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) Gd2Zr2O7 (pyrochlore phase), (ii) Gd2Zr2O7 (fluorite phase), (iii) Gd2.58Zr1.57O7 (fluorite phase), (iv) Nd2Zr2O7 (pyrochlore phase), and (v) Sm2Zr2O7 (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.

have nearly the same thermal conductivities in the temperature range 25-700°C, all of which are approximately 30% lower than that of 7 wt% yttria-stabilized zirconia. These desirable thermal, mechanical, and physical properties of the rare-earth zirconates make them attractive candidates for use in thermal barrier coatings for gas-turbine engine applications. -(WU, J.; WEI, X.; PADTURE*, N. P.; KLEMENS, P. G.; GELL, M.; GARCIA, E.; MIRANZO, P.; OSENDI, M. I.; J. Am.

Graphene nanoplatelets and reduced graphene oxide (rGO) were selected as fillers to develop reinforced silicon carbide (SiC)/graphene composites. The mechanical properties of the materials were investigated as a function of the type of graphene source and graphene content. Composites containing just 5 vol.% of rGOs exhibited an outstanding mechanical performance, increasing both the fracture toughness in ~162%, with a maximum value of 8.3 MPa•m1/2, and the strength in ~ 60% (600 MPa) when compared to monolithic SiC. The preferential alignment of the graphene fillers, their dimensions, and the graphene-SiC mechanical interlock are key factors to promote crack shielding mechanisms.

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Si 3 N 4 materials with distinct microstructures were prepared by hot-pressing, varying the holding time at the maximum temperature, and using different types and amounts of sintering additives. Materials with thermal conductivities of 15-82 W⅐(m⅐K) ؊1 were obtained by changing the processing variables. The highest conductivity was measured for the material with the coarsest microstructure. The effect of microstructural parameters, such as percentage of secondary phases, grain size, and texture on thermal properties of Si 3 N 4 ceramics, were studied. Hot-pressed Si 3 N 4 ceramics were modeled as a twophase composite made of large grains of high conductivity and a small-grained phase of low conductivity.