• Korean Chemical Engineering Research
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• v.43 no.6
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• pp.745-750
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• 2005

Naphtha cracking bottoms(NCB) oil was reformed by varying the heat treatment temperature, treatment time, and nitrogen flow rate in preparation of precursor pitch for isotropic pitch-based carbon fibers and activated carbon fibers. The reformed pitches were investigated in the yield, softening point, elementary analysis, and molecular weight distribution, and then the precursors reformed were melt spun to certify the optimum reforming conditions. The optimum precursor pitch was prepared when the NCB oil was reformed at $380^{\circ}C$, 3 h and 1.25 vvm $N_2$, and it's the softening point was around $240^{\circ}C$. The reforming resulted in product yield of 21 wt％. The C/H mole ratio of the precursor pitch increased from 1.07 to 1.34, the aromaticity increased from 0.85 to 0.88. The insolubles in benzene and quinoline were 30.0 wt％ and 1.5 wt％, respectively. The spinning temperature was about $50^{\circ}C$ higher than the softening point. The molecular weights of the precursor components were distributed from 250 to 1250, and 80％ of them were in the range of 250 to 700.

• Journal of Hydrogen and New Energy
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• v.13 no.2
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• pp.101-109
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• 2002

This work was focused on the thermal decomposition of methane into hydrogen and carbon black without emitting carbon dioxide. Extensive experimental investigation on the thermal decomposition of methane has been carried out using a continuous flow reaction system with tubular reactor. The experiments were conducted at the atmospheric pressure condition in the wide range of temperature ($950-1150^{\circ}C$) and flow rate (250 - 1500 ml/min) in order to study their dependency on hydrogen yield. During the experiments the carbon black was successfully recovered as an useful product. Undesirable pyrocarbon was also formed as solid film, which was deposited on the inside surface of tubular reactor. The film of pyrocarbon in the reactor wall became thicker and thicker, finally blocking the reactor. The design of an efficient reactor which can effectively suppress the formation of pyrocarbon was thought to be one of the most important subjects in the thermal cracking of methane.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.620-625
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• 2002

Considering the fuel consumption of car, a light structure of aluminum alloys is desired for car body nowadays. However, fusion welding of aluminum alloys has some problems of reduction of joint efficiency, porosity formation and hot cracking. ill the present work, investigation to improve the joint performance of laser welded joint has been carried out by addition of Cu, Ni, and Zr to A6N01 alloy welds. Aluminum alloy plate of 2.0mm in thickness with filler metal bar was welded by twin beam Nd:YAG laser facility (total power:5kW). The filler metals were prepared by changing the chemical compositions for adding the elements into the weld metal. Thirteen filler metal bars were prepared and pre-placed into the base metal before welding. Ar gas shielding with a flow rate of 10 l/min was used. The defocusing distance is kept at 0 mm. At travel speeds of 3 to 9 m/min and at laser power of 5kW (front beam 2kW rear beam 3kW), full penetration welds were obtained, whereas at travel speeds of 12 to 18 m/min and same power, partial penetration was observed. The joint efficiency of laser-welded joint was improved by the addition of Cu, Ni, and Zr due to the solid solution hardening, grain refining and precipitation hardening. The type of hardening has been further considered by metallurgical examination.

• International Journal of Korean Welding Society
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• v.2 no.2
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• pp.26-31
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• 2002

Considering the fuel consumption of car, a light structure of aluminum alloys is desired fer car body nowadays. However, fusion welding of aluminum alloys has some problems of reduction of joint efficiency, porosity formation and hot cracking. In the present work, investigation to improve the joint performance of laser welded joint has been carried out by addition of Cu, Ni, and Zr to A6NO 1 alloy welds. Aluminum alloy plate of 2.Omm in thickness with filler metal bar was welded by twin beam Nd: YAG laser facility (total power: 5kW). The filler metals were prepared by changing the chemical compositions for adding the elements into the weld metal. Thirteen filler metal bars were prepared and pre-placed into the base metal before welding. Ar gas shielding with a flow rate of 10 1/min was used. The defocusing distance is kept at 0 mm. At travel speeds off 3 to 9 and at laser power of 5kW (front beam 2kW rear beam 3kW), full penetration welds were obtained, whereas at travel speeds of 12 to 18 m/min and same power, partial penetration was observed. The joint efficiency of laser-welded joint was improved by the addition of Cu, Ni, and Zr due to the solid solution hardening, grain refining and precipitation hardening. The type of hardening has been further considered by metallurgical examination.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2007.04a
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• pp.33-36
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• 2007

In order to select the optimum mix for the required fluidity and strength of mass concrete which is applied to transfer girder and to choose the optimum curing method depending on circumstances through hydration heat analysis of mass concrete, this study examined slump flow, air content and elapsed variation (0, 30, 60, 90) in unhardened concrete properties and reviewed compressive strength characteristics in hardening properties. And hydration heat analysis results through simulation are as follows; 1) Fluidity changes of unhardened concrete showed no significant difference, and those of elapsed variation also showed no difference but a bit of tendency to increase in comparison with the initial properties. 2) The higher the water-binder ratio was, the lower the compressive strength properties were, and the higher the fly ash replacement rate was, the lower the compressive strength development was. 3) In case of $Fc=40N/mm^2$, the optimum mix was fly ash replacement rate of 15% from water-binder ratio of 33.0%. 4) Hydration heat analysis results showed that in case of bundle cast, concrete temperature profile characteristics around transfer girder was unfavorable, and in case of separate cast, constant curing for at least seven days guaranteed thermal cracking index of 1.2.

