• Nuclear Engineering and Technology
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• v.16 no.1
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• pp.18-20
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• 1984

The detection limit of boron has been lowered further in the capture gamma-ray measurement after preconcentration of boron by placing natural lithium brick in front of Ge(Li) detector. The experimental detection limit is found to be 0.30ppm, 0.18ppm, 0.045ppm and 0.090ppm for the samples of aluminum, steel, uranium dioxide and graphite, respectively. An alternate counting technique kas been also used for neglecting the error caused by the fluctuation of neutron flux during counting.

• Bulletin of the Korean Chemical Society
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• v.31 no.10
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• pp.2913-2917
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• 2010

When rubber dissolved in toluene was used as a binding material of graphite powder, the mechanical robustness of the carbon paste was guaranteed by the fast volatility of the solvent immediately after electrode construction. This characteristic of the rubber solution met qualifications for practical use of carbon paste electrodes and enabled the design of a new enzyme electrode bound with EPDM. In order to confirm whether the electrode shows quantitative electrochemical behaviors or not, its kinetic parameters, e. g. the symmetry factor (0.2), the exchange current density ($3.66\;{\mu}A/cm^2$), the capacity of the double layer ($2.0{\times}10^{-5}\;F$), the Michaelis constant ($4.39{\times}10^{-3}\;M$), the diffusion coefficient of substrate ($2.58{\times}10^{-12}\;cm^2/sec$), the time constant (0.018 sec) and other factors were investigated.

• Journal of the Korean Ceramic Society
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• v.26 no.3
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• pp.402-408
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• 1989

$\beta$-Sialon powder was synthesized by the simultaneous reduction and nitridation of the mixed powder of Hadong kaolin and Kimcheon quartzite, using graphite as a reducing agent. The synthesized $\beta$-Sialon powder (Z=1) was hot-pressed at 175$0^{\circ}C$, for 90min under 30MPa in N2 atmosphere, after Yttria and YAG composition material were added as sintering agents. The effects of grain-boundary crystallization on high-temperature mechanical properties of $\beta$-Sialon ceramics were investigated. Strength degradation was observed at above 1,00$0^{\circ}C$ for the $\beta$-Sialon (Z=1)-8wt% Y2O3 composition, but it was not observed up to 1,20$0^{\circ}C$ for the $\beta$-Sialon-8wt% YAG composition which was annealed at 1,40$0^{\circ}C$ for 4 hours in N2 atmosphere. After the $\beta$-Sialon-8wt% YAG composition was annealed, the decrease of fracture toughness was observed.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.5
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• pp.530-536
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• 2021

This paper presents the performance measurement results of a hybrid sheet with both shielding and heat dissipation functions developed by laminating copper mesh sheets and natural graphite sheets, which are used widely as electromagnetic shielding and heat-dissipating materials in electronic devices, without a pressure-sensitive adhesive (PSA). The results were compared by measuring the vertical and horizontal thermal conductivity with two other products to confirm the heat dissipation performance. A radiation emission test confirmed the electromagnetic shielding performance using a 3m electromagnetic anechoic chamber according to the CISPR 11 standard. In the case of vertical thermal conductivity, the proposed hybrid sheet was approximately 8.63 times higher than that of an aluminum sheet with heat dissipation coating and 18.7 times higher than that of a copper sheet laminated with artificial graphite with PSA. The proposed hybrid sheet was approximately 0.64 times that of the sheet, and approximately 1.76 times that of the heat-dissipated aluminum sheet in case of horizontal thermal conductivity. Measurements after applying each sheet in the same heat source revealed the proposed hybrid sheet to have the best heat dissipation performance. The radiation emission test showed that significantly radiation noise had been removed.

• Korean Journal of Materials Research
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• v.4 no.2
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• pp.194-205
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• 1994

In this research, we attempt to fabricate an excellent CFRC(Carbon Fiber Reinforced Carbon), which has good thermal and mechanical properties, with 8H/satin woven fabric prepreg, high modulus and high strength type continuous carbon fiber and raw coal tar pitch(RCTP) matrix or THF soluble fraction(THFSP) matrix which has good graphitizability. Green bodies were fabricated with hot press molding technique and CFRC samples were made after carbonization, impregnation, recarbonization and graphitization steps. For the purpose of characterization of the physical properties, SEM, polarized light microscope, TGA were observed, and tested flexural strength, modulus and ILSS. After heat treating the THFSP matrix up to $2300^{\circ}C$, the value of $C_0$/2 was 3.380$\AA$, which is analogous to the structure of natural graphite and the value of 2$\theta$ is $26.276^{\circ}$ approached to the Bragg's angle of natural graphite. As a result of TGA to test the high temperature air oxidation, the THFSP matrix, graphitized up to $2300^{\circ}C$, exhibited the best air oxidation resistance. And mechanical properties were increased up to 65~70% as fiber volume fraction increased. Because of the good orientation graphitizability, the fracture surface of THFSP matrix CFRC is very good.

