• Journal of the Korean Ceramic Society
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• v.28 no.2
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• pp.167-175
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• 1991

In synthesizing hydrated zirconia powder by hydrolysis of Zr-alkoxides using ethanol as mutual solvent, three experimental parameters, namely, concentration of alkoxides and hydrolysis water and addition rate of hydrolysis water were varied systematically. Spherical, monodispersed, nonagglomerated and submicrometer sized powders were prepared at 0.3 M of Zr(n-OPr)4 and 0.05M of Zr(n-OBu)4 with wide ranges of hydrolysis water conditions i.e. 0.5-2.0M concentration and 1-20ml/min addition rate. During the hydrolsis, careful attention have to be paid to maintain homogeneous reaction by controlling the agitation of the reactant and the addition of the hydrolysis water. For more improved condition of monodispersity it was found that the key point is to shorten the self-nucleation time within several seconds as rapid as possible. In both alkoxides system, with higher concentration of alkoxide and hydrolysis water and with slow addition rate of hydrolysis water, hydrated zirconia powders synthesized showed tendency to fall in worse powder conditions.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.22 no.4
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• pp.924-938
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• 1998

Densification behavior of ceramic powder under cold compaction was investigated. Experimental data were obtained for zirconia powder and alumina powder under triaxial compression with various loading conditions. A special form of the Cap model was proposed from experimental data under triaxial compression for a yield function of ceramic powder. The proposed yield function was inplemented into a finite element program (ABAQUS) to study densification behaviors of zirconia and alumina powders under die compaction. The effect of friction between the powder and die wall was also investigated. Density distributions of powder compacts were measured and compared with finite element results.

• Journal of the Korean Ceramic Society
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• v.46 no.1
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• pp.35-40
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• 2009

Using zirconia and poly (methyl methacrylate-coethylene glycol dimethacrylate) (PMMA) microbeads, macroporous zirconia ceramics were fabricated by a simple pressing method. Effects of template size and content on microstructure, porosity, and flexural and compressive strengths were investigated in the processing of the macroporous zirconia ceramics. Three different sizes of microbeads (8, 20, and $50{\mu}m$) were used as a template for fabricating the macroporous ceramics. The porosity increased with increasing the template size at the same template content. The flexural and compressive strengths were primarily influenced by the porosity rather than the template size. However, the strengths increased with decreasing the template size at the same porosity. By controlling the template size and content, it was possible to produce macroporous zirconia ceramics with porosities ranging from 58% to 75%. Typical flexural and compressive strength values at 60% porosity were ${\sim}30\;MPa$ and ${\sim}75\;MPa$, respectively.

• Journal of the Korean Ceramic Society
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• v.45 no.1
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• pp.65-68
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• 2008

A simple pressing process using zirconia and microbead for fabricating porous zirconia ceramics is demonstrated. Effects of microbead content and sintering temperature on microstructure, porosity, compressive and flexural strengths were investigated in the processing of porous zirconia ceramics using microbead as a pore former. By controlling the microbead content and the sintering temperature, it was possible to produce porous zirconia ceramics with porosities ranging from 43% to 70%. Typical compressive and flexural strength values at ${\sim}50%$ porosity were ${\sim}150\;MPa$ and ${\sim}35\;MPa$, respectively.

• Journal of Powder Materials
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• v.4 no.1
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• pp.9-17
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• 1997

The mullite-zirconia composites were prepared by the pressureless sintering with addition of 10~20 vol% ZrO$_2$(TZ3Y) in the fused mullite and sol-gel mullite matrix. The densification rate of sol-gel mullite was higher than that of fused mullite, and the addition of ZrO$_2$(TZ3Y) was effective on the densification of fused mullite. The enhancement of densification and anisotropic growth of mullite in ZrO$_2$added specimen can be explained by the solid solution effect of $Zr^{+4}$ ion in mullite. Both mechanical strength and fracture toughness of mullite-zirconia composite were enhanced compared to those of mullite. The enhancement of mechanical properties is attributed to the hinderance of grain growth and the combined toughening effects of tetra-mono phase transformation and crack deflection due to the residual stress between mullite/ZrO$_2$.

• Journal of Powder Materials
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• v.24 no.2
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• pp.147-152
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• 2017

Spherical-type zirconia granules are successfully fabricated by a spray-drying process using a water solvent slurry, and the change in the green density of the granule powder compacts is examined according to the organic polymers used. Two organic binders, polyvinyl alcohol (PVA) and 2-hydroxyethyl methacrylate (HEMA), which are dissolved in a water solvent and have different degrees of polymerization, are applied to the slurry with a plasticizer (polyethylene glycol). The granules employing a binder with a higher degree of polymerization (PVA) are not broken under a uniaxial press; consequently, they exhibit a poor green density of $2.4g/cm^3$. In contrast, the granule powder compacts employing a binder with a lower degree of polymerization (HEMA) show a higher density of $2.6g/cm^3$ with an increase in plasticizer content. The packing behavior of the granule powders for each organic polymer system is studied by examining the microstructure of the fracture surface at different applied pressures.

• Journal of the Korean Ceramic Society
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• v.33 no.6
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• pp.637-644
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• 1996

Phase stability and isothermal phase transformation during gaging at 25$0^{\circ}C$ were investigated in yttria stabilized zirconia powders prepared from hydrolysis of zirconium isopropoxide. The stability of tetragonal phase at room temperature in zirconia powder was decreased with calcination temperature but increased with the addition of yttria content. During aging at 25$0^{\circ}C$ in humid atmosphere isothermal phase transformation occurred in tetragonal zirconia powder stabilized by constraint effect not by alloying effect and grain size effect. Many twins and microcrackings were found in transformed monomlinic zirconia particles.

• Journal of the Korean Ceramic Society
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• v.37 no.5
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• pp.497-504
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• 2000

In this study, mullite-zirconia comosite was fabricated by adding ZrOCl2.8H2O using of boehmite gel coating to Hadong kaolin (pink A grade) in order to enhance strength of the mullite specimens. The influence of ZrOCl2.8H2O content and fireing temperature on the crystall phase, microstructure, bulk density, strength of the specimens was investigated. Mullite-zirconia composite was produced in the process of coating zirconia to mullite powder synthesized thereafter and mixing simultaneously of starting materials with boehmite-zirconia gel. Maximum strength with in this study was 251 sintered at 1$600^{\circ}C$ for 2h. Bulk density and strength of the composite with zirconia coated mullite was higher than simultaneous on mixture of starting materials.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2000.04a
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• pp.7-8
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• 2000

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2000.11a
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• pp.298-303
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• 2000

The 3 mol% yttria stabilized zirconia (3-Y PSZ) powder was heat treated at 50 0$^{\circ}C$ to evaporate the polymer binder and stabilize the tetragonal phase. The wear experiments were carried out on a ring-on-plate type reciprocating wear tester at selected temperatures with in the range room temperature to 600$^{\circ}C$ The results show that the heat treatment of powder decreases the wear rate due to the reduction of microcracks and pores in coatings and the stabilization of the tetragonal phase. Powder heat treatment enhanced the quality of the coating layer by removing remnant gases during coating process and the powder heat treatment at which tetragonal phase is stable diminished phase ratio of monoclinic. These two effects improved wear resistance characters.