High temperature protection performance of sandwich structure Al2O3/Si3N4/YAlO multilayer films for Pt–Pt10%Rh thin film thermocouples

Abstract

The composition and microstructure of sandwich structure Al2O3/Si3N4/YAlO multilayer films deposited by magnetron sputtering were investigated. The results of X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDS) show that α-SiAlON and Y-doped α-SiAlON are formed at the interface of Al2O3/Si3N4 and Si3N4/YAlO respectively after nitrogen annealing at 1300 °C. The thermoelectric properties of S-type (Pt/Pt–10%Rh) thin film thermocouples (TFTCs) with Al2O3 and Al2O3/Si3N4/YAlO protective layers deposited by magnetron sputtering were investigated from 700 °C to 1550 °C. The high temperature static calibration results show that the thermoelectric performance of TFTCs with an Al2O3 protective layer begins to decline at 1350 °C, the drift rate of the TFTCs is 13.27 °C/h, and the TFTCs fail at 1550 °C. However, the drift rate of TFTCs with an Al2O3/Si3N4/YAlO protective layer is only 2.19 °C/h at 1350 °C, and the performance begins to decline significantly at 1550 °C with a drift rate of 82.89 °C/h. The S-type TFTCs with sandwich structure Al2O3/Si3N4/YAlO multilayer provides a good prospect for the application of TFTCs in ultra-high temperature environment.