• Journal of the Korean Ceramic Society
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• v.37 no.4
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• pp.354-358
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• 2000

Tetragonal (t)-ZrO2/Al2O3 composites doped with Y2O3, Nb2O5, and Fe2O3 ((Y, Nb, Fe)-TZP/Al2O3) were prepared over the range containing Fe2O3 from 0.1 to 0.5 mol% with 0.1 mol% intervals to evaluate the effect of Fe2O3 addition on chromaticity, hydrothermal stability, and mechanical property of the composites. After autoclaving for 20 h at 18$0^{\circ}C$ under 3.5 MPa water vapor pressure, no tlongrightarrowm phase transformation was observed probably due to the preferential solid solubility of Fe2O3 in Al2O3, the presence of the rigid Al2O3 particles, and the inherent phase stability of (Y, Nb)-TZP. The optimized strength and the fracture toughness of the composite were 700 MPa and 8.5 MPa.m1/2, respectively, when 0.1 mol% Fe2O3 was added. The composites have shown a gradual color change from a slightly white ivory to a pale yellowish brown with increasing the Fe2O3 concentration.

• Journal of the Korean Ceramic Society
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• v.29 no.10
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• pp.797-805
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• 1992

Al2O3-20 wt% ZrO2 composite powders to be used as the starting materials of the Al2O3/ZrO2-Spinel composite system were prepared by the use of the emulsion-hot kerosene drying method. The crystalline phase of ZrO2 in the synthesized Al2O3-ZrO2 composite powders was 100% tetragonal but the small amount of t-ZrO2 was transformed into m-ZrO2 after crushing. The hardness, fracture toughness, and flexural strength of the composite, which was sintered at 1650$^{\circ}C$ for 4 hrs after calcining at 1100$^{\circ}C$ for 2 hrs and had the relative density of 99%, were 15.7 GPa, 4.97 MN/m3/2, and 390 MPa, respectively. The fracture form in the sintered composites was found to be the intergranular fracture.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.11
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• pp.2015-2022
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• 2008

The effect of content of $Al_2O_3+Y_2O_3$ sintering additives on the densification behavior, mechanical and electrical properties of the pressureless-sintered $SiC-ZrB_2$ electroconductive ceramic composites was investigated. The $SiC-ZrB_2$ electroconductive ceramic composites were pressurless-sintered for 2 hours at 1,700[$^{\circ}C$] temperatures with an addition of $Al_2O_3+Y_2O_3$(6 : 4 mixture of $Al_2O_3$ and $Y_2O_3$) as a sintering aid in the range of $8\;{\sim}\;20$[wt%]. Phase analysis of $SiC-ZrB_2$ composites by XRD revealed mostly of $\alpha$-SiC(6H), $ZrB_2$ and In Situ YAG($Al_5Y_3O_{12}$). The relative density, flexural strength, Young's modulus and vicker's hardness showed the highest value of 89.02[%], 81.58[MPa], 31.44[GPa] and 1.34[GPa] for $SiC-ZrB_2$ composites added with 16[wt%] $Al_2O_3+Y_2O_3$ additives at room temperature respectively. Abnormal grain growth takes place during phase transformation from $\beta$-SiC into $\alpha$-SiC was correlated with In Situ YAG phase by reaction between $Al_2O_3$ and $Y_2O_3$ additive during sintering. The electrical resistivity showed the lowest value of $3.l4{\times}10^{-2}{\Omega}{\cdot}cm$ for $SiC-ZrB_2$ composite added with 16[wt%] $Al_2O_3+Y_2O_3$ additives at 700[$^{\circ}C$]. The electrical resistivity of the $SiC-TiB_2$ and $SiC-ZrB_2$ composite was all negative temperature coefficient resistance (NTCR) in the temperature ranges from room temperature to 700[$^{\circ}C$]. Compositional design and optimization of processing parameters are key factors for controlling and improving the properties of SiC-based electroconductive ceramic composites.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.05c
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• pp.15-18
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• 2001

