Polycrystalline Yttrium Aluminum Garnet Fibers from Colloidal Sols

Polycrystalline yttrium aluminum garnet (YAG) fibers were prepared from commercially available colloidal sols of Y,O, and AlOOH and water-soluble polymers. The fibers were dry spun and all processing was performed in air. Transfor-mation to YAG was complete by =1300"C, and the fibers were mostly dense by 1600°C with a final fired diameter of 120 pm. A bend test was used to characterize mechanical strength, and an average of 522 2 186 MPa with a Weibull modulus of 3.5 was determined. The bend stress relaxation (BSR) test was used to characterize creep properties. The creep resistance was better than that of all commercially available oxide fibers with the exception of Saphikon single-crystal alumina (c-axis oriented). The creep strain of the YAG fibers compared well with that calculated for YAG monoliths with roughly the same grain size. I