• 한국토양비료학회지
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• 제44권1호
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• pp.48-52
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• 2011

The effect of soil water content on the transformation potential of N compounds derived from hydrolysis of urea applied in a reclaimed tidal soils which was saline-sodic was observed to evaluate nitrification rates of urea. Soil samples were collected from Moonpo series at the newly reclaimed area in Saemanguem. For the transformation potential of N compounds from urea (46% N), newly reclaimed tidal soils (RS) were amended with urea at the rates of 0, 10, and 20 kg $10a^{-1}$. With leachate obtained from the incubated RS in a leaching tube at $25^{\circ}C$, urea hydrolysis and nitrification were measured for a total of 30days. The cumulative amounts of $NO_3{^-}$-N in each of the four soils treated with urea was linear with time of incubation. Results showed that increase in pH occurred with increasing application rate of urea and volumetric water content due to hydrolysis of urea. The total N in the RS was decreased with incubation time, indicating that rates of urea hydrolysis was influenced by soil moisture conditions. Also, the cumulative amount of nitrate in RS gradually increased with increase in time of incubation.

• Journal of Applied Biological Chemistry
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• 제43권2호
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• pp.86-93
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• 2000

An experiment was conducted to obtain the quantitative data on the transformation and loss of applied urea-N in waterlogged soil columns. The soil columns were pre-incubated for 35 days to develop oxidized and reduced soil conditions prior to urea application. After urea application at the rate of $150kg\;N\;ha^{-1}$(29.5 mg N), the amounts of nitrogen which were volatilized, leached, and remained in soil column were measured during 38 days of incubation period. On 2 and 4 days of incubation, 54.1%(15.9 mg N) and 98.4%(29.0mg N) of the applied urea was hydrolyzed, respectively. Most of the applied urea was completely hydrolyzed within 6 days. After urea application, the rates of ammonia volatilization were increased with the floodwater pH when the floodwater pH were higher than 7.0. The maximum rate of ammonia volatilization was $0.3mg\;d^{-1}$ when pH of the floodwater showed maximum value of 7.6. The total amount of volatilized nitrogen was 6.1% (1.8mg N) of the applied urea-N. A 63.2 % (18.6mg N) of the applied urea was remained in soil as $NH_4{^+}-N$ and 28.0% (8.2mg N) of the applied urea was leached as $NH_4{^+}-N$ at the end of the incubation. Amount of $NO_3{^-}-N$ in soil was smaller than 2.0 mg throughout the incubation period. The total amount of $NO_3{^-}-N$ leached was very small, which value was 1.8 mg. It suggested that nitrification process was not significant in waterlogged soil column of this study due to high infiltration rate of urea solution applied to the soil column. Therefore only small amount of $NO_3{^-}-N$ was lost by denitrification and leaching process.

• 한국토양비료학회지
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• 제44권1호
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• pp.84-90
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• 2011

It is imperative to study the hydrolysis of urea in high saline-sodic condition of a newly reclaimed tidal land in order to overcome the problems associated with use of urea fertilizer. The methodology adopted in this study tried to get a convenient way of estimating rate for N transformation needed in N fate and transport studies by reviewing pH and salt contents which can affect the microbial activity which is closely related to the rate of urea hydrolysis. The hydrolysis of urea over time follows first-order kinetics and soil urease activity in reclaimed soils will be represented by Michaelis-Menten-type kinetics. However, high pH and less microorganisms may delay the hydrolysis of urea due to decrease in urease activity with increasing pH. Therefore, the rate of urea hydrolysis should adopt $V_{max}$ referring enzyme activity ($E_0$) accounting for urease concentration which is indicative for urea hydrolysis, especially in a high saline and sodic soils.

• 한국토양비료학회지
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• 제21권1호
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• pp.73-78
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• 1988

답토양(畓土壤)에서 요소(尿素)의 분해양상(分解樣相)과 관련(關聯)한 urease의 Kinetic특성(特性)을 알기위해서 토양(土壤)의 이화학성(理化學性)과 urease활성(活性)이 상이(相異)한 4개(個) 토양(土壤)을 사용(使用)하여 toluene처리(處理) 및 무처리(無處理) 조건(條件)에서 시간별(時間別) 요소(尿素)의 분해량(分解量)과 요소(尿素) 농도별(濃度別) urease활성(活性)을 측정(測定)한 결과(結果)는 다음과 같았다. Toluene 무처리(無處理) 조건(條件)에서는 총(總) urease활성(活性)이 높은 강서(江西) 사양토(砂壤土)에서 요소(尿素)의 분해(分解)가 가장 빨랐고 1차반응속도정수(次反應速度定數)와 Km 및 Vmax치(値)도 가장 높았으며 그 다음은 호남(湖南) 미사식양토(徵砂値壤土)> 장천양질사토(長川 壤質砂土)> 광포(廣浦)(염해답(鹽害畓)) 사용토(砂壤土) 순(順)이었다. 그리고 tolune처리(處理)는 전(全) 토양(土壤)에서 요소(尿素)의 분해(分解)를 지연(遲延)시켰으며 토양축적(土壤蓄積) urease활성(活性)이 가장 느렸으며 1차반응속도수(次反應速度定數)와 Km 및 Vmax값도 가장 낮았다. 그리고 토양(土壤)에 축적(蓄積)된 urease의 Km치(値)가 미생물(微生物) 분비(分泌) urease의 Km치(値)보다 적었으며, 미생물(微生物) 분비(分泌) urease의 Km치(値)는 토양간(土壤間)에 차이(差異)가 경미(輕微)하였다.

