A transmission electron microscope characterization of sodium sulfate hot corrosion of silicon carbide fiber-reinforced lithium aluminosilicate glass-ceramic matrix composite
Hunt, Richard K.
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Sodium Sulfate hot corrosion of a SiC/LAS composite was studied using conventional transmission electron microscopy and selected area diffraction. Changes in the morphology, composition and crystallography of the phases in the glass-ceramic matrix and the fiber/matrix interface were studied. Microchemical analysis using energy dispersive x-ray spectroscopy (EDS) was also performed on all phases detected. Three samples were studied: (1) as-received, (2) no salt coating and annealed in argon, and (3) sodium sulfate coated and annealed in oxygen. Both heat treatments were performed at 900 C for 100 hours. Sample (1) matrix was comprised of small stoichiometric grains of beta-spodumene (Li2O- Al2O3-4SiO2) and mullite (3Al2O32SiO2) in a high silica glass (88 wt% SiO2 and 12 wt% Al203). The fiber/matrix interface consisted of an amorphous SiO2 and graphitic carbon layer. Sample (2) showed a substantial decrease in mullite content with a concomitant increase in alumina content of the glass and crystalline phases. Lithium aluminosilicate, SiC Fiber-reinforced composites.
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