• 대한전기학회:학술대회논문집
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• 대한전기학회 2000년도 하계학술대회 논문집 C
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• pp.1572-1574
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• 2000

In this paper, study on the properties of the thermal degradated epoxy resin which is used in cast resin transformer is performed to investigate the problems of the decreasing insulation characteristics and crack in the cast resin transformer. In the test, contact angle, weight loss, surface resistivity and relative dielectric constant are measured. As the results of the above measurements, the epoxy resin has increased to 150$^{\circ}C$ in the contact angle and surface resistivity but at the above 150$^{\circ}C$ the values have decreased. The relative dielectric constants have increased in the thermal treated samples with the degradation temperature. Consequently, the insulation properties of the epoxy resin which is used in cast resin transformer have increased by the 150$^{\circ}C$ but decreased in the above 150$^{\circ}C$.

• 유변학
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• 제11권1호
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• pp.9-17
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• 1999

본 연구에서는 페놀 수지/탄소섬유 복합재료가 상온에서부터 $400^{\circ}C$까지의 온도범위에서 유리 전이와 분해반응을 경험하면서 나타내는 점탄성 특징을 연구하였다. 가교 결합된 페놀메트릭스의 전형적인 유리전이에 따라 저장 탄성율(storage modulus)은 유리전이에 의하여 감소하였고 고무상태(rubbery state)에 도달함과 동시에 후경화 반응과 분해 반응 등을 포함하는 복합적인 고온반응에 의하여 증가하다가, 최대점을 보인 후 다시 감소하는 모습을 보였다. 유리전이 과정은 시간-온도 중첩원리에 따라 해석하였으나, 분해반응이 수반된 고온에서의 점탄성 특징은 저장 탄성율을 수직 및 수평 방향으로 이동시키어 마스터 커브를 완성 할 수 있었다. 이러한 실험적 결과를 토대로 아레니우스식과 Havriliak-Negami식에서 유추된 점탄성 모델을 이용하여 유리전이와 분해반응이 연속적으로 진행되는 과정을 정량적을 해석할 수 있었다. 이때의 완화시간은 유전이 과정을 통하여 감소하다가 고무상태에 이르러 최소값을 보여주고 이후로는 고온반응에 의하여 증가하는 모습을 보여주었다. 본 연구에서 제안된 점탄성 해석 방법은 반응이 수반된 열경화성 복합재료가 보여주는 점탄성 계수의 복잡한 거동을 온도와 주파수(frequency)에 따라 정확하게 묘사함으로서 이 모델링의 유용성을 증명 할 수 있었다.

• 환경위생공학
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• 제15권4호
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• pp.98-104
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• 2000

Commercial rubber(IR, NR, BR), SBR, and tire were degraded by thermal degradation process. The oil yield of rubbers and tire ranges about 37~86%, it was increased with increase of operation temperature in pyrolysis. And the yield of pyrolytic oil was increased with increase of heating rate. The maximum oil yields of IR, NR, BR, SBR, and tire were 80, 73, 83, 86 and 55% each at $700^{\circ}C$ with a heating rate of $20^{\circ}C$/min, respectively. The pyrolytic oil components were consisted of about 50 aromatic compounds. The calorific value of purolytic oil of commercial rubber, SBR, and tire was measured by calorimeter, it was 39~40 kJ/g. The BET surface area of pyroblack was $47~63m^2/g$. The optimum condition of pyrolysis was operating temperature of $700^{\circ}C$ with heating rate of $20^{\circ}C$. Therefore, the pyrolytic oil and pyroblack are possible to alternative fuel and carbon black.

