• 한국식품영양학회지
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• 제8권3호
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• pp.172-183
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• 1995

The nucleophilic substitution reactions of p-substituted benzyl bromide with l-substituted N,N-dimethylanilines in methanol and acetonitrile binary solvent mixture which is known to an isodielectric solvent system kinetically and the results are as follows. The positive charge is developed on the reaction center of the substrate and it means that the bond cleavage is preceded more than bond formation in the transition state on the analogy of Hammett px values. The bond form3tlon is not progressed in the case of electron donating substituent of substrate. However, the bond formation is much developed in the case of electron withdrawing substituent of substrate on the analogy of Hammett py values. The nucleophilic attacking ability is shown a highest at 80% (V/V) methanol content and the bond formation is well progressed at the same methanol composition on the result of a cross interaction coefficient, pxy. The result of transition state structure that is applicated to the potential energy surface model is in accord with the result that Is applicated to the reaction susceptibilities. The reaction Is subject to the polarity-polarizability term more than the hydrogen bond donor acidity term by application to the solvatochromic parameter eouation.

• 한국세라믹학회지
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• 제35권5호
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• pp.458-464
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• 1998

Variations of reaction sequence of $Pb(Zn_{0.6}Mg_{0.4})_{1/3}Nb_{2/3}O_3$[PZMN] with precusor mixing methods were ex-amined using X-ray diffraction and dielectric characteristics. In the present study three different types of precursor mixing methods (oxide mixing PbO+$ZnNb_2O_6+MgNb_2O_6$[Zn+MN] and PbO+(Zn,Mg)$Nb_2O_6$[ZMN] precursor mixing) were adopted. When the oxide mixing method was used for the PZMN synthesis a Zn-rich perovskite phase and pyrochlore phase were formed. Compared with PbO+ZN+MN precursor mixing method the PbO-ZMN precursor led to a lowering of the formation temperature for perovskite sin-gle phase. These variation of composition and formation temperature of the perovskite phase were dis-cussed in terms of the difference in the solid-reaction requence between these three different types of pre-cursor mixing.

• 치과방사선
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• 제7권1호
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• pp.9-15
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• 1977

The author observed the effect of X-ray irradiation on the secondary palate formation of the rat fetuses. The mothers were exposed to X-radiation on the 10½th, 11½th and 12½th day of gestation with respectively 150, 200, 250, 300 and 350 rads. The fetuses were removed from mothers on 15½h, 16½th and 18½th day of gestation. Morphological changes in palate formation were examined and histochemical preparations were made. 1. In control fetuses, the secondary palates were fully developed on the 15½th to 18½th day of gestation. But in experimental fetuses, many cleft palates were observed in accordance with increase of X-radiation dose. 2. Frequency of incidence of horizontal position of both palated shelves in cleft palate was highest. 3. Accordig to the dislocation of palatal processes, the stain ability of palatal crest was varied. 4. The thickened area of palatal epithelium of palatal crest showed intense methyl green-pyronin and PAS reaction 5. Mesenchymal cell condensation was appeared under the thickened epithelium of palatal process and this mesenchymal tissue showed strong colloidal iron reaction. 6. The stain ability of alizarin red S and alkaline phosphatase reaction of tectal ridge were decreased, in accordance with increase of irradiation doses.

• 상하수도학회지
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• 제11권4호
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• pp.126-132
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• 1997

Trihalomethanes (THMs) are formed during the chlorination of waters containing precusors compounds, most commonly humic substances, changes in pH, TOC, temperature, precusor source and concentration chlorine dosage, bromide level and reaction time directly influence trihalomethane formation potential (THMFP) and kinetics. A standard THMFP experiment was conducted for each water under the following conditions ; $20^{\circ}C$, pH 7.4, reaction time of 48hr, TOC 5.7mgC/L. A series of kinetic experiments was conducted for each water to provide THM formation under varying conditions of reaction time, pH, temperature and TOC, chlorine dosage. The resultant mutiple parameter powre function predicts a THM which allows direct calculation of THM, is $[THM]=0.00039(pH-2.81)[TOC][Cl_2]^{0.321}\;t^{0.266}\;T^{0.286}$ Characteristics of raw water in advanced drinking water treatment pilot plant were, TOC levels ran from 4.42~6.84mgC/L, pH 7.2~7.8, temperature $7.0{\sim}18.4^{\circ}C$, UV-254 absorbance $0.057{\sim}0.85cm^{-1}$, THM levels ranged from 0.031~0.049mgC/L.

