• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.23 no.12
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• pp.956-960
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• 2010

CuO doped $WO_3-SnO_2$ thick film gas sensors were fabricated by screen printing method on alumina substrates and heat-treated at $350^{\circ}C$ in air. The effects of mixing ratio of $WO_3$ with $SnO_2$ on the structural and morphological properties of $WO_3-SnO_2$ were investigated X-ray diffraction and Scanning Electron Microscope. The structural properties of the $WO_3-SnO_2$:CuO thick film by XRD showed that the monoclinic of $WO_3$ and the tetragonal of $SnO_2$ phase were mixed. Nano CuO was coated on the $WO_3-SnO_2$ surface and then the surface of $WO_3$ was coated with $SnO_2$ particles with $1\sim1.5{\mu}m$ in diameters, as confirmed form the SEM image. The sensitivity of the $WO_3-SnO_2$:CuO sensor to 2000 ppm $CO_2$ gas and 50 ppm $H_2S$ gas for the various ratio of $WO_3$ and $SnO_2$ was investigated. The 4 wt% CuO doped $WO_3-SnO_2$(75:25) tkick films showed the highest sensitivity to $CO_2$ gas and $H_2S$ gas.

• Journal of Sensor Science and Technology
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• v.15 no.2
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• pp.120-126
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• 2006

Physicochemical and electrical properties for hydrogen gas sensors based on Pd-deposited $WO_3$ thin films were investigated as a function of Pd thickness, annealing temperature, and operating temperature. $WO_3$ thin films were deposited on an insulating material by thermal evaporator. XRD, FE-SEM, AFM, and XPS were used to evaluate the crystal structure, microstructure, surface roughness, and chemical property, respectively. The deposited films were grown $WO_3$ polycrystalline with rhombohedral structure after annealing at $500^{\circ}C$. The addition effect of Pd is not the crystallinity but the suppression of grain growth of $WO_3$. Pd was scattered an isolated small spherical grain on $WO_3$ thin film after annealing at $500^{\circ}C$ and it was agglomerated as an irregular large grain or diffused into $WO_3$ after annealing at $600^{\circ}C$. 2 nm Pd-deposited $WO_3$ thin films operated at $250^{\circ}C$ showed good response and recovery property.

• Solar Energy
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• v.12 no.2
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• pp.18-27
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• 1992

Multilayer coatings of $WO_3$ were deposited by the sol-gel technique on microscope slide glass and ITO coated glass. These films were characterized optically, chemically, and structurally by XRD, spectro-photometry, DTA/TGA, SEM/EDAX and RBS. Uniform $WO_3$ sol-gel films were dip coated on slide glass at dipping speed of 5mm/s. This sample indicated a low near IR transmittance in optical properties as a result of coloration using a dilute HCI electrolyte as the $H^+$ion sources. Differential thermal analysis results have allowed the accurate determination of the formation temperature of the $WO_3$ crystalline phase from the gel data in the range of $380^{\circ}C{\sim}500^{\circ}C$, consistent with crystallization temperature of sol-gel film. RBS spectrometry was performed on the uncolored $WO_3$ sol-gel film, yielding a chemical composition of $WO_3$.

• Korean Journal of Metals and Materials
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• v.47 no.9
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• pp.597-603
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• 2009

The hydrogen reduction behavior of ultrasonic ball-milled $WO_3-CuO$ nanopowder, which is highly related with micro-pore structure, was investigated by thermogravimetry(TG) and hygrometry system. EDS and TEM results represented that the ultrasonic ball-milled $WO_3-CuO$ nanopowder consisted of the agglomerates which was confirmed as a homogeneous mixture of $WO_3$ and CuO particles. It was found that the reduction reaction of CuO was retarded by initial micro-pores which are smaller than 40 nm in the ultrasonic ball-milled $WO_3-CuO$ nanopowder. The earlier agglomeration of Cu particles at comparably low temperature decreased the volume of micro-pores in the $WO_3-CuO$ nanopowder which caused the retardation of $WO_3$ reduction reaction. These results clearly explain that the micro-pore structure significantly affected the reduction reaction of $WO_3$ and CuO in the $WO_3-CuO$ nanopowder.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.59 no.9
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• pp.1621-1625
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• 2010

Recently, due to increase in the usage of toxic gas and inflammability gas, the ability to monitor and precisely measurement of these gases is crucial in preventing the occurrence of various accidents. CuO doped and undoped $WO_3$ thick films gas sensors were prepared using screen-printing method on alumina substrates. A structural properties of $WO_3$:CuO thick films had monoclinic phase and triclinic phase of $WO_3$ together. Sensitivity of $WO_3$:CuO sensor at 2000 ppm of $CO_2$ gas and 50 ppm of $H_2S$ gas was investigated. 4 wt% Cu doped $WO_3$ thick films had the highest sensitivity of $CO_2$ gas and $H_2S$ gas.

• Journal of Sensor Science and Technology
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• v.5 no.5
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• pp.39-46
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• 1996

The Pd or Pt-doped $WO_{3}$ thin-film NOx sensor was fabricated. The $WO_{3}$-based thin films as a gas-sensing layer were deposited at ambient temperature in a high-vacuum resistance heated evaporator and annealed at $500^{\circ}C$. The gas sensitivity ($R_{gas}/R_{air}$) to 5 ppm $NO_{2}$ measured at the operating temperature of $300^{\circ}C$ was 50 (highest sensitivity) for the 0.5 wt.% $Pt-WO_{3}$ sensor.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2012.11a
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• pp.161-161
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• 2012

• Clean Technology
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• v.18 no.4
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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.

• Applied Chemistry for Engineering
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• v.33 no.2
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• pp.159-165
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• 2022

To enhance the photocatalytic activities of WO₃ photocatalysts, fluorine doping was performed to induce the oxygen vacancies. Both plasma and direct vaper fluorination were carried out for fluorine doping, and photocatalytic activities were examined by using methylene blue dye. Oxygen vacancies of the plasma and direct vaper fluorinated WO₃ photocatalysts were measured to be 14.65 and 18.59%, which increased to about 23 and 56% at pristine WO₃ photocatalysts. The degradation efficiency of methylene blue was also determined about 1.7 and 3.4 times higher than pristine WO₃ photocatalysts, respectively, depending on oxygen vacancies increased. In addition, it was confirmed that the bandgap process energy decreased from 2.95 eV to 2.64 and 2.45 eV after fluorine doping. From this result, it is considered that the direct vaper fluorination has an advantage for increasing the photocatalytic activities of WO₃ compared to that of the plasma fluorination.

• Bulletin of the Korean Chemical Society
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• v.28 no.10
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• pp.1763-1770
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• 2007

Strong solid acid catalysts, NiO/Al2O3-TiO2/WO3 for ethylene dimerization were prepared by the addition of Al2O3 and the modification with WO3. The acid sites and acid strength were increased by the inductive effect of WO3 species bonded to the surface of catalysts. The larger the dispersed WO3 amount, the higher both the acidity and catalytic activity for ethylene dimerization. The addition of Al2O3 to TiO2 up to 5 mol% enhanced acidity and catalytic activity gradually due to the interaction between Al2O3 and TiO2 and consequent formation of Al-O-Ti bond.