• Applied Chemistry for Engineering
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• v.24 no.5
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• pp.476-482
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• 2013

In this work, the effects of electrochemical oxidation of carbon fiber surfaces on mechanical interfacial properties of carbon fibers-reinforced polarized-polypropylene matrix composites were studied with various current densities during the treatments. Surface properties of the fibers before and after treatments were observed by SEM, AFM, XPS, and contact angle measurements. Mechanical interfacial properties of the composites were measured in terms of critical stress intensity factor ($K_{IC}$). From the results it was found that $O_{1s}$ peaks of the fiber surfaces were strengthened after electrochemical oxidation which led to the enhancement of surface free energy of the fiber, resulting in good mechanical performance of the composites. It can be concluded that electrochemical oxidation of the carbon fiber surfaces can control the interfacial adhesion between the carbon fibers and polarized-polypropylene in this composites system.

• Journal of the Korean Ceramic Society
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• v.45 no.7
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• pp.411-417
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• 2008

Aerosol Deposition Method (ADM) is a novel technique to grow ceramic thick films with high density and nano-crystal structure at room temperature. $^{1,2)}$ For these unique advantages of ADM, it would be applied to the fabrication process of 3-D integration ceramic modules effectively. However, it is critical to control the properties of starting powders, because a film formation through ADM is achieved by impaction and consolidation of starting powders on the substrates. We fabricated alumina thick films by ADM for the application to integral substrates for RF modules. When the as-received alumina powders were used as a starting material without any treatments, it was observed that the dielectric properties of as-deposited alumina films, such as relative permittivity and loss tangent, showed high dependency on the frequency. In this study, some techniques of powder pre-treatments to improve the dielectric properties of alumina thick films will be shown and the effects of starting powders on the properties of AD films will be discussed.

• Bulletin of the Korean Mathematical Society
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• v.56 no.4
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• pp.1007-1025
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• 2019

In the present work, the complete convergence and complete moment convergence properties for arrays of rowwise extended negatively dependent (END) random variables are investigated. Some sharp theorems on these strong convergence for weighted sums of END cases are established. These main results not only generalize the known corresponding ones of Cai [2], Wang et al. [17] and Shen [14], but also improve them, respectively.

• Korean Journal of Mathematics
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• v.32 no.1
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• pp.121-135
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• 2024

In this paper, we have presented rough ideal statistical convergence of sequence on neutrosophic normed spaces as a significant convergence criterion. As neutrosophication can handle partially dependent components, partially independent components and even independent components involved in real-world problems. By examining some properties related to rough ideal convergence in these spaces we have established some equivalent conditions on the set of ideal statistical limit points for rough ideal statistically convergent sequences.

• Journal of Powder Materials
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• v.22 no.3
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• pp.197-202
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• 2015

In this study, porous stainless steel (STS316L) sintered body was fabricated by powder metallurgy method and its properties such as porosity, compressive yield strength, hardness, and permeability were evaluated. 67.5Fe-17Cr- 13Ni-2.5Mo (wt%) powder was produced by a water atomization. The atomized powder was classified into size with under $45{\mu}m$ and over $180{\mu}m$, and then they were compacted with various pressures and sintered at $1210^{\circ}C$ for 1 h in a vacuum atmosphere. The porosities of sintered bodies could be obtained in range of 20~53% by controlling the compaction pressure. Compressive yield strength and hardness were achieved up to 268 MPa and 94 Shore D, respectively. Air permeability was obtained up to $79l/min{\cdot}cm^2$. As a result, mechanical properties and air permeability of the optimized porous body having a porosity of 25~40% were very superior to that of Al alloy.

• Proceedings of the KIEE Conference
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• 2004.11c
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• pp.382-384
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• 2004

In this parer, we propose a clustering that perform algorithm using new convergence properties. For detection and optimization of cluster, we use to similarity measure with cumulative probability and to inference the its parameters with MLE. A merits of using the cumulative probability in our method is very effectiveness that robust to noise or unnecessary data for inference the parameters. And we adopt similarity threshold to converge the number of cluster that is enable to past convergence and delete the other influence for this learning algorithm. In the simulation, we show effectiveness of our algorithm for convergence and optimization of cluster in riven data set.

• Bulletin of the Korean Chemical Society
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• v.31 no.6
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• pp.1485-1488
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• 2010

Novel photoluminescent graphene, graphene/europium/picolinate, was made from the reaction of the graphene carboxylate, europium(III) and $\alpha$-pyridoin anion in methanol solution. There was evidence on IR spectroscopic data that europium metal was coordinated by graphene carboxylate. The graphene/europium/picolinate materials emitted the red luminescence with main peaks at 609 and 695 nm, when solid sample was excited by an UV light at the wavelength of 254 nm. The surface morphology and physical properties of the graphene/europium/picolinate product have been investigated by IR, PL, SEM, TEM and TGA measurements.

• Composites Research
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• v.33 no.6
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• pp.321-328
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• 2020

Recently, development of nanocomposite materials for applying in various fields has been actively underway. Of the two-dimensional nanomaterials, graphene nanoplatelets (GnPs) are highly utilized because of their excellent properties, but a problem of strong aggregations is occurred when GnPs are fabricated with polymer nanocomposites, so there is a growing demand for research on the methods of dispersion. In this review paper, the research on GnP nanocomposites with improved properties through various dispersion methods of GnPs. The welldispersed GnP nanocomposites will be applied in more diverse fields in the future.

• Composites Research
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• v.30 no.3
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• pp.169-174
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• 2017

Demand of glass fiber reinforced composites (GFRC) increased with developing aircraft and defense industries using resin transfer molding (RTM) process to produce complex product. In this research, wetting, interfacial, and mechanical properties were evaluated with different Cross-linking Density by Molecular Weight of Hardener. Epoxy resin as matrices was used bisphenol-A type and amine-type hardeners with different molecular weight. Specimens were manufactured via RTM and wetting property of resin and glass fiber (GF) mat was evaluated to viscosity of epoxy and injection time of epoxy matrix. Mechanical property of GFRC was determined via flexural strength whereas interfacial properties were determined by interlaminar shear strength (ILSS) and interfacial shear strength (IFSS). The difference in mechanical property depends upon the fiber weight fraction (wt %) of GFRC by RTM as well as the different Molecular Weight of Hardener.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.31 no.6
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• pp.392-397
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• 2018

In this paper, the ZnS nanoparticles were synthesized according to the process conditions of hydrothermal synthesis. When the molar ratio of Zn to S was 1:1.2, it was confirmed that it had a cubic single phase and a high crystal phase. After the molar ratio is fixed, hydrothermal synthesis was conducted at $180^{\circ}C$ for 24, 36, 72 and 96 h in order to confirm the structural change with the change of hydrothermal synthesis times. As the hydrothermal synthesis times increased, the particle size increased. The hydrothermal synthesized particle size for 72 h was considered to be suitable for sintering. The ZnS ceramic had a density of 99.7% and an excellent transmittance of ~70% in the long-wavelength region.