• Geomechanics and Engineering
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• 제33권1호
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• pp.65-75
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• 2023

Recycled concrete aggregate (RCA) is widely used as a construction material in road construction, concrete structures, embankments, etc. However, it has been reported that calcite (CaCO₃) precipitation from RCA can be a cause of clogging when used in drainage applications. An accelerated calcite precipitation (ACP) procedure has been devised to evaluate the long-term geochemical performance of RCA in subsurface drainage systems. While the ACP procedure was useful for the French Drain application, there remained opportunities for improvement. In this study, key factors that control the formation of calcite precipitation were quantitatively evaluated, and the results were used to improve the current prototype ACP method. A laboratory parametric study was carried out by investigating the effects of reaction temperature and time on the formation of calcite precipitation of RCA, with determining an optimum reaction temperature and time which maximizes calcite precipitation. The improved ACP procedure was then applied to RCA samples that were graded for Type I Underdrain application, to compare the calcite precipitation. Two key findings are (1) that calcite precipitation can be maximized with the optimum heating temperature (75℃) and time (17 hours), and (2) the potential for calcite precipitation from RCA is not as significant as for limestone. With the improved ACP procedure, the total amount of calcite precipitation from RCAs within the life cycle of a drain system can be determined when RCAs from different sources are used as pipe backfill materials in a drain system.

• 한국세라믹학회지
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• 제11권1호
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• pp.29-35
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• 1974

Effect of calcium sulfate and barium sulfate on the formation of portland cement clinker was studied by means of chemical analysis. DTA and X-ray diffraction analysis. In the presence of liquid phase, effect of the additives on the formation of tricalcium silicate was examined according to the reaction, 2CaO.$SiO_3$＋CaO$\longrightarrow$3CaO.$SiO_3$, which is the principal reaction in portland cement clinkerization, and optimum conditions in firing clinker concerning amount of additive, firing time and temperature were determined, and its kinetics was referred to. The experimental results are summerized as follow: (1) Appropriate burning temperature range of cement clinker is more limited as the content of calcium sulfate in clinker is increased. Amount of calcium sulfate, firing time and temperature in proper condition of clinkerization is related to each others. Being added suitable quantity of calcium sulfate, firing temperature of clinker can be lowered about $100^{\circ}C$. (2) When 3-5 mole% of calcium sulfate is added, firing time of 15-30 minutes at about $1380^{\circ}C$ is reasonable, and if the content is over7 mole %, firing for 1 hr. or more at $1350^{\circ}C$ is anticipated to be optimum condition. (3) In the reaction of tricalcium silicate formation, the role of barium sulfate as a mineralizer is similar to that of calcium sulfate, but the optimum firing temperature of cement clinker containing barium sulfate tends to be 20-$30^{\circ}C$ higher than that of clinker containing calcium sulfate. (4) When barium sulfate is used as mineralizer, 2-3 mole % of it to tricalcium silicate is recommended and if it is added more than this amount, free CaO is increased rapidly in clinker and alite formation is inhibited.

• 대한기계학회논문집B
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• 제20권5호
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• pp.1671-1678
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• 1996

