• Journal of the Korean Ceramic Society
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• v.36 no.7
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• pp.705-710
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• 1999

Stability and chemical durability for aqueous casting of BaTiO3 slurry with polycarylic acid(PAA) were studied. PAA was well chemisorbed on surface of BaTiO3 powder at neutral pH but did not chemically adsorbed at low pH. The amount of Ba dissolution in aqueous BaTiO3 slurry was abruptly increased at strong acid pH2 and also at high amount of PAA. Protection of Ba dissolution and stability of slurry could be obtained through the optimization of slurry conditions such as pH amount of surfactant and solid content.

• International Journal of Precision Engineering and Manufacturing
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• v.9 no.1
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• pp.51-53
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• 2008

A new nano-particle deposition system (NPDS) was developed for a ceramic and metal coating process. Nano- and micro-sized powders were sprayed through a supersonic nozzle at room temperature and low vacuum conditions to create ceramic and metal thin films on metal and polymer substrates without thermal damage. Ceramic titanium dioxide ($TiO_2$) powder was deposited on polyethylene terephthalate substrates and metal tin (Sn) powder was deposited on SUS substrates. Deposition images were obtained and the resulting chemical composition was measured using X-ray photoelectron spectroscopy. The test results demonstrated that the new NPDS provides a noble coating method for ceramic and metal materials.

• Bulletin of the Korean Chemical Society
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• v.33 no.10
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• pp.3407-3412
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• 2012

The Ti incorporation at Fe-site in the double perovskite lattice of $Sr_2FeNbO_6$ (SFNO) system is studied. The Ti concentration optimization yielded an efficient photocatalyst. At an optimum composition of Ti as x = 0.07 in $Sr_2Fe_{1-x}Ti_xNbO_6$, the photocatalyst exhibited 2 times the quantum yield for photolysis of $H_2O$ in presence of $CH_3OH$, than its undoped counterpart under visible light (${\lambda}{\geq}420nm$). Heavily Ti-doped $Sr_2Fe_{1-x}Ti_xNbO_6$ lattice exhibited poor photochemical properties due to the existence of constituent impurity phases as observed in the structural characterization, as well as deteriorated optical absorption. The higher electron-density acquired by n-type doping seem to be responsible for the more efficient charge separation in $Sr_2Fe_{1-x}Ti_xNbO_6$ (0.05 < x < 0.4) and thus consequently displays higher photocatalytic activity. The Ti incorporated structure also found to yield stable photocatalyst.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2000.04a
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• pp.11-11
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• 2000

Large-size ceramic/metal bulk FGMs have been fabricated on a recently developed and the world's largest Spark Plasma Sintering(SPS) systems, As a part of the development program for practical production processes and machines for FGMs by SPS, the processes, mechanical properties, dimensional size and shape effects, and production machine systems were investigated. In the past, $ZrO_{2}$/TiAI, $ZrO_{2}$/Ni, $Al_{2}O_{3}$/Ti, WC/Co, WC/Co/Steel, A1/P, Polymide, Cu/Polymide, nano-composites, porous and other combinations of bulk FGMs have already been processed using SPS. However, most of the specimen sizes were small, in a range of 20 to 30mm in diameter. Recently disk-shape sintered compacts with diameters of 100 and 150 mm, and thickness of approximately 15 and 17 mm, $ZrO_{2}$(3Y)/ stainless steel FGMs were homogenous consolidated in a shorter sintering time, while maintaining high quality and repeatability by utilizing a temperature gradient sintering method. The SPS heating up and holding time totaled less than one hour. Therefore, the SPS process in expected to find increased use in the fabrication of large-size FGMs as a new industrial processing technology. This paper introduces SPS systems, the processing principles, features and the characteristies of ceramic/metal bulk FGM.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.217-217
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• 2008

$BaTiO_3$는 perovskite 구조를 가지는 대표적인 강유전체 재료로서 MLCC (Multi Layer Ceramic Capacitor), PTC thermistor 등에 널리 사용되어지고 있으며, 그 특성을 향상시키기 위하여 많은 연구가 진행되고 있다. 현제 $BaTiO_3$ 분말 제조의 대표적인 합성법으로는 하소와 분쇄공정이 없는 수열합성법이 대표적이나, 나노 사이즈로 제작시 $BaTiO_3$는 마이크로 크기와 달리 입방정상으로 우세한 상태로 존재한다. 이는 제조과정 중의 hydroxyl defect의 영향과 나노 분말의 표면에너지 증가 때문이라고 보고된다. 따라서 본 연구는 이러한 문제점을 해결하기 위해 일반적인 세라믹 제조 방법인 고상반응법을 이용한 나노 사이즈의 $BaTiO_3$ 제조를 위한 최적의 공정 조건을 확립하기 위하여 본 연구를 진행하였다. 조성은 $BaTiO_3$와 반응온도를 낮추기 위한 anatase의 $TiO_2$를 사용하였고, $BaCO_3/TiO_2$ 의 조성비 (1. 1.01, 1.02, 1.03)를 제어하여 혼합한 후, 24h ball-mill 하여 하소 온도 ($860^{\circ}C{\sim}1000^{\circ}C$) 변화에 따른 입자 사이즈와 입도 분포를 측정하였다. 제조된 $BaTiO_3$분말의 결정 구조 분석을 위하여 XRD (X-ray diffraction) 분석을 수행 하였는데, 분석 결과로부터 제조된 분말들이 정방정 (tetragonal)의 perovskite구조를 갖고 있음을 확인하였다. 또한 분말의 미세구조 확인을 위하여 SEM (scanning electron microscope) 관찰을 수행하였는데, 나노 사이즈의 구형 분말을 얻을 수 있음을 확인할 수 있었다.

