Derivation of Q* Parameter for Evaluating Creep Crack Growth Rate of Modified 9Cr-1Mo Steel

I.M.W. Ekaputra,Woo-Gon Kim(김우곤),Jae-Young Park(박재영),Seon-Jin Kim(김선진),Min-Hwan Kim(김민환),Yong-Wan Kim(김용완) 대한기계학회 2013 대한기계학회 춘추학술대회 Vol.2013 No.12

The concept of the Q* parameter was first proposed by Yokobori et al. The Q* parameter is defined as the exponent of the exponential function in the thermal activation process equation. In this study, the creep crack growth (CCG) behavior of the modified 9Cr-1Mo steel is evaluated using the Q* parameter. The CCG tests were carried out under various loads at 550oC and 600oC. The K and C* parameters have been used to characterize the CCGR of modified 9Cr-1Mo steel. The results show that the K parameter exhibits the largest scatter data, and there is no systematic trend in each series of tests, while C* showed a narrower scattering of data of CCGR than the K parameter. However, C* decreased during the early stage of crack growth and subsequently increased, i.e., a dual value due to the nose appearance, and it did not distinguish among the series of data under various loads at 550oC and 600oC clearly in a one linear line. The Q* parameter was able to evaluate the CCG by a simple monotical linear function without a dual value owing to nose existing in the early stage, and it exhibited an increase or decrease regardless of the testing conditions. The Q* was regarded as an independent parameter that is not depending on stress and temperature, whereas the C* was regarded as a dependent parameter depending on the creep stress and temperature.

Kinetics and Mechanism of Nucleophilic Displacement Reactions of Y-Substituted Phenyl Benzoates with Cyanide

Song-I Kim,Eun-Hee Kim,Ik-Hwan Um 대한화학회 2010 Bulletin of the Korean Chemical Society Vol.31 No.3

Second-order rate constants (kCN‒) have been measured for nucleophilic substitution reactions of Y-substituted phenyl benzoates (1a-r) with CN‒ ion in 80 mol % H2O/20 mol % DMSO at 25.0 ± 0.1 oC. The Brønsted-type plot is linear with βlg = ‒0.49, a typical βlg value for reactions reported to proceed through a concerted mechanism. Hammett plots correlated with σo and σ‒ constants exhibit many scattered points. In contrast, the Yukawa-Tsuno plot for the same reaction exhibits excellent linearity with ρY = 1.37 and r = 0.34, indicating that a negative charge develops partially on the oxygen atom of the leaving aryloxide in the rate-determining step (RDS). Although two different mechanisms are plausible (i.e., a concerted mechanism and a stepwise pathway in which expulsion of the leaving group occurs at the RDS), the reaction has been concluded to proceed through a concerted mechanism on the basis of the magnitude of βlg and ρY values.

연속측정을 통한 오산천 상류의 수질 거동파악

신동환,최이송,박재영,오종민 경희대학교 2003 環境硏究 論文集 Vol.12 No.-

In this study, the variation of water quality in Aswan stream was investigated through continuous monitoring and matt balance and metabolism occurred into water body environment was estimated to set up effective management plan of small urban stream. Sated on the results, the rate of output to input (O/I rate. in the flux balance was 1.16 and about 16% sae increased between the section of OS1 ∼ OS3. Also, the SS and BOD loadings between the tame section were increased by 29% and 31%, respectively. Although increase of flux influenced on the increase of SS and BOD loading, it was judged that the larger part of o/I rate of pollutants comparing to O/I rate of flux was due to up-take from sediment on the riverbed. The contribution percentage of BS1 and BS2 for flux between the section of OS1 ∼ OS2 was 17.3%, total section was 31.3% (including BS3). However, the contribution of tributaries for SS, BOD and T-N loading wore 50.3%, 33.0% and 57.6%, respectively. Eventually tributaries contributed the pollution of water quality. To reduce pollution of water quality in the section of OS1 ∼ OS3, firstly, it need that effective management plan for tributaries mutt be set up to improve the water quality in main stream. Secondly, the counter plan for ro-eruptyon of pollutants from sediment in main-stream it required to prevent inner pollution. On this study, we showed that small urban stream can be managed effectively by simple investigation to prevent deterioration of water quality. also, it is more important that matter cycle and matt balance happening in the stream environment must be correctly estimated to make up healthy stream environment and to improve water quality.

