• Korean Chemical Engineering Research
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• 제62권3호
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• pp.246-252
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• 2024

본 연구에서는 구연산 처리를 통하여 폐흑연의 Li, F 등의 불순물을 제거하였으며, 이에 따른 재생 흑연의 구조적 특성, 용량 및 내구성 변화를 관찰하였다. 질소 분위기에서 전처리를 진행한 재생 흑연은 구연산에서 산처리를 진행하였고 SEM (Scanning Electron Microscope), FT-IR (Fourier Transform Infrared spectroscopy), XRD (X-ray Diffraction), XPS (X-ray Photoelectron Spectroscopy)를 통해 구조와 특성 분석을 진행하였다. 산처리를 진행하지 않은 폐흑연은 70 사이클 이전에서 용량이 급격하게 감소하였으나 구연산 처리를 진행한 흑연은 100 사이클에서 302.9 mAh g^-1의 용량과 93.1%의 용량 유지율을 나타내었다. 또한 Rate performance의 전류 밀도 변화에도 구연산 처리한 샘플은 용량의 변화없이 1.0C에서 340.2 mAh g^-1의 성능을 나타내었다. 결과적으로 구연산 처리는 효과적으로 불순물을 제거하여 높은 용량 유지율을 나타내었을 뿐만 아니라 높은 전류 밀도에서도 안정적인 모습을 나타내는 것으로 확인하였다.

• 한국전기전자재료학회논문지
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• 제19권10호
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• pp.889-893
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• 2006

Chemical mechanical polishing (CMP) achieves surface planrity through combined mechanical and chemical means. The role of slurry is very important in metal CMP. Slurry used in metal CMP normally consists of oxidizers, complexing agents, corrosion inhibitors and abrasives. This paper investigates the effects of citric acid as a complexing agent for Cu CMP with $H_2O_2$. In order to study chemical effects of citric acid, X-ray photoelectron spectroscopy (XPS) was peformed on Cu sample after etching test. XPS results reveal that CuO, $Cu(OH)_2$ layer decrease but $CU/CU_2O$ layer increase on Cu sample surface. To investigate nanomechanical properties of Cu sample surface, nanoindentation was performed on Cu sample. Results of nanoindentation indicate wear resistance of Cu surface decrease. According to decrease of wear resistance on Cu surface removal rate increases from $285\;{\AA}/min\;to\;8645\;{\AA}/min$ in Cu CMP.

• KSBB Journal
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• 제7권4호
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• pp.252-257
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• 1992

호기성 미생물 고정화를 위해 새로 개발한 평판형막 생물 반응기(FMBR)을 개발하여Aspergillus niger (KCTC 1232)로부터의 구연산 생산을 연구하였다. 반응기는 삼단으로 구성되어 있으며 상층부에는 산소 공급을 위한 공기흐름이 있고 주층부에는 미생물이 고정화되어 있으며 하층부에는 배지가 연속적으로 공급된다. 배지의 초기 pH는 구연산 생성에 있어서 중요한 영향을 미치며 pH가 낮을수록 구연산 생산수율이 높았다. 산소원으로 공기와 순수산소를 이용하여 생산성은 각각0.20, 0.40h/Lh에 달하였다. EH한 배지의 공급속도가 높을수록 생산성이 어느 정도 증가함을 알 수 있었다.

• 한국지하수토양환경학회:학술대회논문집
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• 한국지하수토양환경학회 2004년도 총회 및 춘계학술발표회
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• pp.307-310
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• 2004

Micellar enhanced ultrafiltration (MEUF) is a surfactant-based separation process and it can remove heavy metal ions from aqueous stream effectively. However, it is necessary to recover and reuse surfactants for economic feasibility because surfactant is expensive. Foam fractionation was investigated for both anionic and cationic surfactant recovery. Chelating agent such as ethylenediaminetetraacetic acid (EDTA) was studied for the separation of heavy metals from surfactant solution. Anionic surfactants bound with heavy metals can be recovered by lowering pH (acidification). In this study, citric acid and imminodiacetic acid (IDA) were applied to release copper from sodium dodecyl sulfate (SDS) micellar solution and compared with EDTA. Precipitation of copper by ferricynide and sodium sulfide were also investigated. As a result, ca. 100 % of copper was released from SDS micellar solution by 5 mM of EDTA and citric acid. And 3.3 mM of ferricyanide formed precipitate with 82.7 % of copper. 5 mM of IDA and sodium sulfide released or formed precipitate 82.5 % and 58.9 % of copper, respectively. Citric acid is harmless to environments and ferricyanide precipitates with Cu easily. Therefore, it is considered that citric acid and ferricyanide have competiveness over a famous chelating agent, EDTA, for the separation of Cu from SDS solution.

• 한국연초학회지
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• 제26권2호
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• pp.186-192
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• 2004

This study was carried out to analyze the organic acids, polyphenols, pigments and fiber materials concentration with a different stalk position and grade of korean leaf tobaccos. Eight kinds of flue-cured leaf tobaccos which were different stalk position and grade were used for this study. Three kinds of major organic acids(citric, malic and oxalic), 2 kinds of polyphenols(chlorogenic acid and rutin), 3 kinds of pigments($\beta$-carotene, chlorophyll-a and chlorophyll-b), and 2 kinds of fiber components(pectin and lignin) were analyzed. All of these chemical components were changed with a different stalk position. When the citric acid, malic acid, $\beta-carotene$, chlorophyll-a, and lignin concentration were low in the middle stalk position and high in both bottom and upper position, oxalic acid and chlorogenic acid show the highest concentration in the middle stalk position. All of these chemical components also changed with a different grade of leaf tobaccos. As the citric acid, malic acid, $\beta-carotene$, chlorophyll-b, and lignin concentration decreased as the grade ascended, the oxalic acid and chlorogenic acid concentration increased as the grade ascended. This results assumed that the quality of korean leaf tobacco was directly proportional to oxalic acid and chlorogenic acid concentration but it was inversely proportional to citric acid, malic acid, $\beta-carotene$, chlorophyll-b and lignin concentration.

