• The Korean Journal of Ceramics
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• v.4 no.3
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• pp.183-188
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• 1998

Gas sensitizations of tin oxide film were investigated by measuring the change of film resistance in various gas atmospheres such as $N_2,\; O_2,\; H_2O$. The main test sample, polycrystalline $SnO_2$ film containing small Sb as a dopant was prepared by a sputtering technique and showed a long term stability in base resistance and thus, in gas sensitivity. The adsorption of oxygen on the film surface as a type of $(O_{ads})$ at the temperature of around $300^{\circ}C$ played important roles in sensor operating mechanism. The roles were ⅰ) the increase of base resistance in ambient air, which consequently lead to high sensitivity and ⅱ) the promotion of fast recovery. The reaction of hydrogen gas with the already adsorbed $(O_{ads})$ ions was considered as a decisive sensitization mechanism of tin oxide film. However, the dissociation of hydrogen molecules on film surface, by direct donation of electron to film also took a major part in the sensitization. The effect of humidity on gas sensitization was found to be negligible at the sensor operating temperature of around $300^{\circ}C$.

• The Korean Journal of Ceramics
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• v.2 no.2
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• pp.83-88
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• 1996

Long term stability, sensitization in air, and gas sensing behaviors of tin oxide films were investigated with doping of antimony and palladium. The tin oxide films were prepared on a Corning glass by reactive rf sputtering method and tested for detection of hydrogen gas. Sb-doping improved a long-term stability in the base resistance of $SnO_2$ film sensor. A small amount of Pd doping caused the optimum sensor operating temperature to reduce and also enhanced the gas sensitivity, compared with the undoped $SnO_2$ film. Gas sensitivity depended largely on the film thickness. The important sensitization reactions for sensor operating were $(O_{2ads})+e^-\;{\rightarrow}\;2(O_{ads})^-$ on the surface of $SnO_2$ film at elevated temperature in air and a followed reaction of hydrogen atoms with $(O_{ads})^-$ ions.

• Journal of Sensor Science and Technology
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• v.25 no.3
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• pp.218-222
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• 2016

Pure and V-doped NiO porous structures were prepared by the evaporation-induced surfactant assembly and subsequent pyrolysis of assembled structures, and their gas sensing characteristics were investigated. Pure NiO porous structures showed negligible gas responses (S=$R_g/R_a$, $R_g$: sensor resistance in analytic gas; $R_a$: sensor resistance in air) to 5 ppm trimethylamine (S=1.17) as well as other interfering gases such as ethanol, p-xylene, toluene, benzene and formaldehyde (S=1.02-1.13). In contrast, the V-doped NiO porous structures exhibited a high response and selectivity to 5 ppm trimethylamine (S=14.5) with low cross-responses to other interfering gases (S=4.0-8.7) at $350^{\circ}C$. The high gas response of V-doped NiO porous structures to trimethylamine was explained by electronic sensitization, that is, the increase in the chemoresistive variation due to the decrease in the hole concentration. The enhanced selectivity to trimethylamine was discussed in relation to the interaction between basic trimethylamine gas and acidic V catalysts.

• Journal of the Korean Society for Heat Treatment
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• v.13 no.5
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• pp.337-345
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• 2000

As a case hardening process for stainless steels, nitriding is more preferred and widely used than carburizing which deterioates corrosion resistance severely. In order to add the nitrogen into the stainless steels, passive film on the surface must be removed effectively before nitriding. Conventional gas nitriding process is performed in the temperature range of 500 to $600^{\circ}C$ with $NH_3$ gas, which often leads to sensitization of stainless steels. In this study, we tried to activate passive film of austenitic stainless steels by heating at low pressure. ($900^{\circ}C$, $5{\times}10^{-2}$ Torr.) Nitriding was performed at the solution treatment temperature of $1100^{\circ}C$ with nitrogen molecules instead of $NH_3$ gas. An attainable nitrogen content in a case depends on the nitrogen gas pressure at constant nitriding temperature. A case depth is proportional to the square root of solution time, which suggests that inward diffusion of nitrogen follows the Fick's 2nd law. Surface nitrogen atoms are dissolved as interstitial solutes, or precipitated in the form of MN, $M_2N$ nitrides, which increase the case hardeness. Dissolved nitrogen in the case enhances the cavitation resistance of austenitic stainless steels dramatically.

• Journal of Sensor Science and Technology
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• v.28 no.5
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• pp.271-276
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• 2019

Pure and 0.5, 1, 2, 5, and 10 at% of Mo-doped $Co_3O_4$ yolk-shell spheres were synthesized by ultrasonic spray pyrolysis of droplets containing Co nitrate, ammonium molybdate, and sucrose and their gas sensing characteristics to 5 ppm trimethylamine (TMA), ethanol, p-xylene, toluene, ammonia, carbon monoxide, and benzene were measured at $225-325^{\circ}C$. The sensor using pure $Co_3O_4$ yolk-shell spheres showed the highest response to p-xylene and very low response to TMA at $250^{\circ}C$, while the doping of Mo into $Co_3O_4$ tended to increase the overall responses of gas sensors. In particular, the sensor using 5 at% Mo-doped $Co_3O_4$ yolk-shell spheres exhibited the high response to TMA with low cross-responses to other interfering gases. The high response and selectivity of Mo-doped $Co_3O_4$ yolk-shell spheres to TMA are attributed to the electronic sensitization by higher valent Mo doping and acid-base interaction between TMA and Mo components.

