Precipitation coating of monazite on woven ceramic fibers:: II.: Effect of processing conditions on coating morphology and strength retention of Nextel™ 610 and 720 fibers

Woven cloths of Nextel (TM) 610 and 720 fibers were coated with monazite by precipitation. The cloths were first saturated with concentrated precursor solutions, and then submerged in warm water to initiate precipitation onto the fiber surfaces. Coatings were characterized by scanning electron microscopy, and transmission electron microscopy; thermogravimetric analysis was performed on LaPO4 owders precipitated in solution under the same conditions as the coatings were deposited. Coating thickness distributions were measured and analyzed. Coated fiber strength was measured following heat treatment for 2 h at 1200 degrees C. Processing conditions which retain a substantial fraction of the uncoated fiber strength are identified, and are discussed in the context of current understanding of strength degradation in coated fibers. Strength retention of coated Nextel (TM) 610 fibers following heat treatment was broadly insensitive to precursor solution chemistry and was more strongly affected by intercoat firings which govern the final coating microstructure. For fixed processing conditions, more strength degradation was observed in Nextel (TM) 720 due to higher residual stresses in the fiber.