The measurement of temperatures in gas turbines, boilers, heat exchangers and other
components exposed to hot gases is essential to design energy efficient systems and improve
maintenance procedures. When on-line measurements, such as those performed with
thermocouples and pyrometers, are not possible or inconvenient, the maximum temperatures
of operation can be recorded and measured off-line after operation. Although thermal paints
have been used for many years for this purpose, a novel technique based on irreversible
changes in the optical properties of thermographic phosphors, can overcome some of the
disadvantages of previous methods.
In particular, oxidation of the divalent rare earth ion phosphor BaMgAl10O17:Eu
(BAM:Eu) has shown great potential for temperature sensing between 700 °C and 1200 °C.
The emission spectra of this phosphor change with temperature, which permits to define an
intensity ratio between different lines in the spectra that can be used as a measurand of the
temperature. In this paper, the study of the sensing capabilities of a sensor coating based on
BAM:Eu phosphor material is addressed for the first time. The sensitivity of the intensity
ratio is investigated in the temperature range from 800 °C to 1100 °C, and is proved to be
affected by ionic diffusion of transition metals from the substrate. The use of an interlayer
made of zirconia proves efficient in reducing ionic diffusion and coatings with this diffusion
barrier present sensitivity comparable to that of the powder material.