The phase equilibria in the CaO-Gd2O3-SiO2system were investigated by heat treating precursor-derived powders at 1400 °C and 1600 °C, determining the resulting phase assemblages, and measuring the compositions of the liquid and solid solution phases. The stable ternary phases at 1400 °C include silico-carnotite (Ca3Gd2Si3O12), Ca/Gd-cyclosilicate (Ca3Gd2Si6O26), and the apatite solid solution field extending from Gd9.33(SiO4)6O2to Ca2.75Gd7.25(SiO4)6O1.625. Of these, only apatite remains stable to 1600 °C. The high-temperature α- and α′-Ca2SiO4polymorphs exhibit moderate Gd2O3solubility. The results are compared to the equilibria for the related CaO-Y2O3-SiO2system. The implications for understanding the interaction between rare earth containing thermal barrier coatings (TBCs) and silicate deposits (CMAS) are discussed.
Bibliographical noteFunding Information:
Research supported by ONR grant N00014-16-1-2702 and NAVAIR STTR Phase II N00014-12-M-0340, both monitored by Dr. David Shifler. The work made use of the MRL Shared Experimental Facilities supported by the MRSEC Program of the NSF under Award No. DMR 1121053; a member of the NSF-funded Materials Research Facilities Network (www.mrfn.org). The funding agencies were not involved in the study design, the collection, analysis and interpretation of the data, or the decision to publish. The authors are grateful to G.G.E. Seward (UCSB) for assistance with EPMA analysis, A. Velasco-Hogan and S. Molakalapalli (UCSB) for assistance with specimen preparation, and W. Zhang and N. Hatcher (QuesTek Innovations) for discussions regarding their thermodynamic assessment of the CGS system.
- Phase diagrams
- Rare earth compounds