• Bulletin of the Korean Chemical Society
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• v.32 no.10
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• pp.3707-3711
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• 2011

Silver nanoparticles coated with silica can be obtained by the reduction of $AgNO_3$ with hydrazine in the presence of NaOH-stabilized, active silicic acid (polysilicic acid). The size of the silver nanoparticles and the silica shell thicknesses were affected by varying the hydrazine content, the active silicic acid content and the experimental method (e.g. hydrothermal method). Typically, silver nanoparticles sized around 40 nm were aggregated, connected by silica. The presence of peaks centered around 400 nm in UV-vis spectra corresponds to the surface plasmon resonance of silver nanoparticles. The size of the aggregated silver nanoparticles increased with increasing hydrazine concentration. Under hydrothermal conditions at $150^{\circ}C$ the formation of individual silica particles was observed and the sizes of the silver nanoparticles were reduced. The hydrothermal treatment of silver nanoparticles at $180^{\circ}C$ gives a well-defined Ag@$SiO_2$ core-shell in aggregated silica sol particles. The absorption band observed at around 412 nm were red-shifted with respect to the uncoated silver nanoparticles (${\lambda}_{max}$ = 399 nm) due to the larger refractive index of silica compared to that of water. The formation of silver nanoparticles coated with silica is confirmed by UV-visible absorption spectra, transmission electron microscopy (TEM) and energy-dispersive spectroscopy (EDS) data.

• Economic and Environmental Geology
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• v.21 no.3
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• pp.287-307
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• 1988

The Cheongju gold-silver mine is located at approximately $36^{\circ}28^{\prime}$north latitude and $127^{\circ}31^{\prime}$ east longitude in the Cheongju City of the Chung cheong bug Do, South Korea. Gold-Silver bearing hydrothermal quartz veins, occur in Cheongju Granit of Jurassic age. K-Ar isotope data for sericite in quartz vein indicate that the Au-Ag mineralization took place in early Cretaceous ($97.5{\pm}2.18$ MA. Park, et ai, 1986). Three stage of mineralization recognized anre, from early to later, (I) Sulide stage: pyrite, arsenopyrite, pyrrhotite (Hpo), sphalerite, chalcopyrite, electrum and quartz (II) Electrum stage: pyrite, sphalerite, galena, chalcopyrite, electrum and quartz. (III) Silver mineral stage: pyrite, marcasite, pyrrhotite (Mpo), sphalerite, galena, electrum, native silver argentite, fluorite, calcite and quartz. In this paper, mode of occurrences and chemical compositions of electum and native silver have been investigated by means of microscope and EPMA. Electron probe microanalysis shows that an individual grain of electrum is almost homogeneous in composition. Silver content of electrum ranges from 44.7-67.1 atom.%. Gold content of native silver ranges below 0.2 atom. %. Vicker's hardness number (VHN) of electrum and native silver ranges $78.2-81.8kg/mm^{2}$ respectively. The filling temperature of fluid inclusions in quartz ranges from $130-280^{\circ}C$. On the basis of arsenpyrite geothemometer, the equilibrium temperature and sulfur fugacity of the pyrite-arsenopyrite-pyrrhotite(Hpo) assemblage is assumed to be in ange from $300-310^{\circ}C$ and $10^{-10}$ to $10^{-11}$ atm. The estimated ore reserviors on Cheongju mine area are calculated to 8000 T/M, averaing 8.6g/t Au, 27.8 g/t Ag, 1.25% Pb, l.65% Zn.

• Journal of the Korean Chemical Society
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• v.40 no.9
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• pp.640-648
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• 1996

Crosslinked chitosan was prepared from chitin after reaction with epichlorohydrin followed by deacetylation at C2-position. Epidermal releasing polymeric matrix was prepared after swelling crosslinked chitosan with distilled water and adding silver sulfadiazine and glycerine as a plasticiser. The release behavior of silver sulfadiazine from polymeric matrix was studied in pH 7.4 phosphate buffer solution by varing the drug content, glycerine concentration, and the thickness of the matrix. The drug release time was delayed by increasing the content of silver sulfadiazine and the thickness of the matrix, whereas decreased as glycerine concentration increased. The apparent constant(K) of release rate was independent upon the matrix thickness, but was proportional to the content of drug or glycerine of crosslinked chitosan matrix. These results indicated that chitosan matrix showed some potential as a drug delivery system for transdermal therapeutic application.