순천시 신평천 인공습지 조성 후 3년간 식생 및 생활형에 대한 연구

김창환 ( Chang Hwan Kim ),최영은 ( Young Eun Choi ),김종원 ( Jong Won Kim ),명현 ( Hyun Myong ),이숙이 ( Suk I Lee ) 한국환경생태학회 2011 한국환경생태학회지 Vol.25 No.1

신평천 인공습지 조성 후 3년간의 식생 및 생활형 변화 연구를 위하여 2005년 6월부터 2007년 9월까지 현지조사를 실시하였다. 2004년에 조성된 신평천 인공습지의 식재종은 14과 18속 15종 5변종으로 총 20종류가 식재되었다. 식재종의 생활형 구성비는 전체의 65%인 대부분을 다년생이 차지하고 있으며 목본류는 물푸레나무와 왕버들, 동백나무, 남천 4종류가 식재되었다. 3년간의 조사 기간 동안 생활형의 변화는 수생식물(HH)이 가장 많은 비율을 차지하며 증가하였고 소형지상식물(M), 대형지상식물(MM), 지표식물(Ch), 미소지상식물(N), 다년생식물(H)과 지표식물(Ch) 등도 증가하였다. 식생면적 변화는 애기부들, 달뿌리풀, 갈대 등은 군락면적이 증가하였으나, 다른 식재종의 면적은 급격히 감소하였다. 생활형 면적변화를 살펴보면 수생식물(HH), 1년생 수습식물(Th(w))은 점차 증가하였으며 소형지상식물(M), 지중식물(G), 미소지상식물(N) 등은 감소를 보였다. 결론적으로 식재 식물의 선정은 인공습지의 미래를 결정하는 중요한 요인이며 습지 조성 후 정착된 식물상의 파악 및 이들 식물들의 생활형을 분석하여 인공습지 초기정착에 유리한 종, 천이가 진행되면서 습지의 안정화 및 다양성을 유도하는 종을 선정하는 것은 매우 중요하다. A field survey was conducted from June 2005 to September 2007 to explore changes of the vegetation and life form in the man-made Wetland along the Sinpyeongcheon for 3 years after its creation. A total of 20 species including 14 families, 18 genera, 15 species and 5 varieties were planted in the Wetland which was completed in 2004. Divided by life form of the planted species, a prevalent 65% of them was composed of perennation while 4 species of woody plants i.e. Fraxinus rhynchophylla, Salix glandulosa, Camellia japonica and Nandina domestica were planted there, too. The 3-year study revealed that hydatophytes (HH) scored the biggest increase in number, followed by slight increase in the number of microphanerophytes (M), megaphanerophytes (MM), chamaephytes (Ch), nanophanerophytes (N), perennial plants (H), etc., featuring generally a similar tendency for the whole period of study. The change in vegetation area increases in the area of Typha angustata, Phragmites japonica, Phragmites communis, etc. but a sharp decrease in the area of communities for other planted species. In terms of change in the area for planted species by their life form, hydatophytes (HH), HH Th (Th(w)) reported gradual increase while microphanerophytes (M), geophyte (G), and nanophanerophytes (N) continued to record a decrease. In conclusion, selection of plants to be planted turns out to play a vital role in molding the destiny of a man-made Wetland. It seems therefore extremely important to investigate the flora, and life and growth forms of the plants planted in the man-made Wetland in an effort to choose the species that can adapt themselves to the environment from the early phase on, contributing by thus to stabilization and diversification of the damp ground in line with the progression of their succession.

Including Bioconcentration Kinetics for the Prioritization and Interpretation of Regulatory Aquatic Toxicity Tests of Highly Hydrophobic Chemicals

Kwon, Jung-Hwan,Lee, So-Young,Kang, Hyun-Joong,Mayer, Philipp,Escher, Beate I. American Chemical Society 2016 Environmental science & technology Vol.50 No.21

