• Korean Journal of Materials Research
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• v.21 no.11
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• pp.628-633
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• 2011

Studies on lead-free piezoelectrics have been attractive as means of meeting environmental requirements. We synthesized lead-free piezoelectric $(Bi_{1/2}Na_{1/2})TiO_3-Ba(Cu_{1/3}Nb_{2/3})O_3$ (BNT-BCN) ceramics, and their dielectric, piezoelectric, and strain behavior were characterized. As BCN with a tetragonal phase was incorporated into the rhombohedral BNT lattice, the lattice constant increased. A small amount of BCN increased the density and dielectric constant forming the complete solid solution with BNT. However, BCN above 10 mol% was precipitated into a separate phase, and which was detected with XRD. In addition, EDX measurement revealed that Cu in BCN was not distributed homogeneously but was accumulated in a certain area. A lower density with a large amount of BCN was attributed to the nonsinterable property of BCN with large tetragonaliy. The dielectric constant vs the temperature change and the strain vs the electric field indicated that the ferroelectric property of BNT was diminished and paraelectric behavior was enhanced with the BCN addition. BNT-7.5BCN showed a 0.11% unimorph strain with a 9.0 kV/mm electric field with little hysteresis.

• Journal of Industrial Technology
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• v.17
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• pp.241-247
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• 1997

A numerical model has been proposed for a diffusion flame reactor to manufacture ultrafine $TiO_2$ powders. The model equations such as mass balance equation, the 0th, 1st, and 2nd moment equations of aerosols were considered. The phenomena such as $TiCl_4$ reaction rate, $TiO_2$ nucleation rate and the coagulation of $TiO_2$ powders were included in the aerosol dynamic equation. It is found that the $TiO_2$ particle concentration becomes higher, as the inlet $TiCl_4$ concentration and the total gas flow rate increase, and also as the flame temperature decreases. The $TiO_2$ particle size increases, as the flame temperature and the inlet $TiCl_4$ concentration increase and the total gas flow rate decreases.

• Journal of Korean Society on Water Environment
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• v.26 no.4
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• pp.707-712
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• 2010

Nitrogen-doped $TiO_2$ particles have been successfully prepared using titanium tetraisopropoxide as the Ti source and urea as the nitrogen source. As-prepared nitrogen-doped $TiO_2$ was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer-Emmett-Teller method (BET) and ultraviolet-visible light (UV-vis) absorption spectra techniques. Photocatalytic degradation of Methylene Blue (MB) has been carried out in both solar light (UV-vis) and the visible region (${\lambda}=420nm$). Nitrogen-doped $TiO_2$ exhibits higher activity than the commercial $TiO_2$ photocalyst, particularly under visible-light irradiation because bandgap of nitrogen-doped $TiO_2$ becomes remarkably decreased.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.12
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• pp.2624-2630
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• 2002

Organic/inorganic hybrid materials have rapidly become a fascinating research field. In this study, $polyimide/TiO_2$ composites were synthesized from nano-sized anatase $TiO_2$ and two types of polyimide, that is, BPDA-PPD and PMDA-ODA. Nano-sized $TiO_2$ particles were prepared from $TiOEt_4$ solution by the sol-gel method. The synthesized PI/$TiO_2$ composites were characterized by using XRD, TGA, FT-IR, TEM, and Atomic Force Microscope(AFM). $TiO_2$ particles were dispersed well in polyimides and the mechanical and thermal stability of polyimide was improved with $TiO_2$ nano particles.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.28 no.11
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• pp.715-720
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• 2015

The photoinduced hydrophilicity of $TiO_2/WO_3$ double layer films was fabricated by using a conventional rf-magnetron sputtering method. The photoinduced hydrophilic reaction of the $TiO_2$ surface was enhanced by the presence of $WO_3$ under the $TiO_2$ layer by irradiation of a 10 W cylindrical fluorescent light bulb. However, when the $TiO_2$ and $WO_3$ layers were separated by an insulating layer, the surface did not appeared high hydrophilic, under the same light bulb. The enhanced photoinduced hydrophilic reaction can be explained by the charge transfer between $TiO_2$ and $WO_3$ layers. It was also demonstrated that visible light passing through the $TiO_2$ layer could excite $WO_3$. Thus, visible light can be used for the hydrophilic reaction in the present $TiO_2/WO_3$ system.

