Effect of Water/Alkoxide Molar Ratio on the Synthesis Process and Electrochemical Behavior of Yttria-doped Zirconia Sol-gel Films

The aim of this work is to synthesize and investigate the performance of yttria-doped zirconia solgel coatings in the chemical corrosion prevention of zircaloy-4 (zirconium alloy) in a 1 N H2SO4 environment. The influence of four different molar ratios of water to alkoxide, namely 1, 4, 12, and 20, on the coating quality and its corrosion prevention performance was investigated. Differential thermal analysis and thermogravimetric analysis (DTA-TG) revealed the coating formation process. Surface morphology was examined using scanning electron microscopy (SEM). Microscopic features were obtained by employing energy dispersive spectroscopy (EDX) and X-ray diffraction (XRD). Wet corrosion performance was evaluated by using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. The EDX results approved that the amount of the yttria doped in zirconia was about 8 wt.%. The XRD results showed that the crystallization of zirconia started near 400 °C. The SEM results showed that denser cracks were formed at a water/alkoxide molar ratio of 4. The electrochemical tests revealed that, as the molar ratio of water to alkoxide was increased beyond 4, the coating quality was damaged and the best protection performance was achieved at a water/alkoxide molar ratio of 4.