High-temperature protection performance of Mg-doped Al2O3 2 O 3 protective layers on the thin film thermocouples

Mg-doped Al2O3 2 O 3 protective layers were deposited on Pt-PtRh10 10 (S-type) thin film thermocouples (TFTCs) by reactive magnetron sputtering. The changes in the composition, microstructure, and element distribution of the Mg-doped Al2O3 2 O 3 films before and after annealing at 1200 degrees C for 3 h were investigated using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Scanning electron microscopy (SEM), and energy dispersive Xray spectroscopy (EDS). The results indicate that incorporating MgO into Al2O3 2 O 3 as an enhancement phase not only inhibits the crystallization and phase transformation of Al2O3 2 O 3 but also promotes the formation of MgAl2O4, 2 O 4 , sequentially further enhancing the material's high-temperature protective properties. The thermoelectric properties of S-type TFTCs with 1.6 mu m thick Al2O3 2 O 3 and Mg-doped Al2O3 2 O 3 protective layers were explored, respectively. The results of static calibration at high temperatures demonstrate that the TFTCs with the Mg-doped Al2O3 2 O 3 protective layer can operate at 1148 degrees C for over 96 h and at 1480 degrees C for a brief period. Following 4 calibration cycles, compared to the TFTCs with the Al2O3 2 O 3 protective layer, the average Seebeck coefficients of the TFTCs with the Mg-doped Al2O3 2 O 3 protective layer exhibit a slower decline rate, and its drift rate during the 4th cycle is merely 3.28 degrees C/h. The TFTCs featuring Mg-doped Al2O3 2 O 3 protective layers demonstrate extended lifetimes, superior high-temperature stability, and enhanced reliability when contrasted with those utilizing undoped Al2O3 2 O 3 protective layers. These attributes offer valuable insights into the progression of TFTC technology.