• Journal of the Korean institute of surface engineering
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• v.39 no.4
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• pp.190-197
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• 2006

The effects of blasting and acidic treatment on the corrosion characteristics of dental implant fabricated with Cp-Ti and Ti-6Al-4V alloy have been researched by using electrochemical methods. The fabricated implants were cleaned and sandblasted by $Al_2O_3$ powder and then acidic treatment was carried out in nitric acid solution. The surface morphology were observed using scanning electron microscope. The corrosion behaviors were investigated using potentiosat and EIS in 0.9% NaCl solution at $36.5{\pm}1^{\circ}C$. The potentio-dynamic test in 0.9% NaCl indicated that the corrosion potential of blasting and acidic treated implant was lower than that of non treated implant, but current density was higher than that of non treated implant. From the cyclic potentiodynamic test results of Ti implant, the passivation current density of blasting and acidic treated implant slightly higher than that of non treated implant. From A.C. impedance test results in 0.9% NaCl solution, polarization resistance($R_p$) value of blasting and acidic treated implant was lower than that of non treated implant. In case of blasting and acidic treated implant surface, the pits were observed in valley and crest of implant surface.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.19 no.4
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• pp.202-207
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• 2009

Nanocomposite formation of metal-metal oxide systems by mechanical alloying (MA) has been investigated at room temperature. The systems we chose are the $Fe_3O_4$-M (M = AI, Ti), where pure metals are used as reducing agent. It is found that $Fe/Al_2O_3$ and $Fe/TiO_2$ nanocomposite powders in which $Al_2O_3$ and $TiO_2$ are dispersed in ${\alpha}$-Fe matrix with nano-sized grains are obtained by MA of $Fe_3O_4$ with Al and Ti for 25 and 75 hours, respectively. It is suggested that the shorter MA time for the nanocomposite formation in $Fe/Al_2O_3$ is due to a large negative heat associated with the chemical reduction of magnetite by aluminum. X-ray diffraction results show that the average grain size of ${\alpha}$-Fe in $Fe/TiO_2$ nanocomposite powders is in the range of 30 nm. The change in magnetic properties also reflects the details of the solid-state reduction of magnetite by pure metals during MA.

• The Journal of the Acoustical Society of Korea
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• v.35 no.6
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• pp.445-451
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• 2016

It is very important to obtain non-agglomerated nano particle state for practical application of nano technology. In order to improve the functionality of products using nano particles, more precise control of particle size distribution is required in their synthesis process. However, synthesized nano particles are agglomerated easily due to physical and chemical reasons, and it then veils unique properties of the nano particles and causes some troubles in their practical application. In this study, a separation method for nano particles from suspension by using the droplets as the separation space was proposed. Using the suspension of 0.002 wt. % with $TiO_2$ powder, the particle size distribution of nano particles in the recollected suspension was measured. From the results, it was confirmed that it is possible to separate and to recollect the nano particles monodispersed by using the suggested method.

• Journal of the Korean Ceramic Society
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• v.45 no.12
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• pp.839-844
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• 2008

$TiO_2$ is an environment-friendly semiconducting material, and it has photocatalytic and hydrophilic effect. There are a lot of reports on the photocatalytic characteristics of $TiO_2$, such as organic pollutants resolving, anti-bacterial, and self-purification material. In this paper, $TiO_2$ micron-sized powders were deposited on the glass by room temperature powder spray in vacuum process, so called aerosol deposition (AD), and nano-grained $TiO_2$ photocatalytic thin films were fabricated. The thickness of the films were controlled by changing the number of deposition cycle. Morphologies and characteristics of the AD-$TiO_2$ thin films were examined by SEM, TEM, XRD, and UV-Visible Spectrophotometer. As the thickness of $TiO_2$ films increased, surface roughness increased. By this increment, the reaction area between film and pollutant was enlarged, resulting in better photocatalytic property.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.16 no.5
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• pp.216-221
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• 2006

An investigation of the influence of $WO_3$ and $V_2O_5$ catalysts on the microstructure, phase formation and selective catalytic reduction (SCR) efficiency of the synthesized SCR powders has been carried out. A commercial anatase-$TiO_2$ was used as the catalysts support. For $WO_3(10wt%)/TiO_2$, the W loading to the $TiO_2$ support led to the lower in anatase to rutile transition temperature from $1200^{\circ}C$ of $TiO_2$ support to ${\sim}900^{\circ}C$. The transition temperature was also lowered to below $650^{\circ}C$ in the $V_2O_5$(5 and 10 wt%) added composition. The $WO_3(10wt%)/TiO_2$ SCR powder obtained at $450^{\circ}C$ showed near 100% of $NO_x$ conversion efficiency at $350{\sim}400^{\circ}C$ and for the powder prepared at $650^{\circ}C$ the same efficiency was achieved in wider temperature range $300{\sim}400^{\circ}C$. The highest $NO_x$ conversion efficiency of 100% was obtained in the $V_2O_5(5wt%)/TiO_2$ SCR composition calcined at $650^{\circ}C$ in the relatively wider temperature range $250{\sim}350^{\circ}C$, while the catalytic efficiency considerably decreased for the $V_2O_5(10wt%)/TiO_2$. The lowered conversion efficiency of $NO_x$ observed in the $V_2O_5(10wt%)/TiO_2$ composition calcined at $650^{\circ}C$ was considered to be correlated with the lowered surface area resulting from the increased crystallite growth by highly reactive vanadium loading.