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Laser flash measurements of thermal diffusivity of ZrO2 single crystals partially and fully stabilized with Y2O3 were compared with measurements for polycrystalline cubic ZrO2, and single crystals and polycrystals of Al2O3 and MgAl2O4. In general, the thermal diffusivities of the ZrO2 materials examined initially decrease with increasing temperature, although significantly less than for the Al2O3 and MgAl2O4 materials. The diffusivity subsequently rises with increasing temperature for the single crystals of ZrO2 but not for polycrystalline cubic ZrO2, with this increase for ZrO2 crystals occurring at much lower temperatures than for Al2O3 and MgAl2O4 crystals. As the ZrO2 materials went from fully stabilized with 20 wt% Y2O3 to partially stabilized with 5 wt% Y2O3, the room-temperature diffusivity increased from 0.70x10-6 to 0.97x10-6 m2/s. This indicated that the lattice defects, which increase with Y2O3 content, are more important sources of phonon scattering than are the precipitates which appear at lower Y2O3 compositions. On the other hand, at 1000°C the diffusivity of the fully cubic ZrO2 crystals with 20 wt% Y2O3 was 1.10x10-6 m2/s while that of the partially stabilized ZrO2 crystals with 5 wt% Y2O3 was 1.05x10-6 m2/s. The increased diffusivity at higher temperatures can be attributed to radiative heat transfer, with the lower relative diffusivity of the partially stabilized crystals resulting from photon scattering by the precipitate structures present.

The effect of interfacial decohesion, due to the thermal expansion mismatch, on the thermal diffusivity of a hot-pressed glass matrix with a dispersed phase of nickel was investigated by the laser-flash technique at 25° to 600°C. The interfacial gap formed on cooling acts as a barrier to heat flow and lowers the thermal diffusivity to values below those predicted from composite theory and also creates a strongly positive temperature dependence of the thermdl diffusivity. Preoxidation of the Ni spheres promotes interfacial bonding and yields values of thermal diffusivity higher than those for nonoxidized spheres and a thermal diffusivity which is relatively temperature-independent. The results of the present study also confirm the criteria for the effective thermal diffusivity of composites established by Lee and Taylor.

The hypothesis is presented that the maximum tensile thermal stresses in brittle ceramics can be reduced significantly by a redistribution of the temperature profile using a spatially varying thermal conductivity. On the basis of a hollow circular cylinder subjected to radially inward or outward steady-state heat flow, it is shown that such a spatially varying thermal conductivity can lead to significant decreases in magnitude of the maximum tensile thermal stress. Possible techniques of creating such thermal conductivity variations are discussed briefly.

The hypothesis is presented that the maximum tensile thermal stresses in brittle ceramics can be reduced significantly by a redistribution of the temperature profile using a spatially varying thermal conductivity. On the basis of a hollow circular cylinder subjected to radially inward or outward steady-state heat flow, it is shown that such a spatially varying thermal conductivity can lead to significant decreases in magnitude of the maximum tensile thermal stress. Possible techniques of creating such thermal conductivity variations are discussed briefly.