• Korean Journal of Materials Research
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• v.9 no.4
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• pp.428-433
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• 1999

An objective of this study is to compare the characteristics of coating layer of plasma sprayed fine $Al_2O_3$ and those of layer by commercial $Al_2O_3$(Metco 105). The microstructure of fine $Al_2O_3$ coating layer was denser compared with commercial $Al_2O_3$ coating layer. The surface roughness$(R_a)$ of the layer by the fine $Al_2$O$_3$ was lower compared with that of commercial $Al_2O_3$. Thickness of splat for fine $Al_2O_3$ was $1.4\mu\textrm{m}$ while the commercial $Al_2O_3$ was $3.53\mu\textrm{m}$. The main phase existing in coating layer was of $\gamma-Al_2O_3$ and the fraction of $\alpha-Al_2O_3$ in fine $Al_2O_3$ coating layer was 8.39% and that of commercial $Al_2O_3$ was 13.79%. Microhardness was no great difference between the fine and commercial $Al_2O_3$ but deviation of the fine $Al_2O_3$ coating layer was relatively large. Accordingly, the strength of splat of the coating was expected that fine $Al_2O_3$was lower than commercial $Al_2O_3$ powder.

• Journal of the Korean Ceramic Society
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• v.33 no.10
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• pp.1138-1146
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• 1996

Al2TiO5 powder was prepared by the sol-gel processing from th metal alkoxides ; aluminium sec-butoxide (Al(OC4H9)3 and tetraethyl orthotitanate (Ti(OC2H5)4) The particles of Al2TiO5 produced from alkoxides were measured to be below $1.5mutextrm{m}$ and mre than 90% weere below 1 ${\mu}{\textrm}{m}$ however those from commercial alumina and titania were over 0.5-7${\mu}{\textrm}{m}$ and only 60% were below 1${\mu}{\textrm}{m}$ and 90% were below 2.5${\mu}{\textrm}{m}$ Therefore Al2TiO5 powder produced from alkoxides had the narrower distributionin size than that produced from the commercial alumina and titania powders. The addition of mullite or Al2O3 powder to the prepared aluminum titanate inhibited the grain growth and this resulted in decreased and increase in density.

• Korean Journal of Materials Research
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• v.9 no.10
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• pp.1025-1031
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• 1999

Alloys of TiAl with six different compositions. i. e., Ti-(42, 44)Al-2Nb-4V. Ti-(42, 44)Al-4Nb-2V and Ti -(42, 44)Al-4Nb-2Cr, were manufactured by arc-melting. and their oxidation behavior was studied. Both isothermal and cyclic oxidation tests were performed at 700, 800 and $900^{\circ}C$ in air for 50hr. The oxidation resistance increased in the order of Ti-(42, 44)Al-2Nb-4V, Ti-(42, 44)Al-4Nb-ZV and Ti-(42, 44)Al-4Nb-2Cr. It was found that V was a deleterious element, while Cr was a beneficial element in terms of oxidation resistance. During oxidation, a simultaneous interdiffusion was observed. All the constituent elements in the base alloys diffused outward. whereas oxygen from the atmosphere diffused inward, to form triple oxide layers composed of an outermost $\textrm{TiO}_2$ layer. upper ($\textrm{TiO}_2+\textrm{Al}_2\textrm{O}_3$) mixed layer, and lower $\textrm{TiO}_2$-rich layer.

• Journal of the Korean Institute of Telematics and Electronics T
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• v.36T no.3
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• pp.7-12
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• 1999

In this paper, dielectric and strain properties of (1-f-y)PMN-yPT-xST ceramics investigated with the amount of $\textrm{SrTiO}^3$(ST). The $\textrm{SrTiO}^3$ content is ranged within 1~6㏖%. Another compositions with excess MgO also investigated. As the amount of ST is increased, dielectric constant has a maximum value at 5㏖% composition. The Curie temperature is decreased linearly with increasing the amount of ST. Coercive field and ramnant polarization has a maximum value at l㏖% composition. As for the effects of excess MgO, the dielectric constant has been increased by the addition of excess MgO up to 3㏖% to a 0.8PMN-0.12PT-0.04ST specimen. But the strain has been decreased by the addition of excess MgO.

• Korean Journal of Materials Research
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• v.7 no.1
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• pp.57-61
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• 1997

Formation of fluorite structure and other related crystal structures in the $Y_{0.8}Ta_{0.2}O_{1.7}$-MO(M=Ba, Sr, Ca and Mg) system has been studied $Ba_2YTaO_6,\;Sr_2YTaO_6$ of cubic perovskite type ordered structure anti $Y_2O_3$ of cubic structure were produced besides the defect fluorite structure when 4 moIob of BaO or SrO was added to $Y_{0.8}Ta_{0.2}O_{1.7}$ When CaO more than 8 nlol"/o was added to $Y_{0.8}Ta_{0.2}O_{1.7}$, monoclinic: $Ca_2YTaO$, and cubic $Y_2O_3$ were pri~tlucecl ;IS this sec:onci phases hesides the main fluorite truc,ture. Smglc phase of fluorite structure \vas 1)roduc:ciI when MgO was added up to 12 mol%, however, MgO appeared as the second phase besides the main fluorire structure when MgO was added more than lti moI0'. Consquently, it is considered rh;it the formation of tluorite structure is related with the formation of the cubic perovskite type ordered structure of $A_2(B'B")O_6$ as well as the cation radii of the additives.additives.

