• 한국재료학회지
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• 제30권4호
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• pp.155-159
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• 2020

Nanoporous silica aerogel insulation material is both lightweight and efficient; it has important value in the fields of aerospace, petrochemicals, electric metallurgy, shipbuilding, precision instruments, and so on. A theoretical calculation model and experimental measurement of equivalent thermal conductivity for nanoporous silica aerogel insulation material are introduced in this paper. The heat transfer characteristics and thermal insulation principle of aerogel nano are analyzed. The methods of SiO₂ aerogel production are compared. The pressure range of SiO₂ aerogel is 1Pa-atmospheric pressure; the temperature range is room temperature-900K. The pore diameter range of particle SiO₂ aerogel is about 5 to 100 nm, and the average pore diameter range of about 20 ~ 40 nm. These results show that experimental measurements are in good agreement with theoretical calculation values. For nanoporous silica aerogel insulation material, the heat transfer calculation method suitable for nanotechnology can precisely calculate the equivalent thermal conductivity of aerogel nano insulation materials. The network structure is the reason why the thermal conductivity of the aerogel is very low. Heat transfer of materials is mainly realized by convection, radiation, and heat transfer. Therefore, the thermal conductivity of the heat transfer path in aerogel can be reduced by nanotechnology.

• Nuclear Engineering and Technology
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• 제56권4호
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• pp.1385-1397
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• 2024

Bentonite is a recommended material for the multiple barriers in the final disposal of low-level radioactive waste (LLW) to prevent groundwater intrusion and nuclear species migration. However, after drying-wetting cycling during the repository construction stage and ion exchange with the concrete barrier in the long-term repository, the bentonite mechanical behaviors, including swelling capacity and hydraulic conductivity, would be further influenced by the groundwater intrusion, resulting in radioactive leakage. To comprehensively examine the factors on the mechanical characteristics of bentonite, this study presented scenarios involving MX-80 and KV-1 bentonites subjected to drying-wetting cycling and accelerated ion migration. The experiments subsequently measured free swelling, swelling pressure, and hydraulic conductivity of bentonites with intrusions of seawater, high pH, and low pH solutions. The results indicated that the solutions caused a reduction in swelling volume and pressure, and an increase in hydraulic conductivity. Specifically, the swelling capability of bentonite with drying-wetting cycling in the seawater decreased significantly by 60%, while hydraulic conductivity increased by more than three times. Therefore, the study suggested minimizing drying-wetting cycling and preventing seawater intrusion, ensuring a long service life of the multiple barriers in the LLW repository.

• 오토저널
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• 제12권4호
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• pp.75-82
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• 1990

To study on the behavior of the early stage of the spark kernel at constant pressure condition, the expressions of the thermal properties such as compressibility factor, thermal conductivity, and electrical conductivity of the high temperature air were newly suggested. The newly suggested simple expressions of the thermal properties of the high temperature air showed good results. Under the assumption of constant pressure, one dimensional numerical analysis was executed by varying surrounding conditions and discharging current of electrical spark. Numerical results show tat high surrounding pressure suppresses the growth of the spark kernel but supplies much electrical energy into the air, on the other hand high surrounding temperature increases the growth of the spark kernel but supplies less electrical energy. Also the result shows that , in case of direct current discharge, deposited electrical energy is able to be expressed in linear function of time approximately.

• 한국축산식품학회지
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• 제35권5호
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• pp.630-637
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• 2015

In the dairy industry, natural plant-based powders are widely used to develop flavor and functionality. However, most of these ingredients are water-insoluble; therefore, emulsification is essential. In this study, the efficacy of high pressure homogenization (HPH) on natural plant (chocolate or vanilla)-based model emulsions was investigated. The particle size, electrical conductivity, Brix, pH, and color were analyzed after HPH. HPH significantly decreased the particle size of chocolate-based emulsions as a function of elevated pressures (20-100 MPa). HPH decreased the mean particle size of chocolate-based emulsions from 29.01 μm to 5.12 μm, and that of vanilla-based emulsions from 4.18 μm to 2.44 μm. Electrical conductivity increased as a function of the elevated pressures after HPH, for both chocolate- and vanilla-based model emulsions. HPH at 100 MPa increased the electrical conductivity of chocolate-based model emulsions from 0.570 S/m to 0.680 S/m, and that of vanilla-based model emulsions from 0.573 S/m to 0.601 S/m. Increased electrical conductivity would be attributed to colloidal phase modification and dispersion of oil globules. Brix of both chocolate- and vanilla-based model emulsions gradually increased as a function of the HPH pressure. Thus, HPH increased the solubility of plant-based powders by decreasing the particle size. This study demonstrated the potential use of HPH for enhancing the emulsification process and stability of the natural plant powders for applications with dairy products.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2000년도 춘계학술발표대회 논문집
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• pp.190-194
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• 2000

The fabrication process and thermal properties of 50∼76vo1% SiCp/Al metal matrix composites (MMCs) were investigated. The 50∼76vo1% SiCp/Al MMCs fabricated by pressure infiltration casting process showed that thermal conductivities were 85∼170W/mK and coefficient of thermal expansion (CTE) were ranged 10∼6ppm/K. Specially, the thermal conductivity and CTE of 71vo1%SiCp/Al MMCs were ranged l15∼156W/mK and 6∼7ppm/K, respectively, which showed a improved thermal properties than the conventional electronic packaging materials such as ceramics and metals.

