• Journal of the Korean Chemical Society
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• v.10 no.1
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• pp.32-42
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• 1966

The electrolysis of tungstic oxide dissolved in the bath of calcium chloride and calcium oxide was studied to produce metallic tungsten using carbon as anode and iron as cathode in the temperature range of 900^{\circ}$ to $1200^{\circ}C$. The binary phase diagrams $CaCl_2$-CaO and $CaCl_2-CaWO_4$ systems were constructed to determine the suitability of bath composition and the range of temperatures for the electrolysis. As $WO_3$ reacted with $CaCl_2$ to form oxychloride in the fused salt, the addition of the proper amount of CaO was necessary to avoid the loss of $WO_3$. The optimum compositions of fused bath were $CaCl_2$ 100 parts, CaO and $WO_3$ each 10 to 20 parts, with the CaO, $WO_3$ ratio greater than unity, to keep freezing point low and to prevent the vaporization of $CaCl_2$. The observed decomposition voltage at which $WO_3$ decomposes to W and CO was-0.1 volt, whereas the calculated was -0.3 volt. Metallic tungsten deposited at the cathode reacted easily with CO formed secondarily at the anode surface, to form WC below $1050^{\circ}C$, so that the cell temperature should be above $1050^{\circ}C$. The effects of cathode current densities on current efficiency were minor in the range of 1 to 5 $amp/cm^2$.

• Journal of the Korean Ceramic Society
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• v.38 no.3
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• pp.280-286
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• 2001

10 이하의 저유전율을 갖는 (1-x)BaWO$_4$-xMg$_2$SiO$_4$(x=0.1~0.9) 세라믹스의 미세구조와 고주파 유전특성을 조사하였다. (1-x)BaWO$_4$-xMg$_2$SiO$_4$(x=0.1~0.9) 세라믹스는 정방정(tetragonal) 구조를 가진다. 0.1BaWO$_4$-0.9Mg$_2$SiO$_4$세라믹스는 BaWO$_4$와 $Mg_2$SiO$_4$의 상들이 공존하는 혼합상을 보였으며, $Mg_2$SiO$_4$가 이차사으로 형성된 것이 관찰되었다. 120$0^{\circ}C$~140$0^{\circ}C$에서 2시간 동안 소결된 (1-x)BaWO$_4$-xMg$_2$SiO$_4$(x=0.1~0.9) 세라믹스는 $\varepsilon$$_{r}$=6.37~8.21, Q.f=15000~99422 그리고 $ au$$_{f}$=73.9~48.9 ppm/$^{\circ}C$의 고주파 유전특성을 가졌다. $\tau$$_{f}$를 보정하기 위해, CaTiO$_3$(1,5 wt%)가 (1-x)BaWO$_4$-xMg$_2$SiO$_4$(x$\geq$0.9) 세라믹스에 첨가되었다. 135$0^{\circ}C$에서 2시간 동안 소결된 0.1BaWO$_4$-0.9Mg$_2$SiO$_4$+CaTiO$_3$(5 wt%) 세라믹스는 $\varepsilon$$_{r}$=7.3, Q.f=30532 그리고 $\tau$$_{f}$=-30 ppm/$^{\circ}C$의 고주파 유전특성을 얻었다. 얻었다.

• Proceedings of the IEEK Conference
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• 1998.10a
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• pp.601-604
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• 1998

NOX detecting gas sensors using TiO2 doped tungsten oxide semiconductor were prepared and their electrical and sensing characteristics have been investigated. In normal air condition, the sensors of WO3, TiO2 doped WO3 show grain boundary heights of 0.34 eV, 0.25 eV, respectively. The grain boundary barrier energy variation was increased by doping TiO2 into large variation of resistance to NOX gases. And doping the TiO2 4 wt.%, the particle size of WO3 polycrystal films showed higher sensitivity and better sorption characteristics to NOX gas than the pure WO3 films material in air at operating temperature of $350^{\circ}C.$ The TiO2 doped WO3 semiconductor gas sensor shows nano-sized particle size and good sensitivity to sub-ppm concentration of NOX.

• Proceedings of the Materials Research Society of Korea Conference
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• 1992.05a
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• pp.54-54
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• 1992

ITO투명전극/WO$_3$박막/LiClO$_4$-PC/백금 대향전극 구조를 갖는 일렉트로 크로믹 소자를 구성하여 WO$_3$박막의 일렉트로크로믹 특성을 조사하였다. WO$_3$박막의 coloration의 LiClO$_4$-PC 유기전해질과 ITO 투명전극으로부터 Li$^{+}$이온과 전자들의 이중주입에 의하여 청색으로 나타났으며, 전기화학전인 산화반응에 의하여 bleaching 현상이 가역적으로 일어났다. Coloration 과 bleaching 현상, 광학밀도, 구동전압 및 응담속도등의 일렉트로크로믹 특성은 WO$_3$ 박막의 성장 조건, WO$_3$박막 두께, ITO 투명전극의 sheet resistance, 대향전극 및 인가전압에 크게 의존하는 것으로 밝혀졌다.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.07a
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• pp.536-539
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• 2000

The effects of annealing on the electrical and structural characteristics for the rf sputter deposited WO$_3$thin film. The sputtered thin films are annealed at 773K for 1 hour in air atmosphere. Oxygen flow rate were changed from 0 to 70% during sputtering. It is observed from the results of the AFM measurement that the average roughness for the rf sputter deposited WO$_3$thin film would be increased from 2.45 angstrom to 152 angstrom by annealing. The sheet resistance of the sputtered WO$_3$film is changed from insulting to MOhm after annealing. According to the results of the XRD, the as-deposited films revealed the amorphous state whereas the peaks of X-ray diffraction at 2 theta= 28 degrees and 2 theta = 25 degrees corresponding to the (111) and (200) plane of the WO$_3$film respectively are observed after annealing.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.20 no.2
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• pp.130-134
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• 2007

