Effects of crystal structure and cation size on molten silicate reactivity with environmental barrier coating materials

Jamesa L. Stokes, Bryan J. Harder, Valerie L. Wiesner, Douglas Edward Wolfe

Research output: Contribution to journalArticle

Abstract

Rare earth (RE) disilicates are utilized in environmental barrier coatings to protect Si-based engine components from destructive reactions with water vapor and other combustion species. These coating materials, however, degrade when exposed to molten silicate deposits in the engine. Four RE-disilicates (RE2Si2O7, RE = Er, Dy, Gd, Nd) are analyzed herein in thermochemical interactions with glassy calcium-magnesium-aluminosilicate (CMAS) compositions at 1400°C. Crystalline reaction products included RE2Si2O7, SiO2, and a Ca2+ yRE8+ x(SiO4)6O2+3 x /2+ y apatite-type silicate. RE2Si2O7 formation was favored in interactions with CMAS having low CaO:SiO2 ratios. Increased reactivity was observed for higher CaO:SiO2 ratios in CMAS combined with larger RE3+ cation size, resulting in apatite formation of varying stoichiometry and changes in lattice parameters. The crystallization of SiO2 was dependent on both thermodynamic equilibrium at low CaO:SiO2 ratios and sequestration of silicate modifiers at higher CaO:SiO2 ratios, although residual amorphous content after CMAS exposure in both cases was still substantial.

Original languageEnglish (US)
JournalJournal of the American Ceramic Society
DOIs
StateAccepted/In press - Jan 1 2019

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All Science Journal Classification (ASJC) codes

  • Ceramics and Composites
  • Materials Chemistry

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