• Journal of Korean Society of Environmental Engineers
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• v.34 no.9
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• pp.613-622
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• 2012

A chrome absorbent that is useful in rapid magnetic recovery and recycling was developed though a synthesis of Multi-Terminalized Magnetic-core Dendrimer (MTMD). Divergence through coprecipitation and rotation growth was used for synthesis. The dendrimer was multi-terminilized through methyl propionate and glutaric acid. The property analysis of the synthesized sample was performed through XRD, FT-IR, TEM, EDS, TGA and zeta potential analyzer. A magnetic-core of MTMD had a magnetite crystal and the size of 4th generation dendrimer was identified to be from 15 nm to 20 nm. Through the analysis of the TGA, the rate of the dendrimer branch for the first generation dendrimer was about 7% and 3% of diminished weight occurred as the generation grows. Also, the potential of the dendrimer when multi-terminalized, had variation from 25.26 mV to -6.53 mV. As a result of MTMD adsorption experiment, it absorbed more than 80% within 5 minutes and indicated absorptivity of 6.308 mg/g. When it was compared with COOH Dendrimer (COOH-D) after magnetic recovery, the recovery time was rapidly reduced by more than half and it could recover 100% within 30 minutes. In case of the regeneration experiment that used chrome, it was identified to maintain the same adsorptivity for four runs.

• Journal of Sericultural and Entomological Science
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• v.35 no.1
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• pp.60-68
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• 1993

It has been known that the silk degumming treated by hot alkali solution is easy to handle but is liable to yield poor-quality silk due to the degree of degumming loss, incomplete-degumming or over-degumming. Therefore, many studies have been carried out on the silk degumming by enzyme in order to improve the quality of silk. However, no attention has been paid to the physicochemical analysis of enzymatic degummed silk. In this paper, two different degumming methods, soap and enzymatic, are compared in aqueous solution state of silk fibroin. The results can be summarized as follows: There was no significant difference between two solutions on the bases of polarizing microscopy, TEM observation and SDS-PAGE. Spherulite of silk fibroin was not observed in polarizing microscopy, however the leaf-shape fibril structure was developed upon solidification. The size of spherulites of silk fibroin in TEM observation were 30~120nm with a wide range of size distribution. The intrinsic viscosity of enzymatic degummed fibroin solution was lower than that of soap degummed solution. This can be explained that the silk fibroin was more degraded by enzymatic degumming method compared with the soap degumming method. SDS-polyacrylamide gel electrophoresis showed that the fibroin molecule was composed of large component of molecule weight above 50 kd and small component of molecule weight about 20 kd. There was no difference in crystallinity between two degumming methods on the bases of results of DSC thermograms and IR spectra.

• Korean Journal of Materials Research
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• v.8 no.4
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• pp.328-336
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• 1998

In metal-carbon system with no mutual solubility between matrix and alloying elements as solid or liquid phases, Cu-C-X nanocomposite metal powders were prepared by high energy ball milling for solid-lubricating bronze bearings. Elemental powder mixtures of Cu-lOwt.%C- 5wt. %Fe and Cu- lOwt. %C- 5wt. %Al were mechanically alloyed with an attritor in an argon atmosphere, and then microstructural evolution of the Cu-C-X nanocomposite metal powders was examined. It has been found that after 10 hours of MA, the approximately 10$\mu\textrm{m}$ sized Cu-C- X nanocomposite metal powders can be produced in both compositions. Morphological characteristics and microstructural evolution of the Cu-C-X powders have shown a similar MA procedure compared to those of metal-metal system. As a result of X - ray diffraction analysis, diffraction peaks of Cu and C were broaden and peak intensities were decreased as a function of MA time. Especially, the gradual disappearance of C peaks in the X- ray spectra is proved to be due to the lower atomic scattering factor of C. The calculated Cu crystallite sizes in Cu- C- X nanocomposite metal powders by Williamson- Hall equation were about lOnm size, on the other hand, the observed ones by TEM were in the range of 10 to 30nm.

