Thermal properties and NDT of materials by IR thermography

Ceramic thermal barrier coatings (TBCs) are widely applied for protecting hot path components of gas turbines from combustion gases. To estimate the effective insulation performances of TBCs in protecting gas turbine, their thermo-physical characterisation is required because, apart from lattice properties of the material, the low thermal conductivity of TBCs strongly depends on the specific microstructural features related to the deposition process parameters. Moreover, the microstructure is affected by the service condition of coated components. The exposure to high temperature promotes sintering phenomena within the TBC by micro-crack healing, neck formation and by reducing the very fine porosity, making the TBC less strain compliant and more thermally conductive. In this talk some photothermal and thermographic techniques are presented to assess the thermophysical properties of porous ceramic materials. Laser Flash is applied in a controlled atmosphere to evaluate the thermal conductivity and its dependence on the microporosity of the material under test. IR thermography, thanks to its imaging capabilities, is applied to assess the conductivity anisotropy of Thermal Barrier Coatings, depending on the deposition technology. Finally, the semitransparency of materials is considered and the measurements process is suitably modeled to improve the accuracy. Various examples of ceramic materials utilized in the power industry are presented. Successively some thermographic applications utilized in the assessment of thermal transmittance in buildings are presented with the possibility of spotting out thermal bridges and to evaluate comfort parameters. Application fields are residential modern buildings and ancient buildings with historical value as well. Finally an uncommon utilization of thermal waves is shown in connection with the inspection of Palazzo Ducale in Venice where the NDT capabilities of IR thermography is utilized together with thermal wave generated by the sun.