• Proceedings of the KIEE Conference
• /
• 2003.07c
• /
• pp.1427-1429
• /
• 2003

The $ZnNb_2O_6$ ceramics with 3wt% CuO were prepared by the conventional mixed oxide method. The ceramics were sintered at the temperature of $1000^{\circ}C{\sim}1075^{\circ}C$ for 3hr. in air. The structural properties were investigated with sintering temperature by XRD and SEM. Also, the microwave dielectric properties were investigated with sintering temperature. Increasing the sintering temperature, the peak of second phase($Cu_3Nb_2O_8$) was increased. In the case of $ZnNb_2O_6$+CuO(3wt%) ceramics sintered at $1025^{\circ}C$ for 3hr, the dielectric constant, quality factor were 21.73, 19.276, respectively.

• Proceedings of the KIEE Conference
• /
• 2004.11a
• /
• pp.180-182
• /
• 2004

Polycrystalline $BaTiO_3/SrTiO_3$ powder was prepared by sol-gel process and the multilayered thick films were prepared on the $Al_2O_3$ substrates by screen printing method. The films were sintered at $1400^{\circ}C$ for 2 hours in the air. The structural and dielectric properties were investigated, The X-ray diffraction (XRD) patterns indicate that the BST phase and porocity were formed in the interface of $BaTiO_3/SrTiO_3$ multilayered thick films. The dielectric constant and the dielectric loss of the BT/ST/BT/ST multilayered thick films were about 247 and 0.84% at 1MHz.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2007.06a
• /
• pp.251-251
• /
• 2007

A new type of a lead-free positive temperature coefficient of resistivity(PTCR) material. based on $(Bi_{1/2}Na_{1/2})TiO_3\;-\;BaTiO_3$ solid solution ceramics has been developed. The effect of $Nb_O_5$ and $Y_2O_3$ content on the electrical properties and the microstructure of (1-x) $(Bi_{1/2}Na_{1/2})TiO_3\;-\;x\;BaTiO_3$ (BNBT) ceramics made using a conventional mixed oxide process has been studied. The Curie Temperature was obviously increased with the increasing of $(B_{0.5}Na_{0.5})TiO_3$ content. The Y-doped BNBT ceramics(x=0.02) display low resistivity values of $10^2-10^3$ ohm*cm at room temperature and the Curie Temperature of $Tc=155^{\circ}C$.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2008.06a
• /
• pp.375-376
• /
• 2008

• 한국초전도학회:학술대회논문집
• /
• v.16
• /
• pp.57-57
• /
• 2006

• Journal of the Korean Electrochemical Society
• /
• v.12 no.3
• /
• pp.234-238
• /
• 2009

In the excitation spectra of $YNbO_4$ : $Eu^{3+}$, the charge transfer (CT) band around 270 nm due to $[NbO_4]^{3-}$$-Eu^{3+}$ interaction and sharp excitation peaks by f-f transition of $Eu^{3+}$ strongly appeared simultaneously. CT band depended on the structural properties of powders, showing the red-shift with increasing the crystallinity, while the f-f transition peaks were independent of the crystallinity. For $YNb_{1-x}Ta_xO_4$ : $Eu^{3+}$ (x = 0.05.0.2), $[TaO_4]^{3-}$. configuration was locally constructed, leading to the blue-shift in CT band and the decrease in the red emission intensity with increasing the Ta content.

• Proceedings of the KSME Conference
• /
• 2004.04a
• /
• pp.1328-1333
• /
• 2004

The Flame length of $CH_4$ with the Oxidizer of air and $O_2$ has been measured respectively for the nozzle diameter of 1.6mm, 2.7mm, 4.4mm and 7.7mm. In all $CH_4$ flame on oxidizer of air and $O_2$. the flame length was independent of the initial jet diameter, dependent only on the flowrate in laminar flame regime, and in turbulent flame dependent on the initial jet diameter. Using correlation equation of Delichatsios, the flame length has been expected exactly for $CH_4/air$ flame, but has been underestimated for $CH_4/O_2$ flame. This paper has proposed correlation equation of $CH_4/O_2$ flame.

• Journal of Surface Science and Engineering
• /
• v.52 no.4
• /
• pp.187-193
• /
• 2019

Electroless Ni-P coatings are widely used in the chemical, mechanical, and electronic industries because of their excellent wear and abrasion resistance. In this study, the effect of $TiO_2$ particles of composite coating was investigated. To improve the corrosion resistance, electroless $Ni-P-TiO_2$composite coating was studied by varying the $TiO_2$ content. The morphology and phase structure of $Ni-P-TiO_2$ composite coatings were analyzed by scanning electron microscopy(SEM), X-ray diffractometry(XRD) and X-ray photoelectron spectroscopy(XPS). The result showed that $Ni-P-TiO_2$composite coating is composed of Ni, P, Ti and O. It exhibits an amorphous structure, high hardness and good corrosion resistance to the substrate. $Ni-P-TiO_2$ composite coatings have higher open circuit potential than that of the substrate, which obtained at $TiO_2$ content of 5.0 g/L optimal integrated properties.

• Bulletin of the Korean Chemical Society
• /
• v.28 no.8
• /
• pp.1401-1404
• /
• 2007

An efficient Pictet-Spengler type reaction of N,O-acetal TMS ethers for the practical synthesis of 1-substituted tetrahydroquinolines, medicinally important alkaloids, has been accomplished. To demonstrate the versatility of this novel procedure, the total synthesis of calycotomine, a representative 1-hydroxymethyl substituted tetrahydroisoquinoline, is also described.

• Proceedings of the KIEE Conference
• /
• 2004.11a
• /
• pp.203-204
• /
• 2004

Suspension effect has been studied by using superconductor of BiPbSrCaCuO ceramics containing $Ag_2O$. It has been cleared that $Ag_2O$ acts as pinning center which plays an important role to the suspension effect. Magnetic repulsive force which affects a superconductor located in magnetic flux from toroidal magnet has been investigated. It has been concluded that the suspension effect arises from the interaction between the pinning effect and the diamagnetic effect.