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        검색결과 41

        21.
        2004.09 KCI 등재 구독 인증기관 무료, 개인회원 유료
        Synthesis gas is a high valued compound as a basic chemicals at various chemical processes. Synthesis gas is mainly produced commercially by a steam reforming process. However, the process is highly endothermic so that the process is very energy-consuming process. Thus, this study was carried out to produce synthesis gas by the partial oxidation of methane to decrease the energy cost. The effects of reaction temperature and flow rate of reactants on the methane conversion, product selectivity, product ratio, and carbon deposition were investigated with 13wt% Ni/MgO catalyst in a fluidized bed reactor. With the fluidized bed reactor, CH4 conversion was 91%, and Hz and CO selectivities were both 98% at 850℃ and total flow rate of 100 mL/min. These values were higher than those of fixed bed reactor. From this result, we found that with the use of the fluidized bed reactor it was possible to avoid the disadvantage of fixed bed reactor (explosion) and increase the productivity of synthesis gas.
        4,000원
        22.
        2004.09 KCI 등재 구독 인증기관 무료, 개인회원 유료
        Although the structure of carbon nanotubes is important factor characterizing its properties, it is very difficult to control the structure of carbon nanotubes (MWNTs) and to predict the range of their diameter, which is the primary factor of MWNTs' physical properties. We tried to control the diameter of MWNTsby governing the feed injection temperature of floating catalyst method. The structure of MWNTs was influenced by the phase change of ferrocene fed as the catalyst,. The carbon nanotubes were very narrow at injection temperatures close to the sublimation pt. of ferrocene, in which most MWNTs had diameters in the range of 20~30 nm. At injection temperatures between the boiling pt. and melting pt. of ferrocene, the diameters became larger and had broad distribution. However, at injection temperatures higher than the boiling pt., the diameters became narrow again and had very uniform distribution.
        4,200원
        23.
        2004.09 KCI 등재 구독 인증기관 무료, 개인회원 유료
        Acrylic resins (HSCs : EA/EMA/2-HEMA/CLA) which contain 70% solid content were synthesized by the copolymerization of monomers (2-hydroxyethyl methacrylate, ethyl acrylate, and ethyl methacrylate) and functional monomer (caprolactone acrylate : CLA) which improves the crosslinking density and physical properties of films. The physical properties of the prepared acrylic resins (HSCs) containing CLA, are as follows : viscosity 245~515 cps ; Mn 2670~2840 ; and conversions, 83~91%, respectively. From the correlation of Tg values, viscosities, and Mn of the HSCs, it was found that viscosity and Mn increased with Tg value.
        4,000원
        24.
        2004.09 KCI 등재 구독 인증기관 무료, 개인회원 유료
        An emulsion of octadecamidoethylaminoethyl dodecate (which provides softness) and an emulsion silicone oil KF-96 (which provides lubricity) were separately synthesized. Then PP finishing softeners (SSA-7) was prepared by blending of the synthesized emulsions with beef tallow hardened oil (a softness improving agent). PP finishing treatment was carried out with the prepared SSA-7 and PP finishing resin by a one bath method, and several physical properties were tested. As a result, crease recovery, tear strength, softness, lubricity, and bending resistance were all good, indicating that the prepared SSA-7 is a good PP finishing softener.
        4,000원
        25.
        2004.06 KCI 등재 구독 인증기관 무료, 개인회원 유료
        Multi-walled carbon nanotubes (CNTs) were prepared by thermal chemical vapor deposition (CVD) and microwave plasma chemical vapor deposition (MPCVD) using various combination of binary catalysts with four transition metals such as Fe, Co, Cu, and Ni. In the preparation of CNTs from acetylene precursor by thermal CVD, the CNTs with very high yield of 43.6 % was produced over Fe-Co/Al2O3. The highest yield of CNTs was obtained with the catalyst reduced for 3 hr and the yield was decreased with increasing reduction time to 5 hr, due to the formation of FeAl2O4 metal-aluminate. On the other hand, the CNTs prepared by acethylene plasma CVD had more straight, smaller diameter, and larger aspect ratio(L/D) than those prepared by thermal CVD, although their yield had lower value of 27.7%. The degree of graphitization of CNTs measured by Id/Ig value and thermal degradation temperature were 1.04 and 602℃, respectively.
        4,000원
        26.
