• Polymer(Korea)
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• v.31 no.6
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• pp.518-525
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• 2007

The thermomechanical properties and morphologies of nanocomposite fibers of poly(ethylene terephthalate)(PET) incorporating thermally stable organoclays are compared. Dodecyltriphenyl-phosphonium-mica($C_{12}PPh-Mica$) and 1-hexadecane benzimidazole-mica ($C_{16}BIMD-Mica$) were used as reinforcing fillers in the fabrication of PET hybrid fibers. Dispersions of organoclays with PET were studied by using the in-situ polymerization method at various organoclay contents to produce nano-scale composites. The thermo-mechanical properties and morphologies of the PET hybrid fibers were determined using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), wide angle X-ray diffraction (XRD), electron microscopy (SEM and TEM), and a universal tensile machine (UTM). Transmission electron microscopy (TEM) micrographs show that some of the clay layers are dispersed homogeneously within the polymer matrix on the nano-scale, although some clay particles are agglomerated. We also found that the addition of only a small amount of organoclay is enough to improve the thermal stabilities and mechanical properties of the PET nanocomposite fibers. Even polymers with low organoclay content (<5 wt%) were found to exhibit much higher thermo-mechanical values than pure PET fibers.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.41 no.6
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• pp.25-31
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• 2004

In this paper, we introduce kinetic Monte Carlo (kMC) methods for simulating diffusion process in nano-scale device fabrication. At first, we review kMC theory and backgrounds and give a simple point defect diffusion process modeling in thermal annealing after ion (electron) implantation into Si crystalline substrate to help understand kinetic Monte Carlo methods. kMC is a kind of Monte Carlo but can simulate time evolution of diffusion process through Poisson probabilistic process. In kMC diffusion process, instead of. solving differential reaction-diffusion equations via conventional finite difference or element methods, it is based on a series of chemical reaction (between atoms and/or defects) or diffusion events according to event rates of all possible events. Every event has its own event rate and time evolution of semiconductor diffusion process is directly simulated. Those event rates can be derived either directly from molecular dynamics (MD) or first-principles (ab-initio) calculations, or from experimental data.

• Korean Journal of Materials Research
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• v.30 no.10
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• pp.542-549
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• 2020

Effects of Sc addition on microstructure, electrical conductivity, thermal conductivity and mechanical properties of the as-cast and as-extruded Al-2Zn-1Cu-0.3Mg-xSc (x = 0, 0.25, 0.5 wt%) alloys are investigated. The average grain size of the as-cast Al-2Zn-1Cu-0.3Mg alloy is 2,334 ㎛; however, this value drops to 914 and 529 ㎛ with addition of Sc element at 0.25 wt% and 0.5 wt%, respectively. This grain refinement is due to primary Al₃Sc phase forming during solidification. The as-extruded Al-2Zn-1Cu-0.3Mg alloy has a recrystallization structure consisting of almost equiaxed grains. However, the as-extruded Sc-containing alloys consist of grains that are extremely elongated in the extrusion direction. In addition, it is found that the proportion of low-angle grain boundaries below 15 degree is dominant. This is because the addition of Sc results in the formation of coherent and nano-scale Al₃Sc phases during hot extrusion, inhibiting the process of recrystallization and improving the strength by pinning of dislocations and the formation of subgrain boundaries. The maximum values of the yield and tensile strength are 126 MPa and 215 MPa for the as-extruded Al-2Zn-1Cu-0.3Mg-0.25Sc alloy, respectively. The increase in strength is probably due to the existence of nano-scale Al₃Sc precipitates and dense Al₂Cu phases. Thermal conductivity of the as-cast Al-2Zn-1Cu-0.3Mg-xSc alloy is reduced to 204, 187 and 183 W/MK by additions of elemental Sc of 0, 0.25 and 0.5 wt%, respectively. On the other hand, the thermal conductivity of the as-extruded Al-2Zn-1Cu-0.3Mg-xSc alloy is about 200 W/Mk regardless of the content of Sc. This is because of the formation of coherent Al₃Sc phase, which decreases Sc content and causes extremely high electrical resistivity.

