• Journal of the Korean Ceramic Society
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• v.25 no.2
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• pp.117-124
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• 1988

The properties of the powders of the system Al2O3-ZrO2-Y2O3 prepared by precipitation method were investigated. Al2(SO4)3$.$18H2O3, ZrOCl2$.$8H2O and YCl3$.$6H2O were used as starting materials. Amorphous aluminum hydrate prepared by precipitation method was completely transformed to alpha Al2O3 as a result of calcining at 1100$^{\circ}C$ for 1 hr and gamma, delta and theta phases appeared as transition phases. In ZrO2-Y2O3 system prepared by co-precipitation method, the crystallization temperature of ZrO2 was increase with Y2O3 contents. The coupled crystallization occured in coprecipitated Al2O3-ZrO2-Y2O3 system, therefore the formation temperature of alpha Al2O3 and ZrO2-Y2O3 system. In this ternary system, the powder morphology showed a particular shape which was composed of large Al2O3 grains having small spherical ZrO2 particles within large Al2O3 grain and relatively large ZrO2 particles along the grian boundaries.

• Journal of the Korean Ceramic Society
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• v.27 no.8
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• pp.991-1003
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• 1990

A precipitation method, one of the most effective liquid phase reaction methods, was adopted in order to prepare high-tech Al2O3/ZrO2 composite ceramics. Al2(SO4)3.18H2O, ZrOCl2.8H2O and YCl3.6H2O were used as starting materials and NH4OH as a precipitation agent, various types of metal hydroxides were obtained by single precipitation(series A) and co-precipitation(series B) method at the pH condition between 7 and 11. Fine Al2O3-ZrO2 powders were prepared at optimum calcination condition and the effects of ZrO2 on microstructures and mechanical properties of Al2O3 were investigated. The composition of Al2O3/ZrO2 composites wax fixed as Al2O3-15 v/o ZrO2(＋3m/o Y2O3). ZrO2 limited the grain growth of Al2O3 and increased grain size homogeneity of Al2O3 more effectively than MgO.Flexural strength values in Al2O3 and Al2O3/ZrO2 composites were 340-430 MPa and 540-820 MPa, respectively, and the effect of strength improvement showed 20-50% by adding ZrO2 to Al2O3. Fracture toughness of Al2O3/ZrO2 composites was improved by stress-induced phase transformation of tetragonal ZrO2 and toughening effect by microcrack was not observed. Also, ZrO2 particles located at Al2O3 grain junction contributed to toughening, while spherical ZrO2 particles located within Al2O3 grain did not contribute to toughening. Weibull moduli of Al2O3 ceramics and Al2O3/ZrO2 composites of series A and series B were 4.34, 5.17 and 9.06, respectively. Above 0.5 of failure probability, strength values in Al2O3 ceramics and Al2O3/ZrO3 composites of series A and series B were above 400 MPa, 700 MPa and 650 MPa, respectively.

• Journal of the Korean Ceramic Society
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• v.25 no.4
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• pp.364-372
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• 1988

The mechanical properties and microstructure of ceramics of the system Al2O3-ZrO2-Y2O3 sintered at 1$650^{\circ}C$ for 2h after powder preparation by the precipitation method from Al2(SO4)3.18H2O, ZrOCl2.8H2O and YCl3.6H2O were investigated. The Al2O3-ZrO2-Y2O3 ceramics sintered at 1$650^{\circ}C$ for 2h after mixing alpha-Al2O3 and ZrO2-Y2O3 powders, both were separately precipitated and calcined, were found to have the relative density higher than 97.5% so that the strengthening and toughening mechanisms could be explained mainly as the stress-induced phase transformation. On the other hand, the sintered bodies prepared by co-precipitating the three starting materials were measured to have the relative density lower than 85% so that the degradation of strength were observed above 15 vol% ZrO2 contents due to the high porosity by which the effect of stress-induced phase transformation was assumed to be depressed.

• Journal of the Korean Ceramic Society
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• v.31 no.8
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• pp.879-885
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• 1994

Coprecipitation technique was used to synthesize ZrO2+12 mol% CeO2 powders with ZrOCl2.8H2O and Ce(NO3)3.6H2O as starting materials. The powders were dried on different conditions such as distilled water, ethanol, and azeotropic distillation. The powders prepared by azeotropic distillation showed weak aggregation of particles and the average particle size of powders calcined at 85$0^{\circ}C$ for 1 hour was 0.19 ${\mu}{\textrm}{m}$. The optimum sintering temperature and holding time are 130$0^{\circ}C$ and 2.5~10 hours, respectively. Beyond the optimum conditions, a phase transition from tetragonal to monoclinic causes to produce cracks in the sintered bodies and to decrease the density.