• Korean Journal of Materials Research
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• v.8 no.4
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• pp.368-374
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• 1998

The corrosion characteristics of zirconium alloys have been investigated in various aqueous solutions of LiOH. NaOH, KOH, RbOH. and CsOH at 3S$0^{\circ}C$. The concentrations of solutions were set to 4.3 mmol and 32.Smmol with equimolar $M^+$ and OH . The oxide characterization was performed using TEM on the samples corroded in 32. Smmol LiOH, NaOH, and KOH solution. The samples were prepared to have the same oxide thickness for the pretransition and post- transition regimes. Considering the trend of experimental data, the cation would playa major role in the corrosion process of Zr alloys in alkali hydroxide solutions. The microstructures of the oxides formed in various solutions were quite different. In LiOH solution the oxides grown in pre-transition as well as post-transition had the equiaxed structures with many pores and open grain boundaries. The oxides grown in NaOH solution had the protective columnar structures in pre-transition and the equiaxed structures with many open grain boundaries in post- transition. On the other hand. in KOH solution the columnar structure was maintained from pre- transition to post- transition. It was considered that the cation incorporation into zirconium oxide controlled the oxide characteristics and the corrosion acceleration in alkali hydroxide solutions.

• Korean Journal of Materials Research
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• v.11 no.2
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• pp.104-114
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• 2001

To investigate the effects of the addition of Nb and Sn on the recrystallization of Zr- Sn-Nb alloys, both Vickers micro-hardness test and TEP measurement were carried out on cold-worked specimens annealed at various temperatures from $300^{\circ}C$ to 75$0^{\circ}C$. The microstructures of heat treated specimens were analyzed by optical microscope, SEM, and TEM. The study of microhardness and microstructures showed that both recrystallization process and grain growth were retarded as the activation energy was increased by the addition of Nb and Sn. Especially, the addition of Sn was more effective on retarding recrystallization. Precipitates were formed more easily when Nb was added because the solubility of Nb into Zr is lower than that of Sn. However, the recrystallization process was affected more by Sn than Nb because the strain field formed by substitutional Sn repressed the dislocation movement. TEP was increased due to the decrease of electron scattering as recovery and recrystallization were proceeded and saturated when the recrystallization completed. However, when precipitates formed, TEP was increased because the decrease of solute concentration near the precipitates caused the decrease of electron scattering.

• Korean Journal of Materials Research
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• v.9 no.12
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• pp.1245-1251
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• 1999

Phase-change optical disk very rapid recording, high densification of data, resulting in high feedback rate and good C/N(carrier to noise) ratio of a feedback signal. However, repetitive thermal energy may cause the deformation of a disk or the lowering of an eliminability and a cyclability of the recording. The lowering of the cyclability can be reduced by insertion of thin layer of ZnS-$SiO_2$ dielectric thin film in appropriate disk structure between the upper and lower part of the recording film. Using the Taguchi method, optimum conditions satisfying both the optimized quality characteristic values and the scattering values for film formation were found to be the target R.F. power of 200W, the substrate R.F. power of 20W, the Ar pressure of 6mTorr, and the electrode distance of 6cm. From the refractive index data, the existence of the strong interaction between the electrode distance and Ar pressure was confirmed, and so was the large effect of the electrode distance on transmittance. According to the analysis of TEM and XRD, the closer the electrode distance was, the finer was the grain size due to the high deposition rate. However, the closer electrode distance brought the negative effect on the morphology of the film and caused the reduction of transmittance. AFM and SEM analyses showed that the closer the electrode distance was, the worse was the morphology due to the high rate of the deposition. Under optimum condition, the deposited thin film showed a good morphology and dense microstructure with less defects.

