• Journal of the Korean Magnetic Resonance Society
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• v.14 no.2
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• pp.55-75
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• 2010

An ion-exchanged reaction of $MnCl_2$ with Al-incorporated solid core/mesoporous shell silica (AlSCMS) followed by calcinations generated manganese species, where average oxidation state of manganese ion is 3+, in the mesoporous materials. Dehydration results in the formation of $Mn^{2+}$ ion species, which can be characterized by electron spin resonance (ESR). The chemical environments of the manganese centers in Mn-AlSCMS were investigated by diffuse reflectance, UV-VIS and ESR spectroscopic methods. Upon drying at 323 K, part of manganese is oxidized to higher oxidation state ($Mn^{3+}$ and $Mn^{4+}$) and further increase in (average) oxidation state takes place upon calcinations at 823 K. It was found that the manganese species on the wall of the Mn-AlSCMS were transformed to tetrahedral $Mn^{3+}$ or $Mn^{4+}$ and further changed to square pyramid by additional coordination to water molecules upon hydration. The oxidized $Mn^{3+}$ or $Mn^{4+}$ species on the surfaces were reversibly reduced to $Mn^{2+}$ or $Mn^{3+}$ species or lower valances by thermal process. Mn(II) species I with a well resolved sextet was observed in calcined, hydrated Mn-AlSCMS, while Mn (II) species II with g = 5.1 and 3.2 observed in dehydrated Mn-AlSCMS. Both species I and II are considered to be non-framework Mn(II).

• Korean Journal of Materials Research
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• v.18 no.7
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• pp.379-383
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• 2008

We report on the light-emitting diode (LED) characteristics of core-shell CdSe/ZnS nanocrystal quantum dots (QDs) embedded in $TiO_2$thin films on a Si substrate. A simple p-n junction could be formed when nanocrystal QDs on a p-type Si substrate were embedded in ${\sim}5\;nm$ thick $TiO_2$ thin film, which is inherently an n-type semiconductor. The $TiO_2$ thin film was deposited over QDs at $200^{\circ}C$ using plasma-enhanced metallorganic chemical vapor deposition. The LED structure of $TiO_2$/QDs/Si showed typical p-n diode currentvoltage and electroluminescence characteristics. The colloidal core-shell CdSe/ZnS QDs were synthesized via pyrolysis in the range of $220-280^{\circ}C$. Pyrolysis conditions were optimized through systematic studies as functions of synthesis temperature, reaction time, and surfactant amount.

• Polymer(Korea)
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• v.28 no.2
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• pp.154-161
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• 2004

Modified poly(4-vinylpyridine) was obtained by partial quarternization of nitrogen atoms in pyridine rings of poly(4-vinylpyridine) with methyl group. By means of laser light scattering and fluorescence, it was found that this modified polymer chains were aggregated in the aqueous solution and its structure was core-shell type. The hydrophobic parts of the chains were densely condensed in core part and the hydrophilic part of quarternized amino with positive charge formed the shell part. In the mixed system of modified poly(4-vinylpyridine) and anionic surfactant, sodium dodecyl sulfate, it was observed that a critical aggregation concentration existed and that this critical concentration was suddenly decreased above 0.1 M NaCl. The size change of aggregates was also investigated by dynamic light scattering while sodium dodecyl sulfate was added into polymer solution upto the critical aggregation concentration.

• International Journal of Naval Architecture and Ocean Engineering
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• v.5 no.3
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• pp.348-363
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• 2013

The use of I-Core sandwich panel has increased in cruise ship deck structure since it can provide similar bending strength with conventional stiffened plate while keeping lighter weight and lower web height. However, due to its thin plate thickness, i.e. about 4~6 mm at most, it is assembled by high power $CO_2$ laser welding to minimize the welding deformation. This research proposes a volumetric heat source model for T-joint of the I-Core sandwich panel and a method to use shell element model for a thermal elasto-plastic analysis to predict welding deformation. This paper, Part I, focuses on the heat source model. A circular cone type heat source model is newly suggested in heat transfer analysis to realize similar melting zone with that observed in experiment. An additional suggestion is made to consider negative defocus, which is commonly applied in T-joint laser welding since it can provide deeper penetration than zero defocus. The proposed heat source is also verified through 3D thermal elasto-plastic analysis to compare welding deformation with experimental results. A parametric study for different welding speeds, defocus values, and welding powers is performed to investigate the effect on the melting zone and welding deformation. In Part II, focuses on the proposed method to employ shell element model to predict welding deformation in thermal elasto-plastic analysis instead of solid element model.

