• Transactions of the Korean hydrogen and new energy society
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• 제4권2호
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• pp.5-15
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• 1993

Hydrogen production in visible light with the following semiconductor systems, $CdS-WO_3$, $CdS-TiO_2$, have been investigated in the presence of redox catalyst (Pt, $RuO_2$). MeOH, EtOH, isopropanol, sulfide/sulfite mixture, lactic acid were used as sacrifical reagents. The optimal condition for $H_2$ evolution was found to be in qgueous lactic acid media for $CdS-WO_3/RuO_2$. The photochemical efficiency for this system was 1.05 % and the $H_2$ evolution rate was 26.5ml/min. at $6.07{\times}10^{-5}$ einstein/sec photon rate

• Applied Chemistry for Engineering
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• 제28권5호
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• pp.576-580
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• 2017

In the present paper, the thermal deactivation characteristics of plate-type commercial $V_2O_5-WO_3/TiO_2$ SCR catalyst were investigated. For this purpose, the plate-type catalyst was calcined at different temperatures ranging from $500^{\circ}C$ to $800^{\circ}C$ for 3 hours. Structural and morphological changes were characterized byXRD, specific surface area, porosity, SEM-EDS and also NOx conversion with ammonia according to the calcine temperature. The NOx conversion decreased with increasing calcine temperature, especially when the catalysts were calcined at temperatures above $700^{\circ}C$. This is because the crystal phase of $TiO_2$ changed from anatase to rutile, and the $TiO_2$ grain growth and $CaWO_4$ crystal phase were formed, which reduced the specific surface area and pore volume. In addition, $V_2O_5$, which is a catalytically active material, was sublimated or vaporized over $700^{\circ}C$, and a metal mesh used as a support of the catalyst occurred intergranular corrosion and oxidation due to the formation of Cr carbide.

• Proceedings of the Materials Research Society of Korea Conference
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• 한국재료학회 2011년도 추계학술발표대회
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• pp.28.2-28.2
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• 2011

The selective catalytic reduction (SCR) of NOx by $NH_3$ is well known as one of the most convenient, efficient, and economical method to prevent NOx emission in flue gas from stationary sources. The degradation of the reactivity is the obstacle for its real application, since high concentrations of sulfur dioxide and thermal factor would deactivate the catalyst. It is necessary to develop high stability of catalysts for low-temperature SCR. Among the transition metal oxides, $WO_3$ is known to exhibit high SCR activity and good thermal stability. The $MnOx-WO_3-TiO_2$ catalysts prepared by sol-gel method with various $WO_3$ contents were investigated for low-temperature SCR. These catalysts were observed in terms of micro-structure and spectroscopy analyses. The $WO_3$ catalyst as a promoter is used to enhance the thermal stability of catalyst since it increases the phase transition temperature of $TiO_2$ support. It was found that the addition of tungsten oxides not only maintained the temperature window of NO conversion but also increased the acid sites of catalyst.

• Journal of the Korean Society of Marine Environment & Safety
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• 제22권2호
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• pp.253-258
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• 2016

The $MnO_x-WO_3-TiO_2$ nanoscale powders were synthesized by sol-gel method in order to prevent the biological fouling on the ships and offshore structures. Powder characteristics and antifouling performance were investigated with respect to the crystalline, microstructure and surface property for application in self-polishing copolymer resins. The high antifouling activity of $TiO_2$-system biocide was attributed to its redox potential and soluble metal ions originating from tungsten oxides according to the improvements in the powder characteristics. Based on their physio-chemical characterizations, the specific surface areas of powders were about $90m^2/g$ and the grain size was in the region 100 ~ 150 nm. Powder characteristics and surface properties were improved by the addition of $WO_3$. Antifouling performance were analyzed according to their surface properties and static immersion tests to determine the effects of the $TiO_2$-system compounds. The surface of 2 wt. % added sample was clean for 5 month. This may be attributed to the ability of $MnO_x-WO_3-TiO_2$ powders to act as a promoter in antifouling agents.

