• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2014.11a
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• pp.185-185
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• 2014

In this study, we investigated surface characteristics of hydroxyapatite coated surface on nano/micro pore structured Ti-35Ta-xNb alloys. This paper was focus on morphology and corrosion resistance of Anodic oxidation. To prepare the samples, Ti-35Ta-xNb (x= 0, 10 wt. %) alloys were manufactured by arc melting and heat-treated for 12 h at $1050^{\circ}C$ in Ar atmosphere at $0^{\circ}C$ water quenching. Micro-pore structured surface was performed using anodization with a DC power supply at 280 V for 3 min, nanotube formed on Ti-35Ta-xNb alloys was performed using DC power supply at 30 V in 60 min at room temperature. Surface morphology and structure were examined by field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy and X-ray diffraction.

• Journal of the Korean institute of surface engineering
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• v.53 no.2
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• pp.53-58
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• 2020

In this study, we developed plasma electrolytic oxidation (PEO) process for aluminum 7075 alloy to improve the corrosion and mechanical properties. The electrolyte consists of potassium hydroxide and sodium silicate. Additionally, sodium stannate was added into the electrolyte to investigate its effect on PEO film formation. Titanium was used as the counter electrode. Plasma generation voltage reduced from 300V to 150 V by adding 4 g/L of sodium stannate. The thin oxide films were observed by SEM(Scanning Electron Microscopy)/EDS (Energy Dispersive Spectroscopy) for quantitative and qualitative analyses. XRD (X-ray diffraction) and XRF (X-ray Fluorescences) analyses were also carried out to identify oxide layer on aluminum 7075 surface. Vicker's hardness test was performed on the PEO-treated aluminum 7075 surface.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.127.1-127.1
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• 2011

Over the past several years the millimeter wave VLBI(Veryl Long Baseline Interferometry) observations have been intensively carried out. However In millimeter and sub-millimeter waves observations for VLBI, it is crucial to calibrate correctly the phase variations of the electromagnetic waves propagation through the troposphere. To do this, KVN(Korean VLBI Network) has a unique multi-frequency bands receiver system which is able to perform the simultaneous observations in up to four bands such as 22, 43, 86, and 129GHz. The phase of a source at 22GHz can be used to calibrate the phase of the same source at higher frequency bands. The phase calibration using multi-frequency bands receiver system is possible because the phase fluctuations from a given amount of waver vapor increase linearly with frequency. That is to say that troposphere is non-dispersive property in terms of tropospheric delay fluctuations. In this talk, We present results of test observation for multi-frequency bands receiver system.

• Transactions on Electrical and Electronic Materials
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• v.16 no.4
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• pp.198-200
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• 2015

The microwave plasma enhanced chemical vapor deposition (PECVD) system was used to grow a carbon nanowall (CNW) on a silicon (Si) substrate with hydrogen (H₂) and methane (CH₄) gases. To find the growth mechanism of CNW, we increased the growth time of CNW from 5 to 30 min. The vertical and surficial conditions of the grown CNWs according to growth time were characterized by field emission scanning electron microscopy (FE-SEM). Energy dispersive spectroscopy (EDS) measurements showed that the CNWs consisted solely of carbon.

• Journal of the Korean Institute of Telematics and Electronics
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• v.23 no.2
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• pp.149-169
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• 1986

Fundamentals of electrodynamics of moving sources with constant velocity in an anisotripic plasma when the do magnetic field and the relative motion are oriented in arbitrary directions are presented. The well-known Minkowski's relations are generalized to accomodate anisotropic and dispersive media, and relativistic transformation formulae of constitutive parameters are derived and expanded into polynomials of the speed ratio \ulcornerto increase the utility of the formulae. The helmholtz wave equation of electromagnetic fields is generalized to the media charactrized by tensor parameters, and is solved in operator form. Also the solution of wave equation is expressed as a porcuct of the inverse of the wave operator matrix and the source function vector, and the inverse of the wave operator matrix is presented in an explicit form. The equations and formulae derived in this paper are all general, and can be reduced to known and proven results upon imposing the restriction called for by specific situations.

