Synthesis of yttria-stabilized zirconia powders for plasma spray by internal gelation

Chemical uniform, high-purity spray-grade zirconia powders doped with variable ratios of yttria for ceramic thermal barrier coatings were prepared by an internal gelation process. Both the morphology and particle size of the powders can be controlled by varying the emulsification conditions. Scanning electron microscopic and optical microscopic observations revealed the materials thus obtained to have a predominantly spherical morphology and the requisite size distribution (5 similar to 50 mu m). The dense, calcined micro-spheres showed good flowability. Differential Thermal Analysis (DTA) of 4.7mol% Y2O3-ZrO2 powders (dried at 80 degrees C) indicated that m --> t' transformation was happened at 468 degrees C. X-ray diffraction results showed that the crystalline phase of such powders after calcination at 800 degrees C was 100% nontransformable tetragonal.