ITO:SiC Ceramic Matrix Composite Thermocouples for Engine Components

Surface temperature measurements of ceramic matrix composite (CMC) based engine components within the hot section of a gas turbine engines are needed to verify engine designs and cooling requirements. Traditional temperature sensors cannot be applied to silicon carbide (SiC) based CMC's for this purpose, since they cannot be welded or embedded in the material. For these reasons, a novel thermocouple was developed for surface temperature measurement of p -type SiC-SiC CMC's. This novel thermocouple uses the p -type SiC-SiC CMC itself as one of the thermoelements and indium-tin-oxide (ITO) as the other thermoelement. Since both thermoelements are wide bandgap semiconductors, this thermocouple has exceptional thermoelectric output. A thermoelectric output of 272 μV/°K was observed for this ITO:SiC CMC thermocouple, which is an order of magnitude larger than that of type- K thermocouples. A drift rate of 3.28 °C/h was measured for this ITO:SiC CMC thermocouple. In addition, indium tin oxynitride (ITON) protective coatings deposited via reactive sputtering enabled these thermocouples to operate at 1000 °C. The ITON coating served as an oxygen diffusion barrier to prevent oxidation at the ITO:SiC CMC junction. Nitrogen and air anneals at 550 and 1000 °C, respectively, were used to improve the high temperature stability of the ITO and ITON coatings. Performance, fabrication details, and challenges using these ITO:SiC CMC thermocouple are discussed within.