• Korean Chemical Engineering Research
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• 제46권6호
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• pp.1052-1056
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• 2008

소다 공정에서 탄산칼슘 결정의 평균입경과 형상 변화를 온도변화와 PAA 용액의 첨가에 대하여 연구하였다. 낮은온도($30^{\circ}C$, $60^{\circ}C$)에서는 Calcite 결정을, 높은 온도($80^{\circ}C$)에서는 Aragonite 결정을 얻었다. $30^{\circ}C$와 $80^{\circ}C$에서 용액에 PAA 용액을 첨가하여도 결정의 형상변화는 없었다. 중간온도($60^{\circ}C$)에서 PAA 용액을 첨가하여 Aragonite 결정을 얻었다. 결정의 형상변화가 PAA 분자 첨가로 인하여 일어났다. PAA 용액의 농도가 높을수록, 더 많은 Aragonite 결정을 얻었다. PAA 수용액의 농도가 높고 분자량이 클수록 탄산칼슘 결정의 평균입경은 증대하였으며, 형상변화가 일어나는 영역에서는 PAA의 분자량이 평균입경변화에 중요한 변수가 된다.

• Korean Chemical Engineering Research
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• 제59권1호
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• pp.11-15
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• 2021

본 연구에서는 전극촉매 내구성 평가를 potentiostat를 사용하지 않고 간단히 로더(Electronic loader)를 사용해 전극을 가속 열화시키는 방법을 개발하고자 하였다. 이를 위해, cathode에 질소를 유입하지 않고 산소를 유입해 자체 발생 전압을 활용해서 계단식 전압변화를 반복해 전극의 내구성을 평가하였다. 정확한 전극 내구평가를 위해 즉 고분자 막이 열화되지 않게 하기 위해 계단식 전압변화에서 고전압은 0.9 V로 낮게하고, 상대습도를 100%하여 라디칼에 의한 고분자 막 열화를 억제하고자 하였다. 전압변화 30,000 cycle (50시간) 만에 전극활성면적이 41.4% 감소했다. 전극은 열화되지만 고분자 막이 열화되지 않음을 수소투과도 증가가 없고 막 두께감소 없으면서 HFR (High Frequency Resistance) 증가 없는 것으로 확인했다.

• Bulletin of the Korean Chemical Society
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• 제30권9호
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• pp.2001-2006
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• 2009

Temperature dependence of the critical micelle concentration (CMC), $x_{CMC}$, in micellization can be described by ln $x_{CMC}$ = A + BT + C lnT + D/T, which has been derived statistical-mechanically. Here A, B, C, and D are fitting parameters. The equation fits the CMC data better than conventionally used polynomial equations of temperature. Moreover, it yields the unique(exponent) value of 2 when the CMC is expressed in a power-law form. This finding is quite significant, because it may point to the universality of the thermal behavior of CMC. Hence, in this article, the nature of the equation ln $x_{CMC}$ = A + BT + C lnT + D/T is examined from a lattice-theory point of view through the Flory-Huggins model. It is found that a linear behavior of heat capacity change of micellization is responsible for the CMC equation of temperature.

• 한국결정성장학회지
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• 제21권3호
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• pp.119-123
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• 2011

Carbon nanotilaments (CNFs) could be synthesized on nickel catalyst layer-deposited silicon oxide substrate using $C_2H_2$ and$H_2$ as source gases under thermal chemical vapor deposition system. By the incorporation of $SF_6$ as a cyclic modulation manner, the geometries of carbon coils-related materials, such as nano-sized coil and wave-like nano-sized coil could be observed on the substrate. The characteristics (formation density and morphology) of as-grown CNFs with or without $SF_6$ incorporation were investigated. Diameter size reduction for the individual CNFs-related shape and the enhancement of the formation density of CNFs-related material could be achieved by the incorporation of $SF_6$ as a cyclic modulation manner. The cause for these results was discussed in association with the slightly increased etching ability by $SF_6$ addition and the sulfur role in SF 6 for the geometry change.

• 열처리공학회지
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• 제33권3호
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• pp.107-116
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• 2020

Four air hardening steels with carbon, silicon, manganese, chromium, and molybdenum variations have been used in this study to find out the optimal chemical compositions of steels with over 1200 MPa tensile strength for automotive subframe. The dimensional changes after heat treatment were determined for two automotive parts with open and closed cross sections using 3D scanner. When four steels were austenitized at 900℃ for 30 seconds, cooled at 3℃/s, reheated to 450℃ for 10 seconds followed by air cooling to simulate hot-dip galvanizing treatment showed ultra high tensile strength over 1200 MPa. Rear floor cross member with open cross section revealed much bigger dimensional changes than subframe with closed cross section after heat treatment at 900℃ for 20 minutes followed by air cooling.

• 한국가스학회:학술대회논문집
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• 한국가스학회 1998년도 추계학술발표회 논문집
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• pp.295-300
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• 1998

• 한국재료학회지
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• 제12권2호
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• pp.135-139
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• 2002

Carbon powders (CP) and carbon fiber (CF) were introduced info glass fiber reinforced plastics (FRP) composites to obtain fracture detection function. The composites were evaluated through the relation between a load-displacement curve and an electrical resistance change curve in three point bending test. CP containing FRP (CP-FRP) has a sensitivity of electrical resistance change at much lower load level than CF containing FRP (CF-FRP). In loading-unloading tests, CP-FRP showed a large amount of residual electrical resistance which enables the estimation of loading hysteresis.

• Tribology and Lubricants
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• 제10권4호
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• pp.59-68
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• 1994

This study is concerned with the change of physical and chemical properties of the used oil in gasoline and LPG engine. The used oils of engine were sampled from dynamometer and cars. The field tests of car were done in city and on highway. The properties of oil were TAN, TBN, visocity, oxidation, ZDTP depletion factor and etc. Also the relation between the chemical change and antiwear property was studied. From the study, it was shown that the decrease of antiwear property of used oil was depended on the changes of ZDTP depletion factor as well as TAN (total acid number). Also, it was found that the oil used by LPG car was deteriorated within the shortest distance among the other gasoline cars. The antiwear property of oil decreased as the running distance increased. The gasoline engine oil drove mainly on highway was the least deteriorate of properities for the same running distance.

• 열처리공학회지
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• 제7권1호
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• pp.11-16
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• 1994

Anatase $TiO_2$ particles prepared by experiment were used to study the change of crystal structure by calcination temperature. The results were as follows. Crystallite size of anatase $TiO_2$ particles increased with calcination temperature. The rate of increasing the crystallite size of anatase $TiO_2$ particles was decreased below $700^{\circ}C$ and was markedly increased above $700^{\circ}C$. Unit cell volume of $TiO_2$ was expanded at low temperature and was contracted at high temperature. This result means that the growth of crystallite size was occured in the direction.

• Bulletin of the Korean Chemical Society
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• 제31권10호
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• pp.2797-2800
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• 2010

For the purpose of developing advanced new absorbents for carbon dioxide, ionic liquids (ILs) are considered as alternative materials due to their superior properties to conventional organic solvents. Since low $CO_2$ solubility in ionic liquids is a major concern for their application as absorbents, it is essential to focus on improving $CO_2$ absorbing capability of ILs. In this paper, strongly basic ionic liquids, namely [$C_n$-mim]OPh (n = 2, 4, 6), have been synthesized and studied over a wide range of temperature and pressure changes. [$C_n$-mim]OPh can be easily synthesized from corresponding [$C_n$-mim]Cl and sodium phenoxide and has been found to be good $CO_2$ absorbents.