• Applied Chemistry for Engineering
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• v.7 no.5
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• pp.1006-1014
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• 1996

A series of catalysts, $NiO-ZrO_2/WO_3$, for ethylene dimerization were prepared by coprecipitation from a solution of nickel chloride - zirconium oxychloride mixture followed by dry impregnation with an aqueous solution of ammonium metatungstate and calcination in air. On the basis of the results obtained from x-ray diffraction and DSC, the addition of NiO and $WO_3$ to $ZrO_2$ shifted the transition of $ZrO_2$ from amorphous to a tetragonal phase toward higher temperatures due to the interaction between NiO(or $WO_3$) and $ZrO_2$. $NiO-ZrO_2$ without $WO_3$ was inactive for the ethylene dimerization, but $NiO-ZrO_2/WO_3$ was found to be very active even at room temperature. The high catalytic activity of $NiO-ZrO_2/WO_3$ was closely correlated with the increase of acid strength by the inductive effect of $WO_3$.

• Journal of the Korean Ceramic Society
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• v.26 no.2
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• pp.210-220
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• 1989

The properties of the powder of Al2O3-15v/o ZrO2(＋3m/o Y2O3) system prepared by co-precipitation method at the pH values of 7, 9, 10 and 11 were investigated. Al2(SO4)3.18H2O, ZrOCl2.8H2O and YCl3.6H2O were used as starting materials and NH4OH as a precipitation agent. Zirconium hydroxide decreased the specific surface area of aluminum hydroxide of AlOOH type, while increased the specific surface area of aluminum hydroxide of Al(OH)3 type, and formed co-network structure of Al-O-Zr type with the aluminum hydroxides. The rate of transition to $\alpha$-Al2O3 from co-precipitated materials occurred in the order of 7≒10, 9 and 11 of pH values. Al2O3 and ZrO2 interacted to bring about coupled grain growth, and the growth of ZrO2 crystallite size rapidly occurred within $\theta$-Al2O3 matrix. Segregation did not occur in the system Al2O3-15v/o ZrO2(＋3m/o Y2O3) and Y2O3 acted as a stabilizer to ZrO2. The lattice strain of tetragonal ZrO2 was increased by the constraint effect of Al2O3 matrix.

• Journal of the Korean Ceramic Society
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• v.41 no.2
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• pp.111-117
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• 2004

3Y-TZP containing 0.3∼1.2 wt% of $Al_2$O$_3$ was prepared by slip-casting after attrition milling. The specimen was sintered at 1390∼151$0^{\circ}C$ and mechanical characterization and microstructure analysis were conducted. Monoclinic content of the specimen was calculated by XRD. The apparent density of specimen increased with increasing sintering temperature. While above 1470%, the formation of m-ZrO$_2$ degraded the density. The microhardness of specimen decreased with temperature because monoclinic phase increased wit the grain growth. The specimen containing $Al_2$O$_3$ below 0.9 wt% sintered at 143$0^{\circ}C$ showed the highest microhardness of 1360 Hv.

• Journal of the Korean Ceramic Society
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• v.29 no.5
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• pp.341-346
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• 1992

The effects of CaO addition on the low temperature degradation behavior of 2.5Y-TZP ceramics were investigated. Y2O3-CaO-ZrO2 ceramics were prepared from the commercial Y-TZP powder added within 1 mol% of CaO. Fully tetragonal phase could be obtained at each composition under sintering condition of 1500$^{\circ}C$ for 1 hour. As the amount of CaO increased, grain size was decreased. From the result of heat treatment at 200$^{\circ}C$, volume fraction of monoclinic phase formed on the surface of each specimen was decreased with higher CaO amount. Stability of tetragonal ZrO2 phase for low temperature heat treatment was increased by CaO addition without the degradation of mechanical properties.