• Korean Journal of Metals and Materials
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• v.50 no.3
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• pp.201-205
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• 2012

The effects of various manganese precursors for the low-temperature selective catalytic reduction (SCR) of $NO_x$ were investigated in terms of structural, morphological, and physico-chemical analyses. $MnO_x/TiO_2$ catalysts were prepared from three different precursors, manganese nitrate, manganese acetate(II), and manganese acetate(III), by the sol-gel method. The manganese acetate(III)-$MnO_x/TiO_2$ catalyst tended to suppress the phase transition from the anatase structure to the rutile or the brookite after calcination at $500^{\circ}C$ for 2 h. It also had a high specific surface area, which was caused by a smaller particle size and more uniform distribution than the others. The change of catalytic acid sites was confirmed by Raman and FT-IR spectroscopy and the manganese acetate(III)-$MnO_x/TiO_2$ had the strongest Lewis acid sites among them. The highest de-NOx efficiency and structural stability were achieved by using the manganese cetate(III) as a precursor, because of its high specific surface area, a large amount of anatase $TiO_2$, and the strong catalytic acidity.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.21 no.7
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• pp.638-644
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• 2008

The effects of $Nb_2O_5$ and $MnO_2$ on the positive temperature coefficient of resistivity (PTCR) behavior of lead-free $Ba_{0.99}(Bi_{1/2}Na_{1/2})_{0.01}TiO_3$ (BaBiNT) ceramics were investigated in order to fabricate a PTC thermistor available at high temperature of > $120^{\circ}C$. In particular, 0.05 mol% $Nb_2O_5$ added BaBiNT ceramic, which has significantly increased Curie temperature (Tc) of $160^{\circ}C$, showed good PTCR behavior; low resistivity at room temperature $(\rho_r)$ of $80.1{\Omega}{\cdot}cm$, a high $\rho_{max}/\rho_{min}$ ratio of $5.65{\times}10^3$ and a large resistivity temperature factor (a) of 18.5%/$^{\circ}C$. Furthermore, the improved $\rho_{max}/\rho_{min}$ of $6.48{\times}10^4$ and a of 25.4%/$^{\circ}C$ along with higher $T_c$ of $167^{\circ}C$ despite slightly increased $\rho_r$ of $569{\Omega}{\cdot}cm$, could be obtained for the BaBiNT + 0.05 mol% $Nb_2O_5$ + 0.02 wt% $MnO_2$ ceramic cooled down at a rate of $200^{\circ}C/h$.

• Journal of Sensor Science and Technology
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• v.19 no.2
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• pp.155-159
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• 2010

0.96$(Na_{0.5}K_{0.5})NbO_3$-0.04$(Ba_{(1-x)}Sr_x)TiO_3$ lead free piezoelectric ceramics were synthesized to enhance the piezoelectric properties of (Na,K)$NbO_3$. The systhesis and sintering method were the conventional solid state reaction method and general sintering method in air atmosphere. The polymorphic phase transition(PPT) was observed at all composition(0 $\leq$ x $\leq$ 0.05) when $(Ba_{(1-x)}Sr_x)TiO_3$ were added in the $(Na_{0.5}K_{0.5})NbO_3$. As Sr concentration was increased, grain size, dielectric loss(tan$\delta$) and mechanical quality factor($Q_m$) were decreased and piezoelectric constant($d_{33}$) and electromechanical coupling factor($k_p$) were increased within a limited value. The optimized piezoelectric and properties, $d_{33}$, $k_p$, $Q_m$, and tand, of 0.96$(Na_{0.5}K_{0.5})NbO_3$-0.04$(Ba_{(1-x)}Sr_x)TiO_3$ were 139 pC/N, 0.31 %, 95, 0.04 at the composition of x=0.04.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.21 no.11
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• pp.1019-1023
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• 2008

Photoluminescence properties of $SrTiO_3$:Sm red phosphors synthesized by solid state reaction method were studied under 254 nm excitation. Emission bands at 576 nm and 616 nm in heavily $Sm^{3+}$ ion doped $SrTiO_3$:Sm phosphors were observed, which were attributed to $^4G_{5/2}\rightarrow{^6}H_{5/2}$ and $^4G_{5/2}\rightarrow{^6}H_{7/2}$ transition of $Sm^{3+}$, respectively. The $Sm^{3+}$ ion concentration exhibiting the maximum emission intensity in the $SrTiO_3$:Sm was 30 mol%. The luminescence caused by $Sm^{3+}$ in the $SrTiO_3$:Sm phosphors was interpreted by the energy transfer between $Sm^{3+}$ ions.

• Journal of the Korean Ceramic Society
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• v.43 no.8 s.291
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• pp.486-491
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• 2006

A new $TiN-Ti_5Si_3$ bulk composite was synthesized from preceramic, inorganic polymer (methylpolysilsesquioxane) and $TiH_2$ filler powders via polymer pyrolysis. Using this process, ceramics with high melting points can be produced relatively easily to a near net shape. The $TiN-Ti_5Si_3$ composite oxidized slowly during heating to $1000^{\circ}C$. During heating at the temperatures of at 700 and $800^{\circ}C$, TiN oxidized to Rutile-$TiO_2$ whereas $Ti_5Si_3$ resisted to oxidation. The oxide scale formed consisted primarily of $TiO_2$ containing $Ti_5Si_3$.