Thermal characterization of aluminum oxide ceramic rings

Aluminum oxide (Al2O3) rings are frequently embedded into industrial components, such as sealing elements or bearings. The thermal properties of the rings (density, specific heat, thermal conductivity) are a trustworthy indicator of the product quality. To verify the conformity to the design specifications, the thermal properties of six sample elements extracted from three different production batches (Type 1,2,3) are measured. Type 1 and 2 were supposed to comply with the standard while Type 3 was supposed to be anomalous. For each batch two samples (#1 and #2) are tested. Firstly the thermal diffusivity is measured with the Laser Flash Method, that requires a sample pre-processing and a dedicated setup to adapt the traditional procedure applied to flat disks to the ring samples. Numerical simulations are performed to verify that the sample shape is not affecting the measurement. Then the density is evaluated with the Archimedes principle with different liquids, due to the peculiar surface of the samples. Finally the specific heat is measured with the Differential Scanning Calorimetry. The obtained values allow the calculation of the thermal conductivity, that showed compatibility between Type 1 and Type 2 samples and incompatibility between Type 3 and the other batches.