Off-Line Temperature Profiling Utilizing Phosphorescent Thermal History Paints and Coatings

Abstract

Temperature profiling of components in gas turbines is of increasing importance as engineers drive to increase firing temperatures and optimize component’s cooling requirements in order to increase efficiency and lower CO2 emissions. However, on-line temperature measurements and, particularly, temperature profiling are difficult, sometimes impossible, to perform due to inaccessibility of the components. A desirable alternative would be to record the exposure temperature in such a way that it can be determined later, off-line. The commercially available thermal paints are toxic in nature and come with a range of technical disadvantages such as subjective readout and limited durability. This paper proposes a novel alternative measurement technique which the authors call thermal history paints and thermal history coatings. These can be particularly useful in the design process, but further could provide benefits in the maintenance area where hotspots which occurred during operation can be detected during maintenance intervals when the engine is at ambient temperature. This novel temperature profiling technique uses optical active ions in a ceramic host material. When these ions are excited by light they start to phosphoresce. The host material undergoes irreversible changes when exposed to elevated temperatures and since these changes are on the atomic level they influence the phosphorescent properties such as the life time decay of the phosphorescence. The changes in phosphorescence can be related to temperature through calibration such that in situ analysis will return the temperature experienced by the coating. A major benefit of this technique is in the automated interpretation of the coatings. An electronic instrument is used to measure the phosphorescence signal eliminating the need for a specialist interpreter, and thus increasing readout speed. This paper reviews results from temperature measurements made with a water-based paint for the temperature range 100–800 °C in controlled conditions. Repeatability of the tests and errors are discussed. Further, some measurements are carried out using an electronic hand-held interrogation device which can scan a component surface and provide a spatial resolution of below 3 mm. The instrument enables mobile measurements outside of laboratory conditions. Further, a robust thermal history coating is introduced demonstrating the capability of the coating to withstand long term exposures. The coating is based on thermal barrier coating (TBC) architecture with a high temperature bondcoat and deposited using an air plasma spray process to manufacture a reliable long lasting coating. Such a coating could be employed over the life of the component to provide critical temperature information at regular maintenance intervals for example indicating hot spots on engine parts.

Surface Temperature Measurements in an Industrial Gas Turbine Using Thermal History Paints

“…These materials can be applied as a simple non-toxic paint or as a robust atmospheric plasma spray (APS) coating. The technique has been successfully demonstrated to temperatures up to 900°C with a precision better than ±5 °C (Feist et al, 2015). Recently, THPs were tested in a combustor chamber test and compared favourably with thermochromic paints (Krewinkel et al, 2017) in terms of measurement capability and durability.…”

“…A brief overview of the theory underlying the THP technology is provided. A more detailed description can be found elsewhere (Feist, 2015).…”

Accelerated thermal profiling of gas turbine components using luminescent thermal history paints

“…The doped ceramic material can either be applied directly through atmospheric plasma spraying (APS) or mixed with a binder into a non-toxic paint to generate a durable coating. This method allows 2D temperature mapping across a component's surface with a precision of ±5°C and a spatial resolution of less than 3 mm proven up to 900°C (Feist et al, 2015). THPs were selected for measurement of the NGV.…”

Modeling ex-situ thermal impulse sensor responses to non-isothermal heating profiles

“…While our ex-situ TI sensing technique relies on the spectral properties of p-Dy:Y 2 O 3 and p-Eu:ZrO 2 for temperature sensing, there are other ex-situ techniques based on the same underlying principle (TI-dependent irreversible phase transitions) but utilize different materials and probe techniques. Some examples of these alternative techniques include: lifetime measurements of Eu:YSZ [14][15][16][17][18][19][20][21][22], irreversible changes to the resistance of nanowires [23], thermoluminescent microparticles [24][25][26][27][28][29][30][31][32], photoluminescence of ZnAl 2 O 4 [33] and core-shell quantum dots [34], phosphorescence in Tb:Y 2 SiO 5 [15], Raman spectroscopy of ceramic microparticles [35], Mossbauer parameters of a superconducting ceramic [36], modifications to thermally sensitive glass ceramics [37], photoluminescence and Raman spectroscopy of ZnO and TiO 2 nanoparticles [38,39], irreversible thermochromic behavior of Au/Ag nanorods [40] and polydiacetylene [41], and surface plasmon absorption [42][43][44].…”