• Bulletin of the Korean Chemical Society
• /
• 제29권7호
• /
• pp.1335-1343
• /
• 2008

Theoretical studies on the un-catalyzed and catalyzed aminations of ketene with $NH_3$ and $(NH_3)_2$, respectively, were studied using MP2 and hybrid density functional theory of B3LYP at the 6-31+G(d,p) and 6- 311+G(3df,2p) basis sets in the gas phase and in benzene and acetonitrile solvents. In the gas phase reaction, the un-catalyzed mechanism was the same as those previously reported by others. The catalyzed mechanism, however, was more complicated than expected requiring three transition states for the complete description of the C=O addition pathways. In the un-catalyzed amination, rate determining step was the breakdown of enol amide but in the catalyzed reaction, it was changed to the formation of enol amide, which was contradictory to the previous findings. Starting from the gas-phase structures, all structures were re-optimized using the CPCM method in solvent medium. In a high dielectric medium, acetonitrile, a zwitterions formed from the reaction of $CH_2$=C=O with $(NH_3)_2$, I(d), exists as a genuine minimum but other zwitterions, I(m) in acetonitrile and I(d) in benzene become unstable when ZPE corrected energies are used. Structural and energetic changes induced by solvation were considered in detail. Lowering of the activation energy by introducing additional $NH_3$ molecule amounted to ca. −20 $\sim$ −25 kcal/mol, which made catalyzed reaction more facile than un-catalyzed one.

• 한국재료학회지
• /
• 제24권3호
• /
• pp.166-173
• /
• 2014

The effects of printed circuit board electroless nickel immersion gold (ENIG) and organic solderability preservative (OSP) surface finishes on the electromigration reliability and shear strength of Sn-3.5Ag Pb-free solder bump were systematically investigated. In-situ annealing tests were performed in a scanning electron microscope chamber at 130, 150, and $170^{\circ}C$ in order to investigate the growth kinetics of intermetallic compound (IMC). Electromigration lifetime and failure modes were investigated at $150^{\circ}C$ and $1.5{\times}10^5A/cm^2$, while ball shear tests and failure mode analysis were conducted under the high-speed conditions from 10 mm/s to 3000 mm/s. The activation energy of ENIG and OSP surface finishes during annealing were evaluated as 0.84 eV and 0.94 eV, respectively. The solder bumps with ENIG surface finish showed longer electromigration lifetime than OSP surface finish. Shear strengths between ENIG and OSP were similar, and the shear energies decreased with increasing shear speed. Failure analysis showed that electrical and mechanical reliabilities were very closely related to the interfacial IMC stabilities.

• 한국자기학회지
• /
• 제3권4호
• /
• pp.298-304
• /
• 1993

Pd/Co 다층박막을 동시열증착장치로 제작하여, 토오크 자력계, 홀 효과 측정장치 및 X-선 회절기를 이용하여 기판 온도, Pd하지층에 따른 구조적 자기적 및 열적 특성변화를 연구하였다. 기판 온도가 증가함에 따라 $150^{\circ}C$까지는 계면구조 및 각 층의 결정성이 향상되고, (111) 집합조직이 발달되었으며 따라서 계면자기이방성 및 수직자기 이방성에너지는 증가하였다. 그러나 보자력은 감소 하였는데 이는 입자의 성장으로 인한 자구벽 고착효과 감소에 기인된 것으로 보이며 Pd하지층이 두꺼 울 수록 다층박막의 입자크기는 컸다. $200^{\circ}C$ 이상에서는 계면에서 상호확산에 의하여 다층막의 구조의 열화는 촉진되었다. 열처리 초기에 주 피이크 강도의 변화는 컸으며 그 후부터는 작은 폭으로 감소하였다. 초기의 큰 강도 변화는 구조이완등의 현상에 기인된 것으로 추측되며 그 후는 확산에 의 해서이다. 다층박막의 상호확산에 필요한 활성화 에너지는 14.9 KCal/mole.K 였다.

