Silica Activity Measurements in the Y2O3–SiO2 System and Applications to Modeling of Coating Volatility. Issue 6 (12th May 2014)

• Record Type: Journal Article
• Authors: Jacobson, Nathan S.; Butt, D.
• Is Part Of: Journal of the American Ceramic Society. Volume 97:Issue 6(2014)
• Page Start: 1959
• Page End: 1965
• Publication Date: 2014-05-12
• Subjects: Ceramics -- Periodicals; 620.1405
• DOI: 10.1111/jace.12974
• Languages: English
• ISSNs: 0002-7820

Abstract

<abstract abstract-type="main" id="jace12974-abs-0001"> <title> <x xml:space="preserve">Abstract</x> </title> <p>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 &lt; T(K) &lt; 1670) Y₂O₃·SiO₂ + Y₂O₃·2SiO₂ two phase field: log[a(SiO₂)] = 4.2252(1/T)−0.5531 (1628 &lt; T(K) &lt; 1747) It is shown how these results can be used to predict reduced volatilization rates of the coatings.</p> </abstract>