Thermal properties of sintered alumina at the micrometer-scale were quantitatively measured with a thermal microscope using thermo-reflectance and periodic heating techniques. The average value of thermal conductivity of 28.9 W·m⁻¹K⁻¹ was obtained from a 50 μm×50 μm area, and the average value was also in good agreement with that measured by a laser flash technique.
The anomalous data were found by the measurement with the thermal microscope in some regions, which were correlated with the surface pores or inside defects of the specimen. The portions with very low thermal conductivities, 5 to 10 W·m⁻¹K⁻¹, were found to correspond to around the pore presents.
In addition, unshared 10 square areas of 10 μm×10 μm were randomly selected and were scanned by an area scanning mode in order to calculate the average conductivities at the areas. The conductivity values were in the range of 24.9 to 37.7 W·m⁻¹K⁻¹ and the variation in the conductivities was estimated about 13 W·m⁻¹K⁻¹. The area with maximum thermal conductivity was consisted of large grains and the value was considered to be almost equal to that of one grain. On the other hand, the area including several small grains indicated the minimum conductivity. The decrease of the conductivity was due to the influence of the grain boundaries.