• Korean Chemical Engineering Research
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• 제47권4호
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• pp.441-445
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• 2009

고분자전해질 막의 전기화학적 열화에 미치는 온도의 영향에 대해 연구하였다. 가속 열화 조건(OCV, anode 무가습, cathode 65% RH)에서 셀 온도를 변화시켜 144시간 운전한 후 셀 성능은 12에서 35%까지 감소하였다. 이러한 성능 감소는 FER(Fluoride Emission Rate) 측정에서 알 수 있듯이 과산화수소 혹은 산소라디칼(${\cdot}OH$, $HO_2{\cdot}$)의 공격에 의한 막의 열화에 따른 것으로 라디칼 형성을 위한 가스 crossover의 증가를 가져왔다. 전극에서의 라디칼 생성은 ESR로 확인하였다. 고분자막 열화의 온도 의존성을 나타내는 Arrhenius plot에 얻어진 활성화 에너지 값은 66.2 kJ/mol이었다. 셀 작동온도 증가는 라디칼 형성속도와 라디칼이 막을 공격하는 반응 속도뿐 아니라 가스 crossover 속도도 증가시켜 막 열화를 가속화시켰다.

• Elastomers and Composites
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• 제46권2호
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• pp.144-151
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• 2011

Intermittent CSR 측정법을 이용하여 hydrogenated NBR(이하 HNBR) 오링의 노화 거동과 수명 예측에 관하여 연구하였다. HNBR 오링의 가교 구조는 황 가교와 퍼옥사이드 가교를 이용하여 각각 제조하였다. Intermittent CSR jig는 오링의 실제 사용환경을 고려하여 설계 제작하였다. 각 측정 조건에 따른 마찰 영향, 열 손실 영향 및 Mullins effect에 의한 intermittent CSR의 응력 거동 변화를 관찰하였다. 오링의 노화 거동은 $100{\sim}120^{\circ}C$에서의 가속 노화 연구를 통하여 관찰하였다. 고장조건 50%와 40%에 대하여 HNBR 오링은 선형 노화 거동을 나타내었으며, Arrhenius relationship을 만족시켰다. HNBR-S 오링의 활성화 에너지는 70.6 kJ/mol로 나타났으며, Arrhenius plot으로부터 오링의 예측 수명은 고장 조건 50%와 40%에 대하여 각각 31.1년과 33.7년으로 나타났다. HNBR-P 오링의 활성화 에너지는 72.1 kJ/mol로 나타났으며, Arrhenius plot으로부터 오링의 예측 수명은 고장 조건 50%와 40%에 대하여 각각 34.0년과 36.5년으로 나타났다. 황 가교에 비하여 퍼옥사이드 가교에서 고무의 노화 속도가 느리게 나타났으며, 활성화 에너지는 높게 나타났다.

• Journal of Ginseng Research
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• 제39권4호
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• pp.304-313
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• 2015

Background: Ginsenoside Rg3 is a promising anticancer agent. It is usually produced by heat treatment of ginseng, in which ginsenoside Rb1 is the major ginsenoside. A kinetic study was conducted to optimize ginsenoside Rg3 production by the heat treatment of ginsenoside Rb1. Methods: Ginsenoside Rb1 was heated using an isothermal machine at $80^{\circ}C$ and $100^{\circ}C$ and analyzed using HPLC. The kinetic parameters were calculated from the experimental results. The activation energy was estimated and used to simulate the process. The optimized parameters of ginsenoside Rg3 production are suggested based on the simulation. Results: The rate constants were $0.013h^{-1}$ and $0.073h^{-1}$ for the degradation of ginsenosides Rb1 and Rg3 at $80^{\circ}C$, respectively. The corresponding rate constants at $100^{\circ}C$ were $0.045h^{-1}$ and $0.155h^{-1}$. The estimated activation energies of degradation of ginsenosides Rb1 and Rg3 were 69.2 kJ/mol and 40.9 kJ/mol, respectively. The rate constants at different temperatures were evaluated using the estimated activation energies, and the kinetic profiles of ginsenosides Rb1 and Rg3 at each temperature were simulated based on the proposed kinetic model of consecutive reaction. The optimum strategies for producing ginsenoside Rg3 from ginsenoside Rb1 are suggested based on the simulation. With increased temperature, a high concentration of ginsenoside Rg3 is formed rapidly. However, the concentration decreases quickly after the reaching the maximal concentration value. Conclusion: The optimum temperature for producing ginsenoside Rg3 should be the highest temperature technically feasible below $180^{\circ}C$, in consideration of the cooling time. The optimum reaction time for heat treatment is 30 min.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1996년도 하계학술대회 논문집 C
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• pp.1697-1699
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• 1996

