• Journal of Surface Science and Engineering
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• v.57 no.1
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• pp.8-13
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• 2024

Anodizing of Al6061 alloy was conducted in two different electrolytes of 20% sulfuric acid and 8% sulfuric acid + 3 % oxalic acid solutions at a constant current or decreasing current density conditions, and its dielectric breakdown voltage was measured. The surface morphology of anodic oxide films was observed by TEM and thermal treatment was carried out at 400 ℃ for 2 h to evaluate the resistance of the anodic oxide films to crack initiation. The anodic oxide film formed in 8% sulfuric acid + 3 % oxalic acid solution showed higher dielectric breakdown voltage and better resistance to crack initiation at 400 ℃ than that formed in 20% sulfuric acid solution. The dielectric breakdown voltage increased 6 ~12% by applying decreasing current density comparing with a constant current density.

• Nuclear Engineering and Technology
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• v.40 no.3
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• pp.233-238
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• 2008

This study investigates the surface modification of a Hastelloy X plate and diffusion bonding in the assembly of surface modified plates. These types of plates are involved in the key processes in the fabrication of a process heat exchanger (PHE) for a $SO_3$ decomposer. Strong adhesion of a SiC film deposited onto Hastelloy X can be achieved by a thin SiC film deposition and a subsequent N ion beam bombardment followed by an additional deposition of a thicker film that prevents the Hastelloy X surface from becoming exposed to a corrosive environment through the pores. This process not only produces higher corrosion resistance as proved by electrolytic etching but also exhibits higher endurance against thermal stress above 9$900^{\circ}C$. A process for a good bonding between Hastelloy X sheets, which is essential for a good heat exchanger, was developed by diffusion bonding. The diffusion bonding was done by mechanically clamping the sheets under a heat treatment at $900^{\circ}C$. When the clamping jig consisted of materials with a thermal expansion coefficient that was equal to or less than that of the Hastelloy X, sound bonding was achieved.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.25 no.11
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• pp.862-866
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• 2012

Surface passivation of AlGaN/GaN heterojunction structure was examined through the thermal oxidation of evaporated Al. The Al-oxide passivation increased channel conductance of two dimensional electron gas (2DEG) on the AlGaN/GaN interface. The sheet resistance of 463 ohm/${\Box}$ for 2DEG channel before $Al_2O_3$ passivation was decreased to 417 ohm/${\Box}$ after passivation. The oxidation of Al induces tensile stress to the AlGaN/GaN structure and the stress seemed to enhance the sheet carrier density of the 2DEG channel. In addition, the $Al_2O_3$ films formed by thermal oxidation of Al suppressed thermal deterioration by the high temperature annealing.

• Progress in Superconductivity and Cryogenics
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• v.6 no.4
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• pp.17-21
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• 2004

The butt joint was verified to satisfy the thermal stability of the ITER magnet system through the ITER CS model coil test. Since the contact area in the butt joint is limited to the cross section of the cable, it is necessary to analyze and control the joining parameters precisely for improving the DC resistance. It is difficult to simulate the cables, which are composed of a lot of strands, as three-dimensional models using the commercial code. The random numbers were used to simulate many kinds of contact patterns of the strands on the bonding surface for calculating the bonding area and the DC resistance of the butt joint. The calculated DC resistance decreases with an increase of cable filling factor in terminal. The calculated DC resistance of a 0.9 cable filling factor is about 0.48 n-Ohm, which is about one-tenth of that in the CS model coil test when not considering the electrical contact resistance. From this difference, the electrical contact resistance between the strands and copper sheet was calculated.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2023.05a
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• pp.301-302
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• 2023

In this study, we aimed to identify changes in fire resistance according to the type of sleeves used for pipe penetrations and to examine their accreditation of fire resistance performance and use them as basic data. The test results of fire resistance according to the type of sleeve used in non-metallic pipe facilities showed that the temperature on the support side was higher for sleeves with higher thermal conductivity. For the temperature on the surface of the pipes, in the case of galvanized steel plates, steel pipes, and structures without sleeves, the highest temperature was observed after the expansion of the firestop material for 46 to 53 minutes and then decreased. PVC sleeves showed a steady increase in temperature until 53 minutes, after which the temperature did not increase further. In addition, for non-metallic pipes, the effect of the type of sleeve on fire resistance is considered to be insignificant because the lower part (heating direction of the furnace) under the support structure is cut off to block the heat during the two-hour fire resistance test.

• Journal of the Korean Solar Energy Society
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• v.35 no.1
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• pp.61-68
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• 2015

The advanced counties effort to the supplement of the zero energy buildings for the global building energy saving. In the middle of the development of passive technology, the government has to effort to the energy saving of buildings by enhanced performance of the window thermal insulation. By the method of enhanced performance of window thermal insulation, the use of vacuum double glazing saves the energy consumption in building. This glazing has low U-value(heat transmission coefficient) than normal double glazing. The vacuum glazing enhanced thermal insulation performance by vacuum space of between the glass and glass. For this vacuum glazing, pillar maintain the space between glass and glass. But this structure cause the raising the heat transmission coefficient in pillar approaching glass. This study confirmed the U-value by the test method of thermal resistance for windows and doors. Also this study confirmed the variation of heat transmission coefficient by the structure of vacuum glazing. And this study measured the surface temperature of the vacuum glazing about pillar approaching glass and vacuum space in cool chamber and hot box. That result, this study confirmed U-value of $0.422W/m^2{\cdot}K$ of vacuum glazing. Also this study confirmed U-value of $0.300{\sim}0.422W/m^2{\cdot}K$ by various the structure of vacuum glazing. And this study confirmed the heat flow in pillar approaching glass.