<P>Worldwide, regulations of chemicals require short-term toxicity data for evaluating hazards and risks of the chemicals. Current data requirements on the registration of chemicals are primarily based on tonnage and do not yet consider properties of chemicals. For example, short-term ecotoxicity data are required for chemicals with production volume greater than 1 or 10 ton/y according to REACH, without considering chemical properties. Highly hydrophobic chemicals are characterized by low water solubility and slow bioconcentration kinetics, which may hamper the interpretation of short-term toxicity experiments. In this work, internal concentrations of highly hydrophobic chemicals were predicted for standard acute ecotoxicity tests at three trophic levels, algae, invertebrate, and fish. As demonstrated by comparison with maximum aqueous concentrations at water solubility, chemicals with an octanolwater partition coefficient (Kow) greater than 106 are not expected to reach sufficiently high internal concentrations for exerting effects within the test duration of acute tests with fish and invertebrates, even though they might be intrinsically toxic. This toxicity cutoff was explained by the slow uptake, i.e., by kinetics, not by thermodynamic limitations. Predictions were confirmed by data entries of the OECDs screening information data set (SIDS) (n = 746), apart from a few exceptions concerning mainly organometallic substances and those with inconsistency between water solubility and Kow. Taking error propagation and model assumptions into account, we thus propose a revision of data requirements for highly hydrophobic chemicals with log Kow > 7.4: Short-term toxicity tests can be limited to algae that generally have the highest uptake rate constants, whereas the primary focus of the assessment should be on persistence, bioaccumulation, and long-term effects.</P>

Kinetics and Mechanism of Nucleophilic Displacement Reactions of Y-Substituted Phenyl Benzoates with Cyanide Ion

Kim, Song-I,Kim, Eun-Hee,Um, Ik-Hwan Korean Chemical Society 2010 Bulletin of the Korean Chemical Society Vol.31 No.3

Second-order rate constants ($k_{CN^-}$) have been measured for nucleophilic substitution reactions of Y-substituted phenyl benzoates (1a-r) with $CN^-$ ion in 80 mol % $H_2O$/20 mol % DMSO at $25.0{\pm}0.1^{\circ}C$. The Br${\o}$nsted-type plot is linear with ${\beta}_{1g}$ = -0.49, a typical ${\beta}_{1g}$ value for reactions reported to proceed through a concerted mechanism. Hammett plots correlated with ${\sigma}^{\circ}$ and ${\sigma}^-$ constants exhibit many scattered points. In contrast, the Yukawa-Tsuno plot for the same reaction exhibits excellent linearity with ${\rho}_Y$ = 1.37 and r = 0.34, indicating that a negative charge develops partially on the oxygen atom of the leaving aryloxide in the rate-determining step (RDS). Although two different mechanisms are plausible (i.e., a concerted mechanism and a stepwise pathway in which expulsion of the leaving group occurs at the RDS), the reaction has been concluded to proceed through a concerted mechanism on the basis of the magnitude of ${\beta}_{1g}$ and ${\rho}_Y$ values.

Nucleophilic Substitution Reactions of Y-Substituted-Phenyl Benzoates with Potassium Ethoxide in Anhydrous Ethanol: Reaction Mechanism and Role of K⁺ Ion

Kim, Song-I,Cho, Hyo-Jin,Um, Ik-Hwan Korean Chemical Society 2014 Bulletin of the Korean Chemical Society Vol.35 No.1

Pseudo-first-order rate constants ($k_{obsd}$) have been measured spectrophotometrically for the reactions of Y-substituted-phenyl benzoates (5a-j) with potassium ethoxide (EtOK) in anhydrous ethanol at $25.0{\pm}0.1^{\circ}C$. The plots of $k_{obsd}$ vs. [EtOK] curve upward regardless of the electronic nature of the substituent Y in the leaving group. Dissection of $k_{obsd}$ into the second-order rate constants for the reactions with the dissociated $EtO^-$ and ion-paired EtOK (i.e., $k_{EtO^-}$ and $k_{EtOK}$, respectively) has revealed that the ion-paired EtOK is more reactive than the dissociated $EtO^-$. The Br${\phi}$nsted-type plots for the reactions with the dissociated $EtO^-$ and ion-paired EtOK exhibit highly scattered points with ${\beta}_{lg}$ = -$0.5{\pm}0.1$. The Hammett plots correlated with ${\sigma}^o$ constants result in excellent linear correlations, indicating that no negative charge develops on the O atom of the leaving Y-substituted-phenoxide ion in transition state. Thus, it has been concluded that the reactions with the dissociated $EtO^-$ and ion-paired EtOK proceed through a stepwise mechanism, in which departure of the leaving group occurs after the RDS, and that $K^+$ ion catalyzes the reactions by increasing the electrophilicity of the reaction center through a four-membered cyclic TS structure.

