• 한국분말재료학회지
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• 제21권1호
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• pp.7-15
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• 2014

This study investigated the densification behavior of rhenium alloys including W-25 wt.%Re and Re-2W-1Ta (pure Re) during sintering. The dilatometry experiments were carried out to obtain the in-situ shrinkage in $H_2$ atmosphere. The measured data was analyzed through shrinkage, strain rate and relative density, and then symmetrically treated to construct the linearized form of master sintering curve (MSC) and MSC as a well-known and straightforward approach to describe the densification behavior during sintering. The densification behaviors for each material were analyzed in many respects including apparent activation energy, densification parameter, and densification ratio. MSC with a minimal set of preliminary experiments can make the densification behavior to be characterized and predicted as well as provide guideline to sinter cycle design. Considering the results of linearized form and MSC, it was confirmed that the W-25 wt.%Re compared to Pure Re is more easily densified at the relatively low temperature.

• 한국미생물·생명공학회지
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• 제15권5호
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• pp.312-318
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• 1987

Streptomyces sp. J-350P가 생산하는 세포외 adenine deaminase의 adenine에 대한 Km 값은 5.8$\times$$10^{-5}$M로 측정되었으며 Arrhenius plots에 의한 효소의 활성화 에너지는 3.13 Kcal/mole로 측정되었다. 검토된 purine analogue중에서 6-chloropurine, 2,6-diaminopurine, 6-bromopurine, 4-aminopyrazolo (3,4-d) pyrimidine, 6-iodopurine, 그리고 8-bromoadenine은 본 효소에 의해 기질로 이용되었으며, 6-dimethylaminopurine은 adenine에 대한 경쟁적 저해제로 작용하였다. 본 효소는 0.1mM의 Fe$^{3+}$, Ag$^+$ 등에 의해 저해되었으며, 1mM의 $\alpha$, $\alpha$＇-dipyridyl, Pentachiorophenol, p-CMB 등에 의해 저해되었다.

• 한국세라믹학회지
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• 제32권6호
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• pp.659-668
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• 1995

Zirconium carbide was prepared from the mixture of metal zirconium and carbon powders in argon atmosphere by Self-propagating High-temperature Synthesis (SHS) in order to obtain the best carbon source and dilution contents. The most exellent result was obtained in the case that active carbon was added as a starting material, 20~30 wt% dilution content. From thermal profile analysis an apparent activation energy of 118 KJ/mol was calculated. The maximum heating rate achieved during 15 wt% ZrC reaction by product dilution method was approximately 1.54$\times$105 K/s. Coupling this value with the measured wave velocity of 1.026cm/s yielded a maximum thermal gradient fo $1.5\times$105 K/cm. Using the definition of t* and the measured wave velocity, the effective thermal diffusivity, $\alpha$, was calculated to be 0.62$\times$102 $\textrm{cm}^2$/s.

• 한국세라믹학회지
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• 제24권6호
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• pp.543-552
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• 1987

The effects of deposition variables on SnO2 CVD were investigated for SnCl4＋O2 reaction at 300∼700$^{\circ}C$, Psncl4=1${\times}$10-5∼1${\times}$10-3 atm, and Po2=5${\times}$10-4∼1 atm. A thermodynamic equilibrium study on Sn-Cl-O system has been performed with the computer calculation. The calculation indicates that major species participating the reaction in SnCl4 and not intermediate species, SnCl2. Good uniformity of the film thickness was obtained at the flow rate of 11cm/sec, which resulted from the stable gas flow in our cold wall reactor. The experimental results showed that apparent activation energy of the deposition was about 13.5Kcal/mole below the temperature of 500$^{\circ}C$ and the deposition mechanism was controlled by surface reation. The behavior of deposition rate on the reactant partial pressures could be explained with the Langmuri-Hinshelwood mechanism. X-ray study demonstrated that SnO2 film deposited at temperatures above 400$^{\circ}C$ were polycrystalline with tetragonal rutile structure and grew with (211) and (301) preferred orientations.

• 한국세라믹학회지
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• 제28권4호
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• pp.315-323
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• 1991

The preparation of zirconium carbide powders by the halogenide process of ZrCl4-C-Mg system (1:1:2, molar ratio) was studied between 300。 and 120$0^{\circ}C$ under Ar gas flow (200 mι/min). The formation mechanism and kinetics of zirconium carbide and characteristics of the synthesized powder were examined by TG-DTA, XRD, SEM and PSA. 1) The formation mechanism of zirconium carbide were as follows, above 30$0^{\circ}C$ ZrCl4(S)+Mg(s)longrightarrowZrCl2(s)+MgCl2(s) above 40$0^{\circ}C$ ZrCl2(S)+Mg(s)longrightarrowZr(s)+MgCl2(s) above 50$0^{\circ}C$ Zr(s)+C(s)longrightarrowZrC(s) 2) The apparent activation energy of the reduction-carbonization at temperature of 800$^{\circ}$to 100$0^{\circ}C$ was 11.9 kcal/mol. 3) The lattice parameter and the crystallite size of ZrC which was produced from the mixture powder of ZrCl4, C and Mg (1:1:2, molar ratio) at 100$0^{\circ}C$ for 1 h were 4.700A and 180A, respectively. 4) The powders obtained from the mixture powder of ZrCl4, C and Mg(1:1:2, molar ratio) at 100$0^{\circ}C$ for 1 h were agglomerate with the average size of about 13${\mu}{\textrm}{m}$ in SEM micrograph.