In external chemical vapor deposition processes including VAD and OVD the distribution of flame-synthesized silica particles is determined by heat and mass transfer limitations to particle formation. Combustion gas flow velocities are such that the particle diffusion time scale is longer than that of gas flow convection in the zone of particle formation. The consequence of these effects is that the particles formed tend to remain along straight smooth flow stream lines. Silica particles are formed due to oxidation and hydrolysis. In the hydrolysis, the particles are formed in diffuse bands and particle formation thus requires the diffusion of SiCl$\_$4/ toward CH$\_$4//O$\_$2/ combustion zone to react with H$\_$2/O diffusing away from these same zones on the torch face. The conversion kinetics of hydrolysis is fast compared to diffusion and the rate of conversion is thus diffusion-limited. In the language of combustion, the hydrolysis occurs as a Burke-Schumann process. In selected conditions, reaction zone shape and temperature distributions predicted by the Burke-Schumann analysis are introduced and compared with experimental data available. The calculated centerline temperatures inside the reaction zone agree well with the data, but the calculated values outside the reaction zone are a little higher than the data since the analysis does not consider diffusion in the axial direction and mixing of the combustion products with ambient air. The temperatures along the radial direction agree with the data near the centerline, but gradually diverge from the data as the distance is away from the centerline. This is caused by the convection in the radial direction, which is not considered in the analysis. Spatial distribution of silica particles are affected by convection and diffusion, resulting in a Gaussian form in the radial direction.

• 펄프종이기술
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• 제46권5호
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• pp.27-34
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• 2014

In-situ $CaCO_3$ formation onto recycled wood pulp was studied to improve optical properties and ash attachment to the fiber furnish in papermaking. We controlled initial reaction temperature of in-situ $CaCO_3$ formation method from $30^{\circ}C$ to $50^{\circ}C$. It was found that the attachment of newly formed $CaCO_3$ to recycled fibers, old newspaper (ONP) in this case, was stronger than that of ground calcium carbonate (GCC, mean dia. $2.4{\mu}m$) addition case, but was not much different among those formed at different temperature. Morphologies of newly formed $CaCO_3$ were changed according to the reaction temperature. More aragonite shape was seen at higher temperature. In-situ $CaCO_3$ formation increased brightness and lowered ERIC value of ONP sheet greatly at the same level of ash contents when compared to GCC addition method, but gave equivalent ERIC and brightness when compared to those of the precipitated calcium carbonate (PCC) addition method. However, tensile strength of the handsheets of the in-situ $CaCO_3$ formation method were much greater than those of the PCC addition method.

• 한국결정성장학회지
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• 제14권3호
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• pp.110-114
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• 2004

반응온도 $75^{\circ}C$에서 $Ca(OH)_2$ slurry 및 NaOH의 혼합용액에 $Na_2CO_3$ 수용액의 농도 및 첨가방법을 변화시키면서 아라고나이트 침강성 탄산칼슘의 생성거동을 관찰하였다. 이 반응에서 $Na^+$ 이온은 탄산칼슘 격자내의 $Ca^{2+}$ 이온 자리에 치환되어 칼사이트의 성장을 지연시키고, 특정방향으로의 결정성장이 진행되어 침상형 아라고나이트의 생성을 유리하게 하는 것을 알 수 있었다. 또한, $CO_3^{2-}$ 이온농도 조절에 의한 반응속도의 감소는 균일침전반응을 유도하고, $Na^+$ 이온의 치환능력을 증대시켜 아라고나이트의 생성 및 성장을 촉진하는 것으로 판단되었다.

• 대한화학회지
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• 제10권1호
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• pp.25-31
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• 1966

폴리아크릴로니트릴을 加熱할 때 着色과 同時에 構造變化가 있다는 것은 잘 알려진 事實이며 이것은 部分水素化나프틸리딘型環을 形成함에 基因하는 것으로 알려지고 있다. 本硏究는 이와 같은 構造變化의 反應을 動力學的 및 統計學的으로 取扱하여 지금까지 알려지지 않았던 새로운 事實들을 發見하였다. 첫째로 폴리아크릴로니트릴을 加熱할 때의 니트릴基의 減少는 一次反應이라는 것이며 이는 環形成反應이 긴連鎖反應으로 이루어지지 않는다는 것을 말해 주는 것이다. 다시 말하면 環形成時의 kinetic chain length는 極히 짧다는 것이다. 또 本 構造變化는 반드시 分子間反應(架橋結合)이 아니드라도, 일어날 수 있다는 것을 證明했다. 둘째로 環形成으로 니트릴基가 減少할 때 19~22%의 니트릴基가 殘存한다는 것이며 이를 統計學的으로 解析해본 結果 19.2%라는 計算値를 얻었으며 이는 實驗値와 잘 맞는 數値이다.