• KSBB Journal
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• v.28 no.4
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• pp.249-253
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• 2013

In this study, we analyzed the attachment amount and the surface properties, such as shape and attachment aspect of silver nanoparticles on the surface of salt and sucrose. In addition, we investigated the antimicrobial activity of silver nanoparticles by measuring total colony counts and total coliforms in sewage according to the time and the amount of silver nanoparticles. As a result, it is found that silver nanoparticles are attached on the surface of salt and sucrose from the SEM images and there is no microorganisms on the surface of salt and sucrose. Silver nanoparticles on salt were rod shape but silver nanoparticles on sucrose were round shape. Also, the content of silver was 0.735 mg/g on salt and 0.885 mg/g on sucrose. In all experiments, total colony counts and total coliforms sharply declined initially, and it decreased gradually as change the time. When injection amount of nano silver sucrose and salt increased, the width of decline was greater. The amount of total colony counts and total coliforms of nano silver salt was much lower and the disinfection efficiency was higher comparing with nano silver sucrose. That means the case of nano silver salt is much better at the antimicrobial activity.

• Journal of Information Technology Services
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• v.8 no.4
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• pp.187-199
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• 2009

Content services for silver users on the ubiquitous technologies are getting attention as a new business model, monitoring users in real-time on the real-world and/or cyber-world. A lot of business and service model have been developed to apply silver or elder user. This study explained a state-of-the-art silver IT service to innovative services for users, ranging from home and finance to support for healthcare and living. Due to the variation of subtle terminologies, this study was conducted to restructure an adaptive terminology including some definitions. Current silver IT service model has been evaluated from the technical, functional, and business analyst, and its suitability has also been expressed in a proposed model and service. The purpose of this study was to propose a systematic approach of new IT service business model for silver users. A proposed model was described to explain the feasibility of the silver IT industry.

• Economic and Environmental Geology
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• v.21 no.4
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• pp.367-380
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• 1988

Most of the gold (-silver) vein deposits at Yeongdong District are mainly distributed in the precambrian metamorphic rocks. Based on the Ag/Au total production and ore grade ratios, the chemical composition of electrum and the associated sulfides, the gold(-silver) deposits at Yeongdong District may be classified into 4 classes: pyrrhotite - type gold deposits( I), pyrite - type gold deposits (IT A; massive vein), pyrite - type gold deposits (II B; nonmassive vein) and argentite - type gold - silver deposits(III). The chemical study on electrum(including native gold) revealed that Au content (2.8 to 92.4 atomic%) of electrums varies very widely for different classes of deposits. The Au content of electrum associated with pyrrhotite (Class I), ranging from 47.1 to 92.4 atomic% Au, is clearly higher than that associated with pyrite (Classes IIA, IIB and III). In contrast, classes I, II, and III deposits do not show clear differences in Au content of electrum. In general, pyrrhotite - type gold deposits(I) are characterized by features such as simply massive vein morphology, low values in the Ag/Au total production and ore grade ratios, the absence or rarity of silver - bearing minerals except electrum, and distinctively simple mineralogy. Although the geological and mineralogical features and vein morphology of pyrite - type gold deposits(IIA)are very similar to those of pyrrhotite - type gold deposits (I), Class II A deposits reveal significant differences in the associated iron sulfide (i. e. pyrite) with electrum and Au content of electrum. The Ag/Au total production and ore grade ratios from Class II A deposits are relatively slightly higher than those from Class I deposits. Pyrite - type gold deposits(II B) and argentite - type gold - silver deposits (III) have many common features; complex vein morphology, medium to high values in the Ag/Au total production and ore grade ratios and the associated iron sulfide (i. e. pyrite). In contrast to Class II B deposits, Class III deposits have significantly high Ag/Au total production and ore grade ratios. It indicates distinct difference in the abundance of silver minerals (i. e. native silver and argentite). The fluid inclusion analyses and mineralogical data of electrum tarnish method indicate that the gold mineralization of Classes I and II A deposits was deposited at temperatures between $230^{\circ}$ and $370^{\circ}C$, whereas the gold (-silver) mineralization of Classes ITB and ill formed from the temperature range of $150^{\circ}-290^{\circ}C$. Therefore, Classes I and IT A deposits have been formed at higher temperature condition and/or deeper positions than Classes IIB and III.

