• Advanced Composite Materials
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• 제16권4호
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• pp.377-384
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• 2007

'Green' composites were fabricated from poly lactic acid (PLA) and bamboo fibers by using a conventional hot pressing method. The insulating properties of the PLA-bamboo fiber 'green' composites were evaluated by determination of the thermal conductivity, which was measured using a hot-wire method. The thermal conductivity values were compared with theoretical estimations. It was demonstrated that thermal conductivity of PLA-bamboo fiber 'green' composites is smaller than that of conventional composites, such as glass fiber reinforced plastics (GFRPs) and carbon fiber reinforced plastics (CFRPs). The thermal conductivity of PLA-bamboo fiber 'green' composites was significantly influenced by their density, and was in fair agreement with theoretical predictions based on Russell's model. The PLA-bamboo fiber composites have low thermal conductivity comparable with that of woods.

• 한국재료학회지
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• 제22권10호
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• pp.531-538
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• 2012

Hollow silica spheres were prepared by spray drying of precursor solution of colloidal silica. The precursor solution is composed of 10-20 nm colloidal silica dispersed in a water or ethanol-water mixture solvent with additives of tris hydroxymethyl aminomethane. The effect of pH and concentrations of the precursor and additives on the formation of hollow sphere particles was studied. The spray drying process parameters of the precursor feeding rate, inlet temperature, and gas flow rate are controlled to produce the hollow spherical silica. The mixed solvent of ethanol and water was preferred because it improved the hollowness of the spheres better than plain water did. It was possible to obtain hollow silica from high concentration of 14.3 wt% silica precursor with pH 3. The thermal conductivity and total solar reflectivity of the hollow silica sample was measured and compared with those values of other commercial insulating fillers of glass beads and $TiO_2$ for applications of insulating paint, in which the glass beads are representative of the low thermal conductive fillers and the $TiO_2$ is representative of infrared reflective fillers. The thermal conductivity of hollow silica was comparable to that of the glass beads and the total solar reflectivity was higher than that of $TiO_2$.

• 한국기계기술학회지
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• 제20권6호
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• pp.763-769
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• 2018

In this research, in order to improve the heat retention of greenhouse, comparative analysis of the heat flux of the marketed multi-later insulating curtain was carried out. Experiments is conducted by fabricating a test apparatus for investigating the heat flux characteristics. The multi-later insulating curtain used for the experiment was compared using the P, N, S, U and T company, which are commercially available, and the heat flux due to temperature difference between the experimental apparatus and the outside was compared and analyzed. When the internal temperature of the experimental result is the maximum temperature $60^{\circ}C$, the heat flux of multi-later insulating curtain is T Co.($73.1W/m^2$) > S Co.($119.5W/m^2$) > U Co.($155W/m^2$) > N Co.($163.1W/m^2$) > P Co.($177.7W/m^2$). The heat flux means the quantity of heat passing through the unit time per unit area, and the higher the numerical value, the higher the quantity of heat passing through the multi-layer insulating curtain. This can be determined that high heat fluxes produce low heat resistance. Further, it has been found that the weight of the insulating curtain is largely unrelated to the heat insulating property, and the heat insulating curtain having a thickness containing a high internal air layer is excellent in the heat insulating property. In the future when manufacturing a heat insulating curtain, It is judged that it is desirable to manufacture a combination of heat insulating materials that contain a high internal air layer content and that can maintain the air layer even for long-term use while minimizing the volume.

• 공업화학
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• 제26권1호
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• pp.59-66
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• 2015

본 연구는 유기계 보온단열재의 장점인 경량성과 연질특성을 갖는 무기계 보온단열재의 제조를 위한 새로운 개념의 무기질 저온 발포 공정에 관한 것이다. 새로운 무기질 발포 공정은 섬유상인 해포석 및 규산알루미늄으로 하여금 발포체의 골격을 형성토록 하고, 저온에서 기체 발생이 가능한 발포제를 사용하여 무기질 섬유상 골격체가 팽창되어 공동을 형성하게 하며, 이 형성된 공동 속에 낮은 열전도도를 갖는 무기질 다포체인 팽창진주암을 채우는 것이다. 총괄적으로 무기질 재료를 고온 용융함이 없이 저온에서 무기질 발포체의 제조가 가능하게 된다. 이를 위해서 섬유상인 해포석의 해섬처리과정, 발포를 위한 섬유상 슬러리의 열처리공정 등 다양한 준비공정이 필요하며, 열처리 전 슬러리의 최적 조성물 조건이 요구된다. 제조된 발포체는 경량, 연질의 보온단열재로서의 겉보기 밀도, 내력 강도, 굽힘강도, 고내열성 등의 물성을 보여주었다.

• Journal of Electrical Engineering and Technology
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• 제10권4호
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• pp.1712-1719
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• 2015

In recent days, there was a significant development on the electrical, thermal, mechanical, physical, chemical, magnetic and optical properties of the polyamide enamel, varnish and other insulating materials by the addition of nano fillers to it. Enamel was used in High Voltage Apparatuses used in Medical Electronics as insulation. Insulating materials determine the life time of the electrical apparatuses. The life time of the insulating materials was improved by the addition of nano fillers to it. Hence the life time of the electrical apparatuses was improved by the mixing of nano fillers to the enamel. In this research, the basic dielectric properties of the enamel and enamel mixed with nano composites of silica and alumina were analyzed and compared with each other. The addition of nano fillers has improved the quality factor and capacitance of the enamel. It was also observed that the addition of nano fillers has reduced the dissipation factor and dielectric losses of the enamel. Heat produced by the dielectric losses was also reduced by adding nano fillers to it.

