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931.
The hydrogels composed of chitosan and eugenol were prepared to enhance and sustain antioxidant activities. The vinyl groups of eugenol monomer were directly grafted on the amino groups of chitosan, using ceric ammonium nitrate. The graft of eugenol onto chitosan was confirmed by using Fourier‐transform infrared and proton nuclear magnetic resonance spectroscopies. Results from the swelling behavior, thermal stability, and wide‐angle X‐ray diffraction revealed that the equilibrium water content decreased with increase of graft yields, because of the hydrophobicity of eugenol, although the introduction of eugenol as a side chain disturbed the ordered arrangement of chitosan's crystalline structure. The eugenol‐grafted chitosan hydrogels showed lower pH sensitivity in comparison with chitosan alone, because the amino groups, which were pH sensitive, of chitosan were grafted with eugenol. The scavenging activity of the tested hydrogels increased with graft yield of eugenol, because phenolic groups in the eugenol could play a major role as potent free‐radical terminators, in the results of improved antioxidant activity in eugenol‐grafted chitosan hydrogel in comparison with chitosan alone. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99:3500–3506, 2006 相似文献
932.
Hae Jin Kim Jin Bae Lee Young-Min Kim Myung-Hwa Jung Z. Jagličić P. Umek J. Dolinšek 《Nanoscale research letters》2007,2(2):81-86
We present synthesis, structure and magnetic properties of structurally well-ordered single-crystalline β-MnO2 nanorods of 50–100 nm diameter and several μm length. Thorough structural characterization shows that the basic β-MnO2 material is covered by a thin surface layer (∼2.5 nm) of α-Mn2O3 phase with a reduced Mn valence that adds its own magnetic signal to the total magnetization of the β-MnO2 nanorods. The relatively complicated temperature-dependent magnetism of the nanorods can be explained in terms of a superposition
of bulk magnetic properties of spatially segregated β-MnO2 and α-Mn2O3 constituent phases and the soft ferromagnetism of the thin interface layer between these two phases. 相似文献
933.
The ideal thermodynamic performances of a variety of non-CFC refrigerants and their mixtures were calculated by using the Patel-Teja equation of state. The results indicated that the preferable non-CFC refrigerant mixtures could be HCFC-I24 +HFC-152a, HFC-152a + HFC-134, dimethyl ether + HCFC-22, and dimethyl ether + HCFC-124 for air-conditioning systems, and binary mixtures of HCFC-22 + HFC-125, and HCFC-22 + HFC-143a for low-temperature applications. Those potential non-CFC mixtures were suggested for further investigations. 相似文献
934.
Bo Hyun Ryu Sang Yup Lee Dong Hyun Lee Gui Young Han Tae-Jin Lee Ki June Yoon 《Catalysis Today》2007,123(1-4):303-309
Carbon black has recently been reported to act as an effective catalyst for methane decomposition and to exhibit stable catalytic behavior despite carbon deposition, and thus it can be used for CO2-free production of hydrogen from natural gas. In this work, various carbon blacks with different primary particle size were investigated with respect to methane decomposition under atmospheric pressure from 1123 to 1223 K. Catalytic characteristics, such as activity, activation energy and reaction order, were investigated and compared. It was observed that with decreasing primary particle size (or increasing specific surface area), the specific activity increased and the activation energy decreased. The reaction orders for various pelletized, rubber-reinforcing carbon blacks were 0.6–0.7, about the same regardless of the primary particle size, while they were near 1 for fluffy carbon blacks. Fluffy carbon black showed higher activity and activation energy than the pelletized carbon black of the same primary particle size. Changes of the surface morphology during carbon deposition were observed by TEM. Variations of the number of active sites were discussed in regard of the primary particle size, carbon deposition and binder. The presence of different types of active sites was also suggested. 相似文献
935.
Kwang Ho Kim Soo Won Lee Dong Won Shin Chan Gyung Park 《Journal of the American Ceramic Society》1994,77(4):915-921
Antimony-doped tin oxide films were prepared on Corning glass substrate by chemical vapor deposition from a gas mixture of SnCl4 –SbCl5 –H2 O. The electrical conductivity and optical transmission of tin oxide films were studied with antimony doping. The film conductivity increased largely without losing optical transparency with a small addition of antimony. The increase of the conductivity was attributed mainly to more electrons donated by pentavalent Sb ions in the SnO2 lattice. Large additions of antimony, however, diminished the conductivity, optical transparency, and crystallinity of the film. The diminution was found to be caused by fine Sb2 O5 phases codeposited with SnO2 . 相似文献
936.