• Nuclear Engineering and Technology
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• v.54 no.3
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• pp.975-983
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• 2022

A four-layered W/Cu functionally graded material (FGM) (W90% + Cu10%/W80% + Cu20%/W70% + Cu30%/W60% + Cu40%, wt.% fraction) and a four-layered diamond/W-Cu FGM (W90% + Cu10%/W80% + Cu20%/W70% + Cu30%/W55% + Cu40% + diamond5%, wt.% fraction) were fabricated by microwave sintering. The thermal conductivity and thermal shock resistance of diamond/W-Cu FGM and W-Cu FGM were investigated. The morphologies of the diamond particles and different FGMs were analyzed using AFM, SEM, EDS, and TEM. The results show that a 200 nm rough tungsten coating was formed on the surface of the diamond. The density of the tungsten-coated diamond/W-Cu FGM, obtained by microwave sintering at 1200 ℃ for 30 min, was 94.66%. The thermal conductivity of the fourlayered diamond/W-Cu FGM was 220 W·m^-1·K^-1, which is higher than that of the four-layered W/Cu FGM (209 W m^-1 K^-1). This indicates that adding an appropriate amount of tungsten-coated diamond to the high Cu layer W/Cu FGM improves the thermal conductivity of the composite. The diamond/W-Cu FGM sintered at 1200 ℃ for 10 min exhibited better thermal shock resistance than diamond/W-Cu FGM sintered at 1100 ℃ for 10 min.

• Journal of the Korean Chemical Society
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• v.45 no.4
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• pp.341-350
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• 2001

Aluminum Hydroxide was employed as a thermal retardent and flame retardent for Chloropolyethylene (CPE) rubbery materials which is the construction material of automotive oil cooler hose. and then cure characteristics, physical properties, thermal resistance and flame retardation of compounded rubber were investigated, and optimum mixing conditions of rubber and flame retarding agent were deduced from the experimental results. CPE rubber material which has excellent properties of chemical corrosion resistance and cold resistance and inexpensive in price was used to prepare rubber specimen. The by-product of ething, produced from the process of surface treatment of aluminum was processed to aluminum hydroxide via crushing and purification, which is characterized by XRD, PSA, SEM and ICP-AES techniques in terms of phase, size, distribution, morphology and components of particles and then mixed to CPE rubber materials in the range of 0~80 phr. Hardness, tensile strength, elongation and thermal properties of compounded rubber specimens were tested. The optimum mixing ratio of rubber to additives to give maximum effect on thermal resistance and flame retardation, within the range of tolerable specification for rubber materials, was determined to be 40 phr. The flame retardation of CPE rubber materials was found to be increased by 5 times at this mixing ratio.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.7 s.238
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• pp.805-813
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• 2005

The thermal performance of a flat-strip heat pipe with inner grooves and the screen mesh cover was investigated experimentally. The heat pipes were made of 2024 aluminum alloy of which the dimensions were 30 (W) $\times$ 4 (T) $\times$ 150 (L) mm. The cross sectional dimensions of inner groove were 0.4$\times$0.9 mm and the space between grooves was 0.6 mm. To enhance the capillary force, foe screen meshes were attached to cover the grooved inner surface. In the grooved heat pipes without screen mesh cover, the maximum thermal load of 180 W (12 W/$cm^2$) was achieved for operating temperature below $130^{\circ}C$ at horizontal position. The heat pipes with screen mesh cover showed the thermal resistances less than one third of those without screen mesh cover, and showed less fluctuation in the thermal resistance values. Furthermore, the thermal performance of the former exhibited less dependence on the tilt angle and the fill charge ratio.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.22 no.2
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• pp.103-114
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• 2012

Nowadays membrane material is widely used for large indoor spaces and long spaces such as traditional market. Thermal insulation and sound field control performance is considered as a main properties for design of such buildings. In this paper sound absorption and thermal insulation properties of membrane material was investigated. Firstly, normal incidence sound absorption coefficient of 10 kinds of glass wool textiles showed that sound absorption coefficient was increased in proportion of thickness and surface density of textile. Sound absorption coefficient of 4 kinds of sound absorptive inner membrane with outer membrane was tested in the reverberation chamber. Sound absorption coefficient of mid frequency range was about 0.4 ~ 0.6. Also, sound absorption coefficient was changed by the air space behind the membrane material. Secondly, sound field control performance was investigated using mock-up space. By the installation of sound absorption membrane material, reverberation time was decreased and speech intelligibility was increased. Finally, thermal resistance and room temperature in two kinds of mock-up rooms were tested, simultaneously. Results of thermal properties showed thermal insulation properties ware increased by adding inner membrane material underneath the outer membrane.