• 전자공학회논문지 IE
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• v.49 no.2
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• pp.1-8
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• 2012

The effects of the addition of either monoclinic $ZrO_2(pure)$ or tetragonal $ZrO_2$ containing 5.35wt% $Y_2O_3(Y-TZP)$ on the mechanical properties and thermal shock resistance of $Al_2O_3$ ceramics were investigated. The addition of $ZrO_2$(m) and Y-TZP increased sintered density of $Al_2O_3$. The Vickers hardness also increased as the volume fraction of Y-TZP increased going through a maximum at 20wt%. The hardness of the specimens was found to be dependent on the sintered density. The higher volume fraction of either $ZrO_2(m)$ or Y-TZP resulted in the higher fracture toughness of the composite was. This result may be taken as evidence that toughening of $Al_2O_3$ can be achieved by not only the transformation toughening but microcrack toughening of $ZrO_2$. The thermal shock property for $Al_2O_3-ZrO_2$ composites was improved by increasing the volume fraction of monoclinic $ZrO_2(pure)$. The grain size increased as the volume fraction of $ZrO_2$ did.

• Journal of the Korean Ceramic Society
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• v.48 no.1
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• pp.69-73
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• 2011

A $ZrO_2$ thin film as a corrosion protective layer was deposited on Zircaloy-4 (Z-4) clad material using $N_2O$ as a reactive gas by RF reactive magnetron sputtering at room temperature. The Z-4 substrate was located in plasma or out of plasma during the $ZrO_2$ deposition process to investigate mechanical and corrosive properties for the plasma immersion. Tetragonal and monoclinic phases were existed in $ZrO_2$ thin film immersed in plasma. We observed that a grain size of the $ZrO_2$ thin film immersed in plasma state is larger than that of the $ZrO_2$ thin film out of plasma state. In addition, the corrosive property of the $ZrO_2$ thin films in the plasma was characterized using the weight gains of Z-4 after the corrosion test. Compared with the $ZrO_2$ thin film immersed out of plasma, the weight gains of $ZrO_2$ thin film immersed in plasma were larger. These results indicate that the $ZrO_2$ film with the tetragonal phase in the $ZrO_2$ can protect the Z-4 from corrosive phenomena.

• Journal of the Korean Ceramic Society
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• v.23 no.3
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• pp.44-52
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• 1986

$Al_2O_3-ZrO_2$ ceramics was obtained by the co-precipitation method using $Al_2(SO_4)_2$.$18H_2O$ and $ZrOCl_2$.$8H_2O$ as starting materials $MgCl_2$.$6H_2O$ as a sintering aid and NH4OH as a hydrolyzing agent. The coprecipitate from the above raw materials was calcined at 125$0^{\circ}C$ for 1h and again sintered at 1$650^{\circ}C$ for 2h before measurements of strength hardness and fracture toughness. MgO addition was found to increase mechanical properties of the $Al_2O_3-ZrO_2$ system. The strength and frac-ture toughness of $Al_2O_3-ZrO_2$ ceramics were considered to be increased by stress-induced phase tranforma-tion of $ZrO_2$.

• 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.

• Journal of the Korean Ceramic Society
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• v.29 no.8
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• pp.667-673
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• 1992

The alumina-zirconia composite powders of core particle ZrO2 coated with Al2O3 were prepared by the hydrolysis-deposition of the mixed aluminum salt solution of Al2(SO4)3-Al(NO3)3-Urea. The effects of hydrolysis reaction and coating parameters on characteristics of coated powders and composites were also investigated. The degree of coating could be estimated from the ratio of tetra-/mono-ZrO2 present at the room temperature after heat-treating coated powders at 120$0^{\circ}C$ and the result of TEM observations. When the content of ZrO2 in the dispersed coating system, the coating time, and the volume ratio of water/solution were 50 mg/g, 180 min, and 5, respectively the coating efficiency was maximum (the ratio of tetra-/mono-ZrO2 was 87/13). The relative densities of coated Al2O3-ZrO2 composites sintered at 1$650^{\circ}C$ for 4 hrs were about 91~98% and the maximum ratio of tetra-/mono-ZrO2 in Al2O3-20wt% ZrO2 composites was 62/38.

