• Applied Science and Convergence Technology
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• v.24 no.2
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• pp.33-40
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• 2015

$ZrO_2$ and Al-Zr composite oxide film was prepared by vacuum assisted sol-gel dip coating method and anodizing. $ZrO_2$ films annealed above $400^{\circ}C$ have tetragonal structure. $ZrO_2$ layers inside etch pits were successfully coated from the $ZrO_2$ sol. The double layer structures of samples were obtained after being anodized at 100 V to 600 V. From the TEM images, it was found that the outer layer was $Al_2O_3$, the inner layer was multi-layer of $ZrO_2$, Al-Zr composite oxide and Al hydrate. The capacitance of $ZrO_2$ coated foil exhibited about 28.3% higher than that of non-coating foil after being anodized at 100 V. The high capacitance of $ZrO_2$ coated foils anodized at 100 V can be attributed to the relatively high percentage of inner layer in total thickness. The electrical properties, such as withstanding voltage and leakage current of coated and non-coated Al foils showed similar values. From the results, $ZrO_2$ and Al-Zr composite oxide is promising to be used as the partial dielectric of high voltage capacitor to increase the capacitance.

• Korean Journal of Materials Research
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• v.11 no.6
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• pp.519-526
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• 2001

The effects of methyl isobutyl ketone(MIBK)/ethanol(EtOH) solvent mixtures on the dispension, particle size distribution and rheology of $Al_2$O$_3$/ZrO$_2$ nonaqueous suspensions were investigated by measuring sedimentation density and viscosity. The sedimentation density of $Al_2$O$_3$ and ZrO$_2$ particles increased in MIBK-rich($\geq$60 vol%) solvents with 'Hypermer' KD-1 as a dispersant. The ball-milled suspensions in 80MIBK/20EtOH(vol%) solvent exhibited the narrow and unimodal particle size distribution. Although all Suspensions exhibited the Pseduo-Plastic flow(Shear thinning) the shear thinning behavior was somewhat different depending on the mixture ratio of $Al_2$O$_3$/ZrO$_2$ and MIBK/EtOH. Under a given shear rate( <300 s$^{-1}$ for $Al_2$O$_3$; <3000 s$^{-1}$ for ZrO$_2$) the strongest shear thinning appeared in the $Al_2$O$_3$ and ZrO$_2$ suspensions with pure MIBK solvent. The shear thinning was nearly independable on the mixture ratio of $Al_2$O$_3$/ZrO$_2$ in case of using the identical solvent(80MIBK/20EtOH, vol%).

• Journal of the Korean Ceramic Society
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• v.27 no.4
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• pp.487-494
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• 1990

$Al_2O_3$-20w/o $ZrO_2$ composite powders were prepared by the emulsion-coprecipitation method and the effects of preparative conditions on powder characteristics were investigated. In the preparation of $Al_2O_3$-$ZrO_2$ composite powders, toluene was used instead of kerosene as the oil phase in emulsions. After coprecipitation, the emulsion was easily broken into a single liquid phase by adding methanol, and then precipitates could be effectively collected by filteration. The fact that all $ZrO_2$ phases present at room temperature in composite powders calcined at $1100^{\circ}C$ after washed by methanol had a tetragonal structure confirmed that methanol-washing enhanced the dispersibility of fine $ZrO_2$ particles in $Al_2O_3$ matrix. $Al_2O_3$-$ZrO_2$ composite powders were spherical particles of 0.2${\mu}{\textrm}{m}$ diameter. Pellets sintered at $1650^{\circ}C$ for 2hrs showed the relative theoretical density of 97.3% and the fracture toughness of 5.01MN/$m^{3/2}$.

• Journal of the Korean Ceramic Society
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• v.34 no.1
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• pp.88-94
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• 1997

The oxidation behavior of the NiCrAlY bond coat and thermal fatigue failure in the plasma-sprayed thermal barrier coating system, ZrO2.8wt%Y2O3 top coat/Ni-26Cr-5Al-0.5Y bond coat/Hastelloy X superalloy substrate, in commercial use for finned segment of gas turbine burner were investigated. The main oxides formed in the bond coat were NiO, Cr2O3, and Al2O3. It divided the oxide distribution at this interface into two types whether an Al2O3 thin layer existed beneath ZrO2/bond coat interface before operation at high temperature or not. While a continuous layer of NiO was formed mainly in the region where the Al2O3 thin layer was present, the absence of it resulted in the formation of mixture of Cr2O3 and Al2O3 beneath NiO layer. Analyses on the fracture surface of specimen spalled by thermal cycling showed that spalling occurred mainly along the ceram-ic coat near ZrO2/bond coat oxide layer interface, but slightly in the oxide layer region.