• 한국토양비료학회지
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• 제44권5호
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• pp.745-751
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• 2011

In most agricultural soils, ammonium ($NH_4^+$) from fertilizer is quickly converted to nitrate ($NO_3^-$) by the process of nitrification which is crucial to the efficiency of N fertilizers and their impact on the environment. However, nitrification studies have been studied extensively in agricultural soils, not in a newly reclaimed tidal soil which show saline-sodic and high pH. Therefore, understanding the fate of nitrogen species transformed from urea introduced into reclaimed tidal soil is important for nutrient management and environmental quality. This paper reviewed studies regarding to transformation and fate of nitrogen sources such as urea under the circumstances of a reclaimed tidal soils located in a western coastal area.

• Journal of Photoscience
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• 제6권4호
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• pp.177-181
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• 1999

The photochemical transformation of carbon monoxide in aqueous ammonia solution has been investigated at 25${\pm}$0.1$^{\circ}C$ using 184.9 nm UV light. Amination and carbonylation processes were carried out by irradiating the aqueous ammonia solution saturated with carbon monoxide, and the formation of formamide, urea, hexamethylenetetramine, formaldehyde, glyoxal and hydrazine was observed. The formation of hydrazine was affected by the presence of ammonia, and the formation of carbonyl compounds such as formaldehyde and glyoxal was influenced by the presence of carbon monoxide. The formation of formamide, urea and hexamethylenetetramine was affected by both ammonia and carbon monoxide. The initial quantum yields of the products were determined and probable mechanisms for the photochemical reaction were presented on the basis of product analysis.

• Applied Biological Chemistry
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• 제20권1호
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• pp.58-65
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• 1977

본(本) 시험(試驗)은 현재(現在) 우리나라에서 질소질(窒素質) 비료(肥料)의 주종(主種)인 요소(尿素)가 전(田)과 답토양중(畓土壤中)에서 겪는 화학적(化學的) 변화(變化)와 행동(行動)을 추구(追究)하는 일련(一連)의 실험(實驗)가운데 담수상태(湛水狀態)의 답토양(畓土壤)에서 수도작(水稻作)에 주(主)로 쓰히는 제초제(除草劑), 살균제(殺菌劑) 및 살충제(殺蟲劑)의 수종(數種)이 요소(尿素)의 분해속도(分解速度)와 질소(窒素)의 화학적형태(化學的形態)의 변화(變化)에 미치는 영향을 검토(檢討)한 것이다. 공시(供試)한 농약(農藥)은 제초제(除草劑)로 2, 4-D, Machete, TOK 등의 삼종류(三種類), 살균제(殺菌劑)로는 Rabcide, Neo-asozine, Phenazine 등의 3종류(三種類)를 각각(各各) 20, 100, 200ppm을 일정량(一定量)의 답토양(畓土壤)에 200pprn의 요소비료(尿素肥料)와 함께 처리(處理)하여 $28{\pm}1^{\circ}C$에 정치(靜置)하여 변화(變化)를 조사(調査)하여쓰며 살충제(殺蟲劑)로는 Birlane, Diazinon, Sumithion 및 Bux의 4종류(四種類)를 각각(各各) 50, 250, 500ppm으로 처리(處理)하였으며 얻은 결과(結果)는 다음과 같다. 1. 제초제(除草劑)와 살균제(殺菌劑)를 각각(各各) 20, 100ppm으로 처리(處理)하였을 경우 처리(處理) 1일후(日後)까지는 요소(尿素)의 분해(分解)에 큰 영향을 끼치지 않았고 200ppm처리(處理)에서는 Rabcide와 Neo-asozine을 제외(除外)하고 그밖의 약제(藥劑)에 의하여는 현저히 저해(沮害)되었다. 살충제(殺蟲劑)로 Sumithion과 Bux는 250ppm 처리로 약간 저해(沮害)되었고 500ppm 처리에서는 공시(供試)한 모든 살충제(殺蟲劑)에 의하여 크게 저해(沮害)되었다. 그러나 요소(尿素)는 본실험조건(本試驗條件)에서 처리(處理) 3일후(日後)에 농약(農藥)의 처리(處理)에 관계(關係)없이 거의 완전(完全)히 분해소실(分解消失)되었다. 2. 어느 경우에나 암모늄태질소(態窒素)의 생성(生成)은 기수상태(基水狀態)에서 점차 증가(增加)되었으나 대조(對照) 2주후(週後)에는 대략 20%의 무기태질소(無機態窒素)가 감소(減少)되었으며 농약(農藥)의 처리농도(處理濃度)가 높을수록 암모늄 태질소(態窒素)의 현저한 증가(增加)가 2주(週)째에 나타났다. 그러나 Rabcide에 의하여는 오히려 억제(抑制)되었다. 3. 공시(供試)한 농약재(農藥劑)의 처리(處理)로 담수상태(湛懲水狀態)에서 ($NO_2+NO_3$)-N의 생성(生成)이 억제(抑制)되었고 그 억제효과(抑制效果)는 약제별(藥劑別)로 차이(差異)가 있어 대체(大體)로 살균제(殺菌劑), 제초제(除草劑), 살충제(殺蟲劑)의 순(順)으로 감소(減少)되었다.