• 센서학회지
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• 제13권4호
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• pp.316-320
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• 2004

The possibility to use powder consisting of fullerite microcrystallines as a device sensitive to the external axial mechanical load is considered. We suppose that the change of conductivity of fullerite microcrystalline powder as a function of external mechanical stress will be useful for the creation of nanoscale devices of sensor electronics. This new effect based on changing of intermolecular distance between fullerene molecules due to the action of external mechanical force, which can change the distance between fullerene molecules because of weak van der Waals interaction exists. The founded effect is quite linear and sensitive to external mechanical stress is better then in well-known pressure transducers is based on silicon technology.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2001년도 하계학술대회 논문집
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• pp.729-732
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• 2001

In this study, the effect of oxygen partial pressure on the electrical properties of vanadium oxide(VO$_{x}$) thin films were investigated. The thin films were prepared by r.f. magnetron sputtering from V$_2$O$_{5}$ target in a gas mixture of argon and oxygen. The oxygen partial pressure ratio is changed from 0% to 8%. I-V characteristics were distinguished between linear and nonlinear region. In the low field region the conduction is due to Schottky emission, while at high fields it changes to Fowler-Nordheim tunneling type conduction. The conductivity measurements have shown an Arrhenius dependence of the conductivity on the temperature.ure.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part2
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• pp.922-923
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• 2006

Thermal management is one of the critical aspects in the design of highly integrated microelectronic devices. The reliability of electronic components is limited not only to operating temperature but also by the thermal stresses caused during the operation. The need for higher power densities calls for use of advanced heat spreader materials. A copper diamond composite has been developed with high thermal conductivity $(\lambda)$ and tailorable coefficient of thermal expansion (CTE). Copper diamond composites are processed via gas pressure assisted infiltration with different copper alloys. Emphasis has been placed on the addition of trace elements in deisgning the copper alloys to facilitate a compromise between thermal conductivity and mechanical adhesion. The interfaces between the alloy and the diamond are related to the thermal properties of these copper composites.

• Bulletin of the Korean Chemical Society
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• 제7권5호
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• pp.341-346
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• 1986

The electrical conductivity of the system ${\alpha}-Fe_2O_3-CoO$ was measured in the temperature range 200-1000$^{\circ}C$ and PO$_{2}$ range 10$^{-7}-2{\times}10^{-1}$ atm. Possible defect models were suggested on the basis of conductivity data, which were measured as a function of temperature and of oxygen partial pressure. The observed activation energies were 0.50 eV and 1.01 eV in the low- and high-temperature regions, respectively. The observed conductivity dependences on PO$_{2}$ were ${\sigma}\;{\alpha}\;PO_2^{-1/6}$ in the PO$_{2}$ range $10^{-7}-10^{-4}$ atm and ${\sigma}\;{\alpha}\;PO_2^{-1/4}$ at PO$_{2}$ 's of $10^{-4}-2{\times}10^{-1}$ atm at temperatures from 300-1000$^{\circ}C$. An extrinsic electron conduction due to an Vo defect and an intrinsic electron conduction due to an Fei' defect were suggested at different temperature and oxygen partial pressure regions, respectively.

• 센서학회지
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• 제33권1호
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• pp.7-11
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• 2024

Soft-pressure sensors have numerous applications in soft robotics, biomedical devices, and wearable smart devices. Herein, we present a highly sensitive electronic skin device with an isotropic wrinkled pressure sensor. A conductive ink for soft pressure sensors is produced by a solution process using polydimethylsiloxane (PDMS), poly 3-hexylthiophene (P3HT), carbon black, and chloroform as the solvents. P3HT provides high reproducibility and conductivity by improving the ink dispersibility. The conductivity of the ink is optimized by adjusting the composition of the carbon black and PDMS. Soft lithography is used to fabricate a conductive elastic structure with an isotropic wrinkled structure. Two conductive elastic structures with an isotropic wrinkle structure is stacked to develop a pressure sensor, and it is confirmed that the isotropic wrinkle structure is more sensitive to pressure than when two elastic structures with an anisotropic wrinkle structure are overlapped. Specifically, the pressure sensor fabricated with an isotropic wrinkled structure can detect extremely low pressures (1.25 Pa). Additionally, the sensor has a high sensitivity of 15.547 kpa^-1 from 1.25 to 2500 Pa and a linear sensitivity of 5.15 kPa^-1 from 2500 Pa to 25 kPa.