• Applied Biological Chemistry
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• 제24권2호
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• pp.120-125
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• 1981

전분질원(澱粉質原料)의 종류를 달리하여 양조(釀造)한 3개월 숙성의 찹쌀, 보리쌀, 밀가루, 고구마의 각고추장을 시료로하여 gas chramatography에 의하여 유기산을 분석한 결과 고추장중의 유기산으로 lactic acid, glycolic acid, pyruvic acid, succinic and fumaric acid, malic acid, pyroglutamic acid, citric acid가 모든 시험고추장에서 분리되었고 oxalic acid는 고구마 고추장에서만 검출 되었다. 시험고추장 모두 pyroglutamic acid, pyruvic acid, citric acid가 양적으로 가장 많았으나 밀가루 고추장에서는 이들 함량이 타 고추장에 비하여 다소 적게 나타났다. succinic과 fumaric acid의 함량은 고구마 고추장에서 가장 많았고 보리쌀 고추장이 가장 적었다.

• 한국지역사회생활과학회지
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• 제21권1호
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• pp.71-79
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• 2010

This study was conducted to develop fresh-cut and processed pears. After treatment of citric acid (1%) or N-acetylcysteine (0.2 M), and co-treatment of citric acid (1%) and N-acetylcysteine (0.2 M) into the pears c.v. 'Wonhwang', the quality changes of pears during cold storage ($1^{\circ}C$) for 10 days were investigated respectively. Pear quality and the taste of pears increased much more in those treated with anti-browning agents than those in the control group at 10 days after anti-browning treatment and cold storage. Changes in Hunter b values of pears treated with 0.2 M N-acetylcysteine were insignificant. Those with Polyphenol oxidase (PPO) activity and ethylene production were had the most decreased effects and those with the phenolics compound contents were the most lowered. Firmness of fruits increased in treatment of 0.2 M N-acetylcysteine + 1% citric acid solution. The amount of respiration decreased in the application of 1% citric acid solution. Consequently, fruit freshness can be maintained more effectively by the treatment of the anti-browning agent compared to non-treatment, even if the effectiveness were different among different kinds of anti-browning agents.

• Journal of Ginseng Research
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• 제35권4호
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• pp.497-503
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• 2011

In order to enhance bioactive functionalities of ginseng, an acid impregnation processing was applied as a pre-treatment in producing red ginseng. Acid impregnation studies were conducted, and acids (ascorbic, malic, and citric acid) were selected. The optimal concentration of each acid was investigated in this study in terms of ginsenoside contents. The most concerned ginsenoside, $Rg_3$ was increased by ascorbic, malic, and citric acid pre-treated red ginseng up to 1 M acid concentration. In the case of ascorbic acid pre-treated red ginseng, $Rg_2$ concentration was increased depending on acid concentrations. Citric acid pre-treatment enhanced $Rg_2$, $Rg_3$, and $Rh_1+Rh_2$ formation in red ginseng. Therefore, ginsenoside patterns in red ginseng could be changed by acid impregnation pre-treatment depending on acid concentration and acid types. This research is expected to contribute to the development of the ginseng industry via new red ginseng products with selective and intensified functionality.

• 한국연초학회지
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• 제14권2호
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• pp.151-158
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• 1992

Field experiment was conducted to investigate the effects of stalk position, compound fertilizer application rate (N-P2O5-K2O : 10-10-20 : 75, 100, 125kg/03), paddy and upland soil and varieties, NC82 &KF103, on nonvolatile organic and higher fatty acids of flue-cured tobacco. Followed by stalk position, malic, citric, malonic and succinic acid contents were significantly increased with higher stalk position, but oleic and linoleic acid contents were decreased with higher stalk position. The higher application rate of compound fertilizer results in increasing citric, malic, malonic and succinic acid contents, but the contents of higher fatty acids were not significantly influenced by fertilizer application rate. The cured leaf cultivated in paddy soil was higher citric and malic acid contents than in upland soil, but the contents of higher fatty acids have no difference between paddy and upland soil. The variety of KF103 was higher citric and linoleic acid contents than that of NC82, but the contents of higher fatty acids have no difference between varieties.

• Journal of Periodontal and Implant Science
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• 제23권2호
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• pp.219-227
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• 1993

The purpose of the present study was to evaluate the effects of 5% tetracycline(Tc) with or without citric acid on periodontally diseased root surfaces. Six single-rooted teeth extracted from one patient was selected and received thorough scaling and root planning, followed by saline irrigation. Each one tooth was divided into eight fragments with a thin separating disc. Total 48 fragments were prepared and setted into 4 groups for this study. Group I (control group)were treated with saline. Group II were treated with 5% Tc gel. Group III were treated with 33% citric acid-5% Tc gel. Group IV were treated with Tc solution. All the specimens are evaluated under Scanning Electron Microscope(SEM). Group I showed large amount of debris in spite of thorough scaling and root planing, but Group II, III & IV showed clean and soft root surface texture. In higher magnification(x3, 000), Group II, III & IV showed nunmerous dentinal tubules, especially Group IV showed collagen fibrils. In the present study, Tc gel and Tc gel with citric showed clinically successful result when treated on periodontally diseased root surface, in vitro.