WETTING AND MELT EXTRACTION CHARACTERISTICS OF ZRO2-AL2O3 BASED MATERIALS

A melt extraction technique has been used to produce fine fibers from three eutectic compositions in the systems of ZrO2-Al2O3 (ZA), ZrO2-Al 2O3 SiO2 (ZAS), and ZrO2-Al2O3-TiO2 (ZAT). The liquid surface tension of these ceramics was measured by a new method and estimated to be in the range of 400-567 mJ/m(2) at approximate to 2400 degrees C. The wet ting between Mo (the extraction wheel material) and liquid ceramics wa s found to be poor during transient wetting; however, fiber extraction was achieved due to the shear action induced by the wheel rotation, T he difficulties in the extraction of ZA fibers at speeds of <1.5 m/s, and also the formation of air pockets on these fibers, are attributed to the poor wetting of the Mo wheel by the liquid ZA. In a nide range of wheel velocities, extracted fibers exhibited alternating sections o f uniform diameter and Rayleigh waves, both being the largest for ZAS fibers at any speed. The Rayleigh wave dimensions varied considerably with speed whereas the dimensions of the uniform region of the fibers remained unchanged over the wide range of extraction speeds examined. The fiber dimensions are controlled by both surface tension and viscos ity of the molten ceramics at the extraction temperature.