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Passive oxidation kinetics for glass and cristobalite formation on Hi‐Nicalon™‐S SiC fibers in steam
Author(s) -
Hay Randall S.,
Corns Randall
Publication year - 2018
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/jace.15763
Subject(s) - cristobalite , materials science , kinetics , mineralogy , tridymite , chemical engineering , analytical chemistry (journal) , composite material , chemistry , chromatography , physics , quartz , quantum mechanics , engineering
Parabolic rate constants for SiO 2 glass ( B G ) and cristobalite ( B C ) scale formation during passive oxidation of SiC in steam were determined. Cristobalite scale that originally formed as glass and as scale that formed afterward, directly as cristobalite, was distinguished by TEM . A method to determine B G and B C from many thickness measurements of the 2 different scale layers was developed. The method was applied to Hi‐Nicalon™‐S SiC fiber oxidation in Si( OH ) 4 saturated steam between 500 and 1600°C. At 1500°C and lower temperatures, glass scale formed more rapidly than cristobalite scale. B G and B C had activation energies of 80 ± 5 kJ /mol and 95 ± 5 kJ /mol, respectively. At 1600°C, cristobalite scales formed much faster than glass scales. Many scales spheroidized after oxidation at temperatures beneath 1000°C, and continuous scales that did form had wide variation in thickness. This made kinetics analysis after low temperature steam oxidation problematic.