The thermal conductivities of ceramic top-coats for thermal barrier coatings (TBCs) were investigated in associated with their microstructures. Top-coat specimens with different microstructure were made by the plasma spraying. Some specimens were subjected to the thermal aging in air. Pores and microcracks in the top-coat were evaluated quantitatively using an image analysis. The thermal conductivity in air at room temperature was determined according to the thermal diffusivity, the specific heat capacity and the bulk density. It was found that the thermal conductivity of the top-coat depends strongly on the shape and the size of the individual pores in addition to their total porosity. The microcracks between splats almost perpendicular to the heat flow are effective to decrease the thermal conductivity. However, the thermal aging promotes the local sintering and the crystallization in the top-coat, and increases its thermal conductivity.
We investigated the design of a bimetal MEMS calorimeter as a high-sensitivity photo thermal detector. Using finite element method, the thermo-mechanical sensitivity of large-size bimetal sensors of up to 5 mm × 5 mm area, which can be fabricated by the standard MEMS processes, was simulated. Several designs were found to have noise equivalent power (NEP) of one order smaller than that of conventional thermo module type photo thermal sensors with similar size. Experimental results for the first prototype of the MEMS sensors also supported those numerical predictions. This will be expected to provide high throughput absolute spectral optical power measurement.