• Composites Research
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• v.26 no.2
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• pp.129-134
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• 2013

The strength of adhesive joints employed in composite structures under cryogenic environments, such as LNG tanks, is affected by thermal residual stress generated from the large temperature difference between the bonding process and the operating temperature. Aramid fibers are noted for their low coefficient of thermal expansion (CTE) and have been used to control the CTE of thermosetting resins. However, aramid composites exhibit poor adhesion between the fibers and the resin because the aramid fibers are chemically inert and contain insufficient functional groups. In this work, electrospun meta-aramid nanofiber-reinforced epoxy adhesive was fabricated to improve the interfacial bonding between the adhesive and the fibers under cryogenic temperatures. The CTE of the nanofiber-reinforced adhesives were measured, and the effect on the adhesion strength was investigated at single-lap joints under cryogenic temperatures. The fracture toughness of the adhesive joints was measured using a Double Cantilever Beam (DCB) test.

• Polymer(Korea)
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• v.37 no.1
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• pp.15-21
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• 2013

Encapsulation of a paraffin wax core as a phase change material with polystyrene shell and the its thermal characteristics caused by the encapsulation were studied. For the nanoencapsulation, the miniemulsion polymerization method was selected. The factors affecting the thermal properties of prepared nanocapsule particles of phase change material were analysed in aspect of the structure of crosslinking agents, amounts of surfactant, ratio of paraffin wax to monomer, and hydrophilicity of initiators. It was assumed that Oswald ripening plays the most important role in the changes of particle size, particle morphology, and thermal capacity of nanocapsule core. It was elucidated that the thermal capacity was also dependent on the hydrophilicity and crosslinking density of polystyrene shell components.

• Advances in nano research
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• v.10 no.3
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• pp.295-312
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• 2021

A new ionic liquid functionalized magnetic silica nanoparticle was synthesized and characterized and tested as an adsorbent. The adsorbent was used for magnetic solid phase extraction on ICP-MS method. Simultaneous determination of precious metal Au has been addressed. The method is simple and fast and has been applied to standard water and surface water analysis. A new method for separation/analysis of trace precious metal Au by Magnetron Solid Phase Extraction (MSPE) combined with ICP-MS. The element to be tested is rapidly adsorbed on CoFe2O4@SiO2@[BMIM]PF6 composite nano-adsorbent and eluted with thiourea. The method has a preconcentration factor of 9.5-fold. This method has been successfully applied to the determination of gold in actual water samples. Hydrophobic Ionic Liquids (ILs) 1-butyl-3-methylimidazole hexafluorophosphate ([BMIM]PF6) coated CoFe2O4@SiO2 nanoparticles with core-shell structure to prepare magnetic solid phase extraction agent (CoFe2O4@SiO2@ILs) and establish a new method of MSPE coupled with inductively coupled plasma mass spectrometry for separation/analysis of trace gold. The results showed that trace gold was adsorbed rapidly by CoFe2O4@SiO2@[BMIM]PF6 and eluanted by thiourea. Under the optimal conditions, preconcentration factor of the proposed method was 9.5-fold. The linear range, detection limit, correlation coefficient (R) and relative standard deviation (RSD) were found to be 0.01~1000.00 ng·mL-1, 0.001 ng·mL-1, 0.9990 and 3.4% (n = 11, c = 4.5 ng·mL-1). The CoFe2O4@SiO2 nanoparticles could be used repeatedly for 8 times. This proposed method has been successfully applied to the determination of trace gold in water samples.

