• Applied Chemistry for Engineering
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• v.32 no.5
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• pp.569-573
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• 2021

In this study, high-density carbon blocks were manufactured using coke, binder pitch, and impregnated pitch, then the effect of pitch fluidity on the densification of carbon blocks during the impregnation process was investigated. A green block was manufactured through high-pressure figuration of coke and binder pitch, and a carbon block was obtained through a heat treatment process. An impregnation process was performed to remove pores generated by volatilization of the binder pitch during the heat treatment process. The impregnation process was carried out the high-pressure reaction step of impregnating the pitch into the carbon block followed by the pretreatment step of melting the impregnation pitch. Melting of the impregnation pitch was carried out at 140~200 ℃, and the viscosity of the impregnation pitch decreased as the heat treatment temperature increased. The decrease in the viscosity of the impregnation pitch improved the fluidity and effectively impregnated the pores inside the carbon block, reducing the porosity of the carbon block by 83% and increasing the apparent density by 5%.

• Korean Journal of Materials Research
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• v.7 no.5
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• pp.397-402
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• 1997

석탄계 핏치의 열처리 온도 및 압력에 따른 결정화도와 기공도 그리고 산화저항성 등을 관찰하였으며, hexagonal type 4D 탄소/탄소 복합재를 석탄계 핏치로 가압함침 및 탄화시킨 다음 가해준 압력이 고밀도화에 미치는 영향을 관찰하였다. 석탄계 핏치의 가압탄화 압력이 흑연화도에 크게 영향을 미치지 않았으며, 기공면적비에 있어서는 압력을 600bar로 상승시켜 줌으로써 상압 처리한 경우 보다 1.5배 정도 감소 하였다. $650^{\circ}C$까지 열처리하여 얻은 코우크스의 산화반응 개시온도는 처리압력이 증가함에 따라서 지연되었다. 탄소/탄소 복합재의 함침압력을 100bar에서 600bar로 상승시켜 줄 경우 밀도 증가율이 크게 향상 되었으며 기공도는 감소하였다.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.10 no.2
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• pp.53-67
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• 2000

Coke-oven workers are regularly exposed to coke oven emissions (COE), which consist primarily of polynuclear aromatic hydrocarbons (PAH) and volatile organic components. This study assessed the exposure of coke-oven workers to COE and PAH. The results of this study are as follows. 1. Among the 136 samples on coke-oven workers 33.1% exceeded the occupational exposure limit to the Coal Tar Pitch Volatiles ($0.2mg/m^3$) established by the Korean Ministry of Labor and American Conference of Governmental Industrial Hygienists(ACGIH). 2. The coke-oven workers were classified into twelve job categories and there was statistically significant difference among the airborne concentrations of COE and PAH in twelve job categories(p<0.001). 3. There was no significant difference of the airborne concentrations of COE between NIOSH method and OSHA method applied. 4. There was a significant correlation between the airborne concentrations of total PAH and COE(r=0.733, p<0.01). 5. The percentage of naphthalene in total PAH was 55.9% and the highest among those of 16 PAHs. There was a significant correlation between the airborne concentrations of naphthalene and total PAH(r=0.90, p<0.01) and this study recommends naphthalene as the index component of PAH.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.9 no.1
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• pp.156-172
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• 1999

Potential chemical hazards encountered in painting operation of four shipyards and a ship-repair shop were investigated through the material safety data sheets (MSDS). Material safety data sheets (MSDS) for 307 paints, 50 thinners and 34 binders were collected and reviewed. It was shown that various organic solvents such as aromatic hydrocarbons, aliphatic hydrocarbons, ketones, alcohols, glycols, glycol ether acetates and esters were contained in painting materials. Of these solvents, xylene was found in the largest number of painting materials. sixty percent of the thinners contained xylene in the contents of 20-100%. Other most frequently found solvents were 1-methoxypropanol, 1-methoxypropyl acetate, n-butanol, methyl isobutyl ketone, toluene, isopropanol, and n-butyl acetate, etc. Glycol ethers such as 2-methoxyethanol (2-ME), 2-methoxyethyl acetate (2-MEA), 2-ethoxyethanol (2-EE), 2-ethoxyethyl acetate (2-EEA) and 2-butoxyethanol (2-BA) were regarded as having the potential to cause adverse reproductive effects, embryotoxic effect and hematotoxic effects, and were found in some epoxy panting materials. Coal tar pitch was included in some paints(13%) where polynuclear aromatic hydrocarbons (PAHs) could be contaminated. Inorganic pigments such as lead chromate and zinc potassium chromate were found in some paints (8%). The epoxy resin based paints, which may contain isocyanates such as toluene diisocyanates and hexamethylene diisocyanates causing potential sensitization and asthma to upper respiratory organ, were mostly used in the shipyards. The constituents in the MSDS were significantly different from the results analyzed using gas chromatography/mass detector: minor constituents or impurities were omitted in many MSDS. In conclusion, xylene was the most frequent organic solvent in painting materials, and glycol ethers, including 2-ME, 2-MEA, 2-EE, 2-EEA and 2-BA, were found some products. Also, painting workers may be exposed to PAHs, lead, chromate, isocyanates, organic tin and other various chemicals. The compositions of chemicals in painting materials were variable significantly, and the hazards were changed. These facts should be considered in environmental monitoring and control of the hazards.

• Applied Chemistry for Engineering
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• v.18 no.3
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• pp.227-233
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• 2007

Carbon/carbon (C/C) composites as unique materials possess exceptional thermal resistance with light weight, high stiffness, and strength even at high temperature. However, one serious obstacle for application of the C/C composites is their poor oxidation resistance in high temperature oxidizing environments. SiC coating has been employed to protect the composites from oxidation. This study explored combustion characteristics of 4-directional (4D) carbon/carbon composites using liquid fuel rocket engine to investigate ablative motion of the materials. C/C composites were made of coal tar pitch as a matrix precursor, and heat-treated at $2300^{\circ}C$. Throughout repeated densification process, the density of the material reached $1.903g/cm^3$. After machining 4D C/C composites, the nozzle surface was coated by a SiC layer by pack-cementation method to improve oxidation resistance. Erosion characteristics of SiC-coated C/C composites were measured as function of the ratio of oxygen to fuel. The morphological change of the composites after combustion test was investigated using SEM and erosion mechanism also was discussed.