        2004.03 KCI 등재 구독 인증기관 무료, 개인회원 유료
        The effects of reaction temperature and flow rate of reactants on the methane conversion, product selectivity, product ratio, and carbon deposition were investigated with 13wt% Ni/MgO catalyst. Reaction temperatures were changed from 600 to 850℃, and reactants flow rates were changed from 100 to 200 mL/mim. There were no significant changes in the methane conversion observed in the range of temperatures used. It is possibly stemmed from the nearly total exhaustion of oxygen introduced. The selectiveties of hydrogen and carbon monoxide did not largely depend on the reaction temperature. The selectivities of hydrogen and carbon monoxide were 96 and 90%, respectively. Carbon deposition observed was the smallest at 750℃ and the largest at 850℃. It is found that the proper reaction temperature is 750℃. The best reactant flow rate was 150 ml/min.
        4,000원
        27.
        2003.09 KCI 등재 구독 인증기관 무료, 개인회원 유료
        Synthesis gas is commercially produced by a steam reforming process. However, the process is highly endothermic and energy-consuming. Thus, this study was conducted to produce synthesis gas by the partial oxidation of methane to decrease the energy cost. Supported Ni catalysts were prepared by the impregnation method. To examine the activity of the catalysts, a differential fixed bed reactor was used, and the reaction was carried out at 750~850℃ and 1 atm. The fresh and used catalysts were characterized by XRD, XPS, TGA and AAS. The highest catalytic activity was obtained with the 13wt% Ni/MgO catalyst, with which methane conversion was 81%, and H2 and CO selectivities were 94% and 93%, respectively. 13wt% Ni/MgO catalyst showed the best MgNiO2 solid solution state, which can explain the highest catalytic activity of the 13wt% Ni/MgO catalyst.
        4,000원
        28.
        2003.09 KCI 등재 구독 인증기관 무료, 개인회원 유료
        Electrical properties of carbon filler/PVdF [poly(vinylidene fluoride)] composite were investigated as a funtion of carbon filler/PVdF ratio in the range of 0.2~0.5. Three kinds of comercialzied conductive carbon blacks such as Hiblack 41Y, KE300J, and KE600J, and carbon nanofibers prepared by the catalytic chemical vapor deposition of C2H4 over Ni-Cu catalysts were used as the carbon fillers. The electrical conductivity of carbon filler/PVdF composites were in the range of 0.65 to 13.5 S/cm depending the fillers' electrical conductivity ranging from 5.6 to 23.1 S/cm. Among the carbon fillers used, the KE600J carbon black showed the highest conductivity both in the composite and filler itself because of its high degree of graphitization due to the high-temperature thermal treatment and its high surface area due to the activation treatment.
        4,000원
        29.
        2003.06 KCI 등재 구독 인증기관 무료, 개인회원 유료
        In order to improve the lithium ion battery's performance, the carbon nanofibers were introduced to the anode electrode fabricated with natural graphite particles. The influence of structural adjustment of the particles by the introduction method of carbon nanofibers and the content of carbon nanofibers on the electrical property and charge/discharge characteristics of the electrode were investigated. The electrode fabricated with the mixture of 10 wt% of carbon nanofibers grown separately and 90 wt% of graphite particles showed an excellent discharge capacity of 400 mAh/g and the improved cycle performance. The improved performance could be explained by that the carbon nanofibers shortened and uniformly distributed on the surface of graphite particles by ball milling increased the stability for the intercalation/deintercalation of lithium ion and increased the electrical conductivity due to the closed packing between graphite particles.
        4,200원
        30.
        2003.03 KCI 등재 구독 인증기관 무료, 개인회원 유료
        The impregnated activated carbons were prepared by the incipient wetness method with the contents of KIO3 varied from 1.0~10 wt% as the impregnation material. The specific surface area and micropore volume of the rice hulls activated carbon were 2,600~2,800 m2/g and 1.1~1.4 cc/g, respectively. With increasing the contents of impregnation materials, the surface area and micropore volume decreased by 3~21%. However, The amounts of hydrogen sulfide adsorbed increased by 2.1~2.8 times depending on the impregnation content. The optimum contents of KIO3 were 2.4 wt%. Although the breakthrough time and adsorption capacity of hydrogen sulfide decreased with increasing temperature in the case of the unimpregnated activated carbons, they increased by 1.2~ 3.2 times for the case of the impregnated activated carbons. The optimum aspect ratio(L/D) was 1.0 and the adsorption amount of hydrogen sulfide enhanced with increasing the gas flow rate. The regeneration temperature was determined as 400℃ from the TGA experiment. The adsorption capacity of hydrogen sulfide with the impregnated activated carbon decreased gradually as the regeneration continued. The hydrogen sulfide adsorption amount of the regenerated activated carbon up to 4 times was still higher than that of the unimpregnated activated carbon.
        4,000원
        31.
