• Korean Journal of Materials Research
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• v.15 no.4
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• pp.252-256
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• 2005

We removed the bluish of the natural ruby successfully by vacuum annealing, and measured the color evolution with annealing time and temperature. We varied the anneal temperature and time $800\~1500^{\circ}C$ and $3\~26$ hrs, respectively. The color evolution of rubies with annealing condition was recorded by a digital camera and a color coordination visible spectrometer. We determined the optimum bluish eliminating annealing condition was $1500^{\circ}C-3hr$, which conserving the natural inclusions. We suggest the bluish shrink with diffusion coefficient of $D=(5\times10^{-3}){\exp}(-200.000/RT)[cm^2/s]$. We propose the color of ruby may be determined as the identical red color if the color difference between two samples are less than 1.0, and the color difference nay be an auxiliary standard to evaluate the color of rubies.

• Journal of Environmental Health Sciences
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• v.30 no.5 s.81
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• pp.487-492
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• 2004

Building materials are composed of very complex chemical compounds, and these indoor building materials discharge very much Volatile Organic Compounds(VOCs). We performed the environmental chamber test to investigate the Total VOCs(TVOCs) emission characteristics and emission factors about chemical and natural coating materials. As the result, we concluded that TVOCs emission are high at initial time and decreased in course of time. Natural paint was low emission level for TVOCs than chemical paint by small chamber test. The TVOCs emission factor-time profile showed a good fit with the results from the measured and predicted value.

• Ceramist
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• v.22 no.3
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• pp.301-315
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• 2019

We prepared hybrids between layered double hydroxide (LDH) and natural plant extract such as Peaonia suffruticosa Andrews (PS) and Peaonia Japonica (PJ) which was confirmed anti-bacterial activity through paper disc diffusion assay. According to X-ray diffractometer, scanning electron microscope, zeta-potential measurement and quantification of extract loading amount in hybrids, we confirmed that similar amount of PS and PJ loaded on inter-particle pore of LDH with partial adsorption on surface of LDH through reconstruction process. We also evaluated the bacterial colony forming inhibition of PS extract, PJ extract, PS-LDH and PJ-LDH hybrids against Escherichia coli as gram negative bacterium and Bacillus subtilis as gram positive bacterium, suggesting that both hybrids have enhanced anti-bacterial activity compared with extract itself.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2004.10a
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• pp.92-95
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• 2004

Interfacial shear strength (IFSS) of environmentally- friend natural fiber reinforced polymer composites playa very important role in controlling the overall mechanical properties. In this work the IFSS of Ramie and Kenaf fibers/epoxy systems were evaluated using the combination of micromechanical technique, microdroplet test to find out an optimal condition in accordance with final purpose by comparing to each other. Clamping effect on fiber elongation was determined as well. In addition, the mechanical properties of the natural fibers were investigated using single fiber tensile test and analyzed statistically by both uni- and bimodal Weibull distributions. Microfailure modes of different natural fiber structures were observed using optical microscope.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.18 no.12
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• pp.28-37
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• 2019

Due to their flexible tailoring qualities, composites have become fascinating materials for structural engineers. While the research area of fiber-reinforced composite materials was previously limited to synthetic materials, natural fibers have recently become the primary research focus as the best alternative to artificial fibers. The natural fibers are eco-friendly and relatively cheaper than synthetic fibers. The main concern of current research into natural fiber-reinforced composites is the prediction and enhancement of the effective material properties. In the present work, finite element analysis is used with a numerical homogenization approach to determine the effective material properties of jute fiber-reinforced epoxy composites with various volume fractions of fiber. The finite element analysis results for the jute fiber-reinforced epoxy composite are then compared with several well-known analytical models.

• Journal of the Korean Society of Safety
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• v.12 no.2
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• pp.37-44
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• 1997

Composite materials have various complicated characteristics depending on the ply materials, ply orientations, ply stacking sequences and boundary conditions. Therefore, it is difficult to analyze composite materials. For efficient use of composite materials in engineering applications, the dynamic behavior such as natural frequencies and nodal patterns should be identified. This study presents FEM results for the free vibration of symmetrically and antisymmetrically laminated composite and hybrid composite rectangular plates. The natural frequencies of laminated composite rectangular plates having the various boundary conditions (completely clamped, 2-edge clamped, cantilevered) are experimentally obtained. In order to demonstrate the validity of the experiment, FEM analysis using ANSYS was performed and natural frequencies experimentally obtained is compared with that calculated by FEM analysis. The results obtained from both experiment and FEM analysis show a good agreement.

• Journal of Powder Materials
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• v.30 no.6
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• pp.528-535
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• 2023

Since their initial development in 2012, triboelectric nanogenerators (TENGs) have gained popularity worldwide as a desired option for harnessing energy. The urgent demand for TENGs is attributed to their novel structural design, low cost, and use of large-scale materials. The output performance of a TENG depends on the surface charge density of the friction layers. Several recycled and biowaste materials have been explored as friction layers to enhance the output performance of TENGs. Natural and oceanic biomaterials have also been investigated as alternatives for improving the performance of TENG devices. Moreover, structural innovations have been made in TENGs to develop highly efficient devices. This review summarizes the recent developments in recycling and biowaste materials for TENG devices. The potential of natural and oceanic biowaste materials is also discussed. Finally, future outlooks for the structural developments in TENG devices are presented.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2005.11a
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• pp.165-168
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• 2005

In this paper, the relation between the applied loading sizes and the natural frequency of vibration of some structural elements is presented. Many junior engineers get confused on such relations. It is hoped that this paper gives some guideline to such junior engineers.

• Proceedings of the Korean Society For Composite Materials Conference
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• 1999.11a
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• pp.134-138
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• 1999

For the stable operation of high speed aerostatic spindle, the low rotational inertia and high damping ratio of spindle shafts as well as high fundamental natural frequency are indispensable. Conventional steel spindles are not appropriate for very high speed operation because of their high rotational inertia and low damping ratio. In this study, the composite spindles with aerostatic bearing were designed and manufactured with carbon fiber/epoxy composite. The fundamental natural frequency of the composite spindle was evaluated through the modal testing.

• Advances in materials Research
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• v.9 no.2
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• pp.155-170
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• 2020

In this paper, using the recently introduced analytical approach for the analysis of mass and heat transfer during film growth in reactors for epitaxy from the gas phase, these processes are analyzed taking into account natural convection and the possibility of changing the rate of chemical interaction between reagents. As a result of the analysis, the conditions under which the homogeneity of the grown epitaxial layers increases with a change in the values of the parameters of the growth process are formulated.