Low-Thermal-Conductivity Rare-Earth Zirconates for Potential Thermal-Barrier-Coating Applications.

Rare-earth zirconates have been identified as a class of low-thermal-conductivity ceramics for possible use in thermal barrier coatings (TBCs) for gas-turbine engine applications. To document and compare the thermal conductivities of important rare-earth zirconates, we have measured the thermal conductivities of the following hot-pressed ceramics: (i) Gd[sub 2]Zr[sub 2]O[sub 7] (pyrochlore phase), (ii) Gd[sub 2]Zr[sub 2]O[sub 7] (fluorite phase), (iii) Gd[sub 2.58]Zr[sub 1.57]O[sub 7] (fluorite phase), (iv) Nd[sub 2]Zr[sub 2]O[sub 7] (pyrochlore phase), and (v) Sm[sub 2]Zr[sub 2]O[sub 7] (pyrochlore phase). We have also measured the thermal conductivity of pressureless-sintered 7 wt% yttria-stabilized zirconia (7YSZ)—the commonly used composition in current TBCs. All rare-earth zirconates investigated here showed nearly identical thermal conductivities, all of which were ∼30% lower than the thermal conductivity of 7YSZ in the temperature range 25°-700°C. This finding is discussed qualitatively with reference to thermal-conductivity theory. [ABSTRACT FROM AUTHOR]