• Korean Journal of Materials Research
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• v.6 no.8
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• pp.833-840
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• 1996

Diamond thin films were deposited on p-type (100) Si wafers using MPECVD. Prior to deposition, ultrasonic striking was done to improve density of nucleation sites with dimond powder of 40~$60\mu$m size. Then diamond thin films were deposited at $^900{\circ}C$, 40Torr and 1000W microwave power using ${CH}_{4}$ and ${H}_{2}$ gases. The purity, the morphology and the microstructur'e and microdefects of diamond thin films were characterized by Raman spectroscopy, SEM and TEM, repectively. In Raman spectroscopy the peaks of non-diamond phase increased as ${CH}_{4}$, concentration increased. In SEM, the morphology of diamond thin films varied from crystalline to cauliflower as ${CH}_{4}$, concentration increased. As ${CH}_{4}$ con centration increased, the density of defects increased, with most defects being {III} twin. ${MTP}_{5}$, were formed with five (II]) planes. As these (Ill) Planes were twinned, ${MTP}_{5}$, represented five-fold symmetry. ]n the interfaces, defects in diamond thin films fanned out from small regions implying nucleation sites.

• Parasites, Hosts and Diseases
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• v.33 no.3
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• pp.165-172
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• 1995

A transmission electron microscopic study was performed on the ultrastructure of the tegumental layer of GymophoLloines seoi (Digenea: Gymnophallidae) metacercarlae and adults. The metacercariae were obtained from naturally infected oysters, Crcssosoea gigas, and the adults from experimentally infected C3H mice. The tegumental layer generally revealed a small number of foldings, numerous small vacuoles, sines, and muscle bundles. Beneath the muscle layer, nuclei of the tegumental cells were located. There was little difference in the structure of the tegument between the metacercariae and adults. The oral sucker, having well-developed muscle layers, showed a similar structure to the ventral sucker except numerous foldlngs in the ventral sucker. The ventral pit was surrounded by a thin spcpiu layer, where a number of microtubules and mitochondria were seen. Around the ventral pit located well-developed circular and longitudinal muscles. The results showed that the ultrastructure of the tegumental layer of G. seoi metacercariae and adults revealed little difference from other trematodes in general. The ventral pit, a peculiar structure of this trematode, seems to function as a sphincter or an accessory adhesive organ.

• Korean Journal of Food Science and Technology
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• v.46 no.3
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• pp.347-351
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• 2014

We studied the green synthesis and antibacterial activity of chitosan-silver (Ag) nanocomposite films for application in food packaging. Green synthesis of Ag nanoparticles (AgNPs) was achieved by a chemical reaction involving a mixture of chitosan-silver nitrate ($AgNO_3$) in an autoclave at 0.1 MPa, $121^{\circ}C$, for 15-120 s. The formation of AgNPs in chitosan was confirmed by both UV-Visible spectrophotometry and transmission electron microscopy (TEM) and the effects of chitosan-$AgNO_3$ concentration and reaction time on the synthesis of AgNPs in chitosan were examined. The resulting chitosan-Ag composite films were characterized by various analytical techniques and their antibacterial activity was evaluated based on the formation of halo zones around films, indicating inhibition of the growth of Escherichia coli. A fourier-transform infrared (FTIR) spectroscopy analysis showed that free amino groups in chitosan acted as effective reductants and AgNP stabilizers. The composite films exhibited enhanced antibacterial activity with increasing Ag content on the surface of as-prepared composite films.

• Korean Journal of Materials Research
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• v.4 no.5
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• pp.600-607
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• 1994

Optimum exper~mental conditions were established for the growth of heteroepitaxial GaAs layers on InP using liquid phase epitaxy (LPE) technique. Results showed that the optimum growth temperature was $720^{\circ}C$ at a cooling rate of $0.5^{\circ}C$/min. Surface morphology of the grown layers significantly improved by addition of about 0.005wt% Se to the Ga growth melt, which effectively suppressed melt-back of InP substrates into the melt during the initial stage of growth. It was observed that the quality of GaAs layers also improved substantially when the substrates patterned with grating structure were used, as determined by the (400) double crystal X-ray diffraction. The transmission electron microscopy observation indicated t.hat the misfit dislocations interact with each other at the grating region, resulting in a lower dislocation density in the upper GaAs layer.