• Bulletin of the Korean Chemical Society
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• v.25 no.1
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• pp.122-126
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• 2004

Biofunctional nanohybrids are synthesized from layered double hydroxide (LDH) and the vitamins such as ascorbic acid and topopherol acid succinate. Either ion exchange or copricipitaion leads to successful intercalation of the vitamins into gallery space of LDH that offers a new route to safe preservation of bioactivity as well as controlled release. Intercalations of vitamins are clearly reflected on the increase in the basal spacing of ZnAl-(Nitrate) LDH from 8.5 ${\AA}$ to 10.5 ${AA}$ for ascorbate, and 49.0 ${AA}$ for tocopherol acid succinate, respectively. No significant change in UV-Vis and IR absorption characteristics of the intercalated vitamins strongly supports the safe maintenance of their bioactivities without any deterioration of chemical and structural integrity. Furthermore, it is shown that the hybridized vitamins could be discharged in a controlled kinetics.

• Journal of the Korean Applied Science and Technology
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• v.23 no.2
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• pp.99-109
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• 2006

In order to obtain the maximum flame retardancy as well as the minimum deterioration of physical properties of PU flame-retardant coatings, chlorine and phosphorus functional groups were introduced into the pre-polymer of modified polyesters. In the first step, the tetramethylene bis(orthophosphate) (TBOP) and neohexanediol dichloroacetate (DCA-adduct) intermediates were synthesized. In the second step, 1,4-butanediol and adipic acid monomers were polymerized with the two kinds of intermediates to obtain copolymers. The modified polyesters containing chlorine and phosphorus (ATBA-10C, -20C, and -30C) were synthesized by adjusting that the content of phosphorus compound was fixed as 2wt% and the contents of chlorine compound (dichloroacetic acid) were varied as 10, 20, and 30wt%. Average molecular weight and polydispersity index of the preparation of ATBAs were decreased with increasing DCA content because of the increase in hydroxyl group that retards reaction.

• Progress in Medical Physics
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• v.7 no.1
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• pp.19-23
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• 1996

The chemical bond differences between a normal tissue and a fat tissue make a chemical shift artifact which is caused by a primary inacuracy of resonance signal location. The chemical shift also makes a variation of the transverse time T$_2$. An attempt is made to compare the values of SNR(Signal-to-Noise Ratio), the signal response, and the imaging time computed by applying T$\sub$2/$\^$＊/ for a fat-proton with ones of those computed by applying T$_2$ for a water-proton under the conditions of T$_1$/T$_2$=3 and T$\sub$2/$\^$＊/T$_2$=0.9. The results of the attempt show that the first two reduce to 5％ and 8％ out of 100％, respectively, and the last rather increases up to 10％. This shows that the chemical shift contributes to the deterioration of an MR imaging efficiency in addtion to the image distortion.

• Journal of the Korea Institute of Building Construction
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• v.19 no.5
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• pp.411-419
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• 2019

Underground concrete structures are constructed under a geographical environment called underground and exposed to various environments that promote deterioration. Among them, groundwater promotes deterioration of underground concrete structures due to contaminated water from the ground. In this study, the chemical resistance performance test evaluation of five different receptors for a total of 15-type leakage repair materials of five series was conducted to determine the chemical stability of the leakage repair material used in the crack area. The results show a general increase and decrease in most chemical receptors, but the biggest increase and decrease was shown in acrylic systems, which were found in sodium chloride and sodium hydroxide, and epoxy was found in hydrochloric acid. The cement system is showing a lot of increase and decrease in sodium chloride. It is expected that the results of these studies will be used as a basis for chemical stabilization in the development of new materials.

• Tribology and Lubricants
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• v.11 no.3
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• pp.40-47
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• 1995

The engine oil life was examined experimentally for small size single cylinder engines. This study was conducted in the laboratory. An Eddy Current type engine dynamometer was used with a motorcycle and a cultivator engine. Physical and chemical properties of used oil was analyzed to examine the oil life. Flushed oil was used for the reference instead of the new oil. It were found that deterioration of dynamic viscosity and anti-wear property of engine oil was due to dilution by fuel not depletion of ZDTP.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.10a
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• pp.828-835
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• 2000

In recent years, RC structures need reinforcement due to physical and chemical deterioration, reduction of serviceability and structural capacity. For reinforcement of RC structures, steel plate attachment, area increase and composite fiber sheet attachment methods are used, but there are some problems like weight increase, workability, quality control and fire resistance capacity. This study presents the effectiveness of flexural reinforcement of RC beams using composite rods that are inserted in high strength special purposed polymer mortar.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2017.05a
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• pp.116-117
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• 2017

The most important factor when designing coastal and offshore concrete structures is durability. However, concrete in marine environment is exposed to physical and chemical deterioration of seawater, which might easily lead to low quality. The purpose of the present study is to understand advantages of adding ground solidificaton materials by comparatively analyze the seawater resistance of general concrete and environmental-friendly ground solidification materials.

• Magazine of the Korean Society of Agricultural Engineers
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• v.45 no.3
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• pp.41-49
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• 2003

In this study, durability performance of blended cement mortars is evaluated when various mineral admixtures are used with the cement. A comprehensive evaluation of the effects of mineral admixtures on the mortar performance was made. The properties of fresh and hardened blended mortars investigated include slump flow and compressive strength. The durability characteristics of cement materials incorporating the mineral admixtures under various physical and chemical causes of deterioration was investigated. The laboratory test results indicate that mechanical and durability properties of blended cement mortars have superior performance rather than ordinary cement mortars.

• Magazine of the Korea Concrete Institute
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• v.10 no.4
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• pp.205-212
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• 1998

Frost damage of a storage tank for chemical admixtures caused by a low temperature in winter and quality deterioration of chemical admixtures have been often reported. However, there have been few regulations and researches related to the frost damage of chemical admixtures and facilities. Therefore, this paper is intend to investigate not only, the freezing points of chemical admixtures such as AE admixtures and water-reducing AE admixtures, etc., but also the quality variation of concrete used with chemical admixtures before freezing and after freeze-thaw cycles. According to the results of experiments, most chemical admixtures except anti-freezing agent and accelerating water-reducing AE admixtures should be kept from being frozen in low winter temperatures. However, full agitation of frozen chemical admixtures dose not cause the problems of concrete related to the quality of chemical admixtures.

• Korean Chemical Engineering Research
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• v.59 no.3
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• pp.333-338
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• 2021

The durability of the PEMFC stack for large commercial vehicles should be more than 5 times that for passenger vehicles. If the Chemical Accelerated Stress Test (AST) of PEMFC(Proton Exchange Membrane Fuel Cells) membrane for passenger cars is applied as it is for large commercial vehicles, there is a problem that the AST time becomes more than 2,500 hours. In order to shorten the AST time of DOE (Department of Energy), the chemical durability of the polymer membrane was evaluated using oxygen instead of air as a cathode gas. In this study, Nafion XL was used as a polymer membrane to evaluate accelerated durability under OCV, 90?, RH 30%, H₂/(air or oxygen) conditions. Among the DOE membrane durability target criteria, the decrease rate of short resistance was the fastest. By using oxygen instead of air, the degradation rate of the polymer membrane was accelerated while being less affected by electrode deterioration, reducing the polymer membrane durability evaluation time to less than half.