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Upper Temperature Limit of Environmental Barrier Coatings Based on Mullite and BSASCurrent state-of-the-art environmental barrier coatings (EBCs) for Si-based ceramics consist of three layers: a silicon bond coat, an intermediate mullite (3Al2O3-2SiO2) or mullite + BSAS (1-xBaO-xSrO-Al2O3-2SiO2) layer, and a BSAS top coat. Areas of concern for long-term durability are environmental durability, chemical compatibility, silica volatility, phase stability, and thermal conductivity. Variants of this family of EBCs were applied to monolithic SiC and melt infiltrated SiC/SiC composites. Reaction between BSAS and silica results in low melting (approx. 1300 C) glasses at T > 1400 C, which can cause the spallation of the EBC. At temperatures greater than 1400 C, the BSAS top coat also degrades by formation of a porous structure, and it suffers significant recession via silica volatilization in water vapor-containing atmospheres. All of these degradation mechanisms can be EBC life-limiting factors. BSAS undergoes a very sluggish phase transformation (hexagonal celsian to monoclinic celsian), the implications of which are not fully understood at this point. There was evidence of rapid sintering at temperatures as low as 1300 C, as inferred from the sharp increase in thermal conductivity.
Document ID
Document Type
Technical Memorandum (TM)
Lee, Kang N.
(Cleveland State Univ. Cleveland, OH United States)
Fox, Dennis S.
(NASA Glenn Research Center Cleveland, OH United States)
Eldridge, Jeffrey I.
(NASA Glenn Research Center Cleveland, OH United States)
Zhu, Dongming
(Ohio Aerospace Inst. Brook Park, OH United States)
Bansal, Narottam P.
(NASA Glenn Research Center Cleveland, OH United States)
Miller, Robert A.
(NASA Glenn Research Center Cleveland, OH United States)
Robinson, Raymond C.
(QSS Group, Inc. Cleveland, OH United States)
Date Acquired
September 7, 2013
Publication Date
March 1, 2002
Subject Category
Nonmetallic Materials
Report/Patent Number
NAS 1.15:211372
Funding Number(s)
PROJECT: RTOP 714-04-30
Distribution Limits
Public Use Permitted.
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