Two Phase Monazite/Xenotime 30LaPO 4 –70YPO 4 Coating of Ceramic Fiber Tows

Equiaxed yttrium–lanthanum phosphate nanoparticles (Y 0.7 ,La 0.3 )PO 4 ·0.7H 2 O were made and used to continuously coat Nextel ™ 720 fiber tows. The particles were precipitated from a mixture of yttrium and lanthanum citrate chelate and phosphoric acid (H 3 PO 4 ), and characterized with differential thermal analysis and thermogravimetric analysis, X‐ray diffraction, transmission electron microscopy, and scanning electron microscopy. The coated fibers were heat treated at 1000°–1300°C for 1, 10, and 100 h. Coating grain growth kinetics and coated fiber strengths were determined and compared with equiaxed La‐monazite coatings. The relationships between coating porosity, coating hermeticity, and coated fiber strength are discussed.