• Journal of the Korean Ceramic Society
• /
• v.41 no.2
• /
• pp.97-101
• /
• 2004

W $O_{x}$-based semiconductor type thin film gas sensor was fabricated for the detection of N $O_{x}$ by reactive d.c. sputtering method. The relative oxidation state of the deposited W $O_{x}$ films was approximately compared by the calculation of the difference of the binding energy between Ols to W4 $f_{7}$2/ core level XPS spectra in the standard W $O_3$ powder of known composition. As the annealing temperature increased from 500 to 80$0^{\circ}C$, relative oxygen contents and grain size of the sputtered films were gradually increased. As the results of sensitivity ( $R_{gas}$/ $R_{air}$) measurements for the 5 ppm N $O_2$ gas, the sensitivity was 110 and the sensor showed recovery time as fast as 200 s. The other sensor properties were examined in terms of surface microstructure, annealing temperature, and relative oxygen contents. These results indicated that the W $O_3$ thin film with well controlled structure is a good candidate for monitoring and controlling of automobile exhaust.haust.t.t.t.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.33 no.4
• /
• pp.321-325
• /
• 2020

Atmospheric environmental problems have a major impact on human health and lifestyle. In humans, inhalation of nitrogen oxides causes respiratory diseases, such as bronchitis. In this paper, thermal analysis of a gas sensor was carried out to design and fabricate a wearable nylon-yarn gas sensor for the detection of NO_x gas. In the thermal analysis method, the thermal diffusion process was analyzed while operating the sensors at 40 and 60℃ to secure a temperature range that does not cause thermal runaway due to temperature in the operating environment. Thermal diffusion analysis was performed using the COMSOL software. The thermal analysis results could be useful for analyzing gas adsorption and desorption, as well as the design of gas sensors. The thermal energy diffusion rate increased slightly from 10.05 to 10.1 K/mm as the sensor temperature increased from 40 to 60℃. It was concluded that the sensor could be operated in this temperature range without thermal breakdown.

• Journal of the Korean Chemical Society
• /
• v.30 no.2
• /
• pp.207-215
• /
• 1986

A new method was proposed to improve removal of nitrogen oxides $(NO_x)$ in exhaust gas by the reduction method using ammonia. At the relative humidity of 60%, 50 ppm of $NO_x$ was decomposed at the rate of 1% per hour in the reaction chamber. On the other hand, by adding $NH_3$ which was 5 times more concentrated than NOx, the decomposition rate increased to 6% per hour for 50 ppm $NO_x$ and 10% per hour for 20ppm $NO_x$. Within the actual exhausted gases, the decomposition rate of $NO_x$ reached the maximum 15% per hour because of coexisted reducing gases, such as hydrocarbon and carbon monoxide, and excess humidity containing trace metal ions. In the presence of acidic $SO_2$ gas, the decomposition rate of $NO_x$ decreased. The decomposition of $NO_x$ seems to be caused by the mist which is added to the system, and $NH_3$ in the mist which reduces $NO_x$.

• Journal of the Korean Society of Industry Convergence
• /
• v.9 no.1
• /
• pp.13-19
• /
• 2006

The ozone produced by a dielectric barrier discharge device was injected into the exhaust gas to oxidize a part of NO to $NO_2$, and then the exhaust gas containing the mixture of NO and $NO_2$ was further treated in a catalytic reactor where both NO and $NO_2$ were reduced to $N_2$ in the presence of ammonia as the reducing agent. The $NO_2$ content in the mixture of NO and $NO_2$ was changed by the amount of ozone added to the exhaust gas. The experiments were primarily concerned with the effect of reaction temperature on the catalytic $NO_x$ reduction at various $NO_2$ contents. The increase in the $NO_2$ content by the ozone injection remarkably improved the performance of the catalytic $NO_x$ reduction, especially at low temperatures.

• Journal of Advanced Marine Engineering and Technology
• /
• v.28 no.2
• /
• pp.315-331
• /
• 2004

The effects of intake mixture temperature on performance and exhaust emissions under four kinds of engine loads were experimentally investigated by using a four-cycle. four-cylinder. swirl chamber type. water-cooled diesel engine with scrubber EGR system operating at three kinds of engine speeds. The purpose of this study is to develop the scrubber exhaust gas Recirculation (EGR) control system for reducing $\textrm{NO}_{x}$ and soot emissions simultaneously in diesel engines. The EGR system is used to reduce $\textrm{NO}_{x}$ emissions. And a novel diesel soot-removal device of cylinder-type scrubber with five water injection nozzles is specially designed and manufactured to reduce soot contents in the recirculated exhaust gas to the intake system of the engine. The influences of cooled EGR and water injection. however. would be included within those of scrubber EGR system. In order to survey the effects of cooled EGR and moisture on $\textrm{NO}_{x}$ and soot emissions. the intake mixtures of fresh air and recirculated exhaust gas are heated up using a heater with five heating coils equipped in a steel drum. It is found that intake and exhaust oxygen concentrations are decreased, especially at higher loads. as EGR rate and intake mixture temperature are increased at the same conditions of engine speed and load. and that $\textrm{NO}_{x}$ emissions are decreased. while soot emissions are increased owing to the decrease in intake and exhaust oxygen concentrations and the increase in equivalence ratio. Thus ond can conclude that $\textrm{NO}_{x}$ and soot emissions are considerably influenced by the cooled EGR.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.23 no.5
• /
• pp.515-523
• /
• 2015

