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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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Parametric Control of Melting Gel Morphology and Chemistry via Electrospray Deposition
Melting gels are a class of hybrid organic-inorganic silica based gels prepared via the sol-gel process that are solid below their glass transition temperatures, near room temperature, but show thermoplastic behavior when heated. While this phase change can be repeated multiple times, heating the gel past its consolidation temperatures, typically above 130 oC initiates an irreversible reaction that produces highly crosslinked glassy organic-inorganic materials via hydrolysis and poly-condensation. This ability makes melting gels uniquely compatible with processing techniques inaccessible to other sol-gels. By properly tuning their properties, it should be possible to create protective coatings for electronics and anti-corrosive coatings for metals that are highly hydrophobic and insulating. However, melting gel consolidation reactions are highly dependent on charge interactions, raising the question of how these materials will respond to a processing technique, like electrospray deposition (ESD), which is dependent on charge delivery. In this study, we focus on the role that substrate temperature and charge polarity play on film morphology, consolidation chemistry, and surface properties. Optical images, film thickness measurements, nanoindentation, and FTIR were used to characterize the sprayed melting gel with the goal of developing a robust processing space for producing highly cross linked, hydrophobic, dielectric coatings.
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- Award ID(s):
- 1911509
- PAR ID:
- 10293459
- Date Published:
- Journal Name:
- ASME 2021 16th International Manufacturing Science and Engineering Conference
- Volume:
- 2
- Issue:
- 1
- Page Range / eLocation ID:
- 1-5
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/https://doi.org/10.1115/MSEC2021-63347