• Journal of Periodontal and Implant Science
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• v.38 no.sup2
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• pp.373-384
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• 2008

Purpose: The aim of this study is to compare the healing response of various Hydroxyapatite(HA) coated dental implants by Ion-Beam Assisted Deposition(IBAD) placed in the surgically created circumferential gap in dogs. Materials and methods: In four mongrel dogs, all mandibular premolars and the first molar were extracted. After an 8 weeks healing period, six submerged type implants were placed and the circumferential cylindrical 2mm coronal defects around the implants were made surgically with customized step drills. Groups were divided into six groups : anodized surface, anodized surface with 150nm HA and heat treatment, anodized surface with 300nm HA and heat treatment, anodized surface with 150nm HA and no heat treatment, and anodized surface with 150nm HA, heat treatment and bone graft, anodized surface with bone graft. The dogs were sacrificed following 12 weeks healing period. Specimens were analyzed histologically and histomorphometrically. Results: During the healing period, healing was uneventful and implants were well maintained. Anodized surface with HA coating and $430^{\circ}C$ heat treatment showed an improved regenerative characteristics. Most of the gaps were filled with newly regenerated bone. The implant surface was covered with bone layer as base for intensive bone formation and remodeling. In case that graft the alloplastic material to the gaps, most of the coronal gaps were filled with newly formed bone and remaining graft particles. The bone-implant contact and bone density parameters showed similar results with the histological findings. The bone graft group presented the best bone-implant contact value which had statistical significance. Conclusion: Within the scope of this study, nano-scale HA coated dental implants appeared to have significant effect on the development of new bone formation. And additional bone graft is an effective method in overcoming the gaps around the implants.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.362-362
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• 2010

Today, vast attention has been paid to periodic arrays of nanostructures due to their potential for applications such as memory with huge storage density. Such application requires large-scale fabrication of well ordered nano-sized structures. One of the most widely used methods for the ordered nanostructures is lithography. This top-down process, however, has the limit to reduce size. Here the promising alternative is the self-organization of ordered nano-sized structures such as large scale 2d carbon-induced reconstructions on W(110). In the present study, we report on the first well-resolved atomic resolution STM studies of the well-known R($15{\times}3$) and R($15{\times}12$) carbon induced reconstruction of the W(110). From the atomic image of R($15{\times}3$) for different values of tunneling gap resistance, we can tell there are no missing atoms in unit cells of R($15{\times}3$) and some atomic displacements are substantial from the clean W(110), even though not all the imaged position of atoms correspond to tungsten, but may include those of carbon. We are considering two cases; First case is related to lattice deformation, or top layer of W(110) is deformed in the process of relief of strain caused by random inserting of carbon atoms possibly in the interstitial position. In the second case, R($15{\times}3$) unit cell results from a coincidence lattice between clean W(110) substrate and tungsten carbide overlayer which has rectangular atomic arrangement and giving R($15{\times}3$) coincidence lattice. beta-W2C showing rectangular unit cell should be a candidate. Further, we report on new reconstructions. Unlike the well-known R($15{\times}12$) consisting of two parts, two inner structures between two "Backbone" structures. The new reconstruction, which we found for the first time, contains more parts between the "Backbone"s. Sometimes we can observe the reconstruction consists of only inner parts without "Backbone" parts. Thus, the observed reconstruction can be built by constructing of two types of "Lego"-like block. Moreover, the rectangle shape of "Backbone" transform to parallelogram-like shape over time, the so-called wavy-R($15{\times}12$). Adsorption of hydrogen can be the reason for this transformation.

• Food Engineering Progress
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• v.13 no.4
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• pp.269-274
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• 2009

The main objective of this study was to establish optimum condition of wet grinding process for manufacturing microparticulated seaweed calcium. Process parameters such as concentration of forming agent, rotor speed, bead size, feed rate, and grinding time were adapted during wet-grinding of seaweed calcium. The particle size range of the raw seaweed calcium was 10-20 $\mu$m. The calcium particles were reduced to under 1 $\mu$m as nano scale after grinding. Gum arabic was suitable for forming agent and 5%(w/v) concentration was the most effective in grinding efficiency. A wet-grinding process operated at 4,000 rpm rotor speed, 0,4 mm bead size, and 0.4 L/hr feeding rate, respectively, produced less than 600 mm(>>90%)-sized particles. In batch systems, 8 cycles of grinding showed higher efficiency, but 20 min of grinding time in continuous processing was more efficient to reduce particle size than the batch processing. Based on the result, the optimum conditions of the wet grinding process were established: operation time of 20 minutes, rotor speed of 4,000 rpm, bead size of 0.4 mm, feed rate of 40 mL/min and 30% mixing ration with water. The size of the resulting ultra fine calcium particles ranged between 40 and 660 mm.

