An Evaluation of Vaporizing Rates of SiO^sub 2^ and TiO^sub 2^ As Protective Coatings for Ultrahigh Temperature Ceramic Composites

For temperatures >1973 K, the thermodynamic and kinetic analyses of the major gaseous species for a liquid titanate layer would vaporize significantly less than a silicate layer, when considering these layers as a protective barrier for ultrahigh temperature ceramic composites. At 2500 K, the maj...

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Bibliographic Details
Published in:Journal of the American Ceramic Society 2008-05, Vol.91 (5), p.1448
Main Authors: Bronson, Arturo, Chessa, Jack
Format: Article
Language:English
Subjects:
Ceramic matrix composites
Ceramics
High temperature
Kinetics
Temperature effects
Thermodynamics
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Summary:For temperatures >1973 K, the thermodynamic and kinetic analyses of the major gaseous species for a liquid titanate layer would vaporize significantly less than a silicate layer, when considering these layers as a protective barrier for ultrahigh temperature ceramic composites. At 2500 K, the major species is TiO(g) with p...=0.1 kPa compared with SiO(g) with p...=1.3 x 10... kPa at the Ti/... and Si/... equilibrium, respectively. The SiO(g) attains a partial pressure greater than ambient pressure at 2500 K even with a thermodynamic activity of 0.01 considering equilibration with a silicide (e.g., TiSi...). In addition, at 2500 K the ... layer would vaporize at a rate of 0.23 mm/s compared with the ... layer's loss rate of 207 mm/s. Although the oxygen diffusivity and permeability through titanate solutions must be further analyzed, the thermodynamic and kinetic analyses for vaporization indicate a longer duration for a liquid titanate than for a liquid silicate layer at ultrahigh temperatures. (ProQuest: ... denotes formulae/symbols omitted.)
ISSN:0002-7820
1551-2916