D. J. Twait W. J. Lackey † Arlynn W. Smith Woo Y. Lee John A. Hanigofsky 《Journal of the American Ceramic Society》1990,73(6):1510-1518
Thermodynamic calculations were performed using a modified solgasmix-pv computer program in order to study the feasibility of codepositing boron nitride (BN) plus aluminum nitride (AIN) by chemical vapor deposition. Reactants considered were AICl3 , BCl3 or B2 H6 , NH3 , and H2 . Deposition diagrams were generated for the BCl3 -AICl3 -NH3 system over a range of processing conditions such as temperature, total system pressure, and reagent concentrations. Codeposition of BN + AIN was predicted by the calculations for temperatures in the range of 900 to 1700 K and pressures of 10.13 to 101.3 kPa. The predicted deposition efficiency at equilibrium was much higher for BN than for AlN at most reagent compositions. The AlN deposition efficiency increased with decreasing temperature and decreasing BCl3 content, with increasing NH3 content, or with the addition of H2 . Aluminum chlorides were found to be the dominant gaseous species. 相似文献
937.
Unsaturated polyester resins are the most widely used thermoset resins in the composite industry. In this study, three well‐defined unsaturated polyester resins were used. These resins have similar number‐average molecular weights, and they have different numbers of C?C bonds per molecule. The reaction kinetics of unsaturated polyester resins was studied using a differential scanning calorimeter (DSC) and a Fourier transform infrared (FTIR) spectrometer. The glass transition temperature of the isothermally cured resin was also measured. Trapped radicals were observed in the cured polyester resin from electron spin resonance (ESR) spectroscopy. Considering the diffusion‐limitation effect, a simple kinetic model was developed to simulate the reaction rate and conversion profiles of polyester vinylene and styrene vinyl groups, as well as the total reaction rate and conversion. Experimental results from DSC and FTIR measurements compare favorably with the model prediction. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 211–227, 2002; DOI 10.1002/app.10317 相似文献
938.
Hyun-Seob?Song Joo?Sung?Lee Jae?Chun?HyunEmail author 《Korean Journal of Chemical Engineering》2002,19(6):949-953
A mathematical model for the pyrolysis reaction of polystyrene (PS) in a semi-batch reactor has been presented. The thermal
degradation of PS was flexibly modeled by a combination of random and specific chain-end scissions. Numerical simulation was
used to investigate the effect of operating conditions on the PS products spectrum, the results of which were validated by
the experimental data. It was found that as the reaction temperature increased (decreased), the monomer fraction in the products
became lower (higher) while the trimer higher (lower). No significant variation in the product composition was, however, observed
while constant temperature was maintained. These results indicate the reaction temperature is an effective manipulated variable
for the control of products composition of PS pyrolysis. The calculation of the optimum temperature trajectories through the
optimization study can thus be of interest for achieving productivity enhancement in plastics pyrolysis processes.
This paper is dedicated to Professor Dong Sup Doh on the occasion of his retirement from Korea University. 相似文献
939.
In this paper, manufacturing technology of the tubular single lap adhesive joint was studied to obtain reliable and optimal joint quality. In addition, a surface preparation method and a bonding process for the joint were devised. The effect of the adhesive thickness and the adherend roughness on the fatigue strength of the joint was experimentally investigated. From experiments, it has been found that the fatigue strength of the joint increased as the adhesive thickness decreased and the optimal arithmetic surface roughness of the adherends was about 2 μm. 相似文献
940.
Sang Woo Kim Jong-Ho Lee Joosun Kim Hae-Weon Lee 《Journal of the American Ceramic Society》2004,87(12):2213-2217
The effect of zinc ions added to silica film on the electrical and structural properties of a silica/indium tin oxide two-layer film which had been prepared by solution coating for electromagnetic shielding of displays was studied. The volume resistivity of the undoped silica/indium tin oxide film was more than 3 times as high as that of the zinc-doped silica/indium tin oxide film. The addition of divalent cations, zinc ions, to the overcoated layer led volume resistivity of the two-layer film to decrease significantly and also caused a long-term increase in stability. The decrease in volume resistivity was due to the addition of zinc ions that changed the interface ionization and helped to enhance the electrical conductivity in the two-layer film. 相似文献