• Applied Chemistry for Engineering
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• v.31 no.3
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• pp.291-298
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• 2020

ZITO/Ag/ZITO multilayer transparent electrodes at room temperature on glass substrates were prepared using RF/DC magnetron sputtering. Transparent conductive films with a sheet resistance of 9.4 Ω/㎡ and a transmittance of 83.2% at 550 nm were obtained for the multilayer structure comprising ZITO/Ag/ZITO (100/8/42 nm). The sheet resistance and transmittance of ZITO/Ag/ZITO multilayer films meant that they would be highly applicable for use in polymer-dispersed liquid crystal (PDLC)-based smart windows due to the ability to effectively block infrared rays (heat rays) and thereby act as an energy-saving smart glass. Effects of the thickness of the PDLC layer and the intensity of ultraviolet light (UV) on electro-optical properties, photopolymerization kinetics, and morphologies of difunctional urethane acrylate-based PDLC systems were investigated using new transparent conducting electrodes. A PDLC cell photo-cured using UV at an intensity of 2.0 mW/c㎡ with a 15 ㎛-thick PDLC layer showed outstanding off-state opacity, good on-state transmittance, and favorable driving voltage. Also, the PDLC-based smart window optimized in this study formed liquid crystal droplets with a favorable microstructure, having an average size range of 2~5 ㎛ for scattering light efficiently, which could contribute to its superior final performance.

• Journal of Energy Engineering
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• v.25 no.4
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• pp.13-29
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• 2016

In this study, we analyzed the causes of major faults in the biogas plant through the case of gas engine failure when cogenerating electricity and heat using biogas as a fuel in the actual sewage treatment plant and suggested countermeasures. Hydrogen sulfide in the biogas entering the biogas engine and water caused by intermittent malfunction of the water removal system caused intercooler corrosion in the biogas engine. In addition, the siloxane in the biogas forms a silicate compound with silicon dioxide, which causes scratches and wear of the piston surface and the inner wall of the cylinder liner. The substances attached to the combustion chamber and the exhaust system were analyzed to be combined with hydrogen sulfide and other impurities. It is believed that hydrogen sulfide was supplied to the desulfurization plant for a long period of time because of the high content of hydrogen sulfide (more than 50ppm) in the biogas and the hydrogen sulfide was introduced into the engine due to the decrease of the removal efficiency due to the breakthrough point of the activated carbon in the desulfurization plant. In addition, the hydrogen sulfide degrades the function of the activated carbon for siloxane removal of the adsorption column, which is considered to be caused by the introduction of unremoved siloxane waste into the engine, resulting in various types of engine failure. Therefore, hydrogen sulfide, siloxane, and water can be regarded as the main causes of the failure of the biogas engine. Among them, hydrogen sulfide reacts with other materials causing failure and can be regarded as a substance having a great influence on the pretreatment process. As a result, optimization of $H_2S$ removal method seems to be an essential measure for stable operation of the biogas engine.

• Applied Chemistry for Engineering
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• v.19 no.5
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• pp.526-532
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• 2008

The proposed $CO_2$ storage technology in the present study is a one-step sequestration process that stabilizes $CO_2$ in a reactor with Serpentine. The advantage of this technology is associated with its high stability of final product so that the entire system is recognized as permanent environment-friendly $CO_2$ removal method. Since the sequestration reaction mechanisms are generally understood that carbonation reaction proceeds with very slow rate, so that pretreatment method to increases reaction rate of $CO_2$ carbonation reaction should be developed. To increase the reactivity of Serpentine with $CO_2$, two different methods of pretreatment are carried out in the present investigation. One is heat-treatment, the other is chemical pretreatment. In this study, only chemical pretreatment is considered leaching method of magnesium from Serpentine using sulfuric acid at the various reaction temperatures, times, and acid concentrations. Experimental results illustrated that pretreatment by sulfuric acid increases surface area of serpentine from $11.1209m^2/g$ to $98.7903m^2/g$ and extracts magnesium compounds. Single variable experiment demonstrated the enhancements of magnesium extraction with increased reaction temperature and time. Amount of magnesium extraction is obtained by using the data of ICP-AES as maximum extraction condition of magnesium is 2 M acid solution, $75^{\circ}C$ and 1hr. After performing chemical pretreatment, carbonation yield increased from 23.24% to 46.30% of weight.

