Precipitation Coating of Monazite on Woven Ceramic Fibers: III—Coating without Strength Degradation Using a Phytic Acid Precursor
Abstract:Multiple coatings of La-monazite (LaPO4) were applied to Nextel™ 610 and 720 oxide fibers using a heterogeneous nucleation and growth coating process with phytic acid solution precursors. The as-processed coatings were found to be largely amorphous. Coated fibers were heat treated at 1200°C for 1–2 h, whereupon the coatings crystallized to porous LaPO4 with thin (50–100 nm) layers of AlPO4 at the fiber–coating interface. Heat-treated fibers exhibited full strength retention, in marked contrast to fibers coated by precipitation using citric acid precursors as in a previous work. The microstructural evolution of the amorphous coatings was studied as a function of temperature. AlPO4 forms at the fiber–coating interface between 700° and 800°C, before high-temperature outgassing of the coating as measured by TGA. NMR spectroscopy was used to study as-precipitated powders and as-processed coatings to gain insights into the structural nature of the materials. A possible explanation for the retention of fiber strength through the coating process is proposed and discussed in light of the experimental evidence.
Document Type: Research Article
Affiliations: 1: Ceramics Branch, Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson AFB, Ohio 2: UES Inc., Dayton, Ohio 3: P.O. Box 19303, Newbury Park, CA 91319 4: Department of Physics, Arizona State University, Tempe, Arizona 5: Department of Chemistry and Biochemistry, Arizona State University, Tempe, Arizona
Publication date: February 1, 2010