• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.23 no.6
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• pp.481-486
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• 2010

ENIG (electroless Ni immersion gold) is one of surface finishing which has been most widely used in fine pitch SMT (surface mount technology) and BGA (ball grid array) packaging process. The reliability for package bondability is mainly affected by interfacial reaction between solder and surface finishing. Since the behavior of IMC (intermetallic compound), or the interfacial reaction between Ni and solder, affects to some product reliabilities such as solderability and bondability, understanding behavior of IMC should be important issue. Thus, we studied the properties of ENIG with P contents (9 wt% and 13 wt%), where the P contents is one of main factors in formation of IMC layer. The effect of P content was discussed using the results obtained from FE-SEM(field-emission scanning electron microscope), EPMA(electron probe micro analyzer), EDS(energy dispersive spectroscopy) and Dual-FIB(focused ion beam). Especially, we observed needle type irregular IMC layer with decreasing Ni contents under high P contents (13 wt%). Also, we found how IMC layer affects to bondability with forming continuous Kirkendall voids and thick P-rich layer.

• Microbiology and Biotechnology Letters
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• v.17 no.6
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• pp.545-551
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• 1989

Thermostable alkaline protease of alkalophilic Bacillus sp. No. 8-16 has been purified, and the properties of the enzyme investigated. The characteristic point of the organism used is especially good growth in alkaline and thermal condition. The alkaline protease of the strain No. 8-16 was purified from crude enzyme by acetone precipitation, CM-cellulose ion exchange chromatography, Sephadex G-100 and Sephadex G-75 gel filtration. Through the series of chromatograpies, the enzyme was purified to homogeneity with specific activity of 37 fold higher than that of the crude broth. Characteristics of the purified enzyme were as follow; $K_m$ value for the enzyme was 1.3 mg/ml, the alkaline protease showed a maximal activity at 7$0^{\circ}C$ and from the pH 6.0 through 12.0, and stable for 1 hr. at 6$0^{\circ}C$. The moleclar weight of the enzyme was estimated to be 33,000 by Sephadex G-100 gel filtration. The activity of the alkaline protease was inhibited by iodoacetic acid and Ag$^+$, Hg$^+$, PMSF (phenylmethylsulfonyl fluoride), and activated by $Ca^{2+}$ and Mn$^{2+}$.

• Journal of the Korean Chemical Society
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• v.37 no.11
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• pp.943-950
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• 1993

The determination of trace level germanium in 5.0 ${\times}\;10^{-2}$ M perchloric acid supporting electrolyte solution containing 8.0 ${\times}\;10^{-2}$ M catechol has been investigated by the square wave anodic stripping voltammetry. The optimum conditions in determination of germanium were as follows: deposition time; 120 sec, deposition potential; -0.9 volts vs. Ag/AgCl and frequency; 100 Hz. The determination of germanium was possible regardless of coexistent ion such as copper, lead and silicon. Calibration curve was shown a good linearlity in the range of 0.40 ppb to 2.0 ppm and the detection limit was 0.080 ppb. This method was useful for trace level germanium due to the short analysis time and higher sensitivity.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2017.05a
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• pp.96.2-96.2
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• 2017

This research was conducted to investigate the electrochemical properties of the thin air-formed oxide film-covered AZ31 Mg alloy. In this work, native air-formed oxide films on AZ31 Mg alloy samples were prepared by knife-abrading method and the changes in the electrochemical properties of the air-formed oxide film were investigated in seven different electrolytes containing the following anions $Cl^-$, $F^-$, $SO{_4}^{2-}$, $NO_3{^-}$, $CH_3COO^-$, $CO{_3}^{2-}$ and $PO{_4}^{3-}$. It was observed from open circuit potential (OCP) transients that the potential initially decreased before gradually increasing again in the solutions containing only $CO{_3}^{2-}$ or $PO{_4}^{3-}$ ions, indicating the dissolution or transformation of the native air-formed oxide film into new more protective surface films. The Nyquist plots obtained from electrochemical impedance spectroscopy (EIS) showed that there was growth of new surface films with immersion time on the air-formed oxide film-covered specimens in all the electrolytes; the least resistive surface films were formed in fluoride and sulphate baths whereas the most protective film was formed in phosphate bath. The potentiodynamic polarization curves illustrated that passive behaviour of AZ31 Mg alloy under anodic polarization appears only in $CO{_3}^{2-}$ or $PO{_4}^{3-}$ ions containing solutions and at more than $-0.4V_{Ag/AgCl}$ in $F^-$ ion containing solution.

• Applied Chemistry for Engineering
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• v.4 no.1
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• pp.162-170
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• 1993

Vapor-phase ETBE(ethyl tert-butyl ether) synthesis from TBA(tert-butyl alcohol) and ethanol was carried over solid acid catalysts such as heteropoly acids and proton type zeolites. Heteropoly acids were more active than proton type zeolites and $H_4SiW_{12}O_{40}$ catalyst showed about the same activity as Amberlyst-15 ion exchange resin catalyst used as an industrial catalyst in ETBE synthesis. The catalytic activity of transition metal exchanged heteropoly acids was greatly enhanced, because new acid site was generated with hydrogen reduction. This effect of hydrogen reduction was related to the reduction characteristics of catalysts and the order of reducibility was $Ag^+$>$Cu^{2+}$>$Fe^{2+}$.