The composites were fabricated 61 vol% $\beta$-SiC and $39vol%TiB_2$ powders with the liquid forming additives of 8, 12, 16wt% $Al_2O_3+Y_2O_3$ by hot pressing at $1730^{\circ}C$ and subsequent pressed annealing and pressureless annealing at $1750^{\circ}C$ for 4 hours to form YAG. The result of phase analysis of composites by XRD revealed $\alpha$-SiC(6H), $TiB_2$, and YAG($Al_5Y_3O_{12}$) crystal phase. The relative density of composites were increased with increasing $Al_2O_3+Y_2O_3$ contents. The fracture toughness showed the highest value of $7.77MPa{\cdot}m^{1/2}$ for composites added with 12wt% $Al_2O_3+Y_2O_3$ additives at room temperature. The electrical resistivity and the resistance temperature coefficient showed the lowest of $7.3{\times}10^{-4}{\Omega}{\cdot}cm$ and $3.8{\times}10^{-3}/^{\circ}C$, respectively, for composite added with 12wt% $Al_2O_3+Y_2O_3$ additives at room temperature. The electrical resistivity of the composites was all positive temperature coefficient resistance(PTCR) in the temperature range of $25^{\circ}C$ to $700^{\circ}C$.

• Journal of Power System Engineering
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• v.12 no.3
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• pp.60-65
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• 2008

This study aims at investigating the wear properties of thermally sprayed $Al/Al_2O_3$ metal matrix composite(MMC) coating against different counterparts. $Al/Al_2O_3$ MMC coatings were fabricated using a flame spray system on an Al 6061 substrate. Dry sliding wear tests were performed using the sliding speeds of 0.2m/s and the applied loads of 1 and 2 N. AISI 52100, $Al_2O_3$, $Si_3N_4\;and\;ZrO_2$ balls(diameter: 8mm) were used as counterpart materials. Wear properties of $Al/Al_2O_3$ MMC coatings were analyzed using a scanning electron microscope(SEM) and energy dispersive X-ray spectroscopy (EDX). It was revealed that wear properties of $Al/Al_2O_3$ composite coatings were much influenced by counterpart materials. In the case of AISI 52100 used as counterparts, the wear rate of composites coating layer increased according to the increase of the applied load. On the contrary, in the case of ceramics used as counterparts, the wear rate of composites coating layer decreased according to the increase of the applied load.

• Bulletin of the Korean Chemical Society
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• v.33 no.10
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• pp.3258-3264
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• 2012

Aluminum oxide ($Al_2O_3$) nanofibers were treated thermally under an ammonia ($NH_3$) gas stream balanced by nitrogen to form a thin aluminum nitride (AlN) layer on the nanofibers, resulting in the enhancement of thermal conductivity of $Al_2O_3$/epoxy nanocomposites. The micro-structural and morphological properties of the $NH_3$-assisted thermally-treated $Al_2O_3$ nanofibers were characterized by X-ray diffraction (XRD) and atomic force microscopy (AEM), respectively. The surface characteristics and pore structures were observed by X-ray photoelectron spectroscopy (XPS), Zeta-potential and $N_2$/77 K isothermal adsorptions. From the results, the formation of AlN on $Al_2O_3$ nanofibers was confirmed by XRD and XPS. The thermal conductivity (TC) of the modified $Al_2O_3$ nanofibers/epoxy composites increased with increasing treated temperatures. On the other hand, the severely treated $Al_2O_3$/epoxy composites showed a decrease in TC, resulting from a decrease in the probability of heat-transfer networks between the filler and matrix in this system due to the aggregation of nanofiber fillers.

