• Journal of the Korean Ceramic Society
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• v.40 no.2
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• pp.109-112
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• 2003

The grain-boundary microcracking materials in the system $Al_2$TiO$_{5}$ -ZrTiO$_4$(ZAT) is influenced by the thermal expansion anisotropy. The range of ZAT compositions investigated had showed very low thermal expansions of 0.3~1.3$\times$10$^{-6}$ K loin compared to 8.29$\times$10$^{6}$ K of pure ZrTiO$_4$and 0.68$\times$10$^{6}$ K of polycrystalline $Al_2$TiO$_{5}$ , respectively, compared with the theoretical thermal expansion coefficient for a single crystal of $Al_2$TiO$_{5}$ , 9.70$\times$10$^{6}$ K. The low thermal expansion and microcraking temperature are apparently due to a combination of thermal contraction and expansion caused by the large thermal expansion anisotropy of the crystal a ies of the $Al_2$TiO$_{5}$ phase.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.10a
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• pp.155-159
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• 2002

This paper has studied to obtain the grinding characteristics and optimal grinding conditions of ceramics in the grinding with diamond wheel by Taguchi method. Feed rate was most important factor to the surface roughness. In the case of 4{Si_3}{N_4}$ and ${A1_2}{O_3}$, surface roughness value were small at 3m/min of feed rate. In the case of $ZrO_2$. surface roughness value was small at 4m/min of feed rate. Surface roughness have much influenced by major load for the :ii3N4 and $ZrO_2$. On the other hand, ${A1_2}{O_3}$ have more influenced by grain shedding of brittle fracture phenomenon. The major factors affecting the surface roughness and the optimum grinding conditions were obtained with minimum experiment using Taguchi method.

• Journal of the Korean Ceramic Society
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• v.35 no.10
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• pp.1061-1069
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• 1998

The thermal instability of Al2TiO5 Ceramics was contrlled by solid solution with MgO SiO2 and ZrO2 through electrofusion in an arc furnace. The thermal expansion properties of Al2TiO5 composites show the hysteresis due to the strong anisotropy of The crystal axes of these material. These phenomena are ex-plained by the opening and closing of microcracks. The difference in microcracking temperatures e.g 587.6(ATG2), 405.9(ATG3) and 519.7$^{\circ}C$(ATG4) is caused by the difference in grain size and stabilizer type. The thermal shock behaviour under cyclic conditions between 750-1400-75$0^{\circ}C$ show no change in mi-crostructure and phase assemblage for all three stabilized specimens. After the thermal loading test at 110$0^{\circ}C$ for 100hrs. ATG1 and ATG2 materials decomposes completely to its components corundum and ru-tile in both cases. However with approximatelly 20% retention of the Al2TiO5 Thus in order to prevent decomposition of the stabilized material in the critical temperature range 800-130$0^{\circ}C$ it must be traversed within a short period of time.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.28 no.3
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• pp.170-174
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• 2015

Composite ceramics of alumina-TZP(3Y) have good mechanical and electrical properties. So, They have been used as high strength refractory materials and thick film substrates, etc. In this study, Composite ceramics of alumina-TZP(3Y) were fabricated by uniaxial pressing and sintering at 1,400, 1,500, and $1,600^{\circ}C$, and their microstructures and mechanical properties were investigated. As the TZP(3Y) content in composite ceramics increases from 20 wt.% to 80 wt.%, the fracture toughness increases monotonically, which seems to be related to the higher relative density and/or toughening mechanism by means of stabilized tetragonal zirconia phase at room temperature. In contrast to the fracture toughness, Vickers hardness of the composite ceramics shows maximum value (1,938 Hv) at a 40 wt.% of TZP(3Y). The result of Vickers hardness is likely to be due to more dense sintered microstructure of composite ceramics than pure alumina and reinforcement of composite ceramics with TZP(3Y), considering that Vickers hardness of pure $Al_2O_3$ is greater than that of TZP(3Y). It is also shown that the $ZrO_2$ particles are $l^{\circ}Cated$ between $Al_2O_3$ grains and suppress grain growth each other.

