• Journal of Welding and Joining
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• v.14 no.6
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• pp.109-118
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• 1996

Al$_2$O$_3$-TiO$_2$powders of six different compositions were plasma-sprayed on Ti substrate. The spray powders and the spray coated layers were analysed and compared using SEM and X-RD. The elastic properties (specific elastic constant and damping coefficient) of the coated specimens were measured in order to select the optimum composition range of ceramics for use in a speaker diaphragm. A correlation between the microstructure and elastic properties was also investigated. When $Al_2$O$_3$powders with 0- 13% TiO$_2$were plasma sprayed, the coated layers were composed of metastable y-Al$_2$O$_3$with small amount of $\alpha$-Al$_2$O$_3$and the content of $\alpha$-Al$_2$O$_3$was increased with TiO$_2$content. Specific elastic constant was rapidly increased with 2 and 13% TiO$_2$addition to $Al_2$O$_3$. The internal damping was nearly unchanged with TiO$_2$content The specific elastic constant seemed to be dependent on the content of $\alpha$-Al$_2$O$_3$in the coated layer.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.19 no.4
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• pp.202-207
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• 2009

Nanocomposite formation of metal-metal oxide systems by mechanical alloying (MA) has been investigated at room temperature. The systems we chose are the $Fe_3O_4$-M (M = AI, Ti), where pure metals are used as reducing agent. It is found that $Fe/Al_2O_3$ and $Fe/TiO_2$ nanocomposite powders in which $Al_2O_3$ and $TiO_2$ are dispersed in ${\alpha}$-Fe matrix with nano-sized grains are obtained by MA of $Fe_3O_4$ with Al and Ti for 25 and 75 hours, respectively. It is suggested that the shorter MA time for the nanocomposite formation in $Fe/Al_2O_3$ is due to a large negative heat associated with the chemical reduction of magnetite by aluminum. X-ray diffraction results show that the average grain size of ${\alpha}$-Fe in $Fe/TiO_2$ nanocomposite powders is in the range of 30 nm. The change in magnetic properties also reflects the details of the solid-state reduction of magnetite by pure metals during MA.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.04b
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• pp.5-8
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• 2004

전자빔 증착법 (e-beam evaporation)를 이용하여 $TiO_2$ 박막과 $Al_2O_3/TiO_2$ 이중박막을 제조한 후, $800^{\circ}C$ 공기 중에서 열처리하여, 알루미나 층의 유무에 따른 두 박막의 전기전도 특성과 100 ppm CO 가스에 대한 반응 특성을 고찰하였다. 알루미나 층이 증착되지 않은 순수한 $TiO_2$ 박막의 전기 전도도 (in dry air)는 $100^{\circ}C-500^{\circ}C$ 온도범위에서 온도가 증가함에 따라 증가하였으며 알루미나 층이 증착된 $Al_2O_3/TiO_2$ 이중막보다 높은 전도도를 나타내고 있으나, 약 $300^{\circ}C$이상의 온도에서는 $Al_2O_3/TiO_2$ 이중막의 전기 전도도가 급격히 증가하여 $TiO_2$ 박막의 전기전도도 보다 더 높은 값을 나타내었다. 또한 온도에 따른 CO 가스 감도(sensitivity)는 $TiO_2$ 박막의 경우 $400^{\circ}C$까지는 서서히 증가하여 그 이상의 온도에서 급격히 감소하였으나, $Al_2O_3/TiO_2$ 이중막은 $250^{\circ}C$에서 감도가 급격히 증가하여 최대값을 나타내었으며, $350^{\circ}C$에서 감도가 급격히 감소하는 특성을 나타내었다.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.7 no.2
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• pp.259-270
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• 1997

Reaction kinetics for the solid-state reaction of $\alpha-Al_2O_3$ with amorphous $TiO_2$ to produce $Al_2TiO_5$ (Tialite) was studied in the temperature range of $1200~1300^{\circ}C$. Rate of kinetic reaction were determined by using $TiO_2$-coated $Al_2O_3$ compact containing 50 mol% $TiO_2$ and heating the reactant mixtures in MgO at definite temperature for various times. Amount of products and unreacted reactants were determined by X-ray diffractometry. Data from the volume fraction and ratio of peak intensities of $\beta-Al_2TiO_5$ indicated that the reaction of $\alpha-Al_2O_3$ with $TiO_2$ to form pseudobrookite starts between 1280 and $1300^{\circ}C$. The activation energy for solid-state reaction was determined by using the Arrhenius equation ; The activation energy was 622.4 kJ/mol.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2016.11a
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• pp.107-107
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• 2016

TiCrAlSiN films were developed in order to improve the high-temperature oxidation resistance, corrosion resistance, and mechanical properties of conventional TiN films that are widely used as hard films to protect and increase the lifetime and performance of cutting tools or die molds. In this study, a nano-multilayered TiAlCrSiN film was deposited by cathodic arc plasma deposition. It displayed relatively good oxidation resistance at $700-900^{\circ}C$, owing to the formation protective oxides of $Al_2O_3$, $Cr_2O_3$, and $SiO_2$, and semiprotective $TiO_2$. At $1000^{\circ}C$, the increased temperature led to the formation of the imperfect oxide scale that consisted primarily of the outer ($TiO_2$,$Al_2O_3$)-mixed scale and inner ($TiO_2$, $Al_2O_3$, $Cr_2O_3$)-mixed scale.

