Thermal shock resistance of cubic 8 mol% yttria‐stabilized zirconia (YSZ) can be increased by the addition of dilute second phases. This study addresses how these dilute second phases affect the thermal conductivity for two‐phase ceramic composites of 8 mol% YSZ with 10–20 vol% alumina (Al2O3) or 10–20 vol% mullite (3Al2O3·2SiO2). Thermal conductivity measurements from 310 K (37°C) to 475 K (202°C) were made using the 3ω method and compared with results from 3D analytical models and a 2D computational microstructure‐based model (Object‐Oriented Finite Element Analysis, OOF2). The linear Rule of Mixtures was the least accurate and significantly overestimated the measured thermal conductivity at low temperatures, with errors in some cases exceeding 100%. Calculations using the Bruggeman and OOF2 models were both much better, and the deviation of less than ±2.5% across all compositions and temperatures is within the range of experimental and modeling uncertainty. The Maxwell Garnett equation was a close third in accuracy (±8%). A sensitivity analysis for each model quantifies how small perturbations in the thermal conductivity of the dispersed second phase influence the effective thermal conductivity of the composite, and reveals that the linear Rule of Mixtures model is physically unrealistic and oversensitive to the thermal conductivity of the dispersed phase.

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A low temperature, vapor phase approach to improve the thermal stability of nonrefractory deterministically structured inverse opals is demonstrated. Specifically, pack aluminization at 550 °C was conducted on Ni inverse opals, introducing controlled amounts of Al into the structure. This enabled the formation of a strengthening Ni 3 Al phase, resulting in enhanced high temperature strength and stability. Following aluminization, the deterministic structures remained stable up to 1000 °C, a 500 °C increase relative to the starting Ni inverse opals. The thermal stability of the aluminized structures is comparable to that of much more difficult to fabricate deterministically structured refractory structures. Additionally, the pack aluminized structures exhibited a 17.6% increase in elastic modulus and an 81.6% increase in hardness relative to the initial Ni inverse opal. This is a promising combination of thermo-mechanical properties for very fine, deterministic structures used in high temperature, chemically harsh environments.

Experimental results indicate effective faster diffusion of oxygen in polycrystalline alumina when exposed to water vapor at high temperatures. a-Al 2 O 3 containing Ni metal particles was exposed to dry air or humid environments at 1300°C for up to 20 h. Oxidation of Ni in a-Al 2 O 3 to form NiAl 2 O 4 was used to determine oxygen diffusion depth from the surface. The apparent kinetic rate constant for oxygen diffusion in the presence of water vapor was 79% higher compared with that in a dry atmosphere at 1300°C (1. , which would be expected to lead to faster diffusion. This effect may impact sintering, creep, corrosion, oxidation, and the performance of thermal barrier coatings (TBC).