• Proceedings of the KSME Conference
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• 2000.11a
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• pp.759-765
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• 2000

A composite material consists of two or more different material layers. Copper clad aluminum composite materials are being used for economic and structural reasons. This study is concerned with experimental investigation in the direct extrusion of copper clad aluminum rods through conical dies. The suggestion are given for the proper extrudability of copper clad aluminum rods via hot direct extrusion. This paper presents the variation of flow state and hardness at a variable of extrusion ratio and semi-angle of die. By measuring after and before extrusion radius ratio of Cu sleeve and Al core, proportional flow state has been considered. And also by measuring hardness, through extrusion way, a variation of hardness has been considered.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.729-730
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• 2006

The research involves the development of a powder metallurgical route for producing good quality TiAl targets for making physical vapour deposition (PVD) coatings. Mixtures of elemental titanium and aluminium powders were mechanically milled using a novel discus milling technique under various conditions. Hot isotropic pressing (HIP) was then employed for consolidation of the mechanically alloyed powders. A cathodic arc vapour deposition process was applied to produce a TiAlN coating. Microstructural examination was conducted on the target material and PVD coatings, using X-ray diffractometry (XRD), X-ray photoelectron spectrometry (XPS) and scanning electron microscopy (SEM). It has been found that combining mechanical alloying and HIP enable us to produce fairly good quality of TiAl based target. The PVD coatings obtained from the TiAl target showed very high microhardness values.

• Journal of the Korean Ceramic Society
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• v.25 no.3
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• pp.231-236
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• 1988

In order to investigate the effect of second phase on $Al_2O_3$ matrix, SiC particles were dispersed in $Al_2O_3$ matrix as a second phase over the content range of 5 vol.% to 20 vol.%. To this mixture, $Y_2O_3$ or $TiO_2$ powders were added as a sintering additive before isostatically pressing and pressurelessly sintering at 180$0^{\circ}C$ for 90 min in $N_2$ atmosphere. With increasing SiC content, relative densities of composites were decreased but mechanical properties of composites were improvjed. In the case of adding $Y_2O_3$ as a sintering additive, maximum values of flexural strength, hardness and fracture toughness were 525 MPa, 17.1 GPa, 4.1 MPa.m1/2 respectively. In the case of adding X$TiO_2$ as a sintering additive, maximum values of flexural strength, hardness were 285 MPa, 12.1 GPa respectively. Improved mechanical properties were found to be the results of grain growth control of $Al_2O_3$ matrix and crack deflection by the second phase SiC particles.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.31 no.5
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• pp.324-329
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• 2018

Red phosphor in glasses (PiGs) for automotive light-emitting diode (LED) applications were fabricated with 620-nm $CaAlSiN_3:Eu^{2+}$ phosphor and Pb-free silicate glass. PiGs were synthesized and mounted on high-power blue LED to make a monochromatic red LED. PiGs were simple mixtures of red phosphor and transparent glass powder. After being fabricated with uniaxial press and CIP at 300 MPa for 20 min, the green bodies were thermally treated at $550^{\circ}C$ for 30 min to produce high dense PiGs. As the phosphor content increased, the density of the sintered body decreased and PiGs containing 30% phosphor had a full sintered density. Changes in photoluminescence spectra and color coordination were studied by varying the thickness of plates that were mounted after optical polishing. As a result of the optical spectrum and color coordinates, PiG plate with $210{\mu}m$ thickness showed a color purity of 99.7%. In order to evaluate the thermal stability, the thermal quenching characteristics were measured at temperatures of $30{\sim}150^{\circ}C$. The results showed that the red PIG plates were 30% more thermally stable compared to the AlGaInP red chip.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.21 no.6
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• pp.556-561
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• 2008

This paper reports the characteristics of piezoelectric microspeakers that are audible in open air with high quality piezoelectric AlN thin film according to the materials properties. When we use a tensile-stressed silicon nitride diaphragm as a supporting layer, the Sound Pressure Level (SPL) is relatively small and constant at low frequency region and shows about 70 dB at 10 kHz. However, in case of a compressively stressed composite diaphragm, the SPL of the fabricated microspeakers shows higher output pressure than those of a tensile-stressed diaphragm. It produces more than 66 dB from 100 Hz to 15 kHz and the highest SPL is about 100 dB at 9.3 kHz with $20V_{peak-to-peak}$, sinusoidal input biases and at 10 mm distances from the fabricated microspeakers to the reference microphone. From the experimental results, it is superior to have a compressively composite diaphragm in order to produce a high SPL in piezoelectric microspeaker.

• Journal of the Semiconductor & Display Technology
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• v.12 no.1
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• pp.29-33
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• 2013

We have fabricated transparent polymer composite films with high thermal emissivity, which can be used for heat dissipation of transparent electronics. PMMA (poly(methyl methacrylate)) solution with high transparency and thermal emissivity is mixed with various fillers (carbon nanotubes (CNTs), aluminum nitride (AlN), or silicon carbide (SiC)) with high thermal conductivity. We have achieved the thermal emissivity as high as 0.94 by the addition of CNTs. Compared with the PMMA film on glass, however, the addition of AlN or SiC is shown to rather decrease the thermal emissivity. It is also observed that the thickness of the PMMA film does not affect its thermal emissivity. To avoid any degradation of the thermal conductivity, therefore, the PMMA film thickness is desirable to be $1{\mu}m$. There also exists a tradeoff between the optical transmittance and thermal conductivity on the selection of the amount of fillers.