• The Korean Journal of Ceramics
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• 제4권3호
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• pp.260-267
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• 1998

A homogeneous and stoichimetric fine powder of the ferroelectric $Pb_[0.97}La_{0.02}(Zr_{0.64}Sn_{0.25}Ti_{0.11})O_3$ (PLZST) has been prepared by the hydroxide coprecipitation method. Studies on the crystallization behavior of precursor as a function of temperature by X-ray powder diffraction and transmission electron microscopy technique were consistent with the formation of the pyrochlore phase from amorphous, initially at low temperatures around 500~$550^{\circ}C$. Further heat treatment up to $750^{\circ}C$ resulted in development of the perovskite phase with no significant pyrochlore crystallite growth. At intermediate temperatures the precursor yields a fine mixture of pyrochlore and perovskite phases. When the pyrochlore phase was heat teated in air, slight weight increase was observed in the temperature range of 300~$700^{\circ}C$, which is thought to be caused from oxygen absorption. In argon atmosphere, weight increase was not observed. On the other hand, weight loss began to occur near $700^{\circ}C$, with giving off mostly CO2 gas. This implies that the pyrochlore phase seems to be crystallorgraphycally and thermodynamically metastable. An apparent activation energy of 53.9 ㎉/mol was estimated for the pyrochlore-perovskite phase transformation.

• 대한화학회지
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• 제19권6호
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• pp.463-467
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• 1975

Tetrahydrofuran(THF)중에서 질산코발트(II)를 개시제로 사용하여 methyl methacrylate(MMA)의 중합반응을 연구하였다. 반응속도론적 연구 결과로 다음과 같은 중합속도식을 얻었다. $R_p=k\;[질산코발트(II)]^{0.5}\;[MMA]^{1.5}$ Chelate를 잘 형성하는 옥살산이 중합속도에 미치는 영향을 고려해 보면, 단위체인 MMA가 질산코발트(II)와 배위착물을 형성한다는 것을 추론할 수 있었다. 또 중합계의 겉보기 총 활성화에너지는 14.0kcal/mole이라는 것을 알았다.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2018년도 춘계 학술논문 발표대회
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• pp.47-48
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• 2018

The aim of the research is to suggest the compensating strength values depending on various managing periods of concrete based on the strength development model calculated with equivalent age method for OPC 100 % concrete. As a result, for 28 days of managing period, 6, and 3 MPa of compensating strength values were suggested when the temperatures were from 4 to 9℃, from 9 to 17℃, respectively. Additionally, for 42 days of managing period, 3MPa of compensating strength value was suggested when the temperature was from 4 to 10℃, and for 56 days of managing period, 3 MPa of compensating strength value was suggested when the temperature was from 4 to 5℃. Furthermore, for 28, 42, 56, and 91 days of managing periods, any compensating strength values were needed when the temperature were higher than 17, 10, 5, and 4℃, respectively.

• 한국포장학회지
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• 제24권1호
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• pp.13-16
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• 2018

Powdered infant formula is susceptible to oxidation in the presence of oxygen. Even though the product is usually packaged in nitrogen atmosphere, the oxygen ingress through the package layer may occur in case of flexible pouches and affects the oxidation of the product. $O_2$ barrier of the package is thus important variable to protect the product from oxidative deterioration. $O_2$ barrier property was investigated for aluminum-laminated small pillow packs of $3.5{\times}17.5cm$. Storage temperature and combination of primary and secondary packages were evaluated as variables affecting the barrier for conditions of empty pouch flushed with nitrogen. Apparent oxygen transmission rate of the primary package exposed to air was $2.32{\times}10^{-3}mL\;(STP)\;atm^{-1}\;d^{-1}$ at $30^{\circ}C$ and its temperature dependence could be explained by activation energy of $28.5kJ\;mol^{-1}$ in Arrhenius relationship. The additional secondary package of nylon/PE film containing 20 primary packages was ineffective in modulating package $O_2$ transmission and was only marginally helpful when combined with oxygen scavenger. The same was true in suppressing the product oxidation when the primary package was filled with 14 g of the formula.

• Bulletin of the Korean Chemical Society
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• 제28권9호
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• pp.1489-1492
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• 2007

Belousov-Zhabotinsky (BZ) reaction containing oxalic acid and acetone as a mixed organic substrate catalyzed by Ce(IV) in a flow system has been investigated. The reaction system is analyzed by varying flow rate, inflow concentrations, and temperature. Interchangeable oscillating patterns are observed in a certain range of concentrations, and above or below the condition a steady state is obtained. The increase in temperature increases the frequency and decreases the amplitude of oscillations. The apparent activation energy for the system is calculated by using the Arrhenius equation, which means that temperature has a greater effect on the reaction. Bifurcation phase diagrams for the system show the region of oscillations or steady states along with a small region of multistability. Further the behavioral trend observed in this system is discussed by mechanistic character of the system.