• Elastomers and Composites
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• v.45 no.4
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• pp.286-290
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• 2010

Liquid-crystalline (LC) monomer, which was functionalized with a coumarin group on their extremity, was synthesized by UV light irradiation in their LC phases. LC monomer was converted into the dimers by the cycloaddition reaction of the coumarin group, and the LC phases were maintained after photodimerization reaction. The dimers showed LC phases in the wider temperature range than those of the corresponding monomer. Structures of the compound were identified by FT IR and $^1H$ NMR spectroscopies. Their phase transition temperatures and thermal stability were also investigated by differential scanning calorimetry (DSC), gel permeating chromatography (GPC) and polarized optical microscopy (POM). From optical polarizing microscopy, the prepared polymer shows enantiotropic liquid crystallinity with smectic and nematic textures.

• Journal of Electrochemical Science and Technology
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• v.13 no.3
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• pp.377-389
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• 2022

The current global energy supply depends heavily on fossil fuels. This makes technology such as direct water splitting from harvesting solar energy in photoelectrochemical (PEC) systems potentially attractive due to its a promising route for environmentally benign hydrogen production. In this study, undoped and nickel-doped molybdenum oxide photoanodes (called photoanodes S₁ and S₂ respectively) were synthesized through electrodeposition by applying -1.377 V vs Ag/AgCl (3 M KCl) for 3 hours on an FTO-coated glass substrate immersed in molibdatecitrate aqueous solutions at pH 9. Scanning electron microscopy (SEM), atomic force microscopy (AFM), energy-dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS) were used for microstructural and compositional characterizations of the photoanodes. In addition, the optical and photoelectrochemical characterizations of these photoanodes were performed by UV-Visible spectroscopy, and linear scanning voltammetry (LSV) respectively. The results showed that all the photoanodes produced exhibit conductivity and catalytic properties that make them attractive for water splitting application in a photoelectrochemical cell. In this context, the photoanode S₂ exhibited better photocatalytic activity than the photoanode S₁. In addition, photoanode S₂ had the lowest optical band-gap energy value (2.58 eV), which would allow better utilization of the solar spectrum.

• Tribology and Lubricants
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• v.40 no.3
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• pp.84-90
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• 2024

This study investigates the effect of the surface microstructure on the tribological characteristics of glass substrates. Chemical etching using hydrofluoric acid and ammonium hydrogen fluoride was employed to create controlled asperity structures on glass surfaces. By varying the etching time from 10 to 50 min, different surface morphologies were obtained and characterized using optical microscopy, surface roughness measurements, and water contact angle analysis. Friction tests were performed using a stainless steel ball as the counter surface to evaluate the tribological behavior of the etched specimens. The results showed that the specimen etched for 20 min exhibited the lowest and most stable friction coefficient, which was attributed to the formation of a uniform and dense asperity structure that effectively reduced the stress concentration and wear at the contact interface. In contrast, specimens etched for shorter (10 min) or longer (30-50 min) durations displayed higher friction coefficients and accelerated wear owing to nonuniform asperity structures that led to local stress concentration. Optical microscopy of the wear tracks further confirmed the superior wear resistance of the 20-minute etched specimen. These findings highlight the importance of optimizing the etching process parameters to achieve the desired surface morphology for enhanced tribological performance, suggesting the potential of chemical etching as a surface modification technique for various materials in tribological applications.

• Korean Journal of Optics and Photonics
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• v.17 no.1
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• pp.47-53
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• 2006

The Integrated Ballistics Identification Systems (IBIS) is widely used for bullet and casing signature identification. The IBIS obtains a pair of ballistic signatures from two bullets (or casings) using optical microscopy, and estimates a correlation score which can represent the degree of signature match. However, this method largely depends on lighting and surface conditions because optical image contrast is primarily a function of test surface's slope, shadowing, multiple reflections, optical properties, and illumination direction. Moreover, it can be affected with surface height variation. To overcome these problems and improve the identification system, we used well known surface topographic techniques, such as confocal microscopy and white-light scanning interferometry. The measuring instruments were calibrated by a NIST step height standard and verified by a NIST sinusoidal profile roughness standard and a commercial roughness standard. We also suggest a new analysis method for the ballistic identification. In this method, the maximum cross-correlation function CCFmax is used to quantify the degree of signature match. If the compared signatures were exactly the same, CCFmax would be $100\%$.

• Korean Journal of Materials Research
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• v.10 no.9
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• pp.636-641
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• 2000

The effects of Fe and V content on the characteristics of $\beta$ to $\alpha$ phase transformation for Zr-0.8Sn alloys were studied by optical and transmission electron microscopy. With increasing V content, $\beta{\rightarrow}\alpha+\beta$ transformation temperature decreased, thus allowing the width of $\alpha$-lath to be fine air-cooled Zr-0.8Sn-xV alloys. The width of $\alpha$-lath, however, was slightly increased with Fe content. While the $\beta$ to $\alpha$ transformed microstructures of water-quenched Zr-0.8Sn, Zr-0.8Sn-0.1Fe, Zr-0.8Sn-0.2Fe, Zr-0.8Sn-0.4Fe, Zr-0.8Sn-0.1V and Zr-0.8Sn-0.2V were mainly slipped martensite, that of water-quenched Zr-0.8Sn-0.4V was predominantly twinned martensite. The transition of slipped martensite to twinned martensite in Zr-0.8Sn-Xv was thought to be due to the decrease of $M_S$ temperature.

