• Nuclear Engineering and Technology
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• v.34 no.3
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• pp.218-231
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• 2002

Using a three-dimensional numerical code, B3R developed for nuclide transport of an arbitrary length of decay chain in the buffer between the canister and adjacent rock in a high- level radioactive waste repository by adopting a finite difference method utilizing the control- volume scheme, some illustrative calculations have been done. A linear sorption isotherm, nuclide transport due to diffusion in the buffer and the rock matrix, and advection and dispersion along thin rigid parallel fractures existing in a saturated porous rock matrix as well as diffusion through the fracture wall into the matrix is assumed. In such kind of repository, buffer and rock matrix are known to be important physico-chemical harriers in nuclide retardation. To show effects of buffer and rock matrix on nuclide transport in HLW repository and also to demonstrate usefulness of B3R, several cases of breakthrough curves as well as three- dimensional plots of concentration isopleths associated with these two barriers are introduced for a typical case of decay chain of $^{234}$ Ulongrightarrow$^{230}$ Thlongrightarrow$^{226}$ Ra, which is the most important chain as far as the human environment is concerned.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.10
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• pp.1534-1540
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• 2004

This study aims to obtain fundamental understandings involving the manufacturing processes of nano-composites with chemically surface-modified multi-walled carbon nanotubes(MWCNTs), and explore the role of functionalized MWCNTs in the epoxy/MWCNT composites. For this purpose, MWCNTs were purified by the thermo-chemical oxidation process, and incorporated into an epoxy matrix by in situ polymerization process, the surface of MWCNTs were functionalized with carboxyl functions which were demonstrated by an infrared spectroscopy. The mechanical properties of epoxy/MWCNT nano-composites were measured to investigate the role of a chemically functionalized carbon nanotubes. To improve the dispersion quality of MWCNTs in the epoxy matrix, methanol and acetone were exploited as dispersion media with sonification. The epoxy/MWCNT nano-composites with 1 or 2 wt.％ addition of functionalized carbon nanotubes show an improved tensile strength and wear resistance in comparison with pure epoxy, which shows the mechanical load transfer improves through chemical bonds between epoxy and functionalized MWCNTs. The tensile strength with 7 wt.％ functionalized MWCNTs increases by 28％ and the wear resistance is dramatically improved by 100 times.

• Journal of Powder Materials
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• v.16 no.3
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• pp.209-216
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• 2009

A composite of rapidly solidified Al-6061 alloy powder with graphite particle reinforcements was prepared by ball milling and subsequent hot extrusion. The microstructure and mechanical properties of these composites were investigated as a function of milling time. With increasing milling time, the gas atomized initially and spherical powders became elongated with a maximum aspect ratio after milling for 30 h. Then, refinement and spheroidization were achieved by further milling to 70 h with a homogeneous and fine dispersion of graphite particles forming between the matrix alloy layers. The best compression and wear properties were obtained in the powder milled for 70 h, associated with the increased fine and homogeneous distribution of graphite particles in the aluminum alloy matrix.

• Journal of the Korean Society of Tobacco Science
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• v.36 no.1
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• pp.12-19
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• 2014

A matrix solid-phase dispersion (MSPD) method was developed for extracting and cleaning-up the selected agrochemicals in tobacco using gas chromatography-mass spectrometry with selected ion monitoring (GC/MS-SIM). Different parameters of the method were investigated and optimized, such as the type of solid-phase (alumina, $C_{18}$ and Florisil) and eluent (acetone, acetonitrile, ethylacetate and n-hexane). The best results were obtained using 0.5 g of tobacco sample, 1.0 g of $C_{18}$ as dispersant sorbent, 1.0 g of Florisil as clean-up sorbent and acetonitile saturated with n-hexane as eluting solvent. The method was validated using tobacco samples fortified with agrochemicals at their different concentration levels. This method gave good linearity for the selected agrochemicals of ranging from $0.01{\mu}g/mL$ to $0.1{\mu}g/mL$. Recoveries of the selected agrochemicals in tobacco were more than 80 % and reproducibilities were found to be better than 10 % RSD. Those results suggested that the analytical procedure including MSPD method in combining with GC/MS could be applicable to the rapid determination often the selected agrochemicals in tobacco.

• Composites Research
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• v.29 no.4
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• pp.173-178
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• 2016

Graphene oxide (GO) was concurrently reduced and functionalized using long alkyl chain dodecyl amine (DA). The DA functionalized GO (DA-G) was assumed to disperse homogenously in linear low density polyethylene (LLDPE). Subsequently, DA-G was used to fabricate DA-G/LLDPE composites by melt mixing technique. Fourier transform infrared spectra analysis was performed to ascertain the simultaneous reduction and functionlization of GO. Field emission scanning electron microscopy analysis was performed to ensure the homogenous distribution and dispersion of DA-G in LLDPE matrix. The enhanced storage modulus value of the composites validates the homogenous dispersion of DA-G and its good interfacial interaction with LLDPE matrix. An increased in tensile strength value by ~ 64% also confirms the generation of good interface between the two constituents, through which efficient load transfer is possible. However, no significant improvement in glass transition temperature was observed. This simple technique of fabricating LLDPE composites following industrially viable melt mixing procedure could be realizable to developed mechanically strong graphene based LLDPE composites for future applications.