• Journal of the Korean Ceramic Society
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• v.33 no.2
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• pp.143-148
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• 1996

• Journal of the Korean Ceramic Society
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• v.25 no.3
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• pp.225-230
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• 1988

The strength and thermal shock resistance of $Al_2O_3-ZrO_2$ composites have been studied. The tetragonal $ZrO_2$ powder containing 1 mol.% $Y_2O_3$ and monoclinic $ZrO_2$ powder were prepared by coprecipitation method and subsequently mixed with $Al_2O_3$ powder and granulated by sieving. Duplex composites were prepared by dry mixing matrix agglomerate with 15 to 30 vol.% of dispersion agglomerate, followed by pressing and sintering at 1$600^{\circ}C$ for1 hr. These $Al_2O_3-ZrO_2$ 2 composites having heterogeneous structure showed improved thermal shock behaviors because of the microcracking and pores in dispersed granules, and compressive stresses around dispersed granules resulting from $ZrO_2$ transformation.

• Journal of the Korean Ceramic Society
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• v.18 no.3
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• pp.187-191
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• 1981

The effect of additions, $TiO_2$ and $ZrO_2$ as nucleant on the base glass which composition was determined to 0.97 $Li_2O-Al_2O_3-SiO_2$ has been investigated by means of D.T.A., X-ray diffraction and dilatation. $TiO_2$ and $ZrO_2$ as nucleant were added 0.06mole, in which ratios of $TiO_2$/$ZrO_2$ were varied 1/0, 2/1, 1/1, 1/2 and 0/1. The crystalline phases were appeared to $\beta$-spodumene as principal, $\beta$-eucryptite and $ZrO_2$ as secondary, regardless of nucleant variations. The crystallinity of the crystallized glass added $TiO_2$, $ZrO_2$ mixture as nucleant was higher than that of the glass added $TiO_2$ or $ZrO_2$ only. The crystallinity of the glass added $TiO_2$/$ZrO_2$ =1/1 was highest. Increasing the addition of $ZrO_2$, it has been observed that the crystal growing temperature became higher.

• 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.

• Proceedings of the KIEE Conference
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• 1998.11c
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• pp.853-855
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• 1998

The electrical resistivity and mechanical properties of the hot-pressed and annealed ${\beta}$-SiC+39vol.%$ZrB_2$ electroconductive ceramic composites were investigated as a function of the liquid forming additives of $Al_{2}O_{3}+Y_{2}O_{3}$(6:4wt%). In this microstructures. no reactions were observed between $\beta$-SiC and $ZrB_2$, and the relative density is over 97.6% of the theoretical density. Phase analysis of composites by XRD revealed mostly of a $\alpha$-SiC(6H, 4H), $ZrB_2$ and weakly $\beta$-SiC(15R) phase. The fracture toughness decreased with increased $Al_{2}O_{3}+Y_{2}O_{3}$ contents and showed the highest for composite added with 4wt% $Al_{2}O_{3}+Y_{2}O_{3}$ additives. The electrical resistivity increased with increased $Al_{2}O_{3}+Y_{2}O_{3}$ contents because of the increasing tendency of pore formation according to amount of liquid forming additives $Al_{2}O_{3}+Y_{2}O_{3}$. The electrical resistivity of composites is all positive temperature coefficient resistance(PTCR) against temperature up to $700^{\circ}C$.

• Korean Journal of Materials Research
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• v.24 no.5
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• pp.259-265
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• 2014

$ZrO_2$ films were coated on aluminum etching foil by the sol-gel method to apply $ZrO_2$ as a dielectric material in an aluminum(Al) electrolytic capacitor. $ZrO_2$ films annealed above $450^{\circ}C$ appeared to have a tetragonal structure. The withdrawal speed during dip-coating, and the annealing temperature, influenced crack-growth in the films. The $ZrO_2$ films annealed at $500^{\circ}C$ exhibited a dielectric constant of 33 at 1 kHz. Also, uniform $ZrO_2$ tunnels formed in Al etch-pits $1{\mu}m$ in diameter. However, $ZrO_2$ film of 100-200 nm thickness showed the withstanding voltage of 15 V, which was unsuitable for a high-voltage capacitor. In order to improve the withstanding voltage, $ZrO_2$-coated Al etching foils were anodized at 300 V. After being anodized, the $Al_2O_3$ film grew in the directions of both the Al-metal matrix and the $ZrO_2$ film, and the $ZrO_2$-coated Al foil showed a withstanding voltage of 300 V. However, the capacitance of the $ZrO_2$-coated Al foil exhibited only a small increase because the thickness of the $Al_2O_3$ film was 4-5 times thicker than that of $ZrO_2$ film.