• Journal of the Mineralogical Society of Korea
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• v.19 no.2 s.48
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• pp.81-88
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• 2006

The Yttria Partially Stabilized Zirconia powder was prepared by spontaneous precipitation method using $ZrOCl_2{\cdot}8H_O-YCl_33{\cdot}6H_2O$ solution as a starting materials. The optimal experimental conditions such as concentration and pH of starting solutions, the amounts of stabilizer $Y_2O_3$ used, and sintered temperature were carefully studied. The best condition for synthesizing $ZrO_2$ was experimentally selected and applied throughout this study for the preparation of the 3 mole% $Y_2O_3$ partially stabilized zirconia, 3YSZ. The physical properties of 3YSZ was examined by XRD, Raman, DT A, and SEM. The structural transition from pure monoclinic high temperature $ZrO_2$ to tetragonal room temperature 3YSZ was made possible by the added amount of $Y_2O_3$ in the $ZrO_2+Y_2O_3$ system. All Raman Spectrum band appeared in the lower wave numbers rather than in higher wave numbers as structure changes from monoclinic to tetragonal.

• Journal of the Korean Ceramic Society
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• v.31 no.8
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• pp.835-840
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• 1994

In this study, the synthesis of Ba2Ti9O20 powder having chemically homogeneous and highly pure fine particle size distribution was attempted by the oxalate method. And the effects of ZrO2 addition was investigated. The four compositions (X=0, 0.028, 0.048, 0.068) of Ba2(Ti9-x, Zrx)O20 were prepared by precipitation reaction of BaCl2, TiCl4, and ZrOCl2, with oxalic acid and NH4OH acting as a precipitating agent and a pH regulator respectively, in aqueous solution. In case of 4.8 mol% ZrO2 addition, the single phase Ba2Ti9O20 was obtained at 120$0^{\circ}C$ and its dielectric properties was excellent showing K=40.5, Q=4621 at 5.4 GHz.

• Korean Journal of Crystallography
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• v.14 no.2
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• pp.67-72
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• 2003

Graphite powders were coated with ZrO₂ by the controlled hydrolysis of a DI water, ethanol and DI water+ethanol solutions. The hydrolysis process was carried out with temperature control because of the low wettability of Zr ions to the surface of the graphite. PVA was added to the solution for the enhancement of metal ion adsorption. The surface of the graphite powders coated with ZrO₂ was observed by SEM and TEM. There are two types of ZrO₂ particles with the condition of ZrOCl₂°§8H₂O aqueous solutions were used; (a) primary particles a few nm in size and (b) secondary particles with ∼0.1 ㎛ size were obtained. The graphite powders coated in 50% ethanol-50% DI water solution of Zr(SO₄)₂ㆍ4H₂O have the relatively uniform coating layer and the starting temperature of oxidation was 100℃ higher than the raw graphite.

• Journal of the Korean Chemical Society
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• v.57 no.2
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• pp.260-263
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• 2013

An efficient and environmentally benign protocol for the pseudo four-component synthesis of benzopyranopyrimidines via condensation of salicylic aldehydes, malononitrile and various amines catalyzed by $ZrOCl_2{\cdot}8H_2O$ as an inexpensive and eco-friendly catalyst with high catalytic activity under solvent-free conditions is reported. This protocol provides a new and improved method for obtaining benzopyranopyrimidines in terms of good yields, simple experimental procedure and short reaction time.

• Particle and aerosol research
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• v.4 no.1
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• pp.21-25
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• 2008

$Pb(Zr_{0.53}Ti_{0.47})O_3$ (PZT) was synthesized by a multiple wet dry process. Precipitates prepared from reaction between $ZrOCl_2{\cdot}8H_2O$ and $TiOCl_2$ and $NH_4OH$ in an aqueous solution was dried at $100^{\circ}C$, and calcined at $500^{\circ}C$ and $700^{\circ}C$. The mixture mixed with PbO and as-dried or calcined $Zr_{0.53}Ti_{0.47}O_4$ (ZT) powders was calcined again at 700 and $800^{\circ}C$. Well crystallized ZT and PZT were formed at even $700^{\circ}C$. PZT piezoelectric ceramics of more than 98.5% in a relative density was obtained by sintering at as low as $900^{\circ}C$.

• Journal of the Korean Ceramic Society
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• v.28 no.1
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• pp.11-18
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• 1991

A precipitation method, one of the most effective liquid phase reaction methods, was adopted in order to prepare high-tech Al2O3/ZrO2 composite ceramics, and the effects of stress-induced phase transformation of ZrO2 on thermal shock behavior of Al2O3-ZrO2 ceramics were investigated. Al2(SO4)3.18H2O, ZrOCl2.8H2O and YCl3.6H2O were used as starting materials and NH4OH as a precipitation agent. Metal hydroxides were obtained by single precipitation(process A) and co-precipitation(process B) method at the condition of pH=7, and the composition of Al2O3-ZrO2 composites was fixed as Al2O3-15v/o ZrO2(+3m/o Y2O3). Critical temperature difference showing rapid strength degradation by thermal shock showed higher value in Al2O3/ZrO2 composites(process A : 20$0^{\circ}C$, process B : 215$^{\circ}C$) than in Al2O3(175$^{\circ}C$). The improvement of thermal shock property for Al2O3/ZrO2 composites was mainly due to the increase of strength at room temperature by adding ZrO2. The strength degradation was more severe for the sample with higher strength at room temperature. Crack initiation energies by thermal shock showed higher values in Al2O3/ZrO2 composites than in Al2O3 ceramics due to increase of fracture toughness by ZrO2.