Silica Activity Measurements in the Y2O3-SiO2 System and Applications to Modeling of Coating Volatility

Rare‐earth silicate compounds, such as those in the Y2O3–SiO2 system, are promising candidates for coatings of SiC‐based ceramics and ceramic matrix composites in combustion environments. The predicted lower activity of silica in these silicates will lead to less reactivity with the water vapor comb...

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Bibliographic Details
Published in:Journal of the American Ceramic Society 2014-06, Vol.97 (6), p.1959-1965
Main Author: Jacobson, Nathan S.
Format: Article
Language:English
Subjects:
Ceramic coatings
Ceramic matrix composites
Ceramics
Coating
Combustion
Combustion products
Knudsen effusion
Mass spectrometry
Mathematical models
Rare earth compounds
Silicates
Silicon carbide
Silicon dioxide
Temperature
Two phase
Vapor pressure
Vaporization
Volatility
Water vapor
Yttrium oxide
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Summary:Rare‐earth silicate compounds, such as those in the Y2O3–SiO2 system, are promising candidates for coatings of SiC‐based ceramics and ceramic matrix composites in combustion environments. The predicted lower activity of silica in these silicates will lead to less reactivity with the water vapor combustion products. A procedure for measuring silica activities in this system is discussed. Knudsen effusion mass spectrometry is used and the measured vapor pressure of SiO(g) is correlated to activity. Due to the low vapor pressure of SiO(g) in the temperature range of interest, a reducing agent is utilized to boost this vapor pressure without altering the solid‐state composition. In addition, corrections are made for nonequilibrium vaporization. The measured silica activities are: Y2O3 + Y2O3·SiO2 two phase field: log[a(SiO2)] = −5200.26(1/T) + 0.0567 (1532 
ISSN:0002-7820
1551-2916
DOI:10.1111/jace.12974