• Journal of the Korean Ceramic Society
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• v.22 no.6
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• pp.71-79
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• 1985

In order to fabricate the translucent electrooptic ceramics which are comparable to PLZT, $PNZT^*$ has been prepared from aqueous solutions of their itrate and chlorides. In the quarternary $Pb^{1-x} Nd_x(Zr_{0.63} Ti_{0.37})^{1-\frac{x}{4}O_3$, (PNZT) $(0.02\le x\ge 0.12)$ system cold-pressed PNZT slugs were sintered in $O_2$ in pt-crucible for 45 min. at 118$0^{\circ}C$ and were then heat-treated in air for 60 hrs. at 120$0^{\circ}C$ in Al2O3 crucibles containing $PbZrO_3$ powder to control the atmosphere. Mean particle size of calcined PNZT powders was 0.1~0.15${\mu}{\textrm}{m}$. It was found that the maximum value of optical transmission has been revealed at 6~8 at. % $Nd_2O_3$ added body and that their dielectric constant has been decreased as the frequency increased. Curic temperature has been varied inversely with $Nd^{3+}$ ion content up to 8 at. % and become constant above this value. $^*Pb_{1-x}Nd_x(Zr_{0.63} Ti_{0.37})_{1-2/4}O_3$

• Korean Journal of Materials Research
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• v.16 no.3
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• pp.157-162
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• 2006

Pressable ceramics have many applications in the field of dental industry because of their excellent esthetic, compressive strength, chemical durability. Despite these attractive characteristics, they have not been widely used since they are very brittle and extremly sensitive to porcelain. In this study, the fabrication of pressable dental porcelain ($SiO_2-Al_2O_3-K_2O-Na_2O$) as a function of contents of $Al_2O_3,\;BaO\;and\;ZrO_2$ were investigated. And then compressive strength, Vickers hardness, density and thermal expansion coefficient (TEC) tests have been carried out to evaluate properties of pressable dental porcelain fabricated. The property of pressable dental porcelain fabricated by adding of 15%$Al_2O_3$ and 2%BaO contents was closely approximated to that of natural tooth.

• The Korean Journal of Ceramics
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• v.4 no.4
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• pp.352-355
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• 1998

Dense $ Pb(Zr, Ti)O_3(PZT)/Al_2O_3$ nanocomposites were prepared by the 28 GHz microwave heating method and conventional electric furnace sintering. Electrical and mechanical properties of the composites were investigated. The fracture strength of the PZT composites with 0.1vol% $Al_2O_3$ was significantly improved in both sintering methods. Smaller grain size and effective reinforcement of the PZT matrix by the second phase were considered to be responsible for the excellent fracture strength. Planar electromechanical coupling factor Kp of the composites sintered by 28GHz microwave heating was higher than that of the materical prepared by the conventional route. It seemed that the control of the reaction between PZT and $Al_2O_3$ by the microwave rapid sintering resulted in the high piezoelectric properties.

• 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.

• The Korean Journal of Ceramics
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• v.4 no.4
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• pp.340-344
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• 1998

Failure mechanisms were investigated for the two layer thermal barrier coatings consisting of NiCrAlY bond coat and $ZrO_2$-8wt.% $Y_2O_3$ ceramic coating during cyclic oxidation. $Al_2O_3$ developed at the ceramic coating/bond coat interface first, followed by the Cr/Ni rich oxides such as $NiCr_2O_4$ and $Ni(Al, Cr)_2O_4$ during cyclic oxidation. It was observed that the spalling of ceramic coatings took place primarily within the NiCrAlY bond coat oxidation products or at the interface between the bond coat oxidation products and zirconia based ceramic coating or the bond coat. It was also observed that the fracture within these oxidation products occurred with the formation of $Ni(Cr, Al)_2O_4$ spinel or Cr/Ni rich oxides. It was therefore concluded that the formation of these oxides was a life-limiting event for the thermal barrier coatings.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.3 no.2
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• pp.176-184
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• 1993

The glasses, which the $\beta$-spodumene as the principal crystalline phase could be precipitated, were melted by adding >, $P_2O_5, TiO_2, ZrO_2 in the Li_2O-Al_2O_3-SiO_2$ system. In order to achieve the glass-ceramic body of near-theoritical density by sintering method, the optimum condition of heat treatment, the effect of glass powder size and the properties were investigated by DTA, XRD, bulk density, thermal expansion and SEM. Addition of $P_20_5$ imProved the tendency of sintering and the sample with 9wt% $P_20_5$ content was the most dense OOdy by sintering method. The optimum condition of heat treatmemt was sintered for densitification at $740^{\circ}C$ and crystallized at $950^{\circ}C$. In the optimum condition, the relative density was above 90% and the thermal expansion was negative about $-1{\times}10^{-7}/^{\circ}C$.