cdot}9H_2O$, urea, and trisodium citrate. That is, metal ions were absorbed on the surface of EGO, and Zn-Al LDH material was randomly dispersed on the surface of graphene along with a reduction process of EGO to graphene by hydrothermal treatment. The composition, morphology, and thermal property of the obtained graphene-based hybrid material were studied by FE-SEM, EDX, TEM, FT-IR, XRD, TGA, and DSC.

• Proceedings of the KIEE Conference
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• 1990.11a
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• pp.97-100
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• 1990

Diamond thin films were synthesized by the MPECVD (Microwave Enhanced Chemical Deposition) using the mixture of the hydrogen and organic compounds($CH_3COCH_3$, $CH_3OH$). In X-ray Diffraction, the d values of all the deposits on the Si substrates with the experimental conditions coincide with those of natural diamond in POD (Powder Diffraction Data). The changes of the morphology of all the deposits were examined by SEM. The amount of amorphous carbon or graphite in the diamond films were increased as the acetone concentration was increased. The morphology of the diamond particles can be changed from ball-like to euhedral by adding the small amount of the methanol in the reaction gases of the high acetone concentration.