• Journal of Advanced Marine Engineering and Technology
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• v.22 no.6
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• pp.809-815
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• 1998

This study has been performed to investigate MRR(metal removal rate) surface roughness with various pulse-on duration using the copper and graphite electrode according to the electrode size on the heat treated STD 11 which is extensively used for metallic molding steel in the EDM. The results obtained are as follow ;a)MRR increases a lot when pulse-on duration is 100 $\mu{s}$ or less but MRR has little difference with pulse-on duration of 100 $\mu{s}$ or more b) According to the increase of Pulse-on duration the large the electrode size the more MRR c) Safe discharge is needed to make maximum of MRR and the metallic organization must be complicated for discharge induction. d) Actual machining time is longer than theoretical machining time at the short pulse-on duration because of skin effect of current. e) Graphite electrode needs the larger electric discharge energy than copper electrode to remove remained chips completely.

• Korean Journal of Metals and Materials
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• v.48 no.7
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• pp.625-629
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• 2010

This study investigates the effects of porosity on the thermal stability and the thermal shock resistance of a porous nozzle used for blowing an inert gas. The samples of $Al_2O_3-SiO_2-ZrO_2$ system, which had the apparent porosity of 16~30% and bulk density of $2.6{\sim}3.2g/cm^3$, were prepared by adding different graphite contents (5, 10, 20 wt%) as a pore-forming agent. The thermal shock test was conducted at ${\Delta}T=500$, 1000, and $1400^{\circ}C$ also and the thermal stability was also carried out at 1550, 1600, and $1650^{\circ}C$ for 5 hrs. The specimen contained 10 wt% graphite had uniform pore size distribution, whereas the specimen with 20 wt% graphite showed non-uniform pore size distribution. As a result of thermal shock test, the specimen containing 10 wt% graphite appears to have higher mechanical strength than the other specimens (5, 20 wt% graphite). Both the 5 wt% and 20 wt% graphite specimens developed a non-uniform pore size distribution and cracks that were generated by intensive thermal stress.

• Journal of the Korean Ceramic Society
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• v.35 no.4
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• pp.399-405
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• 1998

The effect of each factor on the porosity and mean pore size of cordierite(2Mg$.$2{{{{ {Al}_{2 } {O }_{3 } }}$.$5{{{{ {SiO}_{2 } }}) ceram-ics which have been mainly used for hot gas filter was investigated by using orthogonal array. The poros-ity was observed to increase with the content of graphite added as pore-forming material and decrease with increasing talc size. The effects of the other factors the graphite size sintering temperature and hold-ing time at sintering temperature were observed to be small relatively. In case of mean pore size the ef-fect of talc size on the mean pore size of cordierity was investigated to be the largest. The mean pore size was observed to increase with increasing talc size.

• Journal of the Korean Society of Industry Convergence
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• v.26 no.1
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• pp.79-86
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• 2023

This study was investigated the effect of carbon on the micro-structure and hardness of ductile cast iron roll with internal curing capacity. Spheroidal graphite existed at roll body with rapid cooling, but granular graphite existed at roll neck with slow cooling. The volume fraction of graphite increased at roll body with rapid cooling, That of roll neck with slow cooling decreased, but graphite size increased. The volume fraction of cementite decreased, but volume fraction increased. The cementite size was larger at roll neck than roll body. The hardness was decreased at roll body and roll neck due to volume fraction of cementite. The hardness of roll body was higher than roll neck.

• Journal of the Korean Ceramic Society
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• v.34 no.12
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• pp.1199-1204
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• 1997

SiC conversion layer was fabricated by the chemical vapor reaction between graphite substrate and silica powder. The CVR process was carried out in nitrogen atmosphere at 175$0^{\circ}C$ and 185$0^{\circ}C$. From the reduction of silica powder with graphite substrate, the SiO vapor was created, infiltrated into the graphite substrate, then, the SiC conversion layer was formed from the vapor-solid reaction of SiO and graphite. In the XRD pattern of conversion layer, it was confirmed that 3C $\beta$-SiC phase was created at 175$0^{\circ}C$ and 185$0^{\circ}C$. Also, in the back scattered image of cross-sectional conversion layer, it was found that the conversion layer was easily formed at 185$0^{\circ}C$, the interface of graphite substrate and SiC layer was observed. It was though that the coke particle size and density of graphite substrate mainly affect the XRD pattern and microstructure of SiC conversion layer. In the oxidation test of 100$0^{\circ}C$, the SiC converted graphites exhibited good oxidation resistance compared with the unconverted graphites.

