• 한국세라믹학회지
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• 제31권10호
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• pp.1089-1098
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• 1994

The effect of Si3N4 addition on the microstructure and PTCR characteristics of BaTiO3 was studied. When 0.1 mol% Sb2O3-doped BaTiO3 codoped with Si3N4 (0.1, 0.25, 0.5, 0.75, and 1 wt%, respectively) were sintered, their microstructures were changed by the amount of the liquid phase as a result of eutectic reaction at 126$0^{\circ}C$. By these microstructural changes, the specific resistivity ratio($\rho$max/$\rho$min) with Si3N4 content variation of 0.1 mol% Sb2O3-doped BaTiO3 ceramics sintered at 130$0^{\circ}C$ for 1 hour varied between 3.70$\times$102(0.1 wt% Si3N4) to 1.16$\times$103 (1wt% Si3N4).

• 한국세라믹학회지
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• 제26권6호
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• pp.843-849
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• 1989

Effect of Bi2O3/Li2CO3 on low temperature sinteirng and dielectric property of BaTiO3 ceramics has been investigated. For the specimen sintered at 110$0^{\circ}C$, it was densified to 96% of BaTiO3 theoretical density by the addition of 1.0-1.25w/o Bi2O3/Li2CO3. Maximum dielectric constant increased and Curie temperature lowered with the increase of Bi2O3/Li2CO3 content, which probably can be explained by thne substitution of Bi3+, Li1+ on BaTiO3 lattice. The volatilization of Li1+, resulting from the increase of soaking time at 110$0^{\circ}C$ leads to the increase of Curie temperature and tetragonality of the specimen.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
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• pp.514-515
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• 2006

In this study, multi-ply SiC fiber reinforced Ti-6Al-4V composites have been manufactured by plasma spraying and subsequent vacuum hot pressing. Two different sizes of Ti-6Al-4V feedstock powders were used for plasma spraying to form matrix. A considerable amount of oxygen was incorporated into as-sprayed Ti matrix during plasma spraying, and consequently caused matrix embrittlement. The use of coarse-sized feedstock powder reduced oxygen contamination, but tended to increase fiber spacing irregularity and fiber strength degradation. Longitudinal tensile strength and ductility of the composites were mainly affected by the matrix oxygen content.

• 한국재료학회지
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• 제24권10호
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• pp.526-531
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• 2014

Thermal shock resistance property has recently been considered to be one of the most important basic properties, in the same way that the transverse-rupture property is important for sintered hard materials such as ceramics, cemented carbides, and cermets. Attempts were made to evaluate the thermal shock resistance property of 10 vol% TaC added Ti(C,N)-Ni cermets using the infrared radiation heating method. The method uses a thin circular disk that is heated by infrared rays in the central area with a constant heat flux. The technique makes it possible to evaluate the thermal shock strength (Tss) and thermal shock fracture toughness (Tsf) directly from the electric powder charge and the time of fracture, despite the fact that Tss and Tsf consist of the thermal properties of the material tested. Tsf can be measured for a specimen with an edge notch, while Tss cannot be measured for specimens without such a notch. It was thought, however, that Tsf might depend on the radius of curvature of the edge notch. Using the Tsf data, Tss was calculated using a consideration of the stress concentration. The thermal shock resistance property of 10 vol% TaC added Ti(C,N)-Ni cermet increased with increases in the content of nitrogen and Ni. As a result, it was considered that Tss could be applied to an evaluation of the thermal shock resistance of cermets.

• 한국결정성장학회지
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• 제9권5호
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• pp.498-503
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• 1999

La가 혼입된 $BaTiO_3$를 균일침전법으로 제조하여 La의 혼입량 및 입자의 크기 변화에 따른 전기적 특성을 관찰하였다. 온도변화에 따른 저항을 측정한 결과 란탄의 농도가 0.6 mol%일 때 그리고 입자의 크기가 1.0 $\mu\textrm{m}$으로 작을 때 가장 큰 PTCR 효과를 나타내었다. 상전이온도($(T_c)$) 이상에서 온도와 1/$\varepsilon_m$(T)의 관계를 나타낸 도시에 의하면 유전상수의 변화가 Curie-weiss 법칙에 잘 다름을 알 수 있었다. 측정한 비저항과 유전상수로부터 계산한 전위장벽의 높이도 란탄의 농도가 0.6 mol%일 때 입자의 크기가 1.0$\mu\textrm{m}$으로 작을 때 가장 큰 전위장벽을 나타내었다.