• Korean Journal of Materials Research
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• 제29권8호
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• pp.491-496
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• 2019

In this study, we prepare pure $WO_3$ inverse opal(IO) film with a thickness of approximately $3{\mu}m$ by electrodeposition, and an ultra-thin $TiO_2$ layer having a thickness of 2 nm is deposited on $WO_3$ IO film by atomic layer deposition. Both sets of photoelectrochemical properties are evaluated after developing dye-sensitized solar cells(DSSCs). In addition, morphological, crystalline and optical properties of the developed films are evaluated through field-emission scanning electron microscopy(FE-SEM), High-resolution transmission electron microscopy(HR-TEM), X-ray diffraction(XRD) and UV/visible/infrared spectrophotometry. In particular, pure $WO_3$ IO based DSSCs show low $V_{OC}$, $J_{SC}$ and fill factor of 0.25 V, $0.89mA/cm^2$ and 18.9 %, achieving an efficiency of 0.04 %, whereas the $TiO_2/WO_3$ IO based DSSCs exhibit $V_{OC}$, $J_{SC}$ and fill factor of 0.57 V, $1.18mA/cm^2$ and 50.1 %, revealing an overall conversion efficiency of 0.34 %, probably attributable to the high dye adsorption and suppressed charge recombination reaction.

• Bulletin of the Korean Chemical Society
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• 제25권12호
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• pp.1881-1888
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• 2004

A series of $NiO-TiO_2$/$WO_3$ catalysts was prepared by drying powdered $Ni(OH)_2-Ti(OH)_4$ with ammonium metatungstate aqueous solution, followed by calcining in air at high temperature. Characterization of prepared catalysts was performed by using FTIR, Raman, XPS, XRD, and DSC and by measuring surface area. Upon the addition of tungsten oxide to titania up to 25 wt%, the specific surface area and acidity of catalysts increased in proportion to the tungsten oxide content due to the interaction between tungsten oxide and titania. Since the -$TiO_2$/stabilizes the tungsten oxide species, for the samples equal to or less than 25 wt%, tungsten oxide was well dispersed on the surface of titania, but for the samples containing above 25 wt%, the triclinic phase of $WO_3$ was observed at calcination temperature above 400 $^{\circ}C$. The catalytic activities of 10-NiO-$TiO_2$/$WO_3$ for 2-propanol dehydration and cumene dealkylation were correlated with the acidity of catalysts measured by ammonia chemisorption method. NiO may attract reactants and enhance the local concentration of reactants near the acid sites, consequently showing the increased catalytic activities.

• Clean Technology
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• 제18권4호
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• pp.355-359
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• 2012

For effectively photochemical hydrogen production, Ti ions (0.01, 0.10, 0.50 mol%) impregnated $WO_3$ ($Ti/WO_3$) nanometer sized particles were prepared using a impregnation method as a photocatalyst. The characteristics of the synthesized $Ti/WO_3$ photocatalysts were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), photoluminescence spectra (PL), atomic force microscope (AFM), and electrostatic force microscope (EFM). The evolution of $H_2$ from methanol/water (1/1) photo-splitting over $Ti/WO_3$ photocatalysts was enhanced compared to those over pure $TiO_2$ and $WO_3$ photocatalysts; 3.02 mL of $H_2$ gas was evolved after 8 h when 0.5 g of a 0.10 mol% $Ti/WO_3$ catalyst was used.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 한국전기전자재료학회 2001년도 하계학술대회 논문집
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• pp.143-148
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• 2001