        2002.12 KCI 등재 구독 인증기관 무료, 개인회원 유료
        Environmental friendly acrylic/urea high-solid paint(MUHC) were prepared through the curing reaction of acrylics resin(EBHC) containing 70wt% of solids content and butylated urea curing agent. The synthesis of EBHC Was done at 150℃ for 6 hours, and the results were obtained as follows : Mn=1830~2190, Mw 3290~4000, Mw/Mn=1.80~1.83 viscosity=110~352 cps, and conversion=82~92%. After the film was coated with MUHC, the various physical properties were measured. They showed that enhancement of the coating properties such as adhesion, flexibility, abrasion resistance, impact resistance, and water resistance could be expected through introdl1cing caprolactone acrylate component in acrylics resin for the high-solids content acrylics/urea coatings.
        4,000원
        32.
        2002.09 KCI 등재 구독 인증기관 무료, 개인회원 유료
        Activated carbons with high surface area of 2,600 m2/g and high pore volume of 1.2 cc/g could be prepared by KOH activation of rice hulls at a KOH:char ratio of 4:1 and 850℃. In order to increase the adsorption capacity of hydrogen sulfide, which is one of the major malodorous component in the waste water treatment process, various contents of Na2CO3 and KIO3 were impregnated to the rice-hull activated carbon. The impregnated activated carbon with 5 wt.% of Na2CO3 showed improved H2S adsorption capacity of 75 mg/g which is twice of that for the activated carbon without impregnation and the impregnated activated carbon with 2.4 wt.% of KIO3 showed even higher H2S adsorption capacity of 97 mg/g. The improvement of H2S adsorption capacity by the introduction of those chemicals could be due to the H2S oxidation and chemical reaction with impregnated materials in addition to the physical adsorption of activated carbon.
        4,000원
        33.
        2002.06 KCI 등재 구독 인증기관 무료, 개인회원 유료
        The cutaneous tolerability of detergent formulations can be improved by means of suitable additives. They complex the surfactant molecules lowering the concentration of their free monomeric species. Proteins derivatives used as additives for detergency are usually prepared by partial hydrolysis of plant reserve proteins. The main purpose of the hydrolytic cleavage is to make them water soluble and suitable for liquid products. Water solubility and stability are obtained by means of complexation with surfactants which also increase their actual hydrophobicity, an important parameter affecting cosmetic properties of proteins. Transepidermal water loss (TEWL) and electric capacitance (EC) have been adopted as investigation technigues to evaluate the skin integrity/damage in vitro tests, The performance of native wheat protein / surfactant complexes has been compared with traditional protein hydrolysates as detergent additives. The results show a noticeable reduction of skin irritation in surfactant formulations with addition of native wheat protein.
        4,000원
        34.
        2001.06 KCI 등재 구독 인증기관 무료, 개인회원 유료
        Due to its low density, good mechanical properties and chemical inertness, glassy carbon(GC) has been studied for appications in several fields. A raw thermosetting resin of furanic resin was polymerized with a curing agent of p-toluenesulfonic acid monohydrate. The maximum yield of GC was obtained at the curing agent content of 1.0 wt% in furanic resin. In order to make thick GC, the affect of graphite filler addition to the furanic resin was investigated. The density and electrical resitivity of GC after graphitization were 1.45 g/cm3 and 47 ×10-4 Ω · cm respectively and the amorphous structure of GC was confirmed by XRD profiles with very broad peaks comparable to those of graphite at 206˚ and 45˚.
        4,000원
        35.
        2001.03 KCI 등재 구독 인증기관 무료, 개인회원 유료
        Acrylic quarternary polymers were synthesized to prepare high-solid coatings. Acrylic resins were synthesized by the radical polymerization of n-butyl acrylate, methyl methacrylate, 2-hydroxyethyl methacrylate and acetoacetoxyethyl methacrylate. From the results of experiment on reaction condition to get high-solid acrylic resins with 70% solid content and viscosity of 1200cps, it was found that di-tert-amyl peroxide among the four types of initiators have lower viscosity and higher degree of conversion. The optinum initiator amount, chain transfer agent, reaction temperature and the dropping time were 5wt%, 4wt%, 150℃ and 5hrs, respectively.
        4,000원
        36.