• Proceedings of the Korea Institute of Fire Science and Engineering Conference
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• 2002.05a
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• pp.21-29
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• 2002

With regard to the personnel safety and other safety when the gas suppressants are discharged into the area where occupants exist, the short term and long term effects to the health of people are discussed mainly with the Carbon dioxide agent and Halon Replacement agents system. To gain the benefits of CO2 extinguishing systems while minimizing risk to people serious attention must be given to personnel safety in the design, installation, and maintenance of CO2 systems. Training of personnel is essential. A major factor in the use of a clean agent fire suppressant in a normally occupied area is toxicity. While all halocarbon agents are tested for long-term health hazards, the primary endpoint is acute or short-term exposure, The primary acute toxicity effects of the halocarbon agents described here are anesthesia and cardiac sensitization. For inert gases, the primary physiological concern is reduced oxygen concentration.

• Journal of Sensor Science and Technology
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• v.27 no.2
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• pp.132-136
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• 2018

We report the development of a room-temperature hydrogen ($H_2$) gas sensor based on carbon nanotubes (CNT) yarn. To detect $H_2$ gas in room temperature, a highly ordered CNT yarn was placed on a substrate from a spin-capable CNT forest, followed by the deposition of a platinum (Pt) layer on surface of the CNT yarn. To examine the effect of the Pt-layer on the response of the CNT sensor, a comparative sensing performance was characterized on both the Pt deposited and non-deposited CNT yarn at room temperature. The Pt-CNT yarn yielded high response, whereas the non-deposited CNT yarn showed negligible response for $H_2$ detection at room temperature. Pt is a reliable and efficient catalyst that can substantially improve the detection of $H_2$ gas by chemical sensitization via a "spillover" effect. It can be efficiently utilized to increase the sensitivity and selectivity as well as to obtain fast response and recovery times.

• Korean Journal of Materials Research
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• v.26 no.12
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• pp.741-750
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• 2016

Nanofibers(NFs), because of their high surface area and nanosized grains, have appropriate morphologies for use in chemiresistive-type sensors for gas detection applications. In this study, a highly sensitive and selective CO gas sensing material based on Au-decorated $SnO_2$ NFs was fabricated by electrospinning. $SnO_2$ NFs were synthesized by electrospinning and subsequently decorated with various amounts of Au nanoparticles(NPs) by sputtering; this was followed by thermal annealing. Different characterizations showed the successful formation of Au-decorated $SnO_2$ NFs. Gas sensing tests were performed on the fabricated sensors, which showed bell-shaped sensing behavior with respect to the amount of Au decoration. The best CO sensing performance, with a response of ~20 for 10 ppm CO, was obtained at an optimized amount of Au (2.6 at.%). The interplay between Au and $SnO_2$ in terms of the electronic and chemical sensitization by Au NPs is responsible for the great improvement in the CO sensing capability of pure $SnO_2$ NFs, suggesting that Au-decorated $SnO_2$ NFs can be a promising material for fabricating highly sensitive and selective chemiresistive-type CO gas sensors.

• Corrosion Science and Technology
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• v.15 no.5
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• pp.226-236
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• 2016

316L stainless steels have been widely used in many engineering fields, because of their high corrosion resistance and good mechanical properties. However, welding or aging treatment may induce intergranular corrosion and stress corrosion cracking etc. Since these types of corrosion are closely related to the formation of chromium carbide in grain boundaries, the alloys are controlled by methods such as the lowering of carbon content, solution heat treatment. This work focused on the intergranular corrosion mechanism of slightly-sensitized and Ultrasonic Nano-crystal Surface Modification (UNSM)-treated 316L stainless steel. Samples were sensitized for 1, 5, and 48 hours at $650^{\circ}C$ in $N_2$ gas atmosphere. Subsequently UNSM treatments were carried out on the surface of the samples. The results were discussed on the basis of the sensitization by chromium carbide and carbon segregation, the residual stress and grain refinement. Even though chromium carbide was not precipitated, the intergranular corrosion rate of 316L stainless steel was drastically increased with aging time, and it was confirmed that the increased intergranular corrosion rate of slightly-sensitized (not carbide formed) 316L stainless steel was due to the carbon segregation along the grain boundaries. However, UNSM treatment improved the intergranular corrosion resistance of aged stainless steels, and its improvement was due to the reduction of carbon segregation and the grain refinement of the outer surface, including the introduction of compressive residual stress.

• Journal of the Korean Physical Society
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• v.73 no.10
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• pp.1444-1451
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• 2018

The surface-to-volume ratio of one-dimensional (1D) semiconductor metal-oxide sensors is an important factor for achieving good gas sensing properties because it offers a wide response area. To exploit this effect, in this study, we determined the optimal calcination temperature to maximize the specific surface area and thereby the sensitivity of the sensor. The $In_2O_3$ nanorods were synthesized by using vapor-liquid-solid growth of $In_2O_3$ powders and were decorated with the Pt nanoparticles by using a sol-gel method. Subsequently, the Pt nanoparticle-decorated $In_2O_3$ nanorods were calcined at different temperatures to determine the optimal calcination temperature. The $NO_2$ gas sensing properties of five different samples (pristine uncalcined $In_2O_3$ nanorods, Pt-decorated uncalcined $In_2O_3$ nanorods, and Pt-decorated $In_2O_3$ nanorods calcined at 400, 600, and $800^{\circ}C$) were determined and compared. The Pt-decorated $In_2O_3$ nanorods calcined at $600^{\circ}C$ showed the highest surface-to-volume ratio and the strongest response to $NO_2$ gas. Moreover, these nanorods showed the shortest response/recovery times toward $NO_2$. These enhanced sensing properties are attributed to a combination of increased surface-to-volume ratio (achieved through the optimal calcination) and increased electrical/chemical sensitization (provided by the noble-metal decoration).