• Food Science and Biotechnology
• /
• 제15권1호
• /
• pp.33-38
• /
• 2006

This study was performed to provide basic rheological data of dandelion root concentrates in order to predict their processing aptitude and usefulness as functional foods material. The hot water and 70% ethanol extracts of dandelion root were concentrated at 5, 20, and 50 Brix, and their static viscosity, dynamic viscosity, and Arrhenius plots were investigated. Almost all hot water concentrates showed the typical flow properties of a pseudoplastic fluid, but evaluation using the power law model indicated that the 70% ethanol concentrates showed a flow behavior close to a Newtonian fluid. The apparent viscosity of hot water and 70% ethanol concentrates decreased with increasing temperature. Yield stresses of hot water and 70% ethanol concentrates by Herschel-Bulkley model application were in the range of 0.026 - 1.368 Pa and 0.022 - 0.238 Pa, respectively. The effect of temperature and concentration on the apparent viscosity was examined by Arrhenius equation. The activation energies of hot water and 70% ethanol concentrates were in the range of $8.762-23.778{\times}10^3\;J/mol{\cdot}kg$ and $3.217-20.384{\times}10^3\;J/mol{\cdot}kg$ with increasing concentration, respectively. Storage (G') and loss (G") moduli were generally increased with increasing frequency. For the 70% ethanol concentrates, G" predominated over G' at all applied frequencies and so they showed the typical flow behavior of a low molecular solution. However, for the hot water concentrates, G' predominated over G" at more than 1.9 rad/sec (cross-over point) and so they showed the typical flow behavior of a macromolecular solution.

• 한국표면공학회지
• /
• 제26권2호
• /
• pp.87-107
• /
• 1993

The grain size of the final products of WC-Co and WC-Ni composite powders is dependent on the size of the starting material and the conditions employed for the reduction and carburization. APT-Co and -Ni com-plex salts were prepared by the substitution reaction between ammonium ions in APT and the metal ions in Co(NO3)2 and Ni(NO3)2 solutions of different concentrations(0.1 to 0.7M) at $50^{\circ}C$ and the grain sizes of the com-plex salts was $0.54~0.76\mu\textrm{m}$. The complex which calcined the complex salts at $700^{\circ}$~80$0^{\circ}C$ for 60min. were 0.2~0.5$\mu\textrm{m}$. W-Co($5.92^{\circ}C$) and -Ni(6.95%) powders which reduced the complex oxides with H2d atmo-sphere(flow rate;600cc/min.) at $700^{\circ}$~$800^{\circ}C$ for 60min. were $0.5~0.6\mu\textrm{m}$. The mean grain sizes of WC-Co and WC-Ni composite powders which carburized both complex metals of W-Co and W-Ni at $800^{\circ}C$ for 60min. were $0.5~0.6\mu\textrm{m}$, and take place the coarsening of the grain above $800^{\circ}C$ and the optmium ratio of C3H8 and H2 was 0.2 for the control of the free carbon. The effect of Co contents on the particle sizes decreased from 0.4 to $0.25\mu\textrm{m}$ with increasing the content from 2.0 to 7.6w%. The activation energies on the reductions of oxides and the formations of carbides were as follows ; W-Co : Q = 8.7 kcal/mole, W-Ni : Q = 8.1 kcal/mole, WC-Co pow-der : Q = 17.8 kcal/mole, WC-Ni powder : Q = 16.6 kcal/mole.

• 한국식품과학회지
• /
• 제21권2호
• /
• pp.289-293
• /
• 1989

콩을 침지하는 동안 콩의 부피증가량은 침지시간의 평방근과 비례하였으며, 침지온도 $4^{\circ}C{\sim}60^{\circ}C$에서의 콩의 부피증가 속도는 수분증가 속도와 높은 정의 상관관계를 보였다. 콩의 부피증가의 활성화에너지 값은 침지온도 $4^{\circ}C{\sim}40^{\circ}C$에서 $3,700{\sim}4,900cal/mole$, 침지온도 $40^{\circ}C{\sim}60^{\circ}C$에서는 $2,700{\sim}5,000cal/mole$이었다. 침지온도 $4^{\circ}C{\sim}60^{\circ}C$에서의 콩의 부피증가로부터 수분함량 50%에 도달하는 시간과 온도와의 관계로부터 계산한 z-값은 $50^{\circ}C{\sim}55^{\circ}C$ 이었다.

• 한국식품영양과학회지
• /
• 제13권2호
• /
• pp.181-187
• /
• 1984

Lysine is known as a limiting amino acid in rice. In addition, it is considered to be important in that it is easily non-activated by the browning reaction during processing or storage. The present study was designed to utilize a kinetic approach to analyse the effect of temperature and water activity on available lysine loss in rice. Simplified kinetic models were used to obtain the various kinetic parameters for available lysine loss in rice subjected to accelerated shelf-life tests (ASLT). These kinetic parameters were then used to predict protein quality loss under the non-steady state storage. The predicted losses were compared to the actual losses. As expected, available lysine loss was increased with increased temperature and water activity. The activation energies and $Q_{10}$ values for available lysine loss ranged from 4.03 to 5.10 Kcal/ mole and 1.22 to 1.27, respectively, The shelf-lives at $25^{\circ}C$, the time to reach 25% loss of the available lysine, which was derived from the accelerated shelf-life tests showed 67 to 107 days according to $a_w$'s. The amount of loss for the fluctuating condition was greater than that occurring at the mean temperature of $45^{\circ}C$. Actually, the differences in effective temperature for the fluctuating storage were between about 4 and $6^{\circ}C$. In predicting the extent of loss using constant state data, the predicted shelf-lives were 2 to 7 days shorter than the actual storage values.

