Phosphorescent thermal history sensors

The operating temperatures of surfaces in the hot sections of gas turbines are of great practical importance, but are often very hard to measure. Thermal indicating paints offer one possible and practical way, but they have many disadvantages. A novel concept for the utilisation of phosphorescent coatings as thermal history sensors was proposed by Feist et al. [1] in 2007. These phosphor coatings undergo irreversible changes when exposed to high temperatures that affect their photoluminescent properties and are a function of both the temperature and duration of exposure. If care is taken to ensure steady state conditions during exposure, subsequent off-line analysis of emission in the laboratory can reveal the temperature experienced by the coating. In this paper, an investigation of the amorphous-to-crystalline change of Y2SiO5Y2SiO5:Tb is reported and used to provide a proof of concept for a phosphorescent thermal history sensor. Phosphor powder was calcined at different temperatures and for different periods, and characterised using photoluminescence spectroscopy. A calibration curve was generated and shows that this phosphor is suitable for temperature measurements over a temperature range from 600 °° C to at least 1000 °°C. With more advanced signal processing routines it is anticipated that the dynamic range might be extended to 1400 °°C. Such routines and other materials/physical processes are the subject of on-going research in the area at Imperial College and Southside Thermal Sciences.