• 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 the Korean Ceramic Society
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• v.22 no.1
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• pp.11-18
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• 1985

The effect of stress induced phase transformation on $Al_2 O_3$ matrix dispersed with $ZrO_2-Y_2O_3$ has been studied. In order to determinate the mechanical properties three $Al_2O_3-ZrO_2$ composite series containing 1, 3 and 5 mole% $Y_2O_3$ were prepared. The starting materials were $Al_2O_3$ and $ZrO_2-Y_2O_3$ which was prepared from the aqueous solution of high purity $YCl_3$.$6H_2O$ and $ZrOCl_2$.$8H_2O$. Powder mixtures of $Al_2O_3-ZrO_2$ containing $Y_2O_3$ have been prepared by ball-milling with methanol and the samples were formed by isostatic press and sintered at 150$0^{\circ}C$ for 2hrs. After sintering. the specimens were polished for mechanical determination. The relative density of sintered specimens were also measured. It was found that the addition of 1, 3mole% to {{{{ { ZrO}_{2 } }} allowed full retention of the tetragonal phase in $Al_2O_3-ZrO_2$ but partially stabilized zirconia (PSZ) was produced by additions of 5 mole% $Y_2O_3$.The critical stress-intensity factor KIc of $A_2O_3-ZrO_2$ (containing 1 mole% $Y_2O_3$) composite materials increased with increasing $ZrO_2$ content, The maximum value of KIC=7Mn/$m^3$/2 at 20 mole% $ZrO_2$ exhibited about twice that of the $Al_2 O_3$ The modulus of rupture exhibited a trend similiar to KIC The maximum value of MOR was 580MN/m2. As the amount of Y2O3 increase it was observed that the maximum of KIC and MOR decreased : Additions of 3 mole% $Al_2O_3$ $Y_2O_3$ allowed the maximum of KIC 6MN/$m^3$/2 MOR 540MN/$m^2$ at 15 mole% $ZrO_2$ additions of 5 mole% $Y_2O_3$ allowed the maximum of KIC 5MN/$m^3$/2 MOR 410MN/$m^2$ at 10 mole% $ZrO_2$.

• Journal of the Korean Ceramic Society
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• v.39 no.4
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• pp.377-385
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• 2002

The possibility of $ZrO_2$ thin film as insulator for Metal-Ferroelectric-Insulator-Semiconductor(MFIS) structure was investgated. $SrBi_2Ta_2O_9$ and $SrBi_2Ta_2O_9$(SBT) thin films were deposited on P-type Si(111) wafer by R. F. magnetron sputtering method. The electrical properties of MFIS gate were relatively improved by inserting the $ZrO_2$ buffer layer. The window memory increased from 0.5 to 2.2V in the applied gate voltage range of 3-9V when the thickness of SBT film increased from 160 to 220nm with 20nm thick $ZrO_2$. The maximum value of window memory is 2.2V in Pt/SBT(160nm)/$ZrO_2$(20nm)/Si structure with the optimum thickness of $ZrO_2$. These memory windows are sufficient for practical application of NDRO-FRAM operating at low voltage.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.2
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• pp.349-351
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• 2011

The formation of oxide superconducting phase fabrication of superconducting wire materials and fabrication of precise superconducting material were studied for developing superconductor application technique. The $ZrO_2$ addition reduced the particle size $BaZrO_3$ trapped in the matrix after the sintering growth. The added $ZrO_2$ was converted to fine particles of $BaZrO_3$ which is the conventional sintering temperature for YBaCuO, $Y_2Ba_1Cu_1O_5$ and CuO are formed as by products of the reaction between $ZrO_2$ and YBaCuO phase. The formation of highly $BaZrO_3$ particle appears to be responsible for the refinement of $BaZrO_3$ phase after the citric acid sintering process.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1997.11a
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• pp.436-439
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• 1997

We investigated a electrical and CO gas sensing properties of pure ZnO and ZnO-ZrO$_2$ composite ceramics. We made 0∼20mo1% ZrO$_2$added ZnO composite ceramics and observed a microstructure of the broken side of the samples. The properties of the samples were studied with temperature, composition, arid a concentration of carbon monoxid. The measured 1000ppm CO sensitivities of pure ZnO were about 1∼1.42, and that of ZnO-ZrO$_2$were about 1∼10.6. In order words, the 1000ppm CO sensitivities of ZnO-ZrO$_2$composite ceramics were about 1∼2 times larger than that of pure ZnO with temperature. The measured 250ppm, 500ppm CO sensitivities of ZnO-ZrO$_2$composite ceramics were about ∼3.28. ∼5.04, respectively.