• Journal of the Korean Ceramic Society
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• v.49 no.3
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• pp.221-225
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• 2012

It is possible to enhance the color of the natural diamond with a high pressure high temperature(HPHT) process. We employed a pyrophyllite tube cell and cubic press apparatus for HPHT treatment on the brown colored Type II (5.6 GPa/ $1700^{\circ}C$/ 52 min), and Type I aB(5.6 GPa/ $1650^{\circ}C$/ 30 min) diamond samples. We investigated the microstructure, Types, fluorescence, properties of the diamonds with an optical microscopy, FT-IR, photoluminescence(PL) spectroscopy, Diamond-View, and micro-Raman spectroscopy. Two tinted brown diamonds changed into colorless just after the HPHT process. Optical microscopy showed that no crack and significant inclusion evolution occurred during the HPHT process except the small graphite spot appeared in Type I aB sample. FTIR spectrum confirmed that no Type, amber center, and platelet defect change with the HPHT treatment. Diamond-View could not distinguish the HPHT treated diamonds from the naturals. PL spectroscopy showed that N3 and H3 color centers remained even after HPHT process. Consequently, we successfully changed the color of diamonds into colorless by 5.6 GPa HPHT process.

• Corrosion Science and Technology
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• v.16 no.5
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• pp.235-240
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• 2017

Regional cathodic protection has significant impact on pipeline integrity management. After risk analyses of a newly built gas distribution station constructed in an area with large dwelling density, risk score was high because of potential threat caused by galvanic corrosion. Except reinforced steel in concrete, there are four kinds of metal buried under earth: carbon steel, galvanized flat steel, zinc rod and graphite module. To protect buried pipeline from external corrosion, design and construction of regional cathodic protection was proposed. Current density was measured with potential using potential dynamic test and boundary element method (BEM) was used to calculate current requirement and optimize best anode placement during design. From our calculation on the potential, optimized conditions for this area were that an applied current was 3A and anode was placed at 40 meters deep from the soil surface. It results in potential range between $-1.128V_{CSE}$ and $-0.863V_{CSE}$, meeting the $-0.85V_{CSE}$ criterion and the $-1.2V_{CSE}$ criterion that no potential was more negative than $-1.2V_{CSE}$ to cause hydrogen evolution at defects in coating of the pipeline.

• Proceedings of the KIEE Conference
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• 1989.07a
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• pp.390-393
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• 1989

Diamond is synthesized from the gaseous mixture of carbon monoxide and hydrogen by microwave PECVD. $10{\times}10mm^2$ silicon wafers are used as the substrate,and it can be raised more than $900^{\circ}C$ by microwave absorption, radiation by plasma and bombardment of ions. The changes of the morphology and the growth rates of the deposits with the experimental conditions are examined by Scanning Electron Microscopy. The d values of all the deposited films concide with those of powder diffraction data in XRD. In Raman spectra, the peak of the deposit coincides with that of the natural diamond which has a value of 1332.5 $cm^{-1}$, and the broad peak from 1360 $cm^{-1}$to 1600 $cm^{-1}$which represents the amorphous graphite was observed in the higher concentration of carbon monoxide.

• Korean Journal of Materials Research
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• v.27 no.2
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• pp.113-118
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• 2017

Natural and expandable graphites were chemically treated in acidic aqueous solutions such as acetic acid or mixtures of acetic acid and nitric acid. Structures and thermal conductivities of the as-treated graphites were characterized in detail. Both graphites were significantly oxidized in the mixed acidic solution of $H_2SO_4$ and $HNO_3$, which condition was generally used for the oxidation of carbon nanotubes. This considerable oxidation of graphites caused a depression of their thermal conductivity. The structural characteristics, obtained by XRD and XPS, show that the graphites treated in the relatively weak acidic conditions (acetic acid or mixture of acetic acid and nitric acid) were quite similar to the untreated graphites. However, the thermal conductivities of both acidic-treated graphites were remarkably increased.

• Korean Journal of Metals and Materials
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• v.50 no.1
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• pp.23-27
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• 2012

The color of a natural diamond that contains nitrogen impurities can be enhanced by a high pressure high temperature (HPHT) treatment. Type IaAB diamond samples containing nitrogen impurities were executed by HPHT process of 5.6 Gpa, 10 min by varying the annealing temperature at 1600, 1650, and $1700^{\circ}C$. Property characterization was carried out using an optical microscope, FT-IR spectrometer, low-temperature PL spectrometer, and micro Raman spectrometer. By observing optical micrographs, it can be seen that diamond sample began to alter its color to vivid yellow at $1700^{\circ}C$. In the FT-IR spectrum, there were no Type changes of the diamond samples. However, amber centers leading to brown colors lessened after $1700^{\circ}C$ annealing. In the PL spectrum, all the H4 centers became extinct, while there were no changes of yellow color center H3 before or after treatment. In the Raman spectrum, no graphite spots were detected. Consequently, diamond color enhancement can be done by higher than $1700^{\circ}C$ HPHT annealing at 5.6 GPa-10 min.