Electrochemical and Oxidation Behavior of Yttria Stabilized Zirconia Coating on Zircaloy-4 Synthesized via Sol-Gel Process

Abstract

Sol-gel 8 wt.% Yttria Stabilized Zirconia (YSZ) thin films were prepared on zirconium (zircaloy-4 alloy) by dip-coating technique followed by heat treating at various temperatures (200°C, 400°C, and 700°C) in order to improve both electrochemical corrosion and high temperature oxidation properties of the substrate. Differential thermal analysis and thermogravimetric analysis (DTA-TG) revealed the coating formation process. X-ray diffraction (XRD) was used to determine the crystalline phase structure transformation. The morphological characterization of the coatings was carried out using scanning electron microscopy (SEM). The electrochemical behavior of the coated and uncoated samples was investigated by means of open circuit potential, Tafel, and electrochemical impedance spectroscopy (EIS) in a 3.5 wt.% NaCl solution. The homogeneity and surface appearance of coatings produced was affected by the heat treatment temperature. According to the corrosion parameters, the YSZ coatings showed a considerable increase in the corrosion resistance, especially at higher heat treatment temperatures. The coating with the best quality, from the surface and corrosion point of view, was subjected to oxidation test in air at 800°C. The coated sample presented a 25% reduction in oxidation rate in comparison with bare substrate.

Dispersant effects on YSZ electrolyte characteristics for solid oxide fuel cells

“…The crystallite size, which is given by the width of the diffraction line, was of 70 Å. Similar results have been reported and show the peaks in 2θ characteristics of YSZ and ZrO 2 [15][16][17]]. …”

Effect of Deposition Conditions on Phase Content and Mechanical Properties of Yttria-Stabilized Zirconia Thin Films Deposited by Sol-Gel/Dip-Coating

“…In stage I, which ranged from room temperature up to approximately 220 °C, a weight loss of ~15% was observed. This weight loss has been associated with the vaporization of superficial and structural water [19,[25][26][27][28]. The stage II, which ranges from 220 to 350 °C, with a weight loss of 19%, has been associated with the combustion and decomposition of organic compounds [19,26,[28][29][30].…”

“…However, a common feature associated with the deposition of YSZ thin films and coatings through sol-gel/dip-coating is the production of materials with cracks or defects if the heat treatment or deposition conditions are not controlled [3,[14][15][16]. For example, it has been observed that coatings thicker than 200 nm are prone to cracking due to the release of gases, thermal mismatch between the coating and the substrate, and internal stresses during heat treatment [17][18][19]. Crack formation can be reduced or avoided by controlling the sol-gel fabrication route (for example, using complexing agents affecting the hydrolysis and condensation reactions or by modifying the viscosity of the gel), the extraction rate, and heat treatment temperature or by depositing several consecutive coatings for the purpose of filling the cracks that are generated [14,16,[19][20][21].…”

“…For example, it has been observed that coatings thicker than 200 nm are prone to cracking due to the release of gases, thermal mismatch between the coating and the substrate, and internal stresses during heat treatment [17][18][19]. Crack formation can be reduced or avoided by controlling the sol-gel fabrication route (for example, using complexing agents affecting the hydrolysis and condensation reactions or by modifying the viscosity of the gel), the extraction rate, and heat treatment temperature or by depositing several consecutive coatings for the purpose of filling the cracks that are generated [14,16,[19][20][21]. Higher heat treatment temperatures tend to reduce the formation of cracks, whereas the deposition of a multilayer system can result in coatings with lower wear life and reduced performance at high temperature due to a weak bonding between each film [22,23].…”

CaO stabilized ZrO2 coating intended to reduce corrosion on steel and aluminum substrates

“…Además, al someter el recubrimiento a un tratamiento térmico se logra una superficie libre de grietas y con mejores propiedades anticorrosivas. Se ha trabajado especialmente con estructuras cristalinas estabilizadas con itria [6,[12][13][14]. Sin embargo, una de las alternativas para obtener películas con fines de protección anticorrosiva podría ser el uso de zirconia estabilizada con calcia, que resulta en un compuesto (CaZrO3) más estable químicamente y con buena resistencia a la corrosión que hasta el momento parece no haber sido estudiado sobre sustratos de acero inoxidable y aluminio comercial.…”