• Composites Research
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• v.12 no.3
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• pp.36-44
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• 1999

The fabrication process of $Al_2O_{3p}/Al$ composite by in-situ process was investigated. The effects of processing variables such as addition type and content of Mg, processing temperature and time on the infiltration behavior of molten Al, microstructure and hardness were investigated. When the pure Al was infiltrated into mixtures of Mg and $Al_2O_3l$ powder, processing temperature required to spontaneous infiltration was decreased, and the content of Mg was the most powerful variable for infiltration of molten Al. But when the Al-Mg alloy was infiltrated into $Al_2O_3l$ particles, infiltration ratio indicated nearly same value regardless of Mg content in alloy and processing temperature, and critical processing temperature required to spontaneous infiltration was $800^{\circ}C$. The $Al_2O_{3p}/Al$ composites which were fabricated by mixtures of Mg and $Al_2O_3l$ powders resulted in high hardness value, but hardness values were scattered due to non uniform dispersion of $Al_2O_3l$ particles by excessive reaction of Mg.

• Journal of Industrial Technology
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• v.20 no.A
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• pp.239-245
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• 2000

Sintered $Al_2TiO_5$ has a very low thermal expansion and an infrared radiative selectively emitting large amounts of far infrared rays. However, it is week in mechanical strength. Spectral infrared emittance, thermal expansion coefficient, and mechanical strength of $Al_2TiO_5$-clay composites were studied to develop a material for far infrared radiators. The composites containing 10~50 mass% Jungsan clay had high emittance in the range of 2,000~500cm-1. The bending strength of the $Al_2TiO_5$-clay composites increased with increasing clay content. The $Al_2TiO_5$-clay composites with a clay content of 50mass% and heat-treated at $1,200^{\circ}C$ had a large strength for infrared radiators ; 86MPa. The average linear thermal expansion coefficient from $200{\sim}1,000^{\circ}C$ of the 50mass% jungsan clay containing compo sited heat-treated at $1,200^{\circ}C$ was lower than $3.87{\times}10-6/^{\circ}C$.

• Journal of the Korean Ceramic Society
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• v.43 no.8 s.291
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• pp.504-508
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• 2006

Functionally gradient porous $Al_2O_3-(t-ZrO_2)/HAp$ composites consist of 3 layers were fabricated using the multi-pass extrusion process at the various temperatures. The continuous pores were homogeneously formed in the $2^{nd}$ passed samples and their size was about $180{\mu}m$ in diameter. In the porous composites sintered at $1200-1400^{\circ}C$, the relative density and bending strength increased with the sintering temperature. The maximum values of relative density and bending strength in the $2^{nd}$ passed $Al_2O_3-(t-ZrO_2)/HAp$ composites were 62.2% and 107.8 MPa, respectively. In order to investigate the growth behavior of osteogenic cells on the functionally gradient porous $Al_2O_3-(t-ZrO_2)/HAp$ composites, an in vitro test was performed, using human osteoblast-like MG-63 cells. The cells were well attached and grown on the rough surface of the inside of the functionally gradient porous body.

• Journal of the Korean Ceramic Society
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• v.37 no.4
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• pp.368-375
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• 2000

Fracture toughness of particulate composites of Al2O3/SiC, Al2O3/ZrO2 and Al2O3/ZrO2/SiC was analysed theoretically. According to the suggested particle bridging model for obtaining the R-curve height, the crack extension resistance for the long crack was linearly proportional to the residual calmping stress at the interface between the second phase and the matrix. It was also a function of the particle size and the content. It was confirmed that the rising R-curve behavior of Al2O3 containing 30 vol% SiC particles of 3${\mu}{\textrm}{m}$ was owing to the strong crack bridging by SiC particles. For Al2O3/ZrO2/SiC composites, the tensional stress from the 3${\mu}{\textrm}{m}$ SiC particles was large enough to activate the spontaneous transformation of the ZrO2. The crack extension resistance due to the particle bridging mechanism did not seem to be affected much by the coupled toughening, but its resultant toughness increase could be significantly smaller due to the dependency on the matrix toughness.