• 한국광학회지
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• 제18권2호
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• pp.171-177
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• 2007

전자빔 증착법을 이용하여 산소 분압에 따라 $TiO_2$ 박막을 제작하고, 열처리 온도에 따른 박막의 구조적 특성과 광학적 특성을 분석 하였다. $TiO_2$ 박막들의 물리적 특성은 주입된 산소량에 의존하였다. 주입된 산소량이 증가 할수록 상전이 온도가 높아지고, 가시광선 영역에서 $TiO_2$ 박막의 투과율이 증가하였다. 그리고 주입된 산소량이 작은 경우, $700^{\circ}C$에서 $1100^{\circ}C$로 열처리 후 $TiO_2$ 박막의 흡수단 이 좀더 장파장으로 이동하였다.

• 대한금속재료학회지
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• 제48권8호
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• pp.741-748
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• 2010

We studied the corrosion and oxidation properties of Fe-18Cr-0.4Nb-(0.1~0.6)Ti-(1~3)Si-(0.5~2)Mo stainless steel. The resistance to general and pitting corrosion was evaluated and the results were analyzed by Response Surface Methodology (RSM) as a function of alloy composition. The effects of alloy composition and heat treatment on the oxidation resistance were also examined. Mo increased both general corrosion resistance and pitting corrosion resistance. Si improved the resistance of the alloys to pitting corrosion. Si was also beneficial for general corrosion resistance of the alloys containing Mo at more than 1 wt.%. However, Mo was detrimental when its content was lower. Effects of Ti on general corrosion properties appeared to be weak and a high concentration of Ti appeared to deteriorate pitting resistance. The thickness of the oxidation scale increased and adhesion of the scale worsened as the temperature increased from $800^{\circ}C$ to $900^{\circ}C$. Weight gain of the alloys due to oxidation at $900^{\circ}C$ clearly showed that the resistance to oxidation is improved by annealing at $860^{\circ}C$ and an increase of Si content.

• Carbon letters
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• 제8권2호
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• pp.108-114
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• 2007

In this work, activated carbon (AC) after $HNO_3$ modification was used as the support during the production of supported $TiO_2$ to increase the high deposition efficiency and the photocatalytic activity. The results of $N_2$ adsorption showed that the BET surface area of samples decreased with an increasing of the concentration of $HNO_3$ due to the penetration of $TiO_2$. From XRD data, a single crystal structure of anatase peak was observed in diffraction patterns for the AC coated with titanium complexes. From the SEM results, almost all particles were aggregated with each other at the carbon surface and AC was covered with $TiO_2$ particles in all of the samples. The EDX spectra show the presence of C, O, Ti and other elements. It was also observed a decreasing of amount of C content with increasing Ti and O content from the EDX. The results of FT-IR revealed that the modified AC contained more surface oxygen bearing groups than that of the original AC. The effect of surface acidity and basity calculated from Boehm titration method was also evaluated from correlations as a function of NaOH, $NaHCO_3$, and $Na_2CO_3$ uptake. The surface modification of AC by $HNO_3$ leads to an increase in the catalytic efficiency of AC/$TiO_2$ catalysts, and the catalytic efficiency increases with increasing of $HNO_3$ concentration.

• The Korean Journal of Ceramics
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• 제2권3호
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• pp.162-166
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• 1996

The effects of NiO addition on the microstructure and microwave dielectric properties of ($Zr_{08}Sn_{02}$)$TiO_4$ (ZST) were investigated. With the NiO addition, a higher density of ZST ceramics than 95% of the theoretical values has been obtained in the sintering temperature range of 1400 to 150$0^{\circ}C$. Energy dispersive X-ray spectrometry (EDS) analysis of sintered specimen shows the presence of second phase at grain boundaries, which is considered to be $NiTiO_3$. Dielectric constant of the specimen is found to increase linearly with density. Q-values and TC$_r$ decrease with increasing NiO content. The variation of dielectric properties with NiO content is discussed in terms of the second phase. The ZST ceramics with 0.25 wt% NiO showed ${\varepsilon}_{\gamma}$=38, Q=7000 at GHz and TC$\gamma$=-0.5 ppm/$^{\circ}C$, comparable with the values obtained by the previous investigations.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1996년도 추계학술대회 논문집
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• pp.59-62
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• 1996

The effect of NiO addition on the microstructure and microwave dielectric properties of (Zr$_{0.8}$Sn$_{0.2}$)TiO$_4$(ZST) was investigated. With the NiO addition, a dense ZST body of density higher than 95% has been achieved in the sintering temperature range of 1400 to 150$0^{\circ}C$. Energy dispersive X-ray spectrometry (EDS) analysis of sintered specimen shows the presence of second phase at grain boundaries, which is considered to be NiTiO$_3$. Dielectric constant of the specimen is found to increase linearly with density. Q-values and TC$_{f}$decrease with increasing NiO content. The variation of dielectric properties with NiO content is discussed in term of the second phase. The ZST ceramics with small amount of additive gave $\varepsilon$$_{r}$=38, Q=7000 at 7 GHz and TC$_{f}$=-0.5 ppm/$^{\circ}C$, comparable with the values obtained by previous investigation.stigation.