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Silica Activity Measurements in the Y 2 O 3 – SiO 2 System and Applications to Modeling of Coating Volatility
Author(s) -
Jacobson Nathan S.
Publication year - 2014
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.12974
Subject(s) - vaporization , volatilisation , analytical chemistry (journal) , vapor pressure , ceramic , phase (matter) , mineralogy , chemistry , materials science , chemical engineering , organic chemistry , engineering
Rare‐earth silicate compounds, such as those in the Y 2 O 3 – SiO 2 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: Y 2 O 3 + Y 2 O 3 ·SiO 2 two phase field: log[a(SiO 2 )] = −5200.26(1/T) + 0.0567 (1532 < T(K) < 1670) Y 2 O 3 ·SiO 2 + Y 2 O 3 ·2SiO 2 two phase field: log[a(SiO 2 )] = 4.2252(1/T)−0.5531 (1628 < T(K) < 1747) It is shown how these results can be used to predict reduced volatilization rates of the coatings.