• Applied Chemistry for Engineering
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• v.24 no.2
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• pp.138-143
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• 2013

This paper studied the possibility to predict a mechanical property variation from changes in created carbonyl bands by irradiating the surface of high-density polyethylene with short-wavelength ultraviolet radiation of 254 nm to induce a fast chemical degradation. The meaning of this study lies in checking whether a mechanical property change with the same chemical property as the induced optical deterioration is caused by using a UVC lamp with high photon energy instead of optical deterioration via xenon arc light source and outdoor exposure test via natural sunlight requiring a long time. The mechanical strength of high-density polyethylene checked by a tensile test and a creep destruction test showed a similar tendency with CI changes. In particular, the yield strength and elongation had a close relationship with the exposure time to ultraviolet radiation. Accordingly, this paper presented a method to grasp the mechanical property change outdoors requiring a long time more fast through the relationship between the mechanical property change and the carbonyl index using a UVC lamp causing the fast surface degradation.

• Journal of Conservation Science
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• v.6 no.1 s.7
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• pp.79-88
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• 1997

It is important and urgent matters to conserve books and documents. Causes to the deterioration of papers, chemical methods to prevent or retard the deterioration of papers. physical methods to preserve the deteriorated papers, preparation of alkaline papers of which hydrolysis is very slow compared with acid ones, and recent requirements for papers used in books and documents are reviewed and discussed.

• Journal of the Korea institute for structural maintenance and inspection
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• v.18 no.4
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• pp.22-32
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• 2014

Durability is one of the most important and attractive subjects in concrete research field because not only durability of concrete is reduced by various degradation factors but also its reduction adversely influences the structural performance and service life of concrete structure. For this reason, a considerable amount of papers associated with concrete durability have been published and those researches were mainly focused on the changes of intrinsic properties of concrete due to chemicophysical degradations. However, the relationship between durability of concrete and structural behavior of concrete member has not been well established yet. In this study, calcium leaching degradation, a cause of concrete strength reduction, was dealt with. The experiments of compressive and flexural behavior of degraded concrete member were performed to evaluate the characteristics of structural behavior according to degradation level. Finally, the results from the experiments were compared with those obtained from nonlinear FEM analysis. The results from this study clearly showed that leaching degradation leads to decrease in compressive strength and compressive behavior evolves from brittle to ductile failure pattern during the degradation process. Load capacity and flexible rigidity of the degraded RC member decreased when the degradation level increased, in compressive zone. Additionally, it was found that the values from nonlinear FEM analysis, CDP model in ABAQUS, coincided well with the experimental results.

• Proceedings of the Korea Forestry Energy Research Society Conference
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• 2011.02a
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• pp.124-126
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• 2011

• Proceedings of the Korean Radioactive Waste Society Conference
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• 2012.10a
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• pp.409-410
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• 2012

• Korean Chemical Engineering Research
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• v.60 no.2
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• pp.202-207
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• 2022

The study on electrode degradation of Proton Exchange Membrane Fuel Cell (PEMFC) was mainly studied on the particle growth and active area reduction of Pt on the electrode. The degradation of the electrode catalyst Pt in contact with the membrane affects the deterioration of the polymer membrane, but there are not many studies related to this. In this study, the phenomenon of the deposition of deteriorated Pt inside the polymer membrane during the accelerated electrode catalyst degradation test and its effects were studied. The voltage change (0.6 V ↔ 0.9 V) was repeated up to 30,000 cycles to accelerate the platinum degradation rate. When the voltage change cycle was repeated while oxygen was introduced into the cathode, the amount of Pt deposited inside the film was larger than when nitrogen was introduced. As the number of voltage change cycles increased, the amount of Pt deposited inside the membrane increased, and Pt dissolved in the cathode moved toward the anode, showing a uniform distribution throughout the membrane at 20,000 cycles. In the process of the accelerated electrode catalyst degradation test, the hydrogen crossover current density of the membrane did not change, and it was confirmed that the deposited Pt did not affect the durability of the membrane.