• Journal of the Korean Ceramic Society
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• v.55 no.4
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• pp.400-405
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• 2018

FCM nuclear fuel, a concept proposed as an accident tolerant fuel in light water reactors, consists of TRISO fuel particles embedded in a SiC matrix. The uniform dispersion of internal TRISO fuel particles in the FCM fuel is very important for improving the fuel efficiency. In this study, FCM sintered pellets with various volume ratios of TRISO-coated particles were prepared by hot press sintering. The distribution of TRISO-coated particles was quantitatively analyzed using X-ray ${\mu}CT$ and expressed as a dispersion uniformity index. TRISO-coated particles were most uniformly dispersed in the FCM pellets prepared using only overcoated TRISO particles without mixing of additional SiC matrix powder. FCM pellets with uniformly dispersed TRISO particle volume fraction of up to 50% were prepared using overcoated TRISO particles with varying thickness.

• Macromolecular Research
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• v.17 no.11
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• pp.842-849
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• 2009

Polycarbonate (PC)/sulfonated polystyrene (SPS) ionomer/organoclay nanocomposites were prepared by a solution intercalation process using the SPS ionomer as a compatibilizer. The effect of an organoclay on the melt crystallization behavior of the ionomer compatibilized PC were examined by differential scanning calorimetry (DSC). The melt crystallization behavior of PC was dependent on the extent of organoclay dispersion. The effect of the ionomer loading and cation size on intercalation/exfoliation efficiency of the organoclay in PC/SPS ionomer matrix was also studied using wide angle X-ray diffraction (WAXD) and transmission electron microscopy (TEM). Dispersion of the organically modified clay in the polymer matrix improved with increasing ionomer compatibilizer loadings and cation size. The SPS ionomer compatibilized PC/organoclay nanocomposite showed enhanced melt crystallization compared to the SPS ionomer/PC blend. Well dispersed organoclay nanocomposites showed better crystallization than the poorly dispersed clay nanocomposites. These nanocomposites also showed better thermal stability than the SPS ionomer/PC blend.

• Journal of the Korean Society for Nondestructive Testing
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• v.27 no.2
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• pp.148-156
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• 2007

The fiber dispersion in fiber-reinferced cementitious composites is a crucial factor with respect to achieving desired mechanical performance. However, evaluation of the fiber dispersion in the composite PVA-ECC (polyvinyl alcohol-engineered cementitious composite) is extremely challenging because of the low contrast of PVA fibers with the cement-based matrix. In the present work, a new evaluation method is developed and demonstrated. Using a fluorescence technique on the PVA-ECC, PVA fibers are observed as green dots in the cross-section of the composite. After capturing the fluorescence image with a charged couple device (CCD) camera through a microscope, the fiber dispersion is evaluated using an image processing technique and statistical tools. In this image processing technique, the fibers are more accurately detected by employing an enhanced algorithm developed based on a discriminant method and watershed segmentation. The influence of fiber orientation on the fiber dispersion evaluation was also investigated via shape analyses of fiber images.

• Journal of Pharmaceutical Investigation
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• v.41 no.3
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• pp.125-142
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• 2011

Solid dispersion, defined as the dispersion of one or more active ingredient in a carrier or matrix at solid state, is an efficient strategy for improving dissolution of poorly water-soluble drugs for enhancement of their bioavailability. Compared to other conventional formulations such as tablets or capsules, solid dispersion which can be prepared by various methods has many advantages. However, despite numerous studies which have been carried out, limitations for commercializing these products remain to be solved. For example, during the manufacturing process or storage, amorphous form of solid dispersion can be converted into crystalline form. That is, the dissolution rate of solid dispersion would continuously decrease during storage, resulting in a product of no value. To resolve these problems, studies have been conducted on the effects of excipients. In fact, modification of the solid dispersions to overcome these disadvantages has progressed from the first generation to the recent third generation products. In this review, an overview on solid dispersions in general will be given with emphasis on the various manufacturing processes which include the use of polymers and on the stabilization strategies which include methods to prevent crystallization.

• Bulletin of the Korean Chemical Society
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• v.31 no.5
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• pp.1237-1240
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• 2010

The mechanical properties of multiwalled carbon nanotubes (MWNTs)-reinforced epoxy matrix composites with different weight percentages of MWNTs have been investigated. Also, the morphologies and failure behaviors of the composites after mechanical tests are studied by SEM and TEM analyses. As a result, the addition of MWNTs into the epoxy matrix has a remarkable effect on the mechanical properties. And the fracture surfaces of MWNTs/epoxy composites after flexural strength tests show different failure mechanisms for the composites under different nanotube contents. Also, a chemical functionalization of MWNTs can be a useful tool to improve the dispersion of the nanotubes in an epoxy system, resulting in increasing the mechanical properties of the composite materials studied.