• Korean Journal of Mineralogy and Petrology
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• v.33 no.4
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• pp.463-475
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• 2020

Presence of microplastics in soil and groundwater has recently been reported and environmental concerns are raised as to the plastic pollution. In the subsurface environment, clay minerals and metal oxide minerals are commonly found as finely dispersed states. Because the minerals have high sorption capacities for diverse pollutants, interactions with mineral surface play an important role in the transport of microplastics in groundwater. Accordingly, environmental mineralogy investigating the interactions between microplastics and mineral surfaces is the essential research area to understand the fate and transport of microplastics in the subsurface environment. The microplastic-mineral surface research requires molecular- to nano-scale analyses to be able to probe the relatively weak interactions between them. The current report introduces a nano-scale analysis tool called quartz crystal microbalance (QCM) that can measure the sorbed/desorbed mass of nanoplastics on mineral surfaces at the level of a few nanograms (~10-9 g). This report briefly reviews the main principles in the QCM measurement and discusses applications of QCM to the environmental mineralogy research.

• Toxicological Research
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• v.28 no.2
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• pp.73-79
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• 2012

While the ability to develop nanomaterials and incorporate them into products is advancing rapidly worldwide, understanding of the potential health safety effects of nanomaterials has proceeded at a much slower pace. Since 2008, Korea Food and Drug Administration (KFDA) started an investigation to prepare "Strategic Action Plan" to evaluate safety and nano risk management associated with foods, drugs, medical devices and cosmetics using nano-scale materials. Although there are some studies related to potential risk of nanomaterials, physical-chemical characterization of nanomaterials is not clear yet and these do not offer enough information due to their limitations. Their uncertainties make it impossible to determine whether nanomaterials are actually hazardous to human. According to the above mention, we have some problems to conduct the human exposure risk assessment currently. On the other hand, uncertainty about safety may lead to polarized public debate and to businesses unwillingness for further nanotechnology investigation. Therefore, the criteria and methods to assess possible adverse effects of nanomaterials have been vigorously taken into consideration by many international organizations: the World Health Organization, the Organization for Economic and Commercial Development and the European Commission. The object of this study was to develop risk assessment principles for safety management of future nanoproducts and also to identify areas of research to strengthen risk assessment for nanomaterials. The research roadmaps which were proposed in this study will be helpful to fill up the current gaps in knowledge relevant nano risk assessment.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.4A
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• pp.761-766
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• 2006

Polymer composite are increasingly considered as structural components for use in civil engineering, on account of their enhanced strength-to-weight ratios. Unsaturated polyester (UP) resin have been widely used for the matrix of composites such as FRP and polymer composite, due to its excellent adhesive. Polymer nanocomposites are new class of composites derived from the nano scale inorganic particles with dimensions typically in the range of 1 to 1000 nm that are dispersed in the polymer matrix homogeneously. Owing to the high aspect ratio of the fillers, mechanical, thermal, flame, retardant and barrier properties are enhanced without significant loss of clarity, toughness or impact strength. To prepare the MMT (Montmorillonite)-UP exfoliated nanocomposites, UP was mixed with MMT at $60^{\circ}C$ for 3 hours by using pan mixer. XRD (X-ray diffraction) pattern of the composites and TEM (Transmission Electron Micrographs) showed that the interlayer spacing of the modified MMT were exfoliated in polymer matrix. The mechanical properties also supported these findings, since in general, tensile strength, modulus with modified MMT were higher than those of the composites with unmodified MMT. The thermal stability of MMT-UP nanocomposite is better than that of pure UP, and its glass transition temperature is higher than that of pure UP. The polymer concrete made with MMT-UP nanocomposite has better mechanical properties than of pure UP. Therefore, it is suggested that strength and elastic modulus of polymer concrete was found to be positively tensile strength and tensile modulus of the MMT-UP nanocomposites.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.421-421
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• 2009

Since carbon nanotubes (CNTs) are discovered, tremendous attentions have been paid to these materials due to their unique mechanical, electrical and chemical properties. Thereupon, many methods to produce a large scale of CNTs have been contrived by many scientists and engineers. Thus the examination of growth mechanisms of CNTs, which is essential to produce CNTs in large scale, has been an attractive issue. Though many scientists have been strived to investigate and understand the growth mechanisms of CNTs, many of them still remain controversial or unclear. Here we introduce representative growth mechanisms of CNTs, based on broadly employed fabrication methods of CNTs. We applied Thermo-electrical Pulse Induced Evaporation (TPIE) method based on field and thermal evaporation to synthesis of CNTs. However TPIE method was originally devised to fabricate graphene sheets and $Ge_2Sb_2Te_5$ nanostructures. While performing TPIE experiments to synthesize graphene, we eventually found experimental results widely supporting the growth model of CNTs proposed already. We observed the procedure of growth of CNTs obtained by TPIE method through Transmission Electron Microscopy (TEM). We believe this study provides an experimental basis on understanding and investigating carbon-based nanomaterials.