• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.06a
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• pp.326-326
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• 2007

Influence of $Nd_2O_3$ addition to $ZnO-B_2O_3$-based glass on the water leaching resistance of the glass was first investigated. The optimized $Nd_2O_3-ZnO-B_2O_3$ (NZB) glass was ball milled for varying time, mixing with followed by $Al_2O_3$ crystalline phase to form $Al_2O_3$-NZB glass composites at $875^{\circ}C$ for 1h. Microwave dielectric properties of the composites were investigated as a function of the ball milling time of the NZB glass. Dielectric constant and quality factor were 5.70 and 9497 GHz, respectively, when the NZB glass was ball milled for 6h prior to mixing with $Al_2O_3$.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.1095-1096
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• 2006

When $Y_2O_3$ was added to Ti-excess $BaTiO_3$ ((Ba+Y)/Ti =1), the area occupied by $Y^{3+}$ ion was confirmed by its microstructure development, electrical conductivity behavior and lattice constant. Grain growth inhibition was observed when the content of donor dopant exceeded a critical value ($x{\approx}.0.01$) in $BaTiO_3+x(0.5Y_2O_3+TiO_2)$ system. A donor-doped behavior was observed at various Y contents ($0.2\sim3.0$ mol% Y) when $Y_2O_3$ was added to $TiO_2$-excess $BaTiO_3$. As Y content was increased, (002) and (200) peaks shifted to higher angles and the lattice constant (a and c axis) decreased gradually.

• Journal of the Korean Ceramic Society
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• v.34 no.1
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• pp.63-69
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• 1997

The effects of Cr2O3 content on the properties of direct-bonded MgO-Cr2O3 bricks were investigated in the range of 10 to 30 wt% of Cr2O3. Modulus of rupture of bricks was excellent in about 20 wt% of Cr2O3 content. The corrosion resistance of bricks was improved by increasing Cr2O3 content and was directly pro-portional to the amount of secondary spinels. On the other hand, the spalling resistance of bricks depended on the amount of flux rather than Cr2O3 content.

• Journal of the Korean Ceramic Society
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• v.30 no.9
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• pp.731-739
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• 1993

R-curve measurements were performed on Al2O3(matrix)-ZrO2-SiC whisker composite and Al2O3-ZrO2, Al2O3-SiC whisker composites in the favor of comparing the effect of ZrO2 and SiC whisker, as a second phase, to Al2O3 matrix. Al2O3-SiC whisker and Al2O3-ZrO2-SiC whisker were fabricated by hot pressing at 1$700^{\circ}C$, 15MPa and Al2O3-ZrO2 by pressureless sintering at 1$600^{\circ}C$. A controlled flaw/strength technique was utilized to determine fracture resistance as a function of crack extension and R-curve behaviour was determined from the relationship which is KR=K0(Δa)m. R-curveresults were KR=6.173$\times$Δa0.031 for Al2O3-ZrO2, KR=18.796$\times$Δa0.172 for Al2O3-SiC whisker and KR=11.96$\times$Δa0.110 for Al2O3-ZrO2-SiC whisker composite. From the analysis of R-curve and expeirmental data above three composites, it is found that R-curve behaviour of Al2O3-ZrO2-SiC whisker composite was dominated initially by the strengthening effect of ZrO2 and after, some extended crack were influenced by the effect of SiC whisker. Analysis of SEM and X-ray data revealed that whisker bridging in the crack wake and whisker pull-out mechanisms were the main mechanism for the R-curve behaviour.

• Korean Journal of Materials Research
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• v.20 no.7
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• pp.370-373
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• 2010

In fabricating plasma display panels, the photolithographic process is used to form patterns of barrier ribs with high accuracy and high aspect ratio. It is important in the photolithographic process to control the refractive index of the photosensitive paste. The composition of this paste for photolithography is based on the $B_2O_3-SiO_2-Al_2O_3$ glass system, including additives of alkali oxides and rare earth oxides. In this work, we investigated the density, structure and refractive index of glasses based on the $B_2O_3-SiO_2-Al_2O_3$ system with the addition of $Li_2O$, $K_2O$, $Na_2O$, CaO, SrO, and MgO. The refractive index of the glasses containing K2O, Na2O and CaO was similar to that of the [BO3] fraction while that of the SrO, MgO and Li2O containing glasses were not correlated with the coordination fraction. The coordination number of the boron atoms was measured by MAS NMR. The refractive index increased with a decrease of molar volume due to the increase in the number of non-bridging oxygen atoms and the polarizability. The lowest refractive index (1.485) in this study was that of the $B_2O_3-SiO_2-Al_2O_3-K_2O$ glass system due to the larger ionic radius of $K^+$. Based on our results, it has been determined that the refractive index of the $B_2O_3-SiO_2-Al_2O_3$ system should be controlled by the addition of alkali oxides and alkali earth oxides for proper formation of the photosensitive paste.

• Journal of the Korean Ceramic Society
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• v.25 no.4
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• pp.373-379
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• 1988

$\alpha$-Al2O3-15m/o ZrO2 powder was prepared by a sol-gel method from boehmite and zirconium acetate. The transformation temperature of boehmite to $\alpha$-Al2O3 in the system Al2O3-ZrO2 was increased due to the coupled crystallization. On the other hand, the transformation temperature from boehmite to $\alpha$-Al2O3-15m/o ZrO2 could be prepared at 110$0^{\circ}C$ for 100min. The specific surface area of the product of $\alpha$-Al2O3-15m/o ZrO2 was 13.2$m^2$/g.

