• Journal of Sensor Science and Technology
• /
• v.33 no.5
• /
• pp.237-241
• /
• 2024

ZnWO₄-WO₃ hetero-composite microspheres were prepared by ultrasonic spray pyrolysis of a solution containing Zn and W cations, followed by heat treatment at 600℃. The gas-sensing characteristics of 5 at% of Zn-added WO₃ (5Zn-WO₃; ZnWO₄-WO₃ hetero-composite) microspheres to 1 ppm acetone, ethanol, 20 ppm hydrogen (H₂), 5 ppm carbon monoxide (CO), 25 ppb toluene, and 5 ppm ammonia (NH₃) were measured at 325-400℃ under 80% relative humidity (RH). The sensor using 5Zn-WO₃ microspheres exhibited highly selective and sensitive gas-sensing properties to acetone at 375℃ even under high humidity conditions. These superior gas-sensing properties were attributed to the increased resistance (electronic sensitization) through n-n heterojunction formation between WO₃ and ZnWO₄ phases and the acidic property of WO₃, which exhibited a low gas response to interfering ethanol gas. The superior acetone gas-sensing characteristics of the 5Zn-WO₃ sensor can be utilized in breath acetone analyzers for rapid, real-time ketogenic diet monitoring.

• Journal of Biosystems Engineering
• /
• v.25 no.6
• /
• pp.481-488
• /
• 2000

This study was initiated in order to find alternative fuel substituting for light oil the most common fuel for heating greenhouse. The tire oil used in this research was produced by pyrolysis process, one of the final products besides steel string and carbon black in which waste tires as a form of chopped pieces broken by shredding machine are heated up to 200~30$0^{\circ}C$ with maximum restraining of oxygen supply. In order to justify light oil equivalent qualities in tire oil combustion characteristics were defined in the way of comparing kinetic viscosities in the wide range of temperature flame sizes and exhaust gas components in the various combustion conditions. We found that kinetic viscosity of tire oil was lower than light oil by 1 to 2 cSt in the temperature range showing better flowing mobility in the fuel line of the burner and no significant difference in flame size between the two oils in the all combustion treatments. However much more NO and SO$_2$ were detected from the exhaust gases of tire oil than light oil combustions. In fact tire oil contains more nitrogen and total sulfur, by 25 times and 40 times respectively than light oil according to the composition analysis. Tolerable limit for SO$_2$discharge amount defined by the national air pollution standards is under 540ppm so tire oil combustion satisfies the requirement though. It is desirable if sulfur and nitrogen filtering process shall be added in the tire oil production line. Except the exhaust gas components all greenhouse heating qualities of tire oil including hot air temperature are very identical to those of light oil.

• Journal of Sensor Science and Technology
• /
• v.30 no.4
• /
• pp.191-195
• /
• 2021

Pure ZnFe₂O₄ and Fe₂O₃-ZnFe₂O₄ hetero-composite spheres were prepared by ultrasonic spray pyrolysis of a solution containing Zn- and Fe-nitrates. Additionally, the sensing characteristics of these spheres in the presence of 5 ppm ethanol, benzene, p-xylene, toluene, and CO (within the temperature range of 275-350 ℃) were investigated. The Fe₂O₃-ZnFe₂O₄ hetero-composite sensor with a cation ratio of [Zn]:[Fe]=1:3 exhibited a high response (resistance ratio = 140.2) and selectivity (response to p-xylene/response to ethanol = 3.4) to 5 ppm p-xylene at 300 ℃, whereas the pure ZnFe₂O₄ sensor showed a comparatively lower gas response and selectivity. The reasons for the superior response and selectivity to p-xylene in Fe₂O₃-ZnFe₂O₄ hetero-composite sensor were discussed in relation to the electronic sensitization due to charge transfer at Fe₂O₃-ZnFe₂O₄ interface and Fe₂O₃-induced catalytic promotion of gas sensing reaction. The sensor can be used to monitor harmful volatile organic compounds and indoor air pollutants.

• Applied Chemistry for Engineering
• /
• v.34 no.4
• /
• pp.383-387
• /
• 2023

The quartz crystal microbalance (QCM), commonly used in high vacuum deposition, becomes difficult to use when a thick film is deposited on the quartz, affecting the crystal's inherent vibration. In this study, a non-destructive optical measurement method was developed to measure the film's deposition rate during the in-situ film deposition process. By measuring the scattered laser intensity caused by the dimer in the parylene gas passing through the gas flow path, it was successfully confirmed that the ratio of the dimer in the parylene gas increases as the pyrolysis temperature decreases. Additionally, it was noted that the film's thickness and haze increase as the pyrolysis temperature decreases by confirming the characteristics of the visible parylene films. Through the research results, we aim to utilize the stable in-situ film deposition rate measurement system to control the precise film deposition rate of parylene films.

• Membrane Journal
• /
• v.28 no.4
• /
• pp.221-232
• /
• 2018

The silica containing carbon ($C-SiO_2$) membranes were fabricated using poly(imide siloxane)(Si-PI) and polyvinylpyrrolidone (PVP) blended polymer. The characteristics of porous carbon structures prepared by the pyrolysis of polymer blends were related with the micro-phase separation behaviors of the two polymers. The glass transition temperatures ($T_g$) of the mixed polymer blends of Si-PI and PVP were observed with a single $T_g$ using differential scanning calorimetry. Furthermore, the nitrogen adsorption isotherms of the $C-SiO_2$ membranes were investigated to define the characteristics of porous carbon structures. The $C-SiO_2$ membranes derived from Si-PI/PVP showed the type IV isotherm and possessed the hysteresis loop, which was associated with the mesoporous carbon structures. For the molecular sieving probe, the $C-SiO_2$ membranes were prepared with the ratio of Si-PI/PVP and the pyrolysis conditions, such as the pyrolysis temperature and the isothermal times. Consequently, the $C-SiO_2$ membranes prepared by the pyrolysis of Si-PI/PVP at $550^{\circ}C$ with the isothermal time of 120 min showed the $O_2$ permeability of 820 Barrer ($1{\times}10^{-10}cm^3(STP)cm/cm^2{\cdot}s{\cdot}cmHg$) and $O_2/N_2$ selectivity of 14.

