• Journal of the Korean Society for Nondestructive Testing
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• v.26 no.6
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• pp.417-426
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• 2006

A Digital X-ray imaging system using Compton backscattering has been developed to obtain a cross-sectional profile and mass loss of corroded lap-splices of aging aircraft from density variation. A slit-type camera was designed to focus on a small scattering volume inside the material, from which the backscattered photons are collected by a collimated scintillator detector for interpretation of material characteristics. The cross section of the lap-joint is scanned by moving the scattering volume through the thickness direction of the specimen. The mass loss of each layer has been estimated from a Compton backscatter A-scan to obtain the thickness of each layer including the aluminum sheet, the corrosion layer and the sealant. Quantitative information such as location and width of planar corrosion in the lap splices of fuselages is obtained by deconvolution using a nonlinear least-square error minimization method(BFGS method): A simple reconstruction model is also introduced to overcome distortion of the Compton backscatter data due to attenuation effects attributed to beam hardening and quantum noise.

• Journal of the Korean Society for Precision Engineering
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• v.26 no.5
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• pp.57-63
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• 2009

Interface friction in blanking dies, cold forging and extrusion of aluminum alloys is a major cause of inefficient process. This paper describes an investigation of femtosecond laser texturing for reduction of interface friction on sliding surfaces in forming process. Femtosecond direct writing technology was used to fabricate a laser micro-machined die and to create microgroove patterns with varying size and density on metal forming dies. A systematic approach to find the optimum parameters and computer simulation comparison of friction coefficients are provided to study the relation of friction coefficients and die profiles. In metal forming tests, the effectiveness of various laser-machined patterns for enhancing interface lubrication is determined.

• Transactions of Materials Processing
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• v.15 no.1 s.82
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• pp.21-26
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• 2006

A optical head unit for nano optical probe array was developed. The optical probe array is generated by Talbot effect. The shape and thickness of microlens array(MLA) were designed to minimize the spot size at the foci of MLA. To increase the optical efficiency of the system and obtain the large tolerance for fabrication, aperture size was theoretically optimized. Then microlens illuminated aperture array(MLIAA) as an optical head unit was fabricated using a ultra violet(UV) molding process on aluminum aperture array. In this process, Al aperture array was fabricated separately using the photolithography and reactive ion etching(RIE) process. Optical properties of the generated optical probes were measured and compared at Talbot distance from the aperture array having a diameter of $1{\mu}m$ and MLIAA.

• Journal of the Korean Society for Precision Engineering
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• v.26 no.1
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• pp.82-88
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• 2009

Ultra-precision turning is highly needed to manufacture molds for precision lens. In this study, micro-turning combined with elliptical vibration cutting (EVC), which is known to enhance micro- machining quality, was investigated by installing a rotary stage into the micro-grooving machine. From machining experiments involving materials of copper, brass, and aluminum and single and poly crystalline diamond tools, it was found that EVC produced thinner and curlier chips and that better surface finish could be achieved, compared with conventional turning, owing to prohibition of formation of burrs and built-up edges. Therefore, we found EVC micro turning could be readily utilized to manufacture precision mold.

• Journal of the Korean Institute of Telematics and Electronics
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• v.26 no.2
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• pp.163-168
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• 1989

In this paper, Rayleigh wave velocity has been measured by detecting the backscattered signal generating near the Rayleigh critical angle in the elastic medium. The rotating system has been made for the measurment of Rayleigh angle. It has been shown that the measured velocity for the stainless steel, brass aluminum, copper has been good agreement with the theoretical value. The method of non-destructive evaluation using backscattering signal has been presented and the c-scan acoustic image for internal of IC sample has been displayed.

• Journal of the Korean institute of surface engineering
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• v.51 no.1
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• pp.21-26
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• 2018

The $Cu_2(btc)_3$ metal-organic frameworks (MOF) coated anodic aluminum oxide (AAO) membrane was successfully prepared by layer-by-layer technique using hand spray method. It was confirmed that the $Cu_2(btc)_3$ layer, which has the pore sized in 2-3 nm, on surface of AAO exhibited the polycrystalline thin film structure by XRD analysis. More than 100 repetitive spray cycles were required to obtain more robust and thick MOFs on AAO and it was possible to uniformly coat both the top and bottom surfaces of the AAO. It should be noted that the MOFs also could be coated on surface of pores resulting in reduce the size of pore from 52 nm to 32 nm.