• Polymer(Korea)
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• v.31 no.2
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• pp.168-176
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• 2007

The sub-micron particles of poly ($\gamma-glutamic$ acid) (PGA) containing lysozyme have been prepared using supercritical antisolvent (SAS) precipitation process at various experimental conditions such as pressure, temperature, inner diameter of nozzle, and concentration. As overall results of the application of SAS process to this system, the smaller size powder has been produced as (i) increasing pressure, (ii) decreasing temperature, (iii) decreasing the inner diameter of nozzle, and (iv) decreasing the concentration of PGA and lysozyme. It is found by means of FT-IR analysis that during SAS process, the composition has changed from the original composition of PGA : lysozyme=50 : 50 into PGA : lysozyme=33 : 67 at final product powder. It means that PGA has higher solubility for the mixed solvent of carbon dioxide and dimethyl sulfoxide (DMSO). Due to such difference of solubility, this particle forms the core-shell structure of which the core consists mainly of lysozyme. It is also found that the residual DMSO amount of $7.8\times10^{-3}wt%$ exists inside the powder.

• Journal of the Korean Ceramic Society
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• v.48 no.6
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• pp.493-498
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• 2011

Optimal atomic configurations in a nanoparticle were predicted by genetic algorithm. A truncated octahedron with a fixed composition of 1 : 1 was investigated as a model system. A Python code for genetic algorithm linked with a molecular dynamics method was developed. Various operators were implemented to accelerate the optimization of atomic configuration for a given composition and a given morphology of a nanoparticle. The combination of random mix as a crossover operator and total_inversion as a mutation operator showed the most stable structure within the shortest calculation time. Pt-Ag core-shell structure was predicted as the most stable structure for a nanoparticle of approximately 4 nm in diameter. The calculation results in this study led to successful prediction of the atomic configuration of nanoparticle, the size of which is comparable to that of practical nanoparticls for the application to the nanocatalyst.

• Proceedings of the Korean Vacuum Society Conference
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• 1994.02a
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• pp.50-50
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• 1994

Half-metallic Heusler alloys (NiMnSb, ppdMnSb, pptMnSb) have attracted much attention due to their unique electronic and magnetic structures. Sppin-ppolarized band structure calculation ppredicts metallic behavior for the majority sppin states and semiconductor behavior for the minority sppin states. We have studied the electronic structures of these half-metallic Heusler alloys by core-level pphotoemission sppectroscoppy of Mn 2pp and 3s XppS sppectra. We found large intensities of Mn 2pp satellites and 3s exchange spplitting comppared with other metal Mn-alloys. These satellite structure can be understood by applying Anderson imppurity model. This fact supports the calculated sppin pprojected ppartial density of states which suggests that the valence electrons be highly sppin ppolarized near Fermi level and that the electrons involved with charge-transfer be mainly minority sppin ones which have semiconducting band structure. The trend of charge transfer energies Δ from ligands (Sb 5pp) to Mn 3d, obtained from our model fitting, is consistent with that calculated from sppin pprojected ppartial density of state. Also the trend of d-d electron correlation energies U calculated from Mn Auger line L3 VV by Mg $K\alpha$ source is comppatible with that resulted from our model fitting. We fitted the Mn 3s curve in the same way as for insulating Mn comppounds by using the same pparameters calculated from Mn 2pp curve fitting exceppt for the Coulomb interaction energy Q between core hole and d-electrons. The 3s sppectra were analyzed by combing the charge transfer model and a simpple model taking into account the configuration mixing effect due to the intra-shell correlation. We found that the exchange interaction between 3s hole and 3d electrons is mainly respponsible for the satellite of Mn 3s sppectra. This is consistent with the neutron scattering data, which suggests local 3d magnetic moment. We find that the XppS analysis results of Mn 2pp and 3s satellite structures of half-metallic Heusler alloys are very similar to those of insulating transition metal comppounds.