Thermographic Phosphor Coatings for Temperature Measurement of an Impinging Supersonic Oscillating Jet

Thermographic Phosphor Thermometry (TPT) is a non-contact luminescence-based technique capable of mapping surface temperatures with high spatial and temporal resolution. It relies on phosphors, ceramic compounds doped with rare-earth or transition-metal ions, that emit temperature-dependent light upon optical excitation. A primary challenge in applying TPT is developing a uniform, durable phosphor coating with strong adhesion and minimal thermal resistance. In this study, phosphor coatings were developed using Magnesium Fluorogermanate (MFG) particles mixed in a 1:3 mass ratio with two different binders from ZYP Coatings: ZAP and hydroxypropyl cellulose (HPC). The mixtures were airbrushed onto test surfaces at a 30° angle, followed by drying in a vacuum chamber for 24 hours and curing in a convection oven at 150 °C for 2 hours. The resulting coatings were evaluated for surface uniformity, mechanical robustness, and optical clarity. HPC-based coatings showed weak adhesion and were easily scratched, while ZAP-based coatings demonstrated greater hardness but exhibited discoloration, possibly due to thermal or chemical degradation. These observations highlight the importance of selecting an appropriate binder, optimizing binder-to-phosphor ratio, and refining curing protocols. Future work includes calibrating the phosphor lifetime over a temperature range of 50 °C to 350 °C to construct a temperature-lifetime correlation curve. The outcomes of this study support the development of reliable TPT coatings for high-temperature environments, enabling accurate surface temperature measurements in supersonic jet impingement experiments.