Kinetics and Mechanism of Michael-type Reactions of Ethyl Propiolate with Alicyclic Secondary Amines in H₂O and MeCN: Solvent Effect on Reactivity and Transition-State Structure

Kim, Song-I,Baek, Hye-Won,Um, Ik-Hwan Korean Chemical Society 2009 Bulletin of the Korean Chemical Society Vol.30 No.12

The amines studied in this study are less reactive toward ethyl propiolate (3) in MeCN than in H$_2$O although they are 7 to 9 pK$_a$ units more basic in the aprotic solvent. The reactivity of morpholine and deuterated morpholine toward 3 is found to be identical, indicating that proton transfer occurs after rate-determining step (RDS). The fact that kinetic isotope effect is absent excludes a stepwise mechanism in which proton transfer occurs in RDS as well as a concerted mechanism in which nucleophilic attack and proton transfer occur concertedly through a 4-membered cyclic transition state (TS). Thus, the reactions have been concluded to proceed through a stepwise mechanism in which proton transfer occurs after RDS. Brønsted-type plots are linear with small ${\beta}_{nuc}$ values, i.e., ${\beta}_{nuc}$ = 0.29 in H$_2$O and ${\beta}_{nuc}$ = 0.51 in MeCN, indicating that bond formation is not advanced significantly in RDS. The small ${\beta}_{nuc}$ value also supports the conclusion drawn from the study of kinetic isotope effect.

Kinetic Study on Nucleophilic Substitution Reactions of 4-Nitrophenyl X-Substituted-Benzoates with Potassium Ethoxide: Reaction Mechanism and Role of K⁺ Ion

Kim, Song-I,Kim, Min-Young,Um, Ik-Hwan Korean Chemical Society 2014 Bulletin of the Korean Chemical Society Vol.35 No.1

A kinetic study on nucleophilic substitution reactions of 4-nitrophenyl X-substituted-benzoates (7a-i) with EtOK in anhydrous ethanol at $25.0{\pm}0.1^{\circ}C$ is reported. The plots of pseudo-first-order rate constants ($k_{obsd}$) vs. [EtOK] curve upward. Dissection of $k_{obsd}$ into the second-order rate constants for the reactions with the dissociated $EtO^-$ and ion-paired EtOK (i.e., $k_{EtO^-}$ and $k_{EtOK}$, respectively) has revealed that the ion-paired EtOK is more reactive than the dissociated $EtO^-$. Hammett plots for the reactions of 7a-i with the dissociated $EtO^-$ and ion-paired EtOK exhibit excellent linear correlations with ${\rho}_X$ = 3.00 and 2.47, respectively. The reactions have been suggested to proceed through a stepwise mechanism in which departure of the leaving-group occurs after the RDS. The correlation of the $k_{EtOK}/k_{EtO^-}$ ratio with the ${\sigma}_X$ constants exhibits excellent linearity with a slope of -0.53. It is concluded that the ion-paired EtOK catalyzes the reaction by increasing the electrophilicity of the reaction center rather than by enhancing the nucleofugality of the leaving group.

Pyridinolyses of 2,4-Dinitrophenyl Phenyl Carbonate and 2,4-Dinitrophenyl Benzoate: Effect of Nonleaving Group on Reactivity and Mechanism

Um, Ik-Hwan,Son, Min-Ji,Kim, Song-I,Akhtar, Kalsoom Korean Chemical Society 2010 Bulletin of the Korean Chemical Society Vol.31 No.7

Second-order rate constants $(k_N)$ have been measured for reactions of 2,4-dinitrophenyl phenyl carbonate (2) with a series of pyridines in 80 mol % $H_2O$/20 mol % DMSO at $25.0{\pm}0.1^{\circ}C$ and compared with the $k_N$ values reported for the corresponding reactions of 2,4-dinitrophenyl benzoate (1) to investigate the effect of nonleaving group on reactivity and mechanism. The reactions of 2 result in larger $k_N$ values than those of 1. The Br${\o}$nsted-type plot for the reactions of 2 exhibits a downward curvature (i.e., ${\beta}2$ = 0.84 and ${\beta}1$ = 0.16), which is typical for reactions reported to proceed through a stepwise mechanism with a change in rate-determining step. The $pK_a$ at the center of the Br${\o}$nsted curvature, defined as $pK_a{^{\circ}}$, has been found to be 8.5 and 9.5 for the reactions of 2 and 1, respectively. Dissection of $k_N$ into the microscopic rate constants (e.g., $k_1$ and $k_2/k_{-1}$ ratio) has revealed that the reactions of 2 result in larger k1 values than those of 1, indicating that PhO behaves as a stronger electron-withdrawing group than Ph. However, the $k_2/k_{-1}$ ratio has been found to be independent of the electronic nature of Ph and PhO.