• E2M - 전기 전자와 첨단 소재
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• 제10권8호
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• pp.800-806
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• 1997

The behavior of de levels in rapid thermal annealed Fe-doped semi-insulating InP(100) was studied by photoinduced current transient spectrocopy(PICTS). In bulk InP, T2(Ec-0.24 eV), T3(Ec-0.30 eV) and T5(Ec-0.62 eV) traps were observed. After annealing the T2 trap was annihilated at 20$0^{\circ}C$ and recreated at 35$0^{\circ}C$. T3 trap was not affected below 40$0^{\circ}C$. With increasing temperature the concentration of T5 trap reduced and it was annihilated at 30$0^{\circ}C$. However the T1(Ec-0.16 eV) and T4(Ec-0.42 eV) traps were began to appear at 40$0^{\circ}C$and these concentrations were increased with annealing temperature. The T1 and T4 traps seem to be related to the isolated phosphorus vacancy( $V_{p}$) and $V_{p}$-indium antisite( $V_{p}$- $P_{in}$ ) or $V_{p}$-indium interstitial( $V_{p}$-I $n_{I}$) respectiely.respectiely.

• 한국표면공학회지
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• 제31권1호
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• pp.12-23
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• 1998

The Thermal Barrier Coating(TBC) has been used to improve the heat barrier and tribological properties of the aircraft engine and the automobile engine in high temperature. Especially, the high temperature tribological propertied of the cylinder haed and the piston crown of diesel engine was emphasized. Therefore, the purpose of this work was to evaluate the microstructure, tribological propeer in high tempearmal shock resistance and bonding strength of five layer functionally gradient TBC for the applications. The five layerwere composed with 100% ceramic insulating later, 75(ceramic):25 (metal) layer, 50:50 layer, 25:75 layer and 100% metal bonding layer to redude the thermal stress. the YSL and MSL poweders were the insulation ceramics powers. The NiCrAly, Inconel625 and SUS powders were the bonding and mixingg powders for plasma spray process. According to the result of high temperature wear test, the wera resistance of YSZ/NiCrAlY siytem was most out standing at 600 and $800^{\circ}C$. At $400^{\circ}C$, the wear resistance of YSZ/Inconel system was better than others. Wear volume at other temperature because of the low temperature degration of zirconia. The thermal shock mechanism of 5 later is the vertical crack gegration in insulating layer. this means that the initial cracks were generated in the top layer, and then developed into the composite layers during thermal shock test. Finally, these cracks werereached to the interface of coating and substrate and also, these vertioal cracks join with the horizontal cracks of the each layers. The bonding strength of YSZ/NiCrAlY and YSZ/Inconel 5 layer system is better than other 5layer systems. The theramal shock resistance of thermal barrier coating s with 5 layer system is better than that of 3 layers and 2 layers.

• 한국세라믹학회지
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• 제56권5호
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• pp.468-473
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• 2019

This study focused on manufacturing an inorganic insulation material set with various amounts of calcium-sulfoaluminate (CSA) (hauyne) content for enhancing both workability (demolding, handling) and the high thermal insulating property. To carry out the experiment, the amounts of CSA utilized were 5%, 10%, 15%, and 20%, with anhydrous gypsum added in equal proportion to produce a stable formation. As the content of CSA increased, a sinking phenomenon occurred because of the hydration reaction from the slurry, so it was difficult to utilize a retarder normally used in the cement manufacturing process. However, an RCOOM surfactant was able to solve the local clumping problem from cement and CSA and obtain a rapid retarding effect, so it was included in this process at 0.3%. Furthermore, the cement fineness was not 7000 ㎠/g but rather 3300 ~ 4000 ㎠/g to prevent a rapid temperature increase in the slurry. The specific gravity of the sample manufactured with 20% CSA was approximately 0.11 g/㎤, and its thermal conductivity was 0.041 W/m·K, providing an excellent insulating property.

• 한국재료학회지
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• 제17권9호
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• pp.493-499
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• 2007

Oil-based nanofluids were prepared by dispersing nonconducting fibrous $Al_2O_3$ and spherical AlN nanoparticles in transformer oil. In this study, the effects of wet grinding and surface modification of particles on thermal and electrical properties of nanofluids were investigated. Grinding experiments were conducted with high-speed bead mill and ultrasonic homogenizer and nanoparticles were surface modified by oleic acid and polyoxyethylene alkyl acid ester(PAAE) in n-hexane or transformer oil, at the same time. It is obvious that the combination of nanoparticle, dispersant and dispersion solvent is very important for the dispersity of nanofluids. For nanofluids containing 1.0vol.% AlN particles in transformer oil, the enhancement of thermal conductivity was 11.6% compared with pure transformer oil. However, the electric-insulating property of AlN nanofluids was very low due to used dispersant itself. Therefore, the effect of the dispersant on thermal/electrical/physical properties of the transformer oil should be considered before selecting a proper dispersant.

• 한국전기전자재료학회논문지
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• 제16권12호
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• pp.1136-1141
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• 2003

The primary insulation materials used in an oil filled transformer are kraft paper, wood, porcelain and oil. Modern transformers use chemically treated paper to improve its tensile strength and resistance to aging caused by immersion in oil. But these insulation papers are mainly aged by thermal stress. Over the life time of the insulation paper and oil, it is exposed to high temperatures, oxygen and water. Its interaction with the steel of the tank and core plus the copper and aluminium of the windings will eventually cause the chemical properties of the oil to decay. High temperature have an effect on mechanical strength of cellulous paper used in the layer insulation. We made two aging cells in which insulation papers and mineral oil are conducted to test thermal properties. It is measured dielectric strength, number of acid, moisture, etc. of insulation paper and oil aged in the aging cells.