• 한국식품영양과학회지
• /
• 제17권3호
• /
• pp.220-225
• /
• 1988

쌀 및 쌀가루의 저장중 품질 변화를 신속하게 예측하기 위해 품질 측정을 위한 유효 지표 물질을 설정하고, 그 변화를 동력학적으로 구명함으로써 shelf- life를 Kinetic 측면에서 구하고자 하였다. 저장중 관능적 품질과 가장 관계가 큰 이화학적 지표는 지방산도이었으며 이는 저장 기간에 따라 1차반응에 따라 변화하였다. 저장중 쌀 및 쌀가루의 지방산도 변화에 대한 활성화 에너지는 쌀의 경우 50.953KJ/Kmol, 쌀가루는 59,750KJ/Kmol이었고 쌀 및 쌀가루의 반응속도 상수와 $Q_10$ 등을 이용해 관능검사(3.0)와의 관계로부터 이들의 품질 수명을 추정해 보면 $13^{\circ}C$에 저장한 경우는 각각 378일, 358일, $23^{\circ}C$에 저장한 경우는 163일과 145일까지 관능적으로 상품성을 유지할 수 있는 것으로 나타났다.

• Preventive Nutrition and Food Science
• /
• 제12권4호
• /
• pp.242-250
• /
• 2007

This study evaluated the storage stability of a variety of sauce products in the Korean market, determined primary quality indices for three typical products, and proposed functional relationships that are useful for determining shelf life at different temperatures. Most of the products examined were found to combine hurdles of low pH, low water activity, and the use of heat processing as methods for producing the required storage stability while maintaining the sensory quality of the products. For a meat extract solution produced for cold noodles (pH=4.3; $a_w=0.98$), the primary quality change determining shelf life was lipid oxidation, determined here by the TBA value. The primary quality index of a soybean paste seasoning mix (pH=4.0; $a_w=0.78$), which had a microbial load of 2.8 log (CFU/g), was a decrease in its pH. The primary quality index for a sandwich spread (pH=4.0; $a_w=0.88$) was changes in its surface color. The temperature dependence of changes in the primary quality indices can be described by the Arrhenius equation, which can estimate the shelf life at any arbitrary limit as a function of temperature. The activation energies for changes in the primary quality indices of the meat extract solution, the soybean paste seasoning, and the sandwich spread were 20.3, 27.2, and 43.5 kJ/mol, respectively.

• 대한화학회지
• /
• 제40권3호
• /
• pp.202-208
• /
• 1996

수열법으로 합성한 SAPO-11 분자체를 $H_4$EDTA로써 골격내의 알루미늄을 부분적으로 탈알루미늄화시킬때 24시간 탈알루미늄화까지는 골격이 안전하였으나 48시간 탈알루미늄화에 의해서는 구조가 붕괴되어 variscite($AIPO_4{\cdot}2H_2O$)와 tridymite($SiO_2$)로 변하였다. SAPO-11의 탈알루미늄화로 인하여 3607$cm^{-1}$과 3453$cm^{-1}$에서 하이드록실기에 의한 IR 흡수띠가 각각 관측되었다. 이들 하이드록실기 피크들의 세기는 탈알루미늄화의 정도에 비례하여 증가하였으며 메틸아민의 흡착에 의하여 피크가 사라지는 것으로 보아 이들은 Bronsted 산 자리임을 알 수 있었다. TPD(Temperature-Programmed Desorption) 및 DSC(Differential Scanning Calorimetry) 실험결과 탈알루미늄화된 SAPO-11에 흡착된 메틸아민과 물 분자는 탈알루미늄화가 되지않은 SAPO-11보다 높은 온도에서 그 피크들이 관측되었으며 메틸아민과 물 분자의 탈착 및 탈수 활성화 에너지는 탈알루미늄화의 정도에 비례하여 증가하였다. 이와 같은 현상은 제올라이트 분자체에 있어서와 유사하게 탈알루미늄으로 인하여 SAPO-11 분자체 내에 생성된 구조 하이드록실(srtuctural hydroxyl)기의 Bronsted 산 자리와 흡착 분자간의 보다 강한 상호작용에 기인되는 것으로 생각되었다.