• Journal of the Korean Institute of Telematics and Electronics
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• v.14 no.1
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• pp.5-14
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• 1977

"Electrical Properties of Barium Titanates with Addition Sb2O3." PTC BaTiO3 in low resistance at room temperature was prepatred. Al2O3, SiO2 and TiO2 were doped with a view to improving reproduction. Sb2O3 was doped as impurity in order to control of resistivity of the specimens. The relations between the amount of Sb3O3 and electrical properties wereinvestigated. Of the compositions studied, additions of 3.75mole% Al2O3, 1.25mole% SiO2, 2.25mole% TiO2 and 0.16~0.25wt% Sb2O3 to BaTiC3 was low resistivity in 14-300 ohm-cm.00 ohm-cm.

• Journal of the Korean Ceramic Society
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• v.32 no.4
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• pp.507-515
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• 1995

The monolithic dry gels of the Li2O-Al2O3-TiO2-SiO2 system were prepared by the sol-gel technique using metal alkoxides as starting materials to obtain monolithic glass-ceramics at low temperature without melting. Activation energy for the crystal growth of the gel with 6.05% TiO2, nucleating ageng, for the preparation of Li2O-Al2O3-TiO2-SiO2 system glass-ceramic was 101.14kcal/mol. As a result of the analysis of DTA & XRD, it was confirmed that the crytallization of Li2O-Al2O3-TiO2-SiO2 system glass-ceramic was the most efficient when 6.05% TiO2, nucleating agent, was added. $\beta$-eucryptite solid solution crystals and $\beta$-spodumene solid solution crystals were detected in the sample heat treated above 85$0^{\circ}C$. The sintered gel heat treated at 85$0^{\circ}C$ had the specific surface area of 185$m^2$/g, the pore volume of 0.19cc/g and the average pore radius of 20.8$\AA$. This shows that the sintered gel is also comparatively porous material. In temperature range of 25~85$0^{\circ}C$ thermal expansion coefficient of the specimen which was crystallized for 10hrs at 85$0^{\circ}C$ was 6.7$\times$10-7/$^{\circ}C$, which indicated that the crystallized specimen was turned out to be the glass-ceramic with low thermal expansion.

• Journal of the Korean Ceramic Society
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• v.34 no.9
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• pp.921-926
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• 1997

Two NbCx-C1-x/Y2O3/Ti sputter-coated Al2O3 substrates (L 5.5 cm$\times$W 0.5 cm) were diffusion bonded together using hot press method at 95$0^{\circ}C$ for 3 hours under 1 MPa of applied pressure. 4 points bending tests were used to evaluate the mechanical performance of these precracked laminate beams. Two types of mechanical responses were observed: crack penetration through the interface for x=0.75, 1 and crack deflection into an interface for x=0.25, 0.5. The Al2O3/NbCx-C1-x/Y2O3/Ti system suggested here has been proves to be effective for the thermokinetical stability and tailorability of the interfaces of Al2O3/Ti composites at 95$0^{\circ}C$.

• Journal of the Korean Ceramic Society
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• v.33 no.10
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• pp.1147-1155
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• 1996

• Journal of Korea Foundry Society
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• v.22 no.2
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• pp.75-81
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• 2002

The main objectives were to investigate the suitability of CaO crucible for melting TiAl alloys and to develop investment mold for investment casting of TiAl alloys. TiAl alloy specimen were prepared by plasma arc furnace under argon atmosphere. After melting of TiAl alloy using CaO crucible, the results showed that there is little contamination of oxygen in the TiAl bulk. Conventional vacuum induction furnaces can be readily adaptable to produce cast parts of TiAl without high skilled techniques. The determination of optical metallography and microhardness profiles in investment cast TiAl alloy rods has allowed the gradation of the relative thermal stability of the oxides examined. The molds used for the present study were $ZrO_2$, $Al_2O_3$, CaO stabilized $ZrO_2$ and $ZrSiO_4$. Even although high temperature of mold preheating, $Al_2O_3$ mold is a promising mold material for investment casting of TiAl alloys in terms of thermal stability, cost and handling strength. It is important to take thermal stability and preheating temperature of mold into consideration for investment casting of TiAl alloys.