|About this Abstract
||MS&T23: Materials Science & Technology
||Thermodynamics of Materials in Extreme Environments
||Thermodynamic and Kinetic Considerations of CMAS Reactions with Rare-earth Monosilicates
||Cameron Miller, Elizabeth Opila
|On-Site Speaker (Planned)
Rare-earth monosilicates (REMS) are proposed for top coats on state-of-the-art environmental barrier coatings (EBCs) for SiC-based composites used in hot-section aeroturbine applications. REMS are relatively resistant to reaction with molten siliceous debris (CMAS – CaO-MgO-Al2O3-SiO2) ingested into the engine compared to their disilicate counterparts. In this study, REMS-CMAS reactions were studied where the RE-cation was varied to identify CMAS-resistant compositions. REMS were exposed to CMAS at 1300C for 1 to 24h. Rare-earth- or calcium-stabilized silicate apatite phases were observed to form from the REMS-CMAS reaction. Periodic trends were observed. REMS containing large lanthanides formed thin dense apatite bi-layers, small lanthanides also formed reasonably dense apatite layers, whereas mid-lanthanide REMS formed thick porous reaction product layers. In contrast, the early and late lanthanide REMS showed higher dissolution rates in CMAS than the mid-lanthanide REMS compositions. Thermodynamic and kinetic aspects of these REMS-CMAS degradation mechanisms will be discussed.