Fiber Strength of Hi Nicalon(TM) S After Oxidation and Scale Crystallization in Si(OH)4 Saturated Steam (Postprint)
AIR FORCE RESEARCH LAB WRIGHT-PATTERSON AFB OH WRIGHT-PATTERSON AFB United States
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Hi-NicalonTM-S SiC fibers were oxidized in SiOH4 saturated steam at 500 to 1500C for 1 100 hours. Fiber tensile strengths were measured for fibers that retained reasonable strength, which did not include any fibers oxidized at temperatures over 1000C. Oxidation and scale crystallization kinetics were characterized by optical and transmission electron microscopy. At 700C and higher, if SiO2 glass scales got too thick they often dewetted the SiC fibers and would spheroidize. SiO2 glass wicked to the spheroids as fast as it formed on the dewetted SiC surface, causing faster oxidation. SiO2 crystallization to cristobalite began after 100 h at 700C, but some glass scales were still present after 1 h oxidation at 1400C. Cristobalite scale that formed as glass before crystallizing was relatively coarse-grained, and scale that formed as cristobalite was fine-grained. Grain growth at 1500C was inferred to consume fine-grained scale, and formed grains with size comparable to the scale thickness.
- Inorganic Chemistry
- Refractory Fibers