PbWO$_4$ can be densified at 85$0^{\circ}C$ and it shows fairy good microwave dielectric properties; dielectric constant($\varepsilon$$_{r}$) of 21.5, quality factor(Q $\times$f$_{0}$) of 37,224 GHz, and temperature coefficient of resonant frequency($\tau$/suf f/) of -31ppm/$^{\circ}C$. Due to its low sintering temperature, PbWO$_4$ can be used as a multilayered chip component at microwave frequency with high electrical performance by using high conductive electrode metals such as Ag and Cu. However, in order to use this material for microwave communication devices, the $\tau$$_{f}$ of PbWO$_4$ must be stabilized to near zero with high Q$\times$f$_{0}$. In present study, PbWO$_4$ was modified by adding TiO$_2$, B$_2$O$_3$, and CuO in order to improve the microwave dielectric properties without increasing the sintering temperature. The addition of TiO$_2$ increased the $\tau$$_{f}$ and $\varepsilon$$_{r}$, due to its high rr(200ppm/$^{\circ}C$) and $\varepsilon$$_{r}$(100). However, the addition of TiO$_2$ reduced the Q$\times$f$_{0}$ value. When the mot ratio of PbWO$_4$ and TiO$_2$ was 0.913:7.087, near zero $\tau$$_{f}$(0.2ppm/$^{\circ}C$) was obtaibed with $\varepsilon$$_{r}$=22.3, and Q$\times$f/$_{0}$=21,443GHz. With this composition, various amount of B$_2$O$_3$ and CuO were added in order to improve the quality factor. The addition, of B$_2$O$_3$ decreased the $\varepsilon$$_{r}$. However, increased Q$\times$f$_{0}$ and $\tau$$_{f}$. When 2.5 wt% of B$_2$O$_3$ was added to the 0.913PbWO$_4$-0.087TiO$_2$ ceramic, $\tau$$_{f}$ =8.2, $\varepsilon$$_{r}$=20.3, Q$\times$f$_{0}$=54784 GHz. When CuO added to the 0.913PbWO$_4$-0.087TiO$_2$ ceramic, $\tau$$_{f}$ was continuously decreased. And $\varepsilon$$_{r}$ . and Q$\times$f$_{0}$ were increased up to 1.0 wt% then decreased. At 0.1 wt% of CuO addition, the 0.913PbWO$_4$-7.087Ti0$_2$ Ceramic Showed $\varepsilon$$_{r}$=23.5, $\tau$$_{f}$=4.4ppm/$^{\circ}C$, and Q$\times$f$_{0}$=32,932 GHz.> 0/=32,932 GHz.X>=32,932 GHz.> 0/=32,932 GHz.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• 제16권5호
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• pp.397-403
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• 2003

Microwave dielectric properties of (1-x)ZnW $O_4$-xTi $O_2$ ceramic systems were investigated with calcination temperatures and Ti $O_2$ contents. The ZnW $O_4$ ceramic could be suitably sintered at 1075$^{\circ}C$ and showed the dielectric constant of 13.6, quality factor(Q$\times$ $f_{O}$value) of 22,000 and temperature coefficient of resonant frequency($\tau$$_{f}$) of -65$\pm$2ppm/$^{\circ}C$. Increasing the amount of Ti $O_2$ in the range of 0.25 to 0.45 mol, the dielectric constant and $\tau$$_{f}$ increased due to the role of Ti $O_2$ but the quality factor decreased due to the increase of phase boundaries. The 0.7ZnW $O_4$-0.3Ti $O_2$ ceramic showed the dielectric constant of 19.8, qualify factor(Q$\times$ $f_{0}$) of 20,000 and $\tau$$_{f}$ of -3$\pm$1ppm/$^{\circ}C$.>.EX>.>.>.

• Journal of the Microelectronics and Packaging Society
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• 제2권2호
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• pp.31-40
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• 1995

Donor dopant로 WO3, Ta2O5 및 Nb2O5를 첨가한 Zr0.8Sn0.2TiO4 세라믹스의 유전상수 $\varepsilon$r 품 질계수 Q 및 공진주파수의 온도계수 rf에 대하여 연구하였다. 139$0^{\circ}C$에서 32시간 소결시 donor dopant 첨가량에 따른 ZST의 유전상수는 소결밀도의 변화 거동과 잘 일치하였다. 5.5 GHz에서 측정 한 ZST의 품질계수 Q는 ~0.5 mol% WO3 Ta2O5 및 Nb2O5 첨가에 의해 6800에서 8500 정도로 증가 하였다. ZST의 $\tau$f는 0.3 mol%까지의 WO3 첨가량 증가에 따라 0 ppm/$^{\circ}C$에서 -4.6 ppm/$^{\circ}C$까지 음 의 값으로 직선적으로 감소하였으며 0.4 mol% 범위의 Ta2O5 및 Nb2O5 첨가에 의해 -7 ppm/$^{\circ}C$ 까지 직선적으로 감소하였다.