• Journal of Welding and Joining
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• v.13 no.2
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• pp.1-11
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• 1995

고온설비에 사용되고 있는 고온재료의 재료특성 변화와 이의 평가방법에 대하여 극히 제한된 범 위에서 개략적으로 기술하였다. 이러한 고온설비의 재질열화에 대한 대책은 초임계압 화력발 전설비 등을 비교적 조기에 도입한 선진국은 물론 최근 발전설비의 보일러 및 터빈을 비롯하여 석유화학 설비의 압력용기 등과 같이 고온.고압 하에서 장시간의 운전이력을 갖는 고온기기의 수가 증가하는 상태에 있는 우리나라에 있어서도 이들 설비의 정확한 수명진단과 장수명화 기 술의 개발은 시급히 해결해야할 과제로 되고 있다. 또 이러한 문제들은 대부분 용접 부위가 문제점으로 제시되고 있다. 따라서 이를 원활히 해결하고 확실한 진단과 잔여수명예측에 대한 기술의 개발을 위해서는 산.학.연의 공동연구를 통하여 종합적이고 체계적인 연구가 절실하게 요구되며, 상호 습득하고 있는 정보교환도 중요하다.

• Journal of the Korea institute for structural maintenance and inspection
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• v.12 no.5
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• pp.55-64
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• 2008

Shotcrete have become a deterioration which was exposed to harmful environments. In this study, in order to evaluate the deterioration properties of shotcrete, visual examination, compressive strength, adhesive strength, microstructural analysis were investigated up to the 60th weeks of exposure. The attack solutions for test are sodium sulfate and hydrochloric acid solution with different concentrations, respectively. From the results, although the compressive strength of shotcrete specimens and the adhesive strength between specimens and rocks were high at the early immersion age, they rapidly dropped in the subsequent phases, especially in 5% sodium sulfate and pH1 hydrochloric acid solution. With continued exposure, various harmful ions penetrated into the shotcrete specimen, reacted with the cement hydrate, and generated expansion substances. It was verified that the shotcrete specimens suffered a serious deterioration by chemical attack.

• Korean Chemical Engineering Research
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• v.61 no.2
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• pp.189-195
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• 2023

As a PEMFC (Polymer Exchange Membrane Fuel Cell) cathode catalyst, Pt-Co/C has recently been widely used because of its improved durability. In a fuel cell, electrodes and electrolytes have a close influence on each other in terms of performance and durability. The effect on the electrochemical durability of the electrolyte membrane when Pt-Co/C was replaced in the Pt/C electrode catalyst was studied. The durability of Pt-Co/C MEA (Membrane Electrode Assembly) was higher than that of Pt/C MEA in the electrochemical accelerated degradation process of PEMFC membrane. As a result of analyzing the FER (Fluorine Emission Rate) and hydrogen permeability, it was shown that the degradation rate of the membrane of Pt-Co/C MEA was lower than that of Pt/C MEA. In the OCV (Open Circuit Voltage) holding process, the rate of decrease of the active area of the Pt-Co/C electrode was lower than that of the Pt/C electrode, and the amount of Pt deposited on the membrane was smaller in Pt-Co/C MEA than in Pt/C MEA. Pt inside the polymer membrane deteriorates the membrane by generating radicals, so the degradation rate of the membrane of Pt/C MEA with a high Pt deposition rate was higher than Pt-Co/C MEA. When the Pt-Co/C catalyst was used, the electrode durability was improved, and the amount of Pt deposited on the membrane was also reduced, thereby improving the electrochemical durability of the membrane.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.7
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• pp.3437-3443
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• 2013

The polymer insulators have been extensively used as an alternate material of ceramic insulators. However, when they are used in practical conditions, there are many problems of decreasing performance and shortening lifetime due to the exposures of degradation factors applied from the outdoor situations. Accordingly, the analysis of polymer degradations has been getting influential too late as one of important subjects for improvements of safety and reliability. Heat, water treatments are arbitrary simulated for finding out the initiations and processes of surface degradation on the polymer surface. Especially, this study is focused on the chemical changes properties. From the analysis of hydrophilic and hydrophobic molecular structures, final modeling of surface degradation is accomplished. We checked the contact angle depending on heat and moisturized accelerated degradation and ran an XPS analysis to check the mechanism change of the surface of the PCB polymer composite. The surface that had a tendency to attract moisture showed a decrease in the contact angle and generated a large amount of carboxyl($-COO^*$) radicals. The hydrophobized surface showed an increase in the contact angle and had a stable chemical composition constituted of the breakaway of oxygen radicals and the formation of double bond by carburization.