• Korean Chemical Engineering Research
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• v.50 no.4
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• pp.627-631
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• 2012

Sodium borohydride, $NaBH_4$, shows a number of advantages as hydrogen source for portable proton exchange membrane fuel cells (PEMFCs). The durability of Co-P-B/Cu catalyst for sodium borohydride hydrolysis reaction was studied. The effect of reaction temperature, $NaBH_4$ concentration, NaOH concentration and calcination temperature of catalyst on the durability of Co-P-B/Cu catalyst were measured. The gel formed during hydrolysis reaction affected the durability of catalyst (loss of catalyst). Formation of gel increased the loss of the catalyst. When $NaBH_4$ concentration was high and reaction temperature was higher than $60^{\circ}C$, loss of catalyst was low because gel was not formed. But under the temperature of $40^{\circ}C$, loss of catalyst increased due to gel formation When $NaBH_4$ concentration was 40 weight % and the reaction temperature was $40^{\circ}C$, the loss of catalyst increased as the NaOH concentration increased. As the calcination temperature of catalyst decreased, the loss of catalyst decreased and the activity of catalyst decreased. Calcination of the catalyst at high temperature enhanced the durability of catalyst but diminished the activity of catalyst.

• Korean Chemical Engineering Research
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• v.59 no.1
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• pp.49-53
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• 2021

The Fenton reaction is often used to evaluate the chemical durability of polymer membranes of Proton Exchange Membrane Fuel Cells (PEMFC). However, due to the violent reaction between hydrogen peroxide and iron ions, it is difficult to compare experimental data because of low reproducibility. In this study, we tried to find the reaction conditions to improve the reproducibility of the durability test of the membrane by the Fenton reaction. The hydrogen peroxide concentration was fixed at 30%, the iron ion concentration, temperature, stirring speed, and sample size were varied, and the fluorine ion concentration of the Nafion polymer membrane deteriorated by radicals was measured. When the iron ion concentration was increased or the membrane sample size was increased, and the reaction temperature was increased to 80 ℃, the experimental deviation increased, so an iron ion concentration of 10 ppm, a temperature of 70 ℃, and a sample size of 0.5 ㎠ were suitable.

• Proceedings of the Korean Geotechical Society Conference
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• 1999.11c
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• pp.21-38
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• 1999

Engineering properties of most polymers used in geosynthetics such as geogrid can be degraded by the chemical reaction (e.g., oxidization, ultraviolet rays, hydrolysis etc.), chemical and mechanical load, microorganism, and so on. In addition, polymer can be damaged by the compaction during construction, and the characteristic of tensile strength of polymer can be changed by the long-term creep effect. In this study, engineering properties of flexible geogrids which are manufactured by weaving/knitting the high-tenacity polymers such as polyester formed in a very open, grid-like configuration, coated with any one of a number of materials (e.g., PVC, latex, etc.), are investigated. Through the analysis of test results, the durability and the long-term design tensile strength of flexible geogrids are evaluated.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.05a
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• pp.196-199
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• 2004

Metakaolin is a cementitious material for producing high-strength concrete. This material is now used as substitute for silica-fume. In this paper, we tested the compressive strength of concrete according to the substitute ratio of metakaolin, silica-fume. And we did the durability test such as chloride ion diffusion and chemical attack. In the compressive strength test, the result shows that $10\%$ substitute of metakaolin & silica-fume for binder is optimum. In the chloride ion diffusion test, according to the increase of substitute of metakaolin & silica-fume for binder, the diffusion coefficient is more reduced. And in the chemical attack test, according to the increase of substitute, the resistance is more excellent. In the durability test, we recognized that metakaolin is able to used as a substitute for silica-fume.

• Corrosion Science and Technology
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• v.15 no.1
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• pp.28-37
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• 2016

Due to the increased construction of offshore concrete structures and the use of de-icing salts for the purpose of snow removal, the needs for the development of anti-corrosive concrete are increasing. To solve these problems, an evaluation of the mechanical and durability properties for concrete were conducted by mixing modified-sulfur as 0 %, 5 %, 10 %, 15 % cement weight ratio. Both strengths and the properties affecting durability such as water absorption coefficient, chloride ion permeability, accelerated carbonation resistance, rapid freezing and thawing, and chemical resistance were evaluated. All evaluations performed were according to the test specifications associated KS. The results indicate that mixing of modified-sulfur lowed chloride ion permeability and improved chemical resistance.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.11a
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• pp.217-220
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• 2004

