• Journal of the Korean Ceramic Society
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• v.45 no.10
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• pp.610-617
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• 2008

Multi-walled carbon nanotube(CNT) reinforced hydroxyapatite composite coating with a thickness of $5{\mu}m$ has been successfully deposited on Ti substrate using aerosol deposition(AD). The coating had a dense microstructure with no cracks or pores, showing good adhesion with the Ti substrate. Microstructural observation using field-emission scanning electron microscopy(FE-SEM) and transmission electron microscopy(TEM) showed that CNTs with original tubular morphology were found in the hydroxyapatite-CNT(HA-CNT) composite coating. Measurements of hardness and elastic modulus for the coating were performed by nanoindentation tests, indicating that the mechanical properties of the coating were remarkably improved by the addition of CNT to HA coating. Therefore, HA-CNT composite coating produced by AD is expected to be potentially applied to the coating for high load bearing implants.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.07b
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• pp.772-775
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• 2004

본 논문에서는 $B_2O_3$ 첨가가 Ba$(Mg_{1/3}Ta_{2/3})O_3$ (BMT)의 유전특성 및 미세구조의 변화에 미치는 영향에 대해 연구하였다 $B_2O_3$가 소량 첨가되었을 때는 결정립의 성장을 야기하여 치밀한 미세구조를 보였지만, 다량이 첨가된 경우 비정상 결정립 성장을 야기하여 치밀화가 떨어지는 미세구조를 보임과 동시에 $Ba_3Ta_5O_{15}$의 2차상을 형성했다. 이는 소량의 $B_2O_3$ 첨가가 유전특성의 향상을 가져왔지만, 다량의 첨가는 오히려 특성의 악화를 가져온 결과의 원인이라 생각된다. 0.5mol%의 $B_2O_3$를 첨가하여 $1500^{\circ}C$에서 6시간 소결한 경우 ${{\varepsilon}_r}=24$, $Q{\times}f=210,000GHz$의 유전 특성 값과 $4.74ppm/^{\circ}C$의 $T_{cf}$ 값을 얻었다.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07b
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• pp.938-941
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• 2003

It is well known that the state of existence of molecules on the surface of water changes during compression of the molecules. Electric methods, such as measurement of the surface potential or displacement current are also useful for investigating dynamic changes of molecular state on the water surface during compression and Transformation of molecular film occurs only usually in air-water interface, 2 dimensions domain's growth and crash are achieved. Organic thin film that consist of growth of domain can understand correct special quality of accumulation film supplying information about fine structure and properties of matter of device observing information and so on that is surface forward player and optic enemy using AFM one of SPM application by nano electronics. In this paper Langmuir (L) that is one of basis technology to manufacture of organic matter device using biology material PBDG that is kind of polypeptide that have biology adaptedness. The Experiment method used ${\pi}-A$ isotherm and BAM(Brewster Angle Microscopy), using the BAM, we can to the molecular orientation of monolayer on the water surface and directly see the morphology of the films on water subphase as well as that of the films.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.07b
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• pp.639-643
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• 2004

[ $Ta_2O_5$ ]가 첨가된 $Ba(Zn_{1/3}Ta_{2/3})O_3$[BZT] 세라믹은 1:2 규칙화 정도가 증가하고 $Ba_3Ta_5O_{15}의 이차상이 새롭게 형성된다. $1580^{\circ}C$ 보다 높은 온도에서 소결된 BZT 세라믹은 $Ta_2O_5$를 첨가하면 입자의 성장이 일어나고 액상이 형성된다. 품질계수(Q) 값은 $1580^{\circ}C$ 보다 높은 온도에서 소결할 경우 미량의 $Ta_2O_5$ 첨가만으로도 상당히 증가한다. 상대밀도는 $Ta_2O_5$ 첨가량에 따라 감소하기 때문에 Q값의 증가는 상대밀도와는 무관하다. 반면에, $Ta_2O_5$의 첨가량에 따라 입자의 성장은 증가하였기 때문에 Q값의 향상은 입자크기와 관계가 있음을 알 수 있다. 많은 양의 $Ta_2O_5$ 첨가시 비록 입자 크기가 증가했음에도 불구하고 Q값이 매우 낮은 것을 볼 때, Q값의 감소는 $Ba_3Ta_5O_{15}$ 상의 영향과 낮은 밀도 값에 기인한 것이다.

• ETRI Journal
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• v.24 no.5
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• pp.349-359
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• 2002

With Ni/Au and Pd/Au metal schemes and low temperature processing, we formed low resistance stable Ohmic contacts to p-type GaN. Our investigation was preceded by conventional cleaning, followed by treatment in boiling $HNO_3$:HCl (1:3). Metallization was by thermally evaporating 30 nm Ni/15 nm Au or 25 nm Pd/15 nm Au. After heat treatment in $O_2$ + $N_2$ at various temperatures, the contacts were subsequently cooled in liquid nitrogen. Cryogenic cooling following heat treatment at $600^{\circ}C$ decreased the specific contact resistance from $9.84{\times}10^{-4}$ ${\Omega}cm^2$ to $2.65{\times}10^{-4}$ ${\Omega}cm^2$ for the Ni/Au contacts, while this increased it from $1.80{\times}10^{-4}$ ${\Omega}cm^2$ to $3.34{\times}10^{-4}$ ${\Omega}cm^2$ for the Pd/Au contacts. The Ni/Au contacts showed slightly higher specific contact resistance than the Pd/Au contacts, although they were more stable than the Pd contacts. X-ray photoelectron spectroscopy depth profiling showed the Ni contacts to be NiO followed by Au at the interface for the Ni/Au contacts, whereas the Pd/Au contacts exhibited a Pd:Au solid solution. The contacts quenched in liquid nitrogen following sintering were much more uniform under atomic force microscopy examination and gave a 3 times lower contact resistance with the Ni/Au design. Current-voltage-temperature analysis revealed that conduction was predominantly by thermionic field emission.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.3A
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• pp.251-260
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• 2011