        2000.09 KCI 등재 구독 인증기관 무료, 개인회원 유료
        A conductimetric study of foam formed from mixture of the protein, β-lactoglobulin, and the nonioinc surfactant, SML, revealed that their stability was reduced at concentrations of SML in the range 3~10mM. The interaction of SML with β-lactoglobulin was investigated by fluorimetry and a dissociation constant of 0.2μM was calculated for the complex. Surface tension studies confirmed the presence of interaction between the two components and provided evidence for the progressive displacement of β-lactogloblin from the air/water interface with increasing SML concentration. Experiments using air-suspended microscopic thin liquid films revealed transitions in the chainage characteristics and thickness of the film at SML concentrations below that which resulted in destabilization of the foam. However, measurements of surface mobility of fluorescent-labeled β-lactoglobulin by a photobleaching method identified that a transition to a mobile system occurred at a SML concentration which correlated with the onset of instability in the disperse phase. The results would indicate that maintenance of the viscoelastic properties of the surface is paramount importance in determining the stability of interfaces comprising mixtures of protein and surfactant.
        4,000원
        37.
        2000.06 KCI 등재 구독 인증기관 무료, 개인회원 유료
        Surface tension as a function of concentration and temperature was measured for aquous solution of sodium N-acyl sarcosinate, RCON(CH3)CH2 COONa, From the intersection points in the (γ-logC) curves, the critical micelle concentration (cmc) was determined at 20, 30, 40, and 50℃. Structural effects on the cmc maximum and the minimum area per molecule at the aquous solution/air interface were discussed. The free energy, enthalpy, and entropy of micellization and adsorption of surfactant solution also were investigated. Numberous investigators have dealt with sodium N-acyl sarcosinates and their applications as wettings, flooding and reducing agents and as corrosion inhibitors.
        4,000원
        38.
        2000.06 KCI 등재 구독 인증기관 무료, 개인회원 유료
        Physical properties and performance characteristics of sodium salt of several pure N-acyl amino acids made from glycine, dl-alanine, sarcosine, dl-valine, l-leucine, l-aspartic acid and l-lysine seven long chain fatty acids are reported. The effect of acyl chain length and the differences in the structure of constituent amino acid of seven homologous series of amide intermediate linked carboxylate surfactant of this class on the properties are discussed.
        4,000원
        39.
        2013.07 KCI 등재 서비스 종료(열람 제한)
        이 연구에서는 수석교사에 대한 역할기대와 수석교사의 역할수행에 대하여 교사들의 지각에는 어떠한 차이가 있으며, 그 원인은 무엇인가를 밝히는 데 목적이 있다. 연구목적을 달성하기 위한 연구문제는 첫째, 수석교사의 역할에 대한 기대와 역할수행에 대하여 교사들의 인식에는 차이가 있는가, 둘째, 수석교사에 대한 역할기대와 역할수행 상의 차이의 원인은 무엇인가로 설정하였다. 연구문제에 대한 결과를 요약하면 다음과 같다. 첫째, 수석교사에 대한 역할기대와 수석교사의 역할수행 간에는 유의한 차이가 있는 것으로 나타났다. 즉, 교사들은 수석교사에 대한 역할기대와 역할수행이 일치하지 않는다고 인식하였다. 반면, 교사들의 배경변인에 따른 역할기대에는 인식의 차이가 없었고, 역할수행 역시 유의한 차이가 없는 것으로 나타났다. 둘째, 수석교사에 대한 역할기대와 수석교사의 역할수행 상의 차이의 원인은 크게 세 가지 측면에서 나타났다. 첫 번째 원인은 교사들이 수석교사에 대한 기대수준이 높아 실제 역할수행이 이에 미치지 못한 경우에 발생하였다. 두 번째 원인은 수석교사의 역량에 대한 불신에서 비롯되었다. 세 번째 원인은 수석교사의 역량 발휘의 여건이 미흡하여 역할기대와 역할 수행 간의 차이가 있는 것으로 나타났다.
        40.
        2009.11 KCI 등재 서비스 종료(열람 제한)
        본 연구는 운동에 따른 스트레스 대처전략의 변화를 검토하기위해 남자 대학교 신입생 115명을 대상으로 16주간의 운동 프로그램을 실시하였다. 운동 프로그램은 주당 3회, 저항성 운동, 유산소성 운동, 유연성 및 평형성 향상 운동 등 복합운동으로 구성하였다. 체력과 스트레스 대처전략은 프로그램 실시 전과 후에 측정되었다. 얻어진 자료를 토대로 운동프로그램의 효과를 입증하기 위해서 체력요소(근력, 근지구력, 심폐지구력, 순발력, 유연성, 민첩성, 평형성)들의 변화 정도로 검토한 후, 스트레스 대처전략의 변화를 검토하였다. 분석결과 체력요소들과 스트레스 대처전략은 운동프로그램 실시 전에 비해 실시 후가 모든 요인에 있어서 통계적으로 유의하게 향상되었다. 따라서 복합운동은 스트레스 대처전략의 변화에 긍정적인 영향을 미친다는 결론을 얻었다.
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