• Korean Journal of Materials Research
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• v.30 no.7
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• pp.359-368
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• 2020

This study is aimed at improving the plasma resistance of Al₂O₃ ceramics on which plasma resistant YAS(Y₂O₃-Al₂O₃-SiO₂) frit is melt-coated using a simple heat-treatment process. For this purpose, the results of phase analysis and microstructural observations of the prepared YAS frits and the coating layers on the Al₂O₃ ceramics according to the batch compositions are compared and discussed with regard to the results of plasma resistance test. The prepared YAS frits consist of crystalline or amorphous or co-existing crystalline and amorphous phases according to the batch compositions, depending on the role and content of each raw material. The prepared YAS frit is melt-coated on the densely sintered Al₂O₃ ceramics, resulting in a dense coating layer with a thickness of at least ~ 80 ㎛. The YAS coating layer consists of crystalline YAG(Y₃Al₅O₁₂), Y₂Si₂O₇, and Al₂O₃ phases, and YAS glass phase. Plasma resistance of YAS coated Al₂O₃ ceramics is strongly dependent on the content of the YAG(Y₃Al₅O₁₂) and Y₂Si₂O₇ crystalline phases in the coating layer, especially on the content of the YAG phase. Comparing the weight loss of YAS coating ceramics with values obtained for commercial Y₂O₃, Al₂O₃, and quartz ceramics, the plasma resistance of the YAS coating ceramics is 6 times higher than that of quartz, 2 times higher than that of Al₂O₃, and 50 % of the resistance of Y₂O₃.

• Journal of the Korean Ceramic Society
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• v.30 no.10
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• pp.811-818
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• 1993

Al2O3/ZrO2-Spinel composites were prepared by infiltrating magnesium sulfate solution into the porous preform made from Al2O3-20wt% ZrO2 composite powders derived through an emulsion route. The microstructure and composition of the modified composites could be controlled by manipulating the presingtering temperature of the preform, infiltration time, and so on. It was found that spinel phases were concentrated near the surface than in the interior of the Al2O3/ZrO2-Spinel composites infiltrated for 6hrs, while spinel phases were uniformly distributed in the comosites infiltrated for 2 days. The relative density and fracture toughness of the composite infiltrated for 6 hrs were 98.6% and 7.2MN/m3/2, respectively.

• Journal of Korean Ophthalmic Optics Society
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• v.7 no.2
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• pp.19-25
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• 2002

Ternary $xSrO-yB_2O_3-0.1Al_2O_3$ and $xSrO-yB_2O_3-0.1SiO_2$ glasses were prepared as a function of R(${\equiv}x/y$). The fraction of four-coordinated brans ($N_4$), symmetric three-coordinated barons ($N_{3S}$), and asymmetric three-coordinated barons ($N_{3A}$) were determined quantitatively to study the structures of these glasses by $^{11}B$ NMR. The values of $Q_{cc}$ and ${\eta}$ for $BO_3$ unit in the glasses were 2.74MHz and 0.22, those for $BO_3{^-}$ unit were 2.54MHz and 0.55, and those for $BO_4$ unit 0.60~0.75MHz and 0.00, respectively. The structure of SrBAl glass at $R_{1st}$ consisted of tetraborate ($[B_8O_{13}]^{-2}$) units and 1st-modified diborate ($[B_2Al_2O_7]^{-2}$) units, and those for the glass at $R_{max}$consisted of diborate ($[B_4O_7]^{-2}$) units, metaborate ($[BO_2^{-1}]$), 1st-modified diborate units, and 2nd-modified diborate ($[B_2Al_2O_8]^{-4}$) units. Due to the oxygens introduced from the strontium oxide. $AlO_4$ units were preferably formed rather than $BO_4$ units. And, the structure of SrBSi glasses in the region $R{\leq}0.5$ could be viewed as binary $SrO-B_2O_3$ glasses structure diluted by silicate oxide: therefore, the Si atoms of the glasses did not contributed to the change the configuration around the boron atoms. The silicate oxide was formed the $SiO_4{^-}$ units rather than the $BO_3{^-}$ units by the oxygens introduced from the storntium oxide in the region of $R{\geq}R_{max}$, and structure of those glass at $R_{max}$ consisted of diborate units, metaborate units loose $BO_4([BO_2]^{-1})$, and $SiO_4{^-}([SiO_{2.5}]^{-1})$ units.

• Journal of the Korean Ceramic Society
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• v.34 no.3
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• pp.281-288
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• 1997

The effects of 0 to 6 mol% excess 91PbO-9WO3 addition on the microstructure and the dielectric pro-perties in 40Pb(Mg1/3Nb2/3)O3-30PbTiO3-30Pb(Mg1/2W1/2)O3 ternary system were investigated. Excess 91PbO-9WO3 addition enhanced densification at relatively lower temperature due to the formation of liquid phase. The dielectric constant of the specimen with standard composition was 16,400 and that of specimen with 1 mol% excess additive was the maximum of 18,500. And more than 2 mol% excess addition decreased dielec-tric constant. Specimens with 2~4 mol% 91PbO-9WO3 addition showed dual peak maxima in the tem-perature dependence of dielectric constant. In the specimens which have more than 5 mol% excess addition a new phase with W-rich composition was formed at grain boundary.