• Journal of the Korean Ceramic Society
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• v.25 no.3
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• pp.201-206
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• 1988

To investigate the effects of Mo addition on the microstructures and mechanical properties of Al_2O_3$ ceramics, two kinds of Mo particles with average sizes of 2-${\mu}{\textrm}{m}$ and 6-${\mu}{\textrm}{m}$ were used as additives. It was shown that Mo particles inhibited the grain growth of Al_2O_3$, and the smaller Mo particles were more effective. In case of 2-${\mu}{\textrm}{m}$ Mo dispersion, the bending strength and the fracture toughness were increased. Dispersion of 6-${\mu}{\textrm}{m}$ MO did not increase the strength but improved the fracture toughness a little. The toughening mechanisms of Al_2O_3$-Mo composites are thought to be the crack deflection and microcracking mechanisms.

• Korean Journal of Materials Research
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• v.9 no.1
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• pp.86-91
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• 1999

We have fabricated high-$\textrm{T}_c$ superconducting $\textrm{YBa}_{2}\textrm{Cu}_{3}\textrm{O}_{7-x}$(YBCO) grain boundary junctions at a step-edge on (001) $\textrm{SrTiO}_3$(STO) substrates. A diamond-like carbon (DLC) film grown by plasma enhanced chemical vapor deposition were used as an ion milling mask to make steps on the STO (100) single crystal and was removed by an oxygen reactive ion etch process. The c-axis oriented YBCO and TO thin films were deposited epitaxially on the STO substrate with a step-edge by pulsed laser deposition. The grain boundary junctions were formed at the top and the bottom of the step. The junctions worked at temperatures above 77 K, and had I\ulcornerR\ulcorner products of 7.5mV at 16K and 0.3 mV at 77K, respectively. The I-V characteristics of these junctions showed the shape of the two noisy resistively shunted junction model.

• Journal of the Korean Vacuum Society
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• v.10 no.1
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• pp.27-30
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• 2001

Electromigration Phenomena in Al-1%Si thin film interconnections under DC and PDC conditions were investigated. Thin film interconnections with $SiO_2$ and PSG/$SiO_2$ dielectric passivation layer were formed by a standard photolithography process method and test line lengths were 100, 400, 800, 1200, and 1600 $\mu\textrm{m}$. The current density of $1.19\times10^7\textrm{A/cm}^2$ was stressed in Al-1%Si thin film interconnections under DC condition. The current density of $1.19\times10^7\textrm{A/cm}^2$ was also applied under PDC condition at the frequency of 1 Hz with the duty factor of 0.5. The electromigration resistance of PSG/SiO2 dielectric passivation test line was stronger than $SiO_2$ dielectric passivation test line. The lifetime under PDC was 2-4 times longer than DC condition. As the thin film interconnection line increased, the lifetime decreased and saturated over the critical length. Failure patterns by an electromigration were dominated by void-induced electrical open and hillock-induced electrical short.

• Korean Journal of Materials Research
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• v.7 no.8
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• pp.635-639
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• 1997

ECR-PECVD법을 사용하여 450-49$0^{\circ}C$이하의 온도에서 Pt/SiO$_{2}$/Si기판 위에 PZT 박막을 증착하였다. 기판 온도가 46$0^{\circ}C$ 이하일 경우에는 페로브스이트 상과 제2상으로 이루어진 박막이 성장하였으며 기판온도가 47$0^{\circ}C$이상일 때에는 페로브스카이트 단일상의 PZT 박막이 성장하였다. 49$0^{\circ}C$에서 매우 얇은 페로브스카이트의 PZT 박막을 증착한 후 $650^{\circ}C$에서 1분간 raped thermal annealing(RTA) 처리한 결과 박막의 조성과 결정성에는 거의 변화가 없었으나 박막의 전하 저장 밀도는 크게 향상되었다. 이는 RTA 처리에 의한 저유전 계면층의 소멸이 주된 이유라고 판단된다. 열처리 후 두께 40-45nm의 PZT박막은 200kV/cm의 전장 하에서 $10^{-6}$$\textrm{cm}^2$이하의 누설전류값을 갖고 있었으며, 인가전압 1V에서 300fF/$\mu$$m^2$의 정전용량, 즉 SiO$_{2}$환산두께 0.12nm를 나타내었다.

• Journal of the Korean Ceramic Society
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• v.18 no.1
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• pp.41-47
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• 1981

The sintering characteristics of the SiC-Clay-Kaolin chamotte system were studied by addition of $Al_2O_3$ for the manufacture of silicate-bonded silicon carbide refractories at $1350^{\circ}C$. The sinterbilit of SiC-Binder mixture was measured by apparent porosity and compressive strength. And its mineral compositions were identified with X-ray diffractometer. The following results were obtained; 1) Optimum amount of mixed clay ($\textrm{Al}_2\textrm{O}_3$ 40 wt% mixed) as a binder was about 25wt% 2) Appropriate mixing ratio of mixed Kaolin chamotte ($\textrm{Al}_2\textrm{O}_3$ 40wt% mixed) was about 30wt% in the clay Kaolin chamotte binder. 3) Variation of apparent porosity and compressive strength of sintered SiC-binder mixture fired at $1350^{\circ}C$ were due to the sinterbility of clay.