• Journal of the Korean Wood Science and Technology
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• v.46 no.1
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• pp.73-84
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• 2018

Recently, the importance of flame retardation treatment technology has been emphasized due to the increase in urban fire accidents and fire damage incidents caused by building exterior materials. Particularly, in the utilization of wood-based building materials, the flame retarding treatment technology is more importantly evaluated. An Intumescent system is one of the non-halogen flame retardant treatment technologies and is a system that realizes flame retardancy through foaming and carbonization layer formation. To apply the Intumescent system, composite material was prepared by using Ethylene vinyl acetate (EVA) as a matrix. To enhance the flame retardant properties of the Intumescent system, a nano-clay was applied together. Composite materials with Intumescent system and nano - clay technology were processed into sheet - like test specimens, and then a new structure of cross laminated timber with improved flame retardant properties was fabricated. In the evaluation of combustion characteristics of composite materials using Intumescent system, it was confirmed that the maximum heat emission was reduced efficiently. Depending on the structure attached to the surface, the CLT had two stages of combustion. Also, it was confirmed that the maximum calorific value decreased significantly during the deep burning process. These characteristics are expected to have a delayed combustion diffusion effect in the combustion process of CLT. In order to improve the performance, the flame retardation treatment technique for the surface veneer and the optimization technique of the application of the composite material are required. It is expected that it will be possible to develop a CLT structure with improved fire characteristics.

• Applied Biological Chemistry
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• v.48 no.2
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• pp.109-114
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• 2005

A bacterium capable of emulsifying hydrocarbon, n-hexadecane, and decreasing surface tension of the culture media using oil collapsing method was isolated. The bacterium was partially identified as Bacillus sp. and named BJS-51. n-Hexadecane was the most effective carbon source for production of biosurfactant. Surface tension was decreased from 76 dyne/cm to 31 dyne/cm and CMD (critical micelle dilution) had the highest value of 5.7 at 3% n-hexadecane. Ammonium phosphate was the most effective nitrogen source, when C/N ratio was 60, surface tension and CMD were 29 dyne/cm and 9.2, respectively. Optimum pH and temperature were 7.2 and $30^{\circ}C$, respectively. Produced biosurfactant was extracted and purified using organic solvent extraction method and preparative HPLC systems. After analysis by various color reaction, this biosurfactant was identified as lipopolysaccharide. Surface tension and CMC (critical micelle concentration) of purified biosurfactant were 27 dyne/cm and 0.08 g/l, repectively. CMD was 9.2, so the yield of biosurfactant was about 0.74 g/l at the optimal conditions. The biosurfactant was very stable at wide range of $pH\;2{\sim}12$ with surface tension $29{\sim}31\;dyne/cm$ and showed $29{\sim}30\;dyne/cm$ of surface tension after heat treatment at $100^{\circ}C$ for 60 min.

• Applied Chemistry for Engineering
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• v.32 no.3
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• pp.326-331
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• 2021

In this study, the preparation conditions for a TiO₂-based vanadium-based catalyst for oxidizing hydrogen sulfide at room temperature were optimized. Four types of commercial TiO₂ were used as a catalyst support and the performance evaluation of hydrogen sulfide oxidation at room temperature of V/TiO₂ by varying vanadium contents prepared using the impregnation method was performed. Among the types of TiO₂ tested, it was confirmed that the catalyst with the vanadium content of 5% and based on TiO₂(A) has the best hydrogen sulfide conversion rate of 58%. By comparing the physical and chemical properties of the catalyst, the specific surface area of the support and the species of dominant vanadium are the major factor in catalyst performance. In order to confirm the regeneration characteristics of the catalyst with reduced activity, heat treatment was performed at 400 ℃ for 2 h, and the amount of hydrogen sulfide oxidation decreased by 10% due to the partial deposition of sulfur in the regenerated catalyst, but it was confirmed that the initial performance was similar.

• Journal of the Microelectronics and Packaging Society
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• v.30 no.4
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• pp.98-104
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• 2023

The feasibility of an efficient process proposed for Cu-Cu flip-chip bonding was evaluated by forming a porous Cu layer on Cu pillar and conducting thermo-compression sinter-bonding after the infiltration of a reducing agent. The porous Cu layers on Cu pillars were manufactured through a three-step process of Zn plating-heat treatment-Zn selective etching. The average thickness of the formed porous Cu layer was approximately 2.3 ㎛. The flip-chip bonding was accomplished after infiltrating reducing solvent into porous Cu layer and pre-heating, and the layers were finally conducted into sintered joints through thermo-compression. With reduction behavior of Cu oxides and suppression of additional oxidation by the solvent, the porous Cu layer densified to thickness of approximately 1.1 ㎛ during the thermo-compression, and the Cu-Cu flip-chip bonding was eventually completed. As a result, a shear strength of approximately 11.2 MPa could be achieved after the bonding for 5 min under a pressure of 10 MPa at 300 ℃ in air. Because that was a result of partial bonding by only about 50% of the pillars, it was anticipated that a shear strength of 20 MPa or more could easily be obtained if all the pillars were induced to bond through process optimization.