Garnet stability in the Al–Ca–Mg–Si–Y–O system with implications for reactions between TBCs, EBCs, and silicate deposits

Eeshani Godbole; Nikhil Karthikeyan; David Poerschke

doi:10.1111/jace.17176

Garnet stability in the Al–Ca–Mg–Si–Y–O system with implications for reactions between TBCs, EBCs, and silicate deposits

Eeshani Godbole, Nikhil Karthikeyan, David Poerschke

Research output: Contribution to journal › Article › peer-review

17 Scopus citations

Abstract

This work expands the understanding of the garnet solid solution field in the yttria-calcia-magnesia-alumina-silica system. The crystal chemistry was used to define the theoretical extent of the garnet homogeneity range based on site-specific substitution rules and charge neutrality constraints. Compositions lying within this range were equilibrated at 1400°C. The resulting phase assemblages were analyzed to determine the identity and compositions of the equilibrium phases. Quantitative chemical analysis was used to infer that Mg²⁺ preferentially partitions into the intermediate-sized octahedral site compared to the larger dodecahedral site, that Ca²⁺ has a higher solubility in the dodecahedral site than Mg²⁺, and that the presence of Mg²⁺increases the total Si⁴⁺ solubility in the garnet structure. The results were also used to map the extent of the garnet solid solution phase field at 1400°C. The findings are discussed in the context of efforts to understand the interactions between Y-containing thermal and environmental barrier coatings and silicate deposits.

Original language	English (US)
Pages (from-to)	5270-5282
Number of pages	13
Journal	Journal of the American Ceramic Society
Volume	103
Issue number	9
DOIs	https://doi.org/10.1111/jace.17176
State	Published - Sep 1 2020
Externally published	Yes

Bibliographical note

Funding Information:
This study was supported by an Office of Naval Research (ONR) funded collaboration with QuesTek Innovations monitored by Dr David Shifler (N00014‐17‐C‐2034). SEM‐EDS characterization was carried out in the Characterization Facility, University of Minnesota, a member of the NSF funded Materials Research Facilities Network ( www.mrfn.org ) supported by the MRSEC program. The Hitachi SU8230 SEM‐EDS instrument was provided by NSF MRI DMR‐1229263. The EPMA facility was supported by NSF EAR‐1625422. The authors are grateful to Drs. Carlos Levi (UCSB), Dana Frankel (QuesTek Innovations) and Weiwei Zhang (ThermoCalc Software) for helpful discussions, Dr Anette von der Handt for EPMA assistance and Uma Venkata for assistance with sample preparation.

Funding Information:
This study was supported by an Office of Naval Research (ONR) funded collaboration with QuesTek Innovations monitored by Dr David Shifler (N00014-17-C-2034). SEM-EDS characterization was carried out in the Characterization Facility, University of Minnesota, a member of the NSF funded Materials Research Facilities Network (www.mrfn.org) supported by the MRSEC program. The Hitachi SU8230 SEM-EDS instrument was provided by NSF MRI DMR-1229263. The EPMA facility was supported by NSF EAR-1625422. The authors are grateful to Drs. Carlos Levi (UCSB), Dana Frankel (QuesTek Innovations) and Weiwei Zhang (ThermoCalc Software) for helpful discussions, Dr Anette von der Handt for EPMA assistance and Uma Venkata for assistance with sample preparation.

Publisher Copyright:
© 2020 The American Ceramic Society

Keywords

CMAS
environmental barrier coatings
garnet
rare earth
solid solution
thermal barrier coatings

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title = "Garnet stability in the Al–Ca–Mg–Si–Y–O system with implications for reactions between TBCs, EBCs, and silicate deposits",

abstract = "This work expands the understanding of the garnet solid solution field in the yttria-calcia-magnesia-alumina-silica system. The crystal chemistry was used to define the theoretical extent of the garnet homogeneity range based on site-specific substitution rules and charge neutrality constraints. Compositions lying within this range were equilibrated at 1400°C. The resulting phase assemblages were analyzed to determine the identity and compositions of the equilibrium phases. Quantitative chemical analysis was used to infer that Mg2+ preferentially partitions into the intermediate-sized octahedral site compared to the larger dodecahedral site, that Ca2+ has a higher solubility in the dodecahedral site than Mg2+, and that the presence of Mg2+increases the total Si4+ solubility in the garnet structure. The results were also used to map the extent of the garnet solid solution phase field at 1400°C. The findings are discussed in the context of efforts to understand the interactions between Y-containing thermal and environmental barrier coatings and silicate deposits.",

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author = "Eeshani Godbole and Nikhil Karthikeyan and David Poerschke",

note = "Funding Information: This study was supported by an Office of Naval Research (ONR) funded collaboration with QuesTek Innovations monitored by Dr David Shifler (N00014‐17‐C‐2034). SEM‐EDS characterization was carried out in the Characterization Facility, University of Minnesota, a member of the NSF funded Materials Research Facilities Network ( www.mrfn.org ) supported by the MRSEC program. The Hitachi SU8230 SEM‐EDS instrument was provided by NSF MRI DMR‐1229263. The EPMA facility was supported by NSF EAR‐1625422. The authors are grateful to Drs. Carlos Levi (UCSB), Dana Frankel (QuesTek Innovations) and Weiwei Zhang (ThermoCalc Software) for helpful discussions, Dr Anette von der Handt for EPMA assistance and Uma Venkata for assistance with sample preparation. Funding Information: This study was supported by an Office of Naval Research (ONR) funded collaboration with QuesTek Innovations monitored by Dr David Shifler (N00014-17-C-2034). SEM-EDS characterization was carried out in the Characterization Facility, University of Minnesota, a member of the NSF funded Materials Research Facilities Network (www.mrfn.org) supported by the MRSEC program. The Hitachi SU8230 SEM-EDS instrument was provided by NSF MRI DMR-1229263. The EPMA facility was supported by NSF EAR-1625422. The authors are grateful to Drs. Carlos Levi (UCSB), Dana Frankel (QuesTek Innovations) and Weiwei Zhang (ThermoCalc Software) for helpful discussions, Dr Anette von der Handt for EPMA assistance and Uma Venkata for assistance with sample preparation. Publisher Copyright: {\textcopyright} 2020 The American Ceramic Society",

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N2 - This work expands the understanding of the garnet solid solution field in the yttria-calcia-magnesia-alumina-silica system. The crystal chemistry was used to define the theoretical extent of the garnet homogeneity range based on site-specific substitution rules and charge neutrality constraints. Compositions lying within this range were equilibrated at 1400°C. The resulting phase assemblages were analyzed to determine the identity and compositions of the equilibrium phases. Quantitative chemical analysis was used to infer that Mg2+ preferentially partitions into the intermediate-sized octahedral site compared to the larger dodecahedral site, that Ca2+ has a higher solubility in the dodecahedral site than Mg2+, and that the presence of Mg2+increases the total Si4+ solubility in the garnet structure. The results were also used to map the extent of the garnet solid solution phase field at 1400°C. The findings are discussed in the context of efforts to understand the interactions between Y-containing thermal and environmental barrier coatings and silicate deposits.

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Garnet stability in the Al–Ca–Mg–Si–Y–O system with implications for reactions between TBCs, EBCs, and silicate deposits

Abstract

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Keywords

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