Thermal decomposition and crystallization behavior of double rare-earth co-doped SrZrO3 precursor used in the solution precursor plasma spray process

Abstract

A double rare-earth (Yb/Gd) co-doped SrZrO3 [Sr1.1(Zr0.9Yb0.05Gd0.05)O3.05] thermal barrier coating (TBC) was prepared by the solution precursor plasma spray (SPPS) using an aqueous solution precursor of nitrates [Sr(NO3)2, Gd(NO3)3·6H2O, Yb(NO3)3·6H2O] and zirconium acetate [Zr(C2H3O2)4]. The thermal decomposition and crystallization process of the solution precursor powders calcined at elevated temperature (~1400 °C) were studied and characterized by X-ray diffraction (XRD) and synchronous thermal analyzer coupled with Fourier transform infrared spectroscopy and quadrupole mass spectrometry (STA/FTIR/QMS) methods. Zr(C2H3O2)4 precursor decomposed into ZrO2, CH3COCH3 and CO2 firstly, followed by decomposition of hydrated nitrate. ZrO2 reacted with SrO (Yb2O3, Gd2O3) and CO2 to generate Yb/Gd co-doped SrZrO3 and SrCO3 simultaneously. SrCO3 decomposed into SrO again at higher temperature, which reacted with ZrO2 to form SrZrO3. The Sr1.1(Zr0.9Yb0.05Gd0.05)O3.05 coating was characterized as single phase with interpass boundary (IPB) structure, nano- and micrometer porosity, and through-thickness vertical cracks, analysed by XRD and the scanning electron microscope (SEM). The average grain size of the coating was calculated to be ~30 nm by Scherrer formula.