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Monazite Coatings on SiC Fibers I: Fiber Strength and Thermal Stability
Author(s) -
Boakye E. E.,
Mogilevsky P.,
Parthasarathy T. A.,
Hay R. S.,
Welter J.,
Kerans R. J.
Publication year - 2006
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1551-2916.2006.01288.x
Subject(s) - materials science , monazite , composite material , scanning electron microscope , fiber , coating , microstructure , ultimate tensile strength , thermal stability , argon , transmission electron microscopy , chemical engineering , nanotechnology , chemistry , paleontology , organic chemistry , engineering , biology , zircon
Commercially available SiC fibers were coated with monazite (LaPO 4 ) using a continuous vertical coater at 1100°C. Coated fibers were heat treated in dry air, argon, and laboratory air at 1200°C for 1–20 h. The tensile strengths of uncoated and coated fibers were measured and evaluated before and after heat treatment. Fiber coating did not degrade SiC fiber strength, but heat treatment afterwards caused significant degradation that correlated with silica scale thickness. Possible strength degradation mechanisms for the coated fibers are discussed. Coating morphology, microstructure, and SiC oxidation were observed with scanning electron microscopy and transmission electron microscopy. Monazite reacted with SiC to form lanthanum silicate (La 2 Si 2 O 7 ) in argon, but was stable with SiC in air. Despite the large coefficient of thermal expansion difference between monazite and SiC, micron thick monazite coatings did not debond from most types of SiC fibers. Possible explanations for the thermomechanical stability of the monazite fiber coatings are discussed.