• Elastomers and Composites
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• 제50권2호
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• pp.92-97
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• 2015

A study on reaction kinetics for a PTMG/TDI prepolymer with 2,2'-dichloro-4,4'-methylenedianiline (MOCA), of which formulations may be generally used for fabricating high performance polyurethane elastomers, was peformed using non-isothermal differential scanning calorimetry (DSC). A number of thermograms were obtained at several constant heating rates, and analysed using Flynn-Wall-Ozawa (FWO) isoconversional method for activation energy, $E_a$ and extended-Avrami equation for reaction order, n. Urea formation reaction of the present system was observed to occur through the simple exothermic reaction process in the temperature range of $100{\sim}130^{\circ}C$ for the heating rate of $3{\sim}7^{\circ}C/min$. and could be well-fitted with generalized sigmoid function. Though activation energy was nearly constant as $53.0{\pm}0.5kJ/mol$, it tended to increase a little at initial stage, but it decreases at later stage by the transformation into diffusion-controlled reaction due to the increased viscosity. Reaction order was evaluated as about 2.8, which was somewhat higher than the generally well-known $2^{nd}$ order values for the various urea reactions. Both the reaction order and reaction rate explicitly increased with temperature, which was considered as the indication of occurring the side reactions such as allophanate or biuret formation.

• 한국결정성장학회지
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• 제14권6호
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• pp.267-271
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• 2004

우레아 가수분해법을 이용하여 리튬이차전지용 $LiCoO_2$ 양극 분말을 합성하였다. Li/Co 몰비가 다르고 가수분해에 의해 얻어진 전구체는 다양한 온도에서 열처리되었다. 저온상 $LiCoO_2(LT-LiCoO_2)$와 고온상 $LiCoO_2(HT-LiCoO_2)$는 $500^{\circ}C$에서 2시간 열처리 후 합성되었고, 저온상에서 고온상으로 상전이는 $700^{\circ}C$ 이상에서 완전히 일어났다. 열처리 온도가 증가함에 따라 $LiCoO_2$의 층상구조가 잘 발달하였다. 충방전 실험결과 Li/Co의 몰비가 1.2이고 $800^{\circ}C$에서 열처리한 $LiCoO_2$의 초기용량이 152 mAh/g으로 높았으며, 40회 충.방전 후에는 9.2%의 용량감소를 나타내는 상대적으로 안정한 충방전 특성을 나타내었다.

• 농약과학회지
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• 제8권1호
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• pp.38-45
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• 2004

Imidacloprid를 물과 물-토양계에 처리후 광에 노출시켜 광분해 특성을 조사하였다. 물중에서 imidacloprid는 극성화합물로 전환이 빠르게 이루어져서 약제 7일에는 수상대 유기상의 분포비가 80 : 20 이었으며, 이러한 경향은 조사 후 60일까지 지속되었다. 광에 의한 imidacloprid의 대사물인 imidacloprid urea는 노출 1 일차에 0.0112 mg/kg이 검출되었으며, 7일차에는 0.0391 mg/kg로 최고 농도에 도달한 후 감소하여 60일에는 검출되지 않았다. 물-토양계에서 imidacloprid의 농도는 약제처리 7일 후 평형상태에 도달하였으며, 극성화합물로 전환은 7 일간 지속되어 수상과 유기상간 분배비는 80 : 20로 전환되었다. 광에 의하여 imidacloprid의 농도는 약제처리 당일에는 1.6538 mg/kg, 1일에 0.8785 mg/kg으로 감소하여 15일에는 검출한 계 미만으로 검출되지 않았으나, 광분해산물인 imidacloprid urea는 약제 처리 3일에 최고 농도인 0.0259 mg/kg에 도달한 후 감소하였다. 물과 물-토양계에서 imidacloprid는 광에 의하여 분해되어 imidacloprid urea가 생성되는 분해경로를 확인하였다.