• Journal of the Korean Ceramic Society
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• v.33 no.2
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• pp.135-142
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• 1996

Fly Ashes which are produced from coal-fired powder plants and classified as general waste can be used as raw materials for bricks and tiles because of their compositional similarity with clays. There was a limit of substituting fly ash for clay because plasticity decreased with increasing fly ash additions. Accordingly this study tried to suggest a feastibility of enhancing the substitution ratio by controlling the interfacial properties of fly ash. The slip with 1:1 volume ratio showed that best dispersive characteristics under the condition of pH 2 Filter pressed cakes made of pH 2 slips also showed better plastickity than those of untreated ones. of pH 2 Filter pressed cakes made of pH 2 also shwoed better plasticity than those of untreated ones.

• Bulletin of the Korean Chemical Society
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• v.33 no.1
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• pp.153-158
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• 2012

The hydrogenation of $AlB_2$-type BaGaGe exhibits a metal to insulator (MI) transition, inducing a puckering distortion of the original hexagonal [GaGe] layers. We investigate the electronic structure changes associated with the hydrogen-induced MI transition, using extended H$\ddot{u}$ckel tight-binding band calculations. The results indicate that hydrogen incorporation in the precursor BaGaGe is characterized by an antibonding interaction of $\pi$ on GaGe with hydrogen 1s and the second-order mixing of the singly occupied antibonding $\pi^*$ orbital into it, through Ga-H bond formation. As a result, the fully occupied bonding $\pi$ band in BaGaGe changes to a weakly dispersive band with Ge pz (lone pair) character in the hydride, which becomes located just below the Fermi level. The Ga-Ge bonds within a layered polyanion are slightly weakened by hydrogen incorporation. A rationale for this is given.

• Proceedings of the Materials Research Society of Korea Conference
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• 2012.05a
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• pp.91.2-91.2
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• 2012

The TiB2-reinforced iron matrix nanocomposite (Fe-TiB2) was in-situ fabricated from titanium hydride (TiH2) and iron boride (FeB) powders by a simple and cost-effective process that combines the mechanical activation (MA) and a subsequent heat treatment (HT). Effect of milling factors and synthesized temperatures on the formation of the nanocomposite were presented and discussed. A differential thermal analyser (DSC-TG) was employed for examination of thermal behavior of MAed powders. Phases of the nanocomposite were confirmed by X-ray diffraction analysis (XRD). The morphologies and microstructure of nanocomposite were investigated by field emission-scanning electron microscopy (FE-SEM) and energy-dispersive X-ray spectroscopy (EDS). Phase composition and distribution were analyzed by electron probe X-ray microanalysis (EPMA). Results showed that TiB2 particles formed in nanoscale were uniformly distributed in alloyed Fe matrix.

• Corrosion Science and Technology
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• v.7 no.1
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• pp.61-67
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• 2008

In this paper, electrochemical and microstructural characteristics of nickel-plated Alloy 600 were investigated in order to identify the performance of electroless Ni-plating on Alloy 600 in high-temperature aqueous condition with the comparison of electrolytic nickel-plating. For high temperature corrosion test of nickel-plated Alloy 600, specimens were exposed for 770 hours to typical PWR primary water condition. During the test, open circuit potentials (OCP's) of all specimens were measured using a reference electrode. Also, resistance to flow accelerated corrosion (FAC) test was examined in order to check the durability of plated layers in high-velocity flow environment at high temperature. After exposures to high flow rate aqueous condition, the integrity of surfaces was confirmed by using both scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). For the field application, a remote process for electroless nickel-plating was demonstrated using a plate specimen with narrow gap on a laboratory scale. Finally, a practical seal design was suggested for more convenient application.

• Corrosion Science and Technology
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• v.9 no.5
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• pp.209-215
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• 2010

To elucidate the effect of aging time on resistance to localized corrosion of hyper duplex stainless steel, a double-loop electrochemical potentiokinetic reactivation test a potentiodynamic anodic polarization test, a scanning electron microscope-energy dispersive spectroscope analysis, and a thermodynamic calculation were conducted. With an increase in aging time, sigma phases are precipitated much more than chi phases due to the meta-stable chi phase acting as a transition phase. As aging time at $850^{\circ}C$ increases, the corrosion resistance decreases owing to an increase in Cr, Mo and W depleted areas adjacent to the intermetallic phases such as sigma phases and chi phases.