• Journal of Microbiology and Biotechnology
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• v.24 no.4
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• pp.522-533
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• 2014

Bionanotechnology has revolutionized nanomaterial synthesis by providing a green synthetic platform using biological systems. Among such biological systems, microalgae have tremendous potential to take up metal ions and produce nanoparticles by a detoxification process. The present study explores the intracellular and extracellular biogenic syntheses of silver nanoparticles (SNPs) using the unicellular green microalga Scenedesmus sp. Biosynthesized SNPs were characterized by AAS, UV-Vis spectroscopy, TEM, XRD, FTIR, DLS, and TGA studies and finally checked for antibacterial activity. Intracellular nanoparticle biosynthesis was initiated by a high rate of $Ag^+$ ion accumulation in the microalgal biomass and subsequent formation of spherical crystalline SNPs (average size, 15-20 nm) due to the biochemical reduction of $Ag^+$ ions. The synthesized nanoparticles were intracellular, as confirmed by the UV-Vis spectra of the outside medium. Furthermore, extracellular synthesis using boiled extract showed the formation of well scattered, highly stable, spherical SNPs with an average size of 5-10 nm. The size and morphology of the nanoparticles were confirmed by TEM. The crystalline nature of the SNPs was evident from the diffraction peaks of XRD and bright circular ring pattern of SAED. FTIR and UV-Vis spectra showed that biomolecules, proteins and peptides, are mainly responsible for the formation and stabilization of SNPs. Furthermore, the synthesized nanoparticles exhibited high antimicrobial activity against pathogenic gram-negative and gram-positive bacteria. Use of such a microalgal system provides a simple, cost-effective alternative template for the biosynthesis of nanomaterials in a large-scale system that could be of great use in biomedical applications.

• Journal of the Korean Chemical Society
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• v.42 no.4
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• pp.432-442
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• 1998

Since the definition of pH, $pH=-Ioga_H$ is based on a single ion activity, pH values can not be determined with measurement itself, but require an approximation method. They are derived from EMF measurement of a liquid junction free cell using hydrogen and Ag/AgCl electrodes. Primary standard materials with certified pH values can be obtained with this approximation method. Standard buffer solutions are used to calibrate pH meters. Thus the accuracy of the pH values of standard buffer solutions limits the reliability of measured pH values can be obtained with this approximation method. Standard buffer solution are used to calibrate pH meters. Thus the accuracy of the pH values of standard buffer solutions limits the reliability of measured pH values of sample solutions. To certify the pH values, we have established the system for the primary standard measurement and certified the pH of buffer solutions in the range of 1.6∼12.5 pH unit within uncertainty of ${\pm}0.005$ pH unit.

• Korean Journal of Food Science and Technology
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• v.36 no.2
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• pp.361-364
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• 2004

EPA and DHA extracted from methyl esterified squid oil were purified by silver exchanged resin, silver nitrate-impregnated silica gel, silver exchanged zeolite, and silica gel column chromatography, among which column chromatography using mixture of silver exchanged resin and silica gel (10% by weight) showed the best result. By this simple purification method, EPA and DHA were concentrated from 12.5 to 27.9% (yield, 86,0%) and from 21.7 to 49.5% (yield, 87.3%), respectively. Silver exchanged resin had additional advantages of outstanding reusability and simple recovery of silver.

• Microbiology and Biotechnology Letters
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• v.30 no.1
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• pp.26-32
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• 2002

For commercial production of Korean fermented anchovy sauce through rapid fermentation, a bacterial strain which showed the high protease activity was isolated from a commercially fermented anchovy sauce. The isolate was Bacillus amyloliquefaciens, and named as B. amyloliquefaciens HTP-8. The incubation temperature, initial pH, and cultivation time for optimal production of protease by B. amyloliquefaciens HTP-8 were $30^{\circ}C$, 7.0, and 3 days, respectively. In jar fermenter, B. amyloliquefaciens HTP-8 showed higher protease activity when grown at pH 7.0. The protease was partially purified by 80% ammonium sulfate precipitation and CM-Sephadex C-50 ion exchange chromatography. The partially purified enzyme had specific activity of 103.3 units/mg, yield of 0.4%, and purification fold of 43.0. The optimal pH and temperature for the protease activity were 10.0 and $50^{\circ}C$, respectively. The protease was relatively stable at the pH range of 7.0~12.0 and at the temperatures below 4$0^{\circ}C$. The activity of the enzyme was inhibited by $Ag^{＋}$ /, $Ba^{2＋}$ and selectively inhibited by PMSF, suggesting that it is a serine protease.

• Journal of the Korean Chemical Society
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• v.23 no.6
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• pp.385-391
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• 1979

It was found that cupric ion selective electrode, which was prepared by mixing CuS and $Ag_2S$ with the ratio four to one and PVC, was hard and durable. The response potentials were reproducible and linear in the range from 1.0 ${\times}$ $10^{-1}M$ to 1.0 ${\times}$ $10^{-5}M$ copper (II) solution and its slope was 25.0 mV per decade concentration at $298^{\circ}K$, slightly different from Nernstian slope. The copper (II) indicating electrode was applied in precipitation titration of 1.0 ${\times}$ $10^{-2} M Cu(II)$ sample solution containing proper amounts $NaNO_3$ with 0.1 M NaOH standard solution. Also, this electrode could be used in complex titration of Zn(II), Mg(II), Ca(II) with EDTA and stability constant of EDTA complex of Ca(II) and Mg(II) was calculated by using known Cu-$EDTA^{2-}$ stability constant.