Apatite and garnet stability in the Al–Ca–Mg–Si–(Gd/Y/Yb)–O systems and implications for T/EBC: CMAS reactions

Eeshani P Godbole, Anette von der Handt, David Poerschke

Research output: Contribution to journalArticlepeer-review

4 Scopus citations

Abstract

This work advances the understanding of the influence of rare earth (RE) ion radius on the stability and extent of the garnet solid solution phase in the (ytterbia/yttria/gadolinia)-calcia-magnesia-alumina-silica systems. Guided by the crystal chemistry and charge neutrality constraints, selected compositions in the notional garnet stability field were synthesized, equilibrated at 1400°C, and characterized to determine the equilibrium phases and their compositions. The results show a significant reduction in the stability of the silicate garnet relative to apatite with increasing RE ion radius. Apatite was not observed for any composition in the Yb-containing system, the Y-containing system formed both garnet and apatite, and there was no evidence of silicate garnets in the Gd-containing system. However, despite the apparent differences in stability relative to apatite, the extent of the garnet solid solution increases only slightly for the Yb- compared to Y-containing systems. The quantitative microchemical analysis suggests that Mg2+ prefers the octahedral site over the dodecahedral site in the garnet structure, and that the solubility of Mg2+ in the dodecahedral site increased in the system containing Yb3+ compared to Y3+. The results are discussed for their relevance to reactions between RE-containing thermal and environmental barrier coatings and CMAS-type silicate deposits.

Original languageEnglish (US)
Pages (from-to)1596-1609
Number of pages14
JournalJournal of the American Ceramic Society
Volume105
Issue number2
DOIs
StatePublished - Feb 2022

Bibliographical note

Funding Information:
Research supported by an Office of Naval Research supported collaboration with QuesTek Innovations, managed by Dr. David Shifler (N00014-17-C-2034). This work utilized shared equipment supported by NSF MRI DMR-1229263 (Hitachi SU8230), NSF EAR-1625422 (EPMA). The NSF MRSEC (DMR-2011401) and NNCI (ECCS-2025124) support of the UMN Characterization Facility, a member of the Materials Research Facilities Network (www.mrfn.org). The authors are grateful to Drs. Carlos Levi (UCSB), Dana Frankel and Pin Lu (QuesTek Innovations LLC), and Weiwei Zhang (Thermo-Calc Software) for the insightful discussions, and to Nikhil Karthikeyan for assistance with sample preparation.

Funding Information:
Research supported by an Office of Naval Research supported collaboration with QuesTek Innovations, managed by Dr. David Shifler (N00014‐17‐C‐2034). This work utilized shared equipment supported by NSF MRI DMR‐1229263 (Hitachi SU8230), NSF EAR‐1625422 (EPMA). The NSF MRSEC (DMR‐2011401) and NNCI (ECCS‐2025124) support of the UMN Characterization Facility, a member of the Materials Research Facilities Network ( www.mrfn.org ). The authors are grateful to Drs. Carlos Levi (UCSB), Dana Frankel and Pin Lu (QuesTek Innovations LLC), and Weiwei Zhang (Thermo‐Calc Software) for the insightful discussions, and to Nikhil Karthikeyan for assistance with sample preparation.

Publisher Copyright:
© 2021 The American Ceramic Society

Keywords

  • apatite
  • CMAS
  • environmental barrier coatings (EBC)
  • garnet
  • rare earth
  • thermal barrier coatings (TBC)

How much support was provided by MRSEC?

  • Shared

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