Metakaolin is a cementitious material for producing high-strength concrete. This material is now used as substitute for silica-fume. In this paper, we did the durability test such as chloride ion diffusion, chemical attack. repeated freezing and thawing, carbonation. In the chloride ion diffusion test, according to the increase of substitute of metakaolin & silica-fume for binder, the diffusion coefficient is more reduced. And in the chemical attack test, according to the increase of substitute, the resistance is more excellent. In the other durability test, the concrete using metakaolin is also compared with those of the portland cement concrete and silica fume concrete. According to these tests, we recognized that metakaolin is able to be used as a substitute for silica-fume.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.16 no.2
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• pp.100-105
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• 2007

Electro-rheological(ER) fluid and valve are fabricated and evaluated experimentally in its durability to utilize the hydraulic control systems for long term operation. The two-ports ER valve used in the experiment consist of twelve parallel multi-layer electrodes and provide a restriction to the passage of ER fluid because of the viscous pressure drop and a component induced by the electric field. The durability test of ER valve are performed by measuring the surface roughness of electrodes with variation of an electric field strength and test time(1000 or 1800min.). Also, the shear stress and shear rate are measured to evaluate the durability of ER fluid as function of time. After durability test, ER shear stress increases approximately proportional to the shear rate with applied electric field intensity, In the ER valve, the center line average height roughness(Ra) of copper electrode increases about 1.56 times and ten-point median height roughness(Rz) increases about 2.2 times after the durability test. An understanding of these durability is essential to predicting the service life of ER fluid and valves.

• Computers and Concrete
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• v.8 no.5
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• pp.511-524
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• 2011

Although concrete is believed to be a durable material, concrete structures have been degraded by severe environmental conditions such as the effects of chloride and chemical, abrasion, and other deterioration processes. Therefore, durability evaluation has been required to ensure the long term serviceability of structures located in chloride exposed environments. Recently, probability-based durability analysis and design have proven to be reliable for the service-life predictions of concrete structures. This approach has been successfully applied to durability estimation and design of concrete structures. However, currently it is difficult to find an appropriate method engineers can use to solve these probability-based diffusion problems. In this paper, computer software has been developed to facilitate probability-based durability analysis and design. This software predict the chloride diffusion using the Monte Carlo simulation method based on Fick's second law, and provides durability analysis and design solutions. A graphic user interface (GUI) is adapted for intuitive and easy use. The developed software is very useful not only for prediction of the service life but for the durability design of the concrete structures exposed to chloride environments.

• Journal of the Korean Society of Industry Convergence
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• v.25 no.6_3
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• pp.1239-1246
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• 2022

This paper introduces the effect of grease on the degradation characteristics of bearings used as key components of packaging equipment and automation systems. Bearings parts are installed to fix and support the rotating body of the system, and performance degradation of the bearings has a great effect on the life of the system too. When bearings are used in various devices and systems, the grease is applied to reduce friction and improve fatigue life. Determining the type of lubricant (grease) is important because it has a great influence on the operating environment and lifespan and ensures long lifespan of systems and facilities. However, studies that simultaneously compared and analyzed the change in mechanical degradation characteristics and the comparison of chemical degradation characteristics according to grease types under actual operating conditions are insufficient. In this paper, three types of small harmonic drive, high-load reducer, and low-load reducer grease used in power transmission joint modules are experimentally selected and finally injected into ball bearings with a load (19,500N) to improve bearing durability. Degradation characteristics were tested by attaching to test equipment. At this time, after the durability test under the same load conditions, the mechanical degradation characteristics, that is temperature, vibration according to the three greases types. In addition, the chemical degradation characteristics of the corresponding grease was compared to present the results of mutual correlation analysis.

• Journal of the Korean Applied Science and Technology
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• v.17 no.4
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• pp.267-272
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• 2000

Dual-actions are the most recently used delivery system in drug study. Dual-action agents are unique chemical entities comprised of two different type of antibacterial compounds covalently linked together in a single molecule in such a way that both components are able to exert their bactericidal properties. Crosslinked sulfadiazine-sulfanilamide such as antibiotics is synthesized by synthetic handle with glutaraldehyde. As a result, New synthetic antibacterial agent exhibited the broad antibacterial activities against gram(+) and gram(-) of 4 strains and a long durability supposing that the stomach and blood.