• Korean Journal of Environmental Agriculture
• /
• v.39 no.3
• /
• pp.171-177
• /
• 2020

BACKGROUND: Recently, biomass conversion from agricultural wastes to carbon-rich materials such as biochar has been recognized as a promising option to maintain or increase soil productivity, reduce nutrient losses, and mitigate greenhouse gas emissions from the agro-ecosystem. This experiment was conducted to select an optimum conditions for enhancing the NH₄-N adsorption capacity of rice hull activated biochar. METHODS AND RESULTS: For deciding the proper molarity of KOH for enhancing its porosity, biochars treated with different molarity of KOH (0, 1, 2, 4, 6, 8) were carbonized at 600℃ in the reactor. The maximum adsorption capacity was 1.464 mg g^-1, and an optimum molarity was selected to be 6 M KOH. For the effect of adsorption capacity to different carbonized temperatures, 6 M KOH-treated biochar was carbonized at 600℃ and 800℃ under the pyrolysis system. The result has shown that the maximum adsorption capacity was 1.76 mg g^-1 in the rice hull activated biochar treated with 6 M KOH at 600℃ of pyrolysis temperature, while its non-treated biochar was 1.17 mg g^-1. The adsorption rate in the rice hull activated biochar treated with 6 M KOH at 600℃ was increased at 62.18% compared to that of the control. Adsorption of NH₄-N in the rice hull activated biochar was well suited for the Langmuir model because it was observed that dimensionless constant (R_L) was 0.97 and 0.66 at 600℃ and 800℃ of pyrolysis temperatures, respectively. The maximum adsorption amount (q_m) and the bond strength constants (b) were 0.092 mg g^-1 and 0.001 mg L^-1, respectively, for the rice hull activated biochar treated with 6 M KOH at 600℃ of pyrolysis. CONCLUSION: Optimum condition of rice hull activated biochar was 6M KOH at 600℃ of pyrolysis temperature.

• Journal of the Korean Ceramic Society
• /
• v.31 no.1
• /
• pp.88-96
• /
• 1994

Hot filament-assisted CVD was carried out to deposit diamond films on Si(100) substrate at 90$0^{\circ}C$ using a 1% CH4-H2 mixture gas. Deposition was made at various conditions of mass flow rate of the feed gas (30~1000 sccm), pressure (2.5~300 Torr), and filament-substrate distance (4~15 mm), and the deposited films were characterized by SEM, XRD, and Raman spectroscopy. As the flow rate increases, the growth rate also increased but the crystallinity of the film was degraded. A longer filament-substrate distance simply caused both the growth rate and the crystallinity to become poorer. On the other hand, the pressure variation resulted in a maximum growth rate of 2.6 ${\mu}{\textrm}{m}$/hr at 10 Torr and the best film quality around 50 Torr, exhibiting an optimum condition. The observed trends were interpreted in terms of the flow velocity-dependent pyrolysis reaction efficiency and mass transport through the boundary layer.

• 한국연소학회:학술대회논문집
• /
• 2013.06a
• /
• pp.55-58
• /
• 2013

A new soot particle generation system has been developed and tested. The soot generation system consists of two sections, a fuel supply and a soot production. In the fuel supply module, either liquid fuel precisely controlled by a syringe pump is mixed with preheated carrier gas and rapidly evaporated or gaseous fuel controlled by a MFC is diluted with dilution gas. The soot production module contains a heater that can raise the gas/fuel temperature up to $1400^{\circ}C$. The physical and chemical properties of produced soot particles depend on the type and concentration of fuel, the residence time, and temperature in the soot production section. The soot generation system will be utilized to produce well-defined soot particles for soot studies such as the evaluation of experimental sampling and analysis processes for the quantitative assessment of PM and BC from ships and the adverse health effects on pulmonary and cardiovascular systems of human body.

• Journal of Energy Engineering
• /
• v.19 no.4
• /
• pp.240-245
• /
• 2010

In this study, characteristics of wood pellet gasification was studied using a Two Stage Gasifier which is consisted of pyrolysis reactor and ultra high temperature reformer. The average yields of $H_2$, $CH_4$, CO, $CO_2$ were 16.7, 11.3, 37.2, 26.6 L/mim, conversion rate from biomass to gas was 65% in pyrolysis reactor and gas yields in reformer were 55.4, 0.8, 120.8, 56.8 L/mim, respectively. The hydrogen flow rate from reformer is obtained 360.1 L/hr. The most of $CH_4$ was decomposed from 12.3 to 0.3 vol.% while $H_2$ is from 18.2 to 23.7 vol.% in reformer by methane dry reforming, Boudouard reaction, oxidation and/or steam reforming. The amount of $H_2O$ generated by hydration reaction from reformer was 1111.8 g, its accelerated conversion of $CH_4$ to other products. The conversion rate from $CH_4$ to other Compounds was 97.2%. Cold gas efficiency was 53.2%.

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