• 한국세라믹학회지
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• 제32권12호
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• pp.1369-1376
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• 1995

The WO3 thin-film NOx sensor which is of practical use and includes the heater and the temperature sensor was fabricated. The WO3 thin films as a gas-sensing layer was deposited at ambient temperature in a high-vacuum resistance heated evaporator. The highest sensitivity of the WO3 thin-film sensor to NOx was obtained under the condition of the annealing temperature of 50$0^{\circ}C$ and the operating temperature of 30$0^{\circ}C$. The gas sensing characteristics of this sensor was excellent, i.e. high sensitivity (Rgas/Rair in 3 ppm NO2=53) and fast response time (4 seconds).

• 센서학회지
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• 제5권5호
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• pp.39-46
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• 1996

$WO_{3}$에 미량의 Pd 또는 Pt가 첨가된 박막을 이용한 NOx 센서를 제조하였다. $WO_{3}$계 박막은 고진공, 저항가연식 evaporator를 이용하여 분위기온도에서 증착한 다음 $500^{\circ}C$에서 열처리하였다. 5 ppm의 $NO_{2}$가스에 대하여 $200^{\circ}C$에서 측정한 가스감도($R_{gas}/R_{air}$)는 0.5 wt.% $Pt-WO_{3}$ 센서에서 50으로서 최대값을 가졌다.

• 한국분말재료학회지
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• 제26권1호
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• pp.28-33
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• 2019

The gas sensor is essential to monitoring dangerous gases in our environment. Metal oxide (MO) gas sensors are primarily utilized for flammable, toxic and organic gases and $O_3$ because of their high sensitivity, high response and high stability. Tungsten oxides ($WO_3$) have versatile applications, particularly for gas sensor applications because of the wide bandgap and stability of $WO_3$. Nanosize $WO_3$ are synthesized using the hydrothermal method. As-prepared $WO_3$ nanopowders are in the form of nanorods and nanorulers. The crystal structure is hexagonal tungsten bronze ($MxWO_3$, x =< 0.33), characterized as a tunnel structure that accommodates alkali ions and the phase stabilizer. A gas detection test reveals that $WO_3$ can detect acetone, butanol, ethanol, and gasoline. This is the first study to report this capability of $WO_3$.

• 전기학회논문지
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• 제59권9호
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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.

• The Korean Journal of Ceramics
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• 제6권3호
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• pp.304-308
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• 2000

WO$_3$/SnO$_2$ceramics has been suggested as an effective sensing material for monitoring offensive odor or pollutant gases. This work was focussed on improving long-term stability, which has been a principal problem generally taking place in SnO$_2$semiconductor gas sensor. Miniaturized thick film gas sensors were fabricated by screen printing technique. Two types of sensor materials, W doped SnO$_2$and WO$_3$mixed SnO$_2$, were comparatively investigated on those long-term stability and sensitivites to several gases. Small amount of W doping(0.1 mol%) into SnO$_2$largely improved the long-term stability. The W(0.1 mol%) doped SnO$_2$gas sensor had higher sensitivities to both acetone and alcohol compared with WO$_3$(5 wt%) mixed SnO$_2$gas sensor. On the contrary, WO$_3$(5 wt%) mixed SnO$_2$gas sensor showed more superior sensitivity to cigarette smoke due to larger W content.

• 센서학회지
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• 제10권2호
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• pp.118-124
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• 2001

입자들이 용액에 녹아있을 때 pH에 따라서 다른 zeta-potential을 가지게 되며, 이것은 입자의 분산상태에 영향을 주게 된다. NO 센서에서 $WO_3$ 입자의 크기는 감도에 큰 영향을 끼치므로 Sol-Coprecipitation법에 의한 $WO_3$ 센서 제조 시에 $WO_3$ precursor 상태에서의 pH의 영향을 알아보았다. 먼저 $WO_3$ precursor의 전기적 포텐셜을 측정하여 pH가 2에서 7로 변함에 따라 mobility가 증가하여 7일 때에 가장 큰 분산도를 가진 것을 알 수 있었고, 이는 powder 제조 후 입도 분석, 감지막의 XRD peak, 표면사진으로부터 확인 할 수 있었다. 결과적으로 감도 특성에도 영향을 끼쳐 pH=7에서 제조한 센서가 다른 pH에서 제조한 센서보다 감도가 우수한 것으로 나타났다.