EPDM compound can be cured with either the sulfur and peroxide based systems. In this study, heat resistance and weatherability of EPDM compounds depending on curing systems were investigated. The test results showed that the peroxide-cured EPDM was more resistant to heat ageing and UV photo-degradation than the sulfur-cured EPDM and it is due to C-C bond is more stable than C-S, S-S bond.

• Corrosion Science and Technology
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• 제20권6호
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• pp.335-346
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• 2021

Since epoxy resin coating shows excellent properties in formability, adhesion, and corrosion resistance, they have been extensively used in many industries. However, various types of damages in the epoxy coated tube within a relative short time have been reported due to cavitation erosion, liquid impingement, variation of temperature and pressure. Nevertheless, there has been little research on the effect of temperature on the cavitation degradation of epoxy coatings. Therefore, this work used an ultrasonic cavitation tester to focus on the effect of solution temperature on the cavitation properties of 3 kinds of epoxy coatings in 3.5% NaCl. The cavitation properties were discussed basis on the material properties and environmental aspects. As the solution temperature increased, even though with large fluctuation, the cavitation degradation rates of A and B coatings were reduced rapidly, but the rate of C coating was decreased gradually. In addition to the cushioning effect, the reason that the cavitation degradation rate reduced with solution temperature was partly related to the brittle fracture and water absorptivity of the epoxy coatings, and the water density, but was little related to the shape and composition of the compound in the coatings or the phase transition of the epoxy coating.

• 한국초전도ㆍ저온공학회논문지
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• 제12권2호
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• pp.5-8
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• 2010

In this study, the effect of bending strain on the transport property and critical current of lap and butt-jointed (non-laminated) BSCCO tapes has been investigated. The samples were joined using a mechanically controlled jointing procedure. To achieve a uniform thickness at the joint a single point loading contact has been devised. GFRP mandrels with different bending radii which support the sample during bending have been used. $I_c$ have been measured at 77 K and self field. In the case of easy bending test for jointed BSCCO tapes, sudden degradation of $I_c$ is caused by the local strain concentration due to non uniform deformation at the edge parts of the joint. In the case of hard bending test of jointed BSCCO tapes transverse macroscopic crack at specific subsection caused a large $I_c$ degradation. The transport property of jointed BSCCO tapes in each bending mode was discussed with the damage morphology occurred.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1997년도 추계학술대회 논문집 학회본부
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• pp.348-350
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• 1997

Because of internal voids ininsulators give rise to partial discharge(PD), which cause local breakdown and even entire insulation breakdown. Treeing due to PD is one of the main causes of breakdown of the insulating materials and reduction of the insulation life. Therefore the necessity for establishing a method to diagnose the aging of insulation materials and to predict the breakdown of insulation has become important. From this viewpoint, our studies diagnose insulation degradation using the method of computer sensing system, which has the advantages of PD and acoustic emission(AE) sensing system. To use advantages of these two methods can be used effectively to search for treeing location and PD in some materials. In analysis method of degradation. We analyzed the PD pulse and AE pulses by regression analysis, compared to these obtained the correlation coefficient and determination coefficient by T-distribution and saw that PD and AE pulses show a similar pattern on the whole. Finally using statically operator such as the center of gravity(G), the gradient of the discharge distribution(C), we have analyzed for the prediction of life which we can be obtained the time, occurred of many pulse of small discharge amplitude.