• Food Science and Preservation
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• v.4 no.3
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• pp.251-258
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• 1997

The quality changes of strawberries packaged using low density polyethylene (LDPE) film filled with 3% silver-coated ceramic (WC30) and filled with it and 0.1% chitin (CWC) were investigated during storage at 2$0^{\circ}C$ for 5 days. In gas composition within film bag, CWC and WC30 kept higher CO2 concentration than LDPE without silver-coated ceramic and chitin (CO) did during 5 day storage. The weight loss of strawberries during storage was the smallest in WC30 and the largest in CWC in 5 days. Hardness of strawberries was the highest in WC30 and the lowest in CO during 5 day storage. pH of strwberries was increased a little until 1 day and was not changed after 1 day storage, and soluble solid content was not changed during storage. Vitamin C content was decreased significantly until 2 day storage and decreased a little after 2 days. There is no differences in the change of vitamin C content among the packaging materials. In color measurement, lightness was the highest in WC 30 and in sensory evaluation, all characteristics also had the highest scores in WC30. In conclusion, better quality of straberries was shown in WC30 than in CWC and CO during storage.

• Korean Journal of Materials Research
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• v.18 no.9
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• pp.503-506
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• 2008

The effect of silver nanoparticles (NPs) incorporation on the electronic properties of poly (3, 4-ethylenedioxythiphene) : poly(styrenesulfonate) (PEDOT : PSS) films was investigated. The surface of silver NPs was stabilized with trisodium citrate to control the size of silver NPs and prevent their aggregation. We obtained ca. 5 nm sized silver NPs and dispersed NPs in PEDOT : PSS solution. Sheet resistance, surface morphology, bonding state, and work function values of the PEDOT : PSS films were modified by silver NPs incorporation as well as annealing temperature. Sodium in silver NPs solution could lead to a decrease of work function of PEDOT : PSS; however, large content of silver NPs have an effect on the increase in work function, resulting from charge localization on the silver NPs and a decrease in the number of charge-trapping-related defects by chemical bond formation.

• Journal of the Korean Chemical Society
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• v.37 no.5
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• pp.527-536
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• 1993

The characteristics of the controlled drug release were studied for biodegradable transdermal drug delivery system. A biodegradable polymeric matrix was prepared from chitosan, silver sulfadiazine, and glycerine. The release behavior of silver sulfadiazine from chitosan matrix was consistent with the Higuchi's diffusion controlled model. The release time was delayed by increasing the content of silver sulfadiazine and thickness of the matrix, whereas decreased as glycerine concentration increased. The apparent constant (K) of release rate was proportional to the content of drug or glycerine and the thickness of chitosan matrix. These results indicated that chitosan matrix shows some potential as a drug delivery system for transdermal therapeutic application.

• Journal of Sericultural and Entomological Science
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• v.49 no.1
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• pp.24-27
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• 2007

Silkworm fed on the mulberry leaf mixed with silver nanoparticle to produce silver-nanoparticle embedded cocoon. Comparative analysis of silver content of cocoon shell, percentage of pupation and percentage of cocoon-shell weight showed that the optimum concentration and the feeding period of mulberry leaf mixed with silver nanoparticle were 500 ppm and the period from 3 day 5 instar to mounting of silkworm. The silver content of cocoon was observed variously by silkworm breedings. C212 variety makes pale yellow cocoon with the highest silver content(69%). Using the scanning electron microscope, we showed that the size of silver nanoparticles in silk was observed from 26.98 to 99.81nm. Silver-nanoparticle embedded silk is expected to use as high valuable application owing to the different functional properties including antibiotic characteristics and mechanical and electronic properties. The applicable fields expected is antistatic and/or electronic products with biological degradable natural materials.