Thermal and crystallization behavior of zirconia precursor used in the solution precursor plasma spray process

Yttria stabilized zirconia (7YSZ) solution precursor has been successfully used in the deposition of high durability thermal barrier coatings. In this paper, the thermal and crystallization behaviors of 7YSZ precursor were investigated by TG-DTA, FTIR and XRD. The results show that the precursor decomposition and crystallization temperatures greatly depend on heating rate e. g. 74 C for the crystallization temperature when tripping the heating rate. With a 10 C/min heating rate, the weight loss due to precursor pyrolysis occurs predominantly at temperatures below 500 C. A small weight loss due to the oxidation of residual carbon is detected from 800 C to 950 C. The complete crystallization of the tetragonal phase was determined to be around 500 C by DTA and XRD analyses with a 10 C/min heating rate. The crystallization kinetics and the activation energy of amorphous 7YSZ precursor were investigated by variable heating rate DTA. The calculated activation energy is 66.2 kJ/mol. The Avrami parameter value was determined to be 2.68, which indicates that crystallization nucleation and growth is diffusion-controlled. The crystalline phase of 7YSZ coatings deposited by the Solution Precursor Plasma Spray process was identified by XRD and Raman spectrum. The average YSZ grain size in the SPPS coating was determined to be 61 nm.