In this study, in order to. develop the low temperature sintering ceramics for multilayer piezoelectric actuator, PMN-PNN-PZT ceramics using CuO, $Bi_{2}O_{3}\;and\;Li_{2}CO_{3}$ as sintering aids were manufactured with the amount of $WO_{3}$ addition. The ceramics were sintered at $900,\;930,\;960^{\circ}C$, respectively. Thereafter, their microstructural, dielectric and piezoelectric properties were investigated. The $WO_{3}$ was proved to lower the sintering temperature of piezoelectric ceramics due to the effects of PbO and $WO_{3}$ liquid phase. At 0.3 wt% $WO_{3}$ added specimen sintered at $930^{\circ}C$, electromechanical coupling factor($k_{p}$), mechanical quality factor($Q_{m}$), dielectric constant and $d_{33}$ showed the optimum values as the values of 0.60, 1,402, 1,440 and 360 pC/N, respectively, for multilayer piezoelectric actuator application.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.21 no.4
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• pp.181-186
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• 2011

Thermal stability of the $TiO_2$ SCR catalyst with W03 loading was investigated in terms of structural and morphological analyses. The $TiO_2$ catalysts with 10 w% $WO_3$ content and without $WO_3$ were prepared. which were heat-treated at $800^{\circ}C$ for 5 h. It was found that the catalytic acidity was decreased by thermal degradation in the $WO_3-TiO_2$ specimen that relatively less than the $TiO_2$ specimen from FT-IR analysis. The phase transition of the $TiO_2$ catalyst from anatase to rutile was increased by heal-treatment, and the percentage of the rutile phase was 28.4 % in the $WO_3-TiO_2$ and 22.9 % in the $TiO_2$. A shell region of $WO_3$ distinguished from a $TiO_2$ particle was also observed in the grain boundary region, and the $WO_3$ led to the suppression of grain growth. It could be confirmed that the suppression of grain growth can contribute to the improvement of catalytic properties for thermal stability more than the increase of anatase-rutile phase transformation which cause the reduction of the catalytic activity in the $TiO_2$ SCR catalyst by the presence of $WO_3$.

• Korean Journal of Materials Research
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• v.23 no.9
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• pp.537-542
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• 2013

Two types of Tb- and Na-substituted green phosphors $Ca_{(1-1.5x)}WO_4:Tb_x^{3+}$: and $Ca_{(1-2x)}WO_4:Tb_x^{3+},Na_x^+$ were synthesized with various x values, using a solid-state reaction. The former phosphors contained both substitutional and vacancy point defects, while the later had only substitutional defects. X-ray diffraction results showed that the main diffraction peak, (112), was centered at $2{\theta}=28.72^{\circ}$ and indicated that there was no basic structural deformation caused by substitutions or vacancies. The photoluminescence emission and photoluminescence excitation spectra revealed the optical properties of trivalent terbium ions, $Tb^{3+}$. Typical transitions, $^5D_3{\rightarrow}^7F_6,\;^7F_5,\;^7F_4$ and $^5D_4{\rightarrow}^7F_6,\;^7F_5,\;^7F_4,\;^7F_3$, and cross relaxations were observed. Subtle differences in the photoluminescence of green phosphors were observed as a result of the point defects. The FT-IR spectra indicated that some of the ungerade vibrational modes had shifted positions and changed shapes, spreading out over a wide range of frequencies. This change can be attributed to the different masses of $Tb^{3+}$ and $Na^+$ ions and $V_{Ca}$" vacancies compared to $Ca^{2+}$ ions. The gerade normal modes of the Raman spectra exhibited subtle differences resulting from point defects in $Ca_{(1-1.5x)}Tb_xWO_4$ and $Ca_{(1-2x)}Tb_xNa_xWO_4$.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.369.1-369.1
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• 2014

Au-functionalized $WO_3$ nanotubes were synthesized using ZnO nanowire templates. Transmission electron microscopy revealed the Au nanoparticles on the outer surface of a typical $WO_3$ nanotube ranged from 5 to 25 nm. The multiple networked Au-functionalized $WO_3$ nanotube sensors showed responses of 820-3, 924% in the $NO_2$ concentration range of 1-5 ppm at $300^{\circ}C$. These responses were approximately 5-12 fold higher than those observed for pristine $WO_3$ nanotube sensors over the same $NO_2$ concentration range. A model describing the gas sensing mechanism of Au-functionalized $WO_3$ nanotubes is discussed.

• Journal of Korean Society for Atmospheric Environment
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• v.6 no.1
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• pp.31-42
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• 1990

In order to suggest an efficient catalyst systems for NOx reduction of flue gases from industrial boilers, $TiO_2$ supported $WO_3-V_2O_5, V_2O_5$ and $WS_2$ catalysts were tested for the performances of NOx reduction at high reactin temperature range (250-500$^\circ$C) using a simulated flue gas system. It was found that while the proposed $WO_3/TiO_2$ and $WO_3-V_2O_5/TiO_2$ catalysts showed a significant high NOx reduction efficiency at about 350-400$^\circ$C, the conventional commercial catalyst of $V_2O_5/TiO_2$ showed a significant drop in NOx reduction efficiency due to the excessive $NH_3$ oxidation. From the measurement of surface acidities of those catalysts, it was found that the acidity are well correlated with the activities of NOx reduction. The reason of high activity of $WO_3$ series catalysts at high reaction temperature seems due to the low value of surface excess oxygen compared with that of $V_2O_5/TiO_2$ seems equivalent to the acid site of that catalyst.