• Journal of the Korean Ceramic Society
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• v.26 no.4
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• pp.453-458
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• 1989

Aluminum nitride powder prepared from the hydroxides, AlOOH and Al(OH)3 which were obtained by hydrolysis of Al-isopropoxide, was densified at 1750 and 180$0^{\circ}C$ for 60 min by hot-pressing under the pressure of 25kg/$\textrm{cm}^2$. Theoretical density could be obtained at 175$0^{\circ}C$. Their flexural strengths were 450MPa and 395MPa for the specimens obtained from Al(OH)3 and AlOOH, respectively. There was no remarkable change in flexural strength up to 100$0^{\circ}C$. Fracture toughness values were 3.50MN/m3/2 for Al(OH)3 and 3.11MN/m3/2 for AlOOH. It is assumed that these differences in mechanical properties are due to the abnormal grain growth for the AlN ceramics obtained from AlOOH.

• Journal of the Korean Ceramic Society
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• v.26 no.2
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• pp.235-241
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• 1989

A study on the APCVD(atmospheric pressure chemical vapor deposition) Al2O3 was done by using the aluminum-tri-isopropoxide/N2 reaction system at 40$0^{\circ}C$. When the flow rate of the carrier gas(N2) was over 2SLPM, heterogeneous reaction was observed. However, when the flow rate of the carrier gas was below 2SLPM, a porously deposited film or powder formation was observed. The film formed by a heterogeneous reaction was optically dense. The dense film is thought to be a kind of a hydrated alumina. After a thermal treatment of the film in the range of temperature from $600^{\circ}C$ to 1, 20$0^{\circ}C$, properties of the film seems to be changed due to dehydration and densification process. In the case of the powder on heat treatment(600~1, 20$0^{\circ}C$), both a phase transformation and the change of OH peak was observed.

• Journal of the Korean Ceramic Society
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• v.26 no.3
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• pp.361-370
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• 1989

Mullite powders were synthesized from the common solution of aluminum sulfate and sodium silicate solutions by the emulsion-hot kerosene technique. The reaction temperature and mechanism for mullitization and the characteristics of synthesized mullite powders were investigated. The effect of Na components introduced from sodium silicate solution on the physical property and microstructure of sintered mullite was also examined. It was proved that mullites were formed at 75$0^{\circ}C$ through the reaction mechanism of Na2O.2.2SiO2＋3.3Al2(SO4)3longrightarrow1.1(3Al2O3.2SiO2)＋Na2SO4＋8.9SO3. Synthetic mullite powders consisted of the compositiion of 3Al2O3.2SiO2 and showed highly agglomeration of hollow spherical particles of 1${\mu}{\textrm}{m}$ diameter. The density and fracture toughness of sintered mullites were somewhat reduced because of the effect of a very small amount of residual Na components.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.55 no.1
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• pp.26-29
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• 2006

Transparent ZnO thin films were prepared by KrF pulsed laser deposition (PLD) technique and applied to a bottom-gate type thin film transistor device as an active channel layer. A high conductive crystalline Si substrate was used as an metal-like bottom gate and SiN insulating layer was then deposited by LPCVD(low pressure chemical vapour deposition). An aluminum layer was then vacuum evaporated and patterned to form a source/drain metal contact. Oxygen partial pressure and substrate temperature were varied during the ZnO PLD deposition process and their influence on the thin film properties were investigated by X-ray diffraction(XRD) and Hall-van der Pauw method. Optical transparency of the ZnO thin film was analyzed by UV-visible phometer. The resulting ZnO-TFT devices showed an on-off ration of $10^6$ and field effect mobility of 2.4-6.1 $cm^2/V{\cdot}s$.