• Analytical Science and Technology
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• v.5 no.1
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• pp.127-134
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• 1992

Effects of boron addition on microstructure and phases of plasma are melted tungsten have been investigated by optical microscopy, scanning electron microscopy, Auger electron spectroscopy, X-ray diffractometer, measurements of grain size and hardness. The change in the microstructure upon boron addition was studied by optical microscopy. It was observed that the grain refinement was induced upon content within the limit of solubility. When the boron content was above the solubility limit, two phases of primary tungsten and eutectic structure were observed and confirmed by AES and XRD analysis. It was also shown that recrystallization temperature was increased and recrystallized grain size was reduced as boron content increased.

• Clean Technology
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• v.19 no.3
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• pp.327-332
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• 2013

Space- and time-resolved in-situ optical and fluorescence microspectroscopy techniques have been applied to investigate the coke formation during aromatization of C5 paraffin and olefin over H-ZSM-5 crystal. In-situ UV/vis absorption measurement offers space- and time-resolved information for the coke formation. Different coking trends have been observed with respect to the location of a crystal as well as the reactant types. From in-situ confocal fluorescence microspectroscopy study, it is revealed that the concentration of certain species photo-excited at 488 nm becomes high at the central region, whereas the compounds emitting fluorescence by 561 nm laser move towards the boundary region of the crystal. The different fluorescence patterns obtained varying excitation lasers suggest the existence of distinct fluorescence emitting species having different degree of coke growth.

• Proceedings of the KWS Conference
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• 2010.05a
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• pp.70-70
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• 2010

In the present study, to estimate the mechanical properties of 800 MPa grade weld metal, welding was carried out using 800 and 600 MPa grade flux cored arc welding (FCAW) consumable and characteristics of the weld metals were investigated. The chemical composition of weld metals was investigated by an optical emission spectroscopy (OES) method. The microstructure of weld metals was analyzed by optical microscopy (OM) and secondary electron microscopy (SEM). The compositions and sizes of inclusions which are the dominant factors for the nuclei of acicular ferrite were analyzed by an transmission electron microscopy (TEM). In addition, mechanical properties of the weld metals were evaluated through tensile tests and charpy impact tests. Mostly the acicular ferrite phase which has high strength and toughness was observed. The 600 MPa grade weld metal was consisted of 75% acicular ferrite and 25% ferrite which was formed at high temperature (grain boundary ferrite, widmanstatten ferrite, polygonal ferrite). However, the 800 MPa grade weld metal was composed of about 73% acicular ferrite and 27% low temperature phase (bainite, martensite). Toughness was considerably decreased due to the increase of tensile strength (from 600 MPa to 800 MPa). The sizes of inclusions which were observed in both weld metal were $0.4{\sim}0.8\;{\mu}m$, it is effective size to form acicular ferrite.

• Korean Journal of Materials Research
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• v.27 no.7
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• pp.386-391
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• 2017

Using a customized diffusion bonder, we executed diffusion bonding for ring shaped white gold and red gold samples (inner, outer diameter, and thickness were 15.7, 18.7, and 3.0 mm, respectively) at a temperature of $780^{\circ}C$ and applied pressure of 2300 N in a vacuum of $5{\times}10^{-2}$ torr for 180 seconds. Optical microscopy, field emission scanning electron microscopy (FE-SEM), and energy-dispersive X-ray spectroscopy (EDS) were used to investigate the microstructure and compositional changes. The mechanical properties were confirmed by Vickers hardness and shear strength tests. Optical microscopy and FE-SEM confirmed the uniform bonding interface, which was without defects such as micro pores. EDS mapping analysis confirmed that each gold alloy was 14K with the intended composition; Ni and Cu was included as coloring metals in the white and red gold alloys, respectively. The effective diffusion coefficient was estimated based on EDS line scanning. Individual values of Ni and Cu were $5.0{\times}10^{-8}cm^2/s$ and $8.9{\times}10^{-8}cm^2/s$, respectively. These values were as large as those of the melting points due to the accelerated diffusion in this customized diffusion bonder. Vickers hardness results showed that the hardness values of white gold and red gold were 127.83 and 103.04, respectively, due to solid solution strengthening. In addition, the value at the interface indicated no formation of intermetallic compound around the bonding interface. From the shear strength test, the sample was found not to be destroyed at up to 100,000 gf due to the high bonding strength. Therefore, these results confirm the successful diffusion bonding of 14K white-red golds with a diffusion bonder at a low temperature of $780^{\circ}C$ and a short processing time of 180 seconds.

• Journal of the Mineralogical Society of Korea
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• v.18 no.3 s.45
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• pp.155-164
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• 2005

Volcanic rocks from the Mt. Mudeung area which are composed of Hwasun andesite, Mudeungsan dacite and Togok rhyolite contain plagioclase phenocrysts in common. Majority of the repeated twins observed in optical microscopy are albite twin and some are pericline twin. EPMA studies of plagioclases from Hwansun andesite, Mudeungsan dacite and Togok rhyolte indicate calcic andesine, andesine-oligoclase, nearly pure albite, respectively Albite twin and pericline twin can be easily distinguished through TEM diffraction patterns, which is quite difficult by optical microscopy. Plagioclases in volcanic rocks from the Mt. Mudeung area do not show e-reflection in (100) electron diffraction patterns, probably because of their high cooling rate, which inhibited phase separations during cooling.