In this paper, we fabricated and evaluated the gas sensor for the detection of CO gas and $NO_X$ gas among the vehicle exhaust emission gasses. The $SnO_2$ (tin dioxide) layer is used as the detection material, and the thin-film type and the nano-fiber type layers are deposited with various thicknesses using sputtering method and electro spinning method, respectively. The experiments are performed in the chamber where the gas concentration is controlled with mass flow controller. The fabricated devices are applied to the CO and $NO_X$ gas, where the device with the thinner $SnO_2$ layer shows better sensitivity. The nano-fiber has the larger surface area, and the shorter response time and recovery time are obtained. From the experimental results, both types of gas sensors successfully detect CO and $NO_X$ gases, which can be applied to measure those gases from the vehicle emissions.

• IEMEK Journal of Embedded Systems and Applications
• /
• v.2 no.2
• /
• pp.76-81
• /
• 2007

A novel multi-layer type micro gas sensor for $NO_X$ detection was designed and fabricated. Micro platform defined as type II-1 in this article for micro gas sensor was fabricated using the MEMS technology to meet the demanding needs of lower power consumption. Nano composite materials were fabricated with nanosized tin oxide powder and $\underline{m}$ulti-$\underline{w}$all $\underline{c}$arbon $\underline{n}$ano $\underline{t}$ube (MWCNT) to improve sensitivity. We investigated characteristics of fabricated multi-layer type micro gas sensor with $NO_2$ concentration variations at constant 2.2 V. Sensitivity (S) of micro gas sensor were observed to increase from 2.9, to 7.4 and 11.2 as concentrations of $NO_2$ gases increased from 2.4 ppm, to 3.6 ppm and 4.9 ppm. When 2.4 ppm of $NO_2$ gas was applied, response time and recovery time of micro gas sensor were recorded as 101 seconds and 142 seconds, respectively.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.11 no.11
• /
• pp.1001-1006
• /
• 1998

$WO_3$ based semiconduction sensor have been reported to have excellent sension properties to $NO_x$ gases by many researchers. In this study appropriate $WO_3$ precursor have been chosen and thin film sensors were fabricated by metallo organic deposition process. Their sensing characteristics were investigated as a function of NO concentration, heat treatment, and measuring temperature. Tungsten dichloro triethoxide was found to be a good precursor for $WO_3$ thin film in this method. Samples heat treated at $600^{\circ}C$ showed sensitivity (S) 200 to 50 ppm NO gas when measuring temperature was $150^{\circ}C$.

• Applied Chemistry for Engineering
• /
• v.28 no.6
• /
• pp.607-618
• /
• 2017

Harmful air pollutants are exhausted from the various industrial facilities including the coal-fired thermal power plants and these substances affects on the human health as well as the nature environment. In particular, nitrogen oxides ($NO_x$) and sulfur dioxide ($SO_2$) are known to be causative substances to form fine particles ($PM_{2.5}$), which are also deleterious to human health. The integrated system composed of selective catalytic reduction (SCR) and wet flue gas desulfurization (WFGD) have been widely applied in order to control $NO_x$ and $SO_2$ emissions, resulting in high investment and operational costs, maintenance problems, and technical limitations. Recently, new technologies for the simultaneous removal of $NO_x$ and $SO_2$ from the flue gas, such as absorption, advanced oxidation processes (AOPs), non-thermal plasma (NTP), and electron beam (EB), are investigated in order to replace current integrated systems. The proposed technologies are based on the oxidation of $NO_x$ and $SO_2$ to $HNO_3$ and $H_2SO_4$ by using strong aqueous oxidants or oxidative radicals, the absorption of $HNO_3$ and $H_2SO_4$ into water at the gas-liquid interface, and the neutralization with additive reagents. In this paper, we summarize the technical improvements of each simultaneous abatement processes and the future prospect of technologies for demonstrating large-scaled applications.

• The Transactions of the Korean Institute of Electrical Engineers C
• /
• v.51 no.12
• /
• pp.567-572
• /
• 2002

In these days, diesel vehicle or power plant emits $NO_X\; and SO_2$ which cause air pollution like acid-rain, ozone layer destroy and optical smoke, therefore there are many kinds of methods considered for removing them such as SCR, catalyst, plasma process, and plasma-catalyst hybrid process. T$TiO_2$ is commonly used as catalyst to remove $NO_X$ gas because it have very excellent chemical characteristic as photo catalyst. In this paper, $NO_X$ sensing characteristic of $TiO_2$ thin film deposited by R.F Magnetron sputtering is investigated. A finger shaped electrode on $Al_2$O$_3$ substrate is designed and $TiO_2$ is deposited on the electrode by the magnetron sputtering deposition system. Chemical composition of the deposited $TiO_2$ thin film is $TiO_{1.9}$ by RBS analysis. When the UV is irradiated on it with flowing air, capacitance of $TiO_2$ thin film increases, however, when NO gas is put into the system with air, it immediately decreases because of photo chemical reaction. and it monotonously decreases with increasing NO concentration.