Emulsion Precipitation and Characterization of Zirconia
- PDF / 1,837,767 Bytes
- 5 Pages / 420.48 x 639 pts Page_size
- 103 Downloads / 226 Views
EMULSION PRECIPITATION AND CHARACTERIZATION OF ZIRCONIA Lieh-Jiun Shyu* and Frank M. Cambria* * Akzo Chemicals Inc., Livingstone Ave.,
Dobbs Ferry,
NY 10522
ABSTRACT powders were (YSZ) Zirconia and yttria-stabilized zirconia prepared from water/oil emulsions followed by high temperature The morphology and particle size were correlated calcination. concenwith several variables such as composition of emulsions, stirring rate, tration of starting materials and surfactants, The powders were hydrolysis rate and calcination temperature. particle size characterized according to crystalline phase, and flow rate. Emulsion precipitation typically distribution, yielded spherical zirconia particles which were either solid or hollow. Particle size could be controlled from submicron to a few hundred microns depending primarily on the composition of the SEM/EDX results emulsion and stirring rate during hydrolysis. yttria was uniformly distributed throughout the showed that zirconia particles. 0 The crystalline phase of the powders after tetragonal. calcination at 800 C was entirely non-transformable The flow rate increased with increasing particle size and with increasing sphericity. INTRODUCTION and Zirconia powder is useful in many advanced structural Because of its low thermal electrical ceramics applications. conductivity and relatively high thermal expansion coefficient, it has been considered a good thermal barrier coating in heat engines [1,2]. The powder is typically coated on the engine, parts This technology requires that the by plasma spray techniques. powder has good flow and large particle size. The performance of the thermal barrier coating is dramatically influenced by the initial powder size distriLution and chemical homogeneity [3]. It is known that zirconia can be stabilized by alloying it In this paper, we have studied yttria with CaO, MgO or Y?0 3 [4]. stabilized zirconia powders which were prepared by emulsion hydrolysis. The emulsion hydrolysis technique has been used to prepare ceramic powders with spherical morphology [5,6,7]. This technique allows precipitating powders with a controlled particle size distribution and shape. The emulsion droplets serve as microreacin this tors during hydrolysis. However, most of the research area has focused on the preparation of fine particles. Our intention in this work was to prepare powders with a particle size range of about 30 to 80 microns suitable for plasma spray coating applicaticns. EXPERIMENTAL Yttria-stabilized zirconia powder was prepared from zirconium compounds, such as zirconium oxyacetate or zirconium oxychloride premixed with yttrium acetate or nitrate in a water-in-oil The organic phase was heptane, hexane, toluene, (w/o) emulsion. or mineral oil. The emulsifier used was either cationic or nonMat. Res. Soc. Symp. Proc. Vol. 180. ©1990 Materials Research Society
838
or ionic surfactant, such as alkyl quaternary ammonium chloride sorbitan monooleate. The emulsion was agitated in a round bottom and precipitation took place when flask with a mechanica
Data Loading...