• Korean Journal of Materials Research
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• v.12 no.3
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• pp.220-224
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• 2002

The oxide scales formed on $Ni_3Al$-7.8%Cr-1.3%Zr-0.8%Mo-0.025%B after oxidation at 900, 1000 and 110$0^{\circ}C$ in air were studied using XRD, SEM, EPMA and TEM. The oxide scales consisted primarily of $NiO,\; NiAl_2O_4,\;{\alpha}-Al_2O_3,\; monoclinic-ZrO_2,\; and \;tetragonal-ZrO_2$. The outer layer of the oxide scale was rich in Ni-oxides, whereas the internal oxide stringers were rich in Al-oxides and $ZrO_2$. Within the above oxide scales, Cr and Mo tended to exist as dissolved ions.

• Journal of the Korean Ceramic Society
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• v.27 no.5
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• pp.613-618
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• 1990

The pure and 6mol% MgO-doped ZrO2 powders were prepared by hot petroleum drying method. The power characterization of homogeneous fine powder was indentified by the method of thermal analysis, BET and electron microscope. The transformation, content of t-ZrO2, crystallite size and apparent strain were measured by X-ray diffraction technique. The prepared powders were transformed in order of amorphouslongrightarrowmetastable cubic ZrO2longrightarrowmetastable tetragonal ZrO2longrightarrowstable monoclinic ZrO2 by a adequate heat treatment. The stabilization of metastable phase can be discussed in terms of energetial concept ; the difference of surface energy and internal strain in particle.

• The Korean Journal of Ceramics
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• v.7 no.1
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• pp.11-15
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• 2001

A thermodynamic assessment for the ZrO$_2$-TiO$_2$ system has been conducted. An optimal thermodynamic data set for this system is evaluated by the CALPHAD(CALculation of PHAse Diagram) method applied to experimental phase diagram and thermodynamic data. The liquid is described by ionic liquid model with two sublattices. The solubilities of the solid phases, tetragonal ZrO$_2$ and TiO$_2$(rutile), were described by subregular substitutional model with one sublattice. Two compounds, ZrTiO$_4$ and ZrTi$_2$O$_6$, are modeled as stoichiometric compounds.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.11a
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• pp.335-338
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• 1999

The effect of monoclinic $ZrO_2$(pure) and tetragonal $ZrO_2$ containing 5.35wt% $Y_2$$O_3$(Y-TZP) addition on the mechanical properties and thermal shock resistance of $Al_2$$O_3$ ceramic were investigated. The addition of $ZrO_2$(m) and Y-TZP increased sintering density of $Al_2$$O_3$. The vickers hardness increased with increasing the volume fraction of Y-TZP going through a maximum at 20wt%. The hardness of the specimens was found to be depend on the sintering density. With increasing the volume fraction of $ZrO_2$(m) and Y-TZP, the fracture toughness of the composite is increased. This result may be taken as evidence that toughening of ${Al_2}{O_3}$ can also be achieved by the transformation toughening and microcrack toughening of $ZrO_2$. The property of the& shock for ${Al_2}{O_3}$-$ZrO_2$ composites was improved by increasing the volume fraction of monoclinic $ZrO_2$(pure).Grain size increased with increasing the volume fraction of $ZrO_2$.

• 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.

• Journal of the Korean Ceramic Society
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• v.31 no.5
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• pp.513-519
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• 1994

Alumina composite was fabricated by introducing tetragonal ZrO2 in alumina composite of $\alpha$-alumina reinforced with in-situ formed La-$\beta$-aluminate (LaAl11O18). The powder mixture of composition (100-x)[88 Al2O3+(La2O3+11 Al2O3)]+x vol% ZrO2 was prepared with x from 0 to 40. Dense composites fabricated by hot-pressing exhibited bending strength up to 1200 MPa. The gain growth inhibiting effect of ZrO2 grains and La-$\beta$-aluminate platelets, and possibly the stress-induced phase transformation of ZrO2 have resulted in the high bending strength. The fracture toughness of the composite also increased up to 8.5 MPa.m1/2. The enhancement in toughness can be explained by transformation and microcrack toughening of ZrO2 and by crack deflection and bridging of La-$\beta$-aluminate platelets and ZrO2.