• Journal of the Microelectronics and Packaging Society
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• v.5 no.1
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• pp.19-30
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• 1998

Aluminium secondary butoxide(ASB)를 출발물질로 하여 졸-겔방법에 의해 소결거 동에 미치는 $\alpha$-Al2O3 seed의 첨가효과에 따른 알루미나의 저온소결 가능성과 알루미나의 상전이에 대하여 TEM, DTA, XRD, FT-IR등으로 고찰을 하였다. TEM 분석결과 초기 생 성물인 boehmite가 비정질에서 단결정질로 진행되어 가고 있음을 확인하였다. 그리고 DTA 분석결과 $\alpha$-Al2O3 seed의 첨가한 경우 seed의 함량이 증가함에 따라 상전이 온도는 점차 낮아졌으며 약 0.4wt%일 때 seed를 첨가하지 않은 시료의 전이온도(약 1126$^{\circ}C$)에 비하여 약 7$0^{\circ}C$ 저하된 약 1056$^{\circ}C$로나타났으며 그 이상의 seedcja가에 있어서는 전이온도에 크게 영향을 나타내지 않았다. 또한 XRD분석결과 $\alpha$-Al2O3 seed를 첨가하지 않은 경우 110$0^{\circ}C$이 상의 온도에서 $\alpha$상이 생성되었음을 알수 있었다. 또한 100$0^{\circ}C$이상의 온도에서 $\alpha$상이 생성 되었음을 나타내는 Al-O 흡수특성 피크가 400~1000cm-1 범위에서 나타내고 있는 것을 FT-IR 분석결과에서도 확인할수 있었다. 그리고 $\alpha$-Al2O3 seed를 약 0.4wt% 첨가시 900~ 95$0^{\circ}C$에서 $\alpha$상이 형성됨을 관찰할 수 있었다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.8
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• pp.1277-1286
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• 2001

Aluminum 5052/Aramid Fiber Reinforced Plastic(Al5052/AFRP) laminates are applied to the fuselage-wing intersection. The Al5052/AFRP laminates suffer from the cyclic bending moment of variable amplitude during the service. Therefore, the influence of cyclic bending moment on the delamination and the fatigue crack propagation behavior in Al5052/AFRP laminate was investigated in this study. Al5052/AFRP laminate composite consists of three thin sheets of Al5052 and two layers of unidirectional aramid fibers. The cyclic bending moment fatigue tests were performed with five different levels of bending moment. The shape and size of the delamination zone formed along the fatigue crack between Al5052 sheet and aramid fiber-adhesive layer were measured by an ultrasonic C-scan. The relationships between da/dN and ΔK, between the cyclic bending moment and the delamination zone size, and between the fiber bridging mechanism and the delamination zone were studied. Fiber failures were not observed in the delamination zone in this study. It represents that the fiber bridging modification factor should turn out to increase and that the fatigue crack growth rate should decrease. The shape of delamination zone turns out to be semi-elliptic with the contour decreased non-linearly toward the crack tip.

• Korean Journal of Materials Research
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• v.27 no.6
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• pp.301-306
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• 2017

The discovery of new luminescent materials for use in light-emitting diodes(LEDs) has been of great interest, since LED-based solid state lighting applications are attracting a lot of attention in the energy saving and environmental fields. Recent research trends have centered on the discovery of new luminescent materials rather than on fine changes in well-known luminescent materials. In a sense, the novelty of our study beyond simple modification or improvement of existing phosphors. A good strategy for the discovery of new fluorescent materials is to introduce activators that are appropriate for conventional inorganic compounds, that have well-defined structures in the crystal structure database, but have not been considered as phosphor hosts. Another strategy is to discover new host compounds with structures that cannot be found in any existing databases. We have pursued these two strategies at the same time using composite search technology with particle swarm optimization(PSO). In this study, using PSO, we have tracked down a search space composed of Sr-Al-Si-O-N and have discovered a new phosphor structure with yellow luminescence; this material is a potential candidate for UV-LED applications.

• Bulletin of the Korean Chemical Society
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• v.34 no.6
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• pp.1755-1762
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• 2013

A graphene-Zn/Al layered double hydroxide composite film was simultaneously prepared by electrochemical deposition on the surface of a glassy carbon electrode (G-LDH/GCE) from the mixture solution containing GO and nitrate salts of $Zn^{2+}$ and $Al^{3+}$. The modified electrode showed good electrochemical performances toward the simultaneous electrochemical detection of hydroquinone (HQ), catechol (CA) and resorcinol (RE) due to the unique properties of graphene (G) and LDH such as large active surface area, facile electronic transport and high electrocatalytic activity. The redox characteristics of G-LDH/GCE were investigated with cyclic voltammetry and differential pulse voltammetry. The well-separated oxidation peak potentials, corresponding to the oxidation of HQ, CA and RE, were observed at 0.126 V, 0.228 V and 0.620 V respectively. The amperometric response of the modified electrode exhibited that HQ can be detected without interference of CA and RE. Under the optimized conditions, the oxidation peak current of HQ is linear with the concentration of HQ from 6.0 ${\mu}M$ to 325.0 ${\mu}M$ with the detection limit of 0.077 ${\mu}M$ (S/N=3). The modified electrode was successfully applied to the direct determination of HQ in a local tap water, showing reliable recovery data.