In this study, the effect of natural jute fiber volume fraction on the bond characteristics of polyolefin based macro fiber in natural jute fiber reinforced cement composites, including bond strength, interface toughness, and microstructure analysis are presented. The experimental results on polyolefin based macro fiber pullout test of different conditions are reported. Natural jute fiber volume fractions ranging from 0.1% to 0.2% are used in the mix proportions. Pullout tests are conducted to measure the bond characteristics of polyolefin based macro fiber from natural jute fiber reinforced cement composites. Test results are found that the incorporation of natural jute fiber can effectively enhance the polyolefin based macro fiber-cement matrix interfacial properties. The bond strength and interface toughness between polyolefin based macro fiber and natural jute fiber reinforced cement composites increases with the volume fraction of natural jute fiber. The microstructural observation confirms the findings on the interface bond mechanism drawn from the fiber pullout test results.

• Journal of Korea Foundry Society
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• v.26 no.5
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• pp.205-210
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• 2006

The structural control of Al-Si alloy, which was not studied among various electromagnetic processing of materials, was considered applying the alternating current and direct current magnetic flux density. The main aim of the present study is to investigate the effects of electromagnetic vibration on the macro and microstructure of Al-Si alloy in order to develop a new process of structural control in Al-Si alloy. When the electromagnetic vibration is conducted for changing the shape of primary aluminum, at low frequency(>60Hz), the shape of dendrite is changed speroidal shape. When the electromagnetic vibration is conducted for changing the shape of eutectic silicon, the fact that a morphological change of the eutectic silicon from coarse platelet flakes to fine fiber shape is observed and the improvement of the mechanical properties is achieved with EMV (Electro Magnetic Vibration) process at high frequency(>500Hz).

• Journal of the Korean Society for Precision Engineering
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• v.26 no.1
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• pp.71-81
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• 2009

Die steel for plastic molding were used as mold material of automobile parts and electronic component industry. The material of this paper has superior to mechanical properties, such as repair weldability, corrosion resistance and high temperature strength, required mold parts for semitransparent. Laser-induced surface hardening technology is widely adopted to improver fatigue life and wear resistance via localized hardening at the surface of mold parts. The objective of this research work is to investigate on the characteristics of surface hardening of the laser process parameters, such as beam travel speed, laser power and defocsued spot position, for the case of die steel for plastic molding. Lens for surface hardening of large area is plano-convex type with elliptical profile to maintain uniform laser irradiation. According to the experimental results, large size of hardened layer at the surface of die steel for plastic molding was achieved, and microstructure of this layer was lath martensite. Optimal surface status and mechanical property of hardened layer could be obtained at 1095Watt, $0.25{\sim}0.3m/min$, 0mm (focal length: 232mm) for laser power, beam travel speed, and focal position. Where, heat input was $0.793{\times}10^{3}J/cm^2$, and width of hardened layer was 27.58mm.

• Journal of Power System Engineering
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• v.14 no.2
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• pp.71-77
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• 2010

This paper was studied on microstructure, mechanical properties and corrosion characteristics of 316L stainless steel pipe welds was fabricated by orbital welding process. S-Ar specimen was fabricated by using Ar purge gas and S-$N_2$ specimen was fabricated by using $N_2$ purge gas. Ferrite was not detected in weld metal of S-$N_2$ specimen but the order of 0.13 Ferrite number(FN) was detected in weld metal of S-Ar specimen. Oxygen and Nitrogen concentration of S-$N_2$ specimen was higher than S-Ar specimen on HAZ and inner bead. The welds microstructural characteristics of S-Ar and S-$N_2$ specimens are similar. The microvickers hardness values of S-Ar and S-$N_2$ specimens welds were similar and average values of each regions were in the range of 174~194. The microstructures of S-Ar and S-$N_2$ weld metal were full austenite by primary austenite solidification. The Solidification structures of S-Ar and S-$N_2$ weld metal were formed directional dendrite toward bead center. The potentiodynamic polarization curve of STS 316L pipe welds exhibited typical active, passive, transpassive behaviour. Corrosion current density$(I_{corr.})$ and corrosion rate values of S-Ar specimen in 0.1M HCl solution were $0.95{\mu}A/cm^2$ and $0.31{\mu}A$/year respectively. The values of S-$N_2$ specimen were $1.4{\mu}A/cm^2$ and $0.45{\mu}m$/year.

• Applied Chemistry for Engineering
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• v.26 no.6
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• pp.681-685
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• 2015

In this study, pure $BiVO_4$ powder and metal-doped $M-BiVO_4$ (M = Mg, Cu) powder, well known as thermochromic materials, were prepared from a mixed aqueous solution of bismuth nitrate ($Bi(NO_3)_3$) and ammonium vanadate ($NH_4VO_3$) in autoclave by hydrothermal method. The crystal structure, microstructure, and thermochromic property of samples were analyzed using FE-SEM, FT-IR, XRD, DSC, UV-Vis-NIR spectroscopy and colorimeter. When heating samples above phase transition temperature, the color of $M-BiVO_4$ (M = Mg, Cu) sample was thermally changed more clearly than that of using only pure $BiVO_4$ sample.