• Journal of Hydrogen and New Energy
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• v.33 no.6
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• pp.786-794
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• 2022

Green ammonia is a promising renewable energy carrier. Green ammonia can be used in various energy conversion devices (e.g., engine, fuel cell, etc.). Ammonia has to be fed with hydrogen for start-up and failure protection of some energy conversion devices. Ammonia can be converted into hydrogen by decomposition and partial oxidation. Especially, partial oxidation has the advantages of fast start-up, thermally self-sustaining operation and compact size. In this paper, thermodynamics, start-up and operation characteristics of ammonia partial oxidation were investigated. O₂/NH₃ ratio, ammonia flow rate and catalyst volume were varied as operation parameters. In thermodynamic analysis, ammonia conversion was maximized in the O₂/NH₃ range from 0.10 to 0.15. Ammonia partial oxidation reactor was successfully started using 12 V glow plug. At 0.13 of O₂/HN₃ ratio and 10 LPM of ammonia flow rate, ammonia partial oxidation reactor showed 90% of ammonia conversion over commercial Ru catalyst. In addition, Increasing O₂/NH₃ ratio from 0.10 to 0.13 was more effective for high ammonia conversion than increasing catalyst volume at 0.10 of O₂/NH₃.

• Journal of Korean Society for Atmospheric Environment
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• v.23 no.1
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• pp.84-96
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• 2007

We performed the experiments to manufacture the hydrophobic $200cells/in^2$-zeolite honeycomb using HY-type zeolite of Si/Al ratio of 80 for separating and removing the VOCs emitted from small and medium size-plants by adsorption and to determine the drying method for the honeycomb at $105^{\circ}C$ without cracking, then measured performances of the honeycomb to adsorb the benzene, o-xylene, and MEK and to desorb the benzene and MEK saturated on the honeycomb by the nitrogen gas as the desorption gas. As a results, the good honeycomb was formed and the honeycomb was not cracked when the mixing ratio of the zeolite to bentonite to methyl cellulose to polyvinyl alcohol to glycerine to water is 100 : 8.73 : 2.18 : 4.19 : 1.38 : 126 and dried the honeycomb at $105^{\circ}C$ for 24 hours in the drying oven. The shape of the dried honeycomb was not changed after calcination, and the compressive strengths of the honeycomb after drying and calcination were 6.7 and $0.69kg/cm^2$, respectively. The adsorption efficiencies of the honeycomb for benzene, o-xylene, and MEK were $92{\sim}96%$ at the room temperature. The desorption efficiency at $180^{\circ}C$ was higher than that at $150^{\circ}C\;by\;1.5{\sim}13.8%$ depending on the flow rate of the nitrogen gas, and it was found that desorption efficiency is higher than 85% at $180^{\circ}C$ and 1.0L/min of the nitrogen gas. At $180^{\circ}C$ and 0.2 L/min, the concentration of the benzene and MEK in the used desorption gas are higher than 40,000 and 50,000ppm, respectively, so it be used as the fuel for preheating the desorption gas fed into the column in desorption cycle.

• Journal of the Korean Institute of Gas
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• v.7 no.2 s.19
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• pp.22-32
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• 2003

Al-brass material is generally used at the state of plastic deformation, for example; bending, extension of bell mouth at shell and tube type heat exchanger. And SCC(stress corrosion cracking) of Al-brass material will be affected by residual stress as plastic deformation. SCC results from synergism between mechanical factor and corrosion environment. Mechanical factor is stress that directly relates with stress intensity factor at the crack tip. This paper was studied on the effect of stress on SCC of Al-brass tube under in $3.5\%$ NaCl. + $0.1\%\;NH_4OH$ solution by constant displacement tester. Increasing of acidified water flow into sea and speeds up corrosion rate of Al-brass which is used as a tube material of vessel heat exchanger by polluted coast seawater. The experimental results are as follow The latent time of SCC occurrence gets longer as the initial stress intensity factor($K_{Ii}$) gets lower The main crack was propagated as the initial stress intensity factor($K_{Ii}$) gets higher, and secondary cracks occurred by electro-chemical factor a(ter stage of released stress. Dezincification phase showed around the crack, and the range of dezincification gets wider as the initial stress intensity factor($K_{Ii}$) gets higher.