• Carbon letters
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• v.25
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• pp.50-54
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• 2018

Large-size graphene samples are successfully prepared by combining ultrosonic assisted liquid phase exfoliation process with oxidation-deoxidation method. Different from previous works, we used an ultrasound-treated expanded graphite as the raw material and prepared the graphene via a facile oxidation-reduction reaction. Results of X-ray diffraction and Raman spectroscopy confirm the crystal structure of the as-prepared graphene. Scanning electron microscopy images show that this kind of graphene has a large size (with a diameter over $100{\mu}m$), larger than the graphene from graphite powder and flake graphite prepared through single oxidation-deoxidation method. Transmission electron microscopy results also reveal the thin layers of the prepared graphene (number of layers ${\leq}3$). Furthermore, the importance of preprocessing the raw materials is also proven. Therefore, this method is an attractive way for preparing graphene with large size.

• Carbon letters
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• v.13 no.1
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• pp.39-43
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• 2012

The size and the physical properties of graphene oxide sheets were controlled by changing the oxidation temperature of graphite. Graphite oxide (GO) samples were prepared at different oxidation temperatures of $20^{\circ}C$, $27^{\circ}C$ and $35^{\circ}C$ using a modified Hummers' method. The carbon-to-oxygen (C/O) ratio and the average size of the GO sheets varied according to the oxidation temperature: 1.26 and 12.4 ${\mu}m$ at $20^{\circ}C$, 1.24 and 10.5 ${\mu}m$ at $27^{\circ}C$, and 1.18 and 8.5 ${\mu}m$ at $35^{\circ}C$. This indicates that the C/O ratio and the average size of the graphene oxide sheets respectively increase as the oxidation temperature decreases. Moreover, it was observed that the surface charge and optical properties of the graphene oxide sheets could be tuned by changing the temperature. This study demonstrates the tunability of the physical properties of graphene oxide sheets and shows that the properties depend on the functional groups generated during the oxidation process.

• Bulletin of the Korean Chemical Society
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• v.35 no.9
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• pp.2630-2634
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• 2014

The surface of natural graphite was modified by the use of hydrogen peroxide and evaluated as an anode material for lithium ion capacitors (LICs). The surface treatment was carried out under various ultrasonic conditions of 200, 300, and 400W, which were applied to a mixture of natural graphite and hydrogen peroxide solution for 1 h. While the bulk structure was maintained, the hexagonal symmetry and physical properties of natural graphite, such as BET surface area, tap density, and particle size, were affected by the surface treatment. FT-IR and XPS measurements confirmed the signature of C=O on the surface of graphite samples after treatment. Both the pristine and surface-treated graphites showed a similar reversible capacity of $370mAhg^{-1}$, and the coulombic efficiency of surface-treated graphite decreased with higher ultrasonic energies (89.1%, 89.0%, and 88.0% for 200, 300, and 400 W) comparing with pristine graphite (89.4%). The capacity retention of LICs was greatly improved with the treated natural graphite. The graphite treated under the ultrasonic energy of 300 W and pristine natural graphite showed capacity retention of 77.5% and 42.9%, implying that the surface treatment was an effective method for the improvement of natural graphite as an anode material for LICs.

• Journal of the Korean Society of Tobacco Science
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• v.25 no.1
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• pp.59-69
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• 2003

The adsorption characteristics of H$_2$S, NH$_3$and $CH_3$SH on the graphite carbon have been investigated using Grand Canonical Monte Carlo(GCMC) method with universal force field (UFF) and dreiding force field. Most of the activated carbons used in vapor phase adsorption have the micropore of 6$\AA$ to 20$\AA$ and the specific surface area of ca. 1000 m$^2$/g, as the result of $N_2$ adsorption by BET method. For the more efficient comparison, the activated carbons have been manipulated with different pore sizes. The adsorption characteristics of H$_2$S, NH$_3$and $CH_3$SH have been considered at various temperatures and pressures. The adsorption amount using Dreiding force field is predicted to be lower than that using UFF. As the temperature is going to high, the adsorption amount of adsorbates is decreased due to their vaporization. Considering the pore size effect, the adsorption characteristic depends on the adsorbate size, polarity and interaction between adsorbates, etc. At all cases employed in this study, NH$_3$ is barely adsorbed and $CH_3$SH is preferentially adsorbed on the graphite carbon. Our theoretical result is qualitatively good agreement with the experimental observation. However, there are some quantitative discrepancies depending on the functional groups and pore size distribution on the real activated carbons used in experiment.

• Transactions on Electrical and Electronic Materials
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• v.13 no.3
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• pp.121-124
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• 2012

Olivine type $LiFePO_4$ cathode material was synthesized by solid-state reaction method including one-step heat treatment. To improve the electrochemical characteristics, graphite nanofiber (GNF) was added into $LiFePO_4$ cathode material. The structure and morphological performance of $LiFePO_4$ were investigated by X-ray diffraction (XRD); and a field emission-scanning electron microscope (FE-SEM). The synthesized $LiFePO_4$ has an olivine structure with no impurity, and the average particle size of $LiFePO_4$ is about 200~300 nm. With graphite nanofiber added, the discharge capacity increased from 113.43 mAh/g to 155.63 mAh/g at a current density of 0.1 $mA/cm^2$. The resistance was also significantly decreased by the added graphite nanofiber.