| Abstract Scope |
Recent work has shown that multicomponent rare-earth (RE) silicates offer promise as thermal/environmental barrier coatings (T/EBCs) for SiC-based composites. Reduced thermal conductivity is attributed to increased phonon scattering caused by variations in RE mass and size, enabling T/EBC capability. However, separation of rare earths, only to recombine them, makes this an expensive concept. Naturally occurring xenotime (REPO4) containing mixed (Y,Gd,Dy,Er,Yb)PO4 offers promise as a more economical T/EBC if rare earth separation is not required. Here we present property data for individual Y,Gd,Dy,Er,Yb phosphates synthesized from RE2O3 and H3PO4 and densified by spark plasma sintering, synthetic mixtures of the RE phosphates, and naturally-occurring xenotime when possible. Thermal expansion was determined from hot stage powder X-ray diffraction, thermal conductivity was measured by time-domain thermoreflectance, and thermochemical stability in high-temperature steam and molten deposits was determined at 1400°C and 1300°C respectively. Viability of xenotime as a T/EBC is discussed. |