Feasibility Study for Determining the Coating State of ISIComp Material with Thermographic Techniques

Featured Application: The aim of the broader research framework to which this work belongs to is to develop a diagnostic system capable of assessing the condition and reusability of a thermal protection system after atmospheric re-entry, without requiring its disassembly. This work investigates the feasibility of using thermographic techniques to identify the three possible states of a silicon-based coating on a carbon–silicon matrix (ISiComp). Experimental tests were therefore carried out on specimens prepared in three different conditions: uncoated, coated, and coated then oxidized. The study compares lock-in thermography and pulsed thermography using both a cooled mid-wave infrared (MWIR) camera and an uncooled long-wave infrared (LWIR) microbolometric camera. The main objective is to distinguish coated from uncoated conditions and oxidized from non-oxidized conditions, while recognizing that the coated and oxidized states cannot coexist simultaneously on the same specimen. The results show that thermographic techniques, when supported by appropriate post-processing, are promising for this purpose. In particular, the uncooled LWIR camera provided better results than the cooled MWIR camera, whereas the current approach did not allow a robust distinction between the pristine-coated and oxidized-coated states. At the same time, the study highlights limitations related to specimen size and to the additional treatments applied to reproduce the different surface states. Future work will address larger specimens and real components, together with the implementation of advanced AI-based classification algorithms to overcome the current limitations of the proposed approach.