• Proceedings of the Korean Magnestics Society Conference
• /
• 1998.05a
• /
• pp.80-81
• /
• 1998

• Proceedings of the Korean Nuclear Society Conference
• /
• 2004.10a
• /
• pp.903-904
• /
• 2004

• Proceedings of the Korean Ceranic Society Conference
• /
• 2000.10a
• /
• pp.148.2-148
• /
• 2000

• Journal of the Korean Ceramic Society
• /
• v.49 no.4
• /
• pp.342-346
• /
• 2012

This work deals with the preparation of dense SiC based ceramics with high electrical conductivity without oxide sintering additives. SiC samples with different content of conductive Ti-NbC phase were hot pressed at $1850^{\circ}C$ for 1 h in Ar atmosphere under mechanical pressure of 30 MPa. The conductive phase is a mixture of Ti-NbC in weight ratio of Ti/NbC 1:4. Composite with 50% of conductive Ti-NbC phase showed the highest electrical conductivity of $30.6{\times}10^3\;S{\cdot}m^{-1}$, while the good mechanical properties of SiC matrix were preserved (fracture toughness 4.5 $MPa{\cdot}m^{1/2}$ and Vickers hardness 18.7 GPa). The obtained results show that use of NbC and Ti as sintering and also electrically conductive additives is appropriate for the preparation of SiC-based composite with sufficient electrical conductivity for electric discharge machining.

• Journal of the Korean Ceramic Society
• /
• v.35 no.3
• /
• pp.294-302
• /
• 1998

$Pb_{1+x}$($Fe_{0.5}$$Nb_{0.5}$)$O_3$ films have been synthesized on Pt/Ti/$SiO_2$/Si substrates using rfmagnetron sputtering Concentration of Fe and Nb in the deposited films was adjusted to near stoichiometry through the control of target composition, Films deposited with adjusted to near stoichiometry showed better electrical properties such as dielectic and leakage characteristics. Crystallinity and dielectric constant increased with increasing excess PbO upto 9 mol% This study also showed that dielectric constant and leakage current characteristics improved by optimum content of $O_2$ flow during deposition.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
• /
• 2004.10a
• /
• pp.60-66
• /
• 2004

Hardness value decreased about 3% for annealed specimens and increased about 60% for one hour aged specimens. But the values of the other specimens aged two hours or more showed almost the same. The yield strength was the highest about 1,800㎫ in 0.06%Nb specimen having twice as much as the base meta1 specimen. Also, the elongation was the highest in 0.03%Nb specimen showing the same as base metal specimen. The higher aging temperature and the longer aging time, the higher fatigue life. On the other hand, the 0.03%Nb specimen showed the highest fatigue life which increased about 12% more than base metal specime. 0.06%Nb specimen aged at 482$^{\circ}C$ for 8 hours simultaneously satisfied the 250 grade strength and 200 grade elongation having the most superior mechanical properties.

• Journal of the Korean Ceramic Society
• /
• v.31 no.9
• /
• pp.1012-1220
• /
• 1994

BaTiO3 ceramics doped with 0.1 to 4.0 mol% Nb2O5 were prepared by conventional solid stage sintering process, so as to investigate the effect of the amount of Nb2O5 on the dielectric properties and complex impedance patterns of barium titanates. From the measurement of capacitance, we found that the dielectric constant of BaTiO3 samples with 1 mol% or more Nb2O5 remained approximately constant around room temperature with values higher than 2500. In this paper, the effect of impurity content as well as temperature on complex impedance patterns was discussed in detail. In particular, the grain and grain boundary behavior of samples which showed PTCR characteristics was discussed in terms of measuring temperature.

• Journal of the Korean Ceramic Society
• /
• v.36 no.12
• /
• pp.1335-1341
• /
• 1999

The electrical conductivity ($\sigma$) of TiO2 doped with 0.05-4.0mol% Nb2O5 was measured in the oxygen partial pressure range of 10-17 to 100 atm and temperature range of 1100 to 130$0^{\circ}C$ to investigate the electrical properties and defect types. The oxygen partial pressure dependence of the electrical conductivity (log$\sigma$/logPo2) above 110$0^{\circ}C$ was divided into the four regions. From these experimental results the following defect regions were proposed ; 1) Magneli phase(extended defect) 2) reduced rutile region where intrinsic defect predominates 3) nearly stoichiometric region which is independent on the oxygen partical pressure and 4) overstoichiometric region which is not observed in pure TiO2 The electrical conductivity of Nb-doped TiO2 depended on the doping content the oxygen partial pressure and the measuring tem-perature.

• Proceedings of the Korean Powder Metallurgy Institute Conference
• /
• 2006.09a
• /
• pp.165-166
• /
• 2006

Nb-Ti alloys were hydrogenated to prepare fine and contamination-free powders. Cracks were introduced in the alloys when they were annealed at 1473 K and cooled in a hydrogen atmosphere. The fragments produced by hydrogen-induced cracking are brittle and the friability enhanced with the Ti content of the alloy, which is beneficial for further refinement of particle size. We also demonstrate that Nb-Ti powders with the average particle size less than 1 m can be produced by ball milling at a temperature lower than 203 K. Furthermore, hydrogen-free powders can then be obtained by annealing above the temperature corresponding to hydrogen desorption from Nb solid solution.

• Korean Journal of Plant Resources
• /
• v.32 no.4
• /
• pp.318-324
• /
• 2019

Angelica gigas Nakai (AGN) is a perennial herb belonging to the family Apiaceae. Its root has been utilized as a traditional medicine in Korea. Also, it contains decursin (D) and decursinol angelate (DA) as major active components. This study was performed to compare the change in content of active components and antioxidant activity between bolting and non-bolting AGN. Bolting AGN (B1) and non-bolting AGN (NB1) were harvested in the end of August. Additional non-bolting AGN (NB2) was harvested in the end of October. The total weight of B1 was 728.7 g, which was 98.5% of NB2 weight. Next, the AGN root (B1, NB1 and NB2) was divided into main root and lateral root. And the AGN aerial part (B1, NB1) was divided into flower, leaf and stem. The two active components, D and DA, and antioxidant activity were analyzed. The D content of B1 was 0.35-1.33% according to the plant parts and the DA content was 0.29-1.07%. In addition, B1 flower and leaf showed higher antioxidant activity than NB2 roots. The results show that B1 contained 15-56% of total major components compared with NB2 main roots, suggesting that B1 could be used as a potential material.