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Abstract Rare‐earth disilicates are a focus of study for use as environmental barrier coatings in gas‐turbine engines. These coatings require thermomechanical and thermochemical stability at elevated temperatures and properties can be tailored through the use of multicomponent rare‐earth disilicates. Producing rare‐earth disilicates via sol–gel is documented in literature, but there are differing procedures with varying phase purities. This work establishes trends that dictate the effects of water content, pH, and heat treatment conditions that determine the final phase purity of Yb, Er, Lu, Sc, and Y disilicate powders made via sol–gel. The phase(s) of the powders were identified and quantified using X‐ray diffraction (XRD) to extract weight fractions. In situ XRD during heating from room temperature to 1200°C was used to observe the crystallization and phase evolution of the sol–gel‐based powders, allowing for the identification of a rarely reported low temperature triclinic phase in ytterbium‐, erbium‐, and lutetium‐based disilicate sol–gels that forms prior to transformation into a monoclinic phase. Ex situ XRD allowed for the phase identification of sol–gels processed at 1400°C. These experiments demonstrated that phase‐pure disilicates could be formed under conditions with no intentional water additions, a target pH of 2, and long heat treatment times at high temperatures (e.g., 1400°C). These conditions remain valid for not only single‐cation rare‐earth disilicates of Yb, Er, Lu, Sc, and Y but also a multicomponent disilicate containing equimolar concentrations of all of these cations.
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This content will become publicly available on November 15, 2025
CMAS corrosion resistance of rare earth phosphates at high temperatures for environmental barrier coatings
Abstract Phase stability, thermal properties, and calcium–magnesium–alumina–silicate (CMAS) resistance of LuPO4at 1300°C, 1400°C, and 1500°C were studied to evaluate its potential as an environmental barrier coating (EBC) for SiC‐based ceramic‐matrix composites (CMCs). Its coefficient of thermal expansion (∼5.69 × 10−6°C−1) is close to that of SiC‐based CMCs. At 1300°C, a dense reaction layer of Ca8MgLu(PO4)7forms and inhibits CMAS penetration; however, no such layer forms at 1400°C and 1500°C, leading to CMAS infiltration along grain boundaries. Prolonged (45 and 96 hours) CMAS corrosion of LuPO4at 1300°C showed the formation of a disilicate (Lu2Si2O7) phase along with Ca8MgLu(PO4)7. A multicomponent rare earth phosphate (Lu0.2Yb0.2Er0.2Y0.2Gd0.2)PO4shows improved CMAS resistance at 1400°C due to higher grain boundary stability and slower dissolution rate of rare earth elements into molten CMAS than single component rare earth phosphate. The mechanisms of CMAS corrosion and the kinetics of the formation of protective reaction layers in LuPO4and (Lu0.2Yb0.2Er0.2Y0.2Gd0.2)PO4were elucidated. Multicomponent design is needed to increase grain boundary stability and reduce dissolution rate into molten CMAS for REPO4‐based EBCs.
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- Award ID(s):
- 2119423
- PAR ID:
- 10639492
- Publisher / Repository:
- Wiley
- Date Published:
- Journal Name:
- Journal of the American Ceramic Society
- Volume:
- 108
- Issue:
- 3
- ISSN:
- 0002-7820
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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