• 한국재료학회지
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• 제21권6호
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• pp.299-302
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• 2011

[ $WO_3$ ]powders were ball-milled with an alumina ball for 0-72 hours. $In_2O_3$ doped $WO_3$ was prepared by soaking ball-milled $WO_3$ in an $InCl_3$ solution. The mixed powder was annealed at $700^{\circ}C$ for 30 min in an air atmosphere. A paste for screen-printing the thick film was prepared by mixing the $WO_3$:In2O3 powders with ${\alpha}$-terpinol and glycerol. $In_2O_3$ doped $WO_3$ thick films were fabricated into a gas sensor by a screen-printing method on alumina substrates. The structural properties of the $WO_3$:$InO_3$ thick films were a monoclinic phase with a (002) dominant orientation. The particle size of the $WO_3$:$InO_3$ decreased with the ball-milling time. The sensing characteristics of the $In_2O_3$ doped $WO_3$ were investigated by measuring the electrical resistance of each sensor in the test-box. The highest sensitivity to 5 ppm $CH_4$ gas and 5 ppm $CH_3CH_2CH_3$ gas was observed in the ball-milled $WO_3$:$InO_3$ gas sensors at 48 hours. The response time of $WO_3$:$In_2O_3$ gas sensors was 7 seconds and recovery time was 9 seconds for the methane gas.

• Bulletin of the Korean Chemical Society
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• 제32권6호
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• pp.1865-1872
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• 2011

This study investigates the sensitivity of a gas sensor to volatile organic compounds (VOCs) at various operating temperatures and catalysts. Nano-sized powdered $WO_3$ prepared by sol-gel and chemical precipitation methods was mixed with various metal oxides. Next, transition metals (Pt, Ru, Pd, and In) were doped on the surface of the mixture. Metal-$WO_3$ thick films were prepared using the screen-printing method. The physical and chemical properties of the films were studied by SEM/EDS, XRD, and BET techniques. The measured sensitivity to VOCs is defined as the ratio ($R_a/R_g$) of resistance ($R_{air}$) of $WO_3$ film in the air to resistance ($R_{gas}$) of $WO_3$ film in a VOCs test gas. The sensitivity and selectivity of the films were tested with various VOCs such as acetaldehyde, formaldehyde, methyl alcohol, and BTEX. The thick $WO_3$ film containing 1 wt % of Ru and 5 wt % of $SnO_2$ showed the best sensitivity and selectivity to acetaldehyde gas at an operating temperature of 300 $^{\circ}C$.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2011년도 추계학술발표대회
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• pp.16.1-16.1
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• 2011

Gas sensor properties of $WO_3$ nanowire structures have been studied. The sensing layer was prepared by deposition of tungsten metal on porous single wall carbon nanotubes followed by thermal oxidation. The morphology and crystalline quality of $WO_3$ material was investigated by SEM, TEM, XRD and Raman analysis. A highly porous $WO_3$ nanowire structure with a mean diameter of 82 nm was obtained. Response to CO, $NH_3$ and $H_2$ gases diluted in air were investigated in the temperature range of $100{\sim}340^{\circ}C$ The sensor exhibited low response to CO gas and quite high response to $NH_3$ and $H_2$ gases. The highest sensitivity was observed at $250^{\circ}C$ for $NH_3$ and $300^{\circ}C$ for $H_2$. The effect of the diameters of $WO_3$ nanowires on the sensor performance was also studied. The $WO_3$ nanowires sensor with diameter of 40 nm showed quite high sensitivity, fast response and recovery times to $H_2$ diluted in dry air. The sensitivity as a function of detecting gas concentrations and gas sensing mechanism was discussed. The effect of dilution carrier gases, dry air and nitrogen, was examined.

• 한국재료학회지
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• 제18권4호
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• pp.193-198
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• 2008

$WO_3$-doped $SnO_2$ thin films were prepared in a solution-deposition method and their gas-sensing characteristics were investigated. The doping of $WO_3$ to $SnO_2$ increased the response ($R_a/R_g,\;R_a$: resistance in air, $R_g$: resistance in gas) to $H_2$ substantially. Moreover, the $R_a/R_g$ value of 10 ppm CO increased to 5.65, whereas that of $NO_2$ did not change by a significant amount. The enhanced response to $H_2$ and the selective detection of CO in the presence of $NO_2$ were explained in relation to the change in the surface reaction by the addition of $WO_3$. The $WO_3$-doped $SnO_2$ sensor can be used with the application of a $H_2$ sensor for vehicles that utilize fuel cells and as an air quality sensor to detect CO-containing exhaust gases emitted from gasoline engines.