Advanced Ceramics (Self-Healing Ceramic Coatings)

Advanced ceramics have many commercial applications due to the high corrosion resistance and mechanical properties, but their implementation is frequently compromised by inherent defects including holes, pores, and microcracks. The number of coating defects can be reduced by using corrosion inhibitors since the corrosion products help to repair the defects. Small cracks and crevices, of which the internal sources are indistinguishable, can proliferate leading to sudden failure. Therefore, it is essential to develop techniques to identify and monitor cracks so that preventive measures can be taken if the cracks are short and remediable, or a self-healing mechanism can be implemented to enable automatic repair. In this respect, non-automatic repair requires that the defects are first identified, but the process can be difficult and costly. From the perspective of thermodynamics, a system away from thermodynamic equilibrium can be combined with a thermodynamic recovery force such as penetration to return the system to equilibrium. In fact, the regenerative power reduces the entropy to assist the repair processes. Therefore, self-repairing coatings are of great importance and have been progressing gradually from the laboratory to industrial adoption. For example, ceramics-based self-healing coatings containing inhibitors such as organic benzotriazole (BTA) have attracted much interest. Here, different formats of ceramics-based self-healing coatings including titania, zirconia, titanium–alumina, and zirconia–alumina incorporated with benzotriazole (BTA) as an inhibitor are described together with the fabrication processes. By releasing the benzotriazole from titania–alumina–benzotriazole coating, the vulnerable locations for corrosion would be confined and a protective layer is fabricated to enhance the corrosion resistance of the Al 2024 alloy. The amount of BTA plays a vital factor regarding the self-healing efficiency and slow release of BTA is observed to produce the optimal self-healing ability. Titania– alumina coating with 3.6% benzotriazole, provides 76% protection efficiency and the self-healing behavior of the coating is confirmed by investigating the impedance with immersion time. Moreover, in the ZrO₂–Al₂O₃–benzotriazole coating, by reaction of oxygen and benzotriazole and subsequently formation of corrosion byproducts, the corrosion resistance and the cathodic reactions would be enhanced and delayed, respectively, lead to an improvement in the properties of double layer. The hardness and elastic modules and plastic deformation of the ZrO₂–Al₂O₃–benzotriazole coating, decreased and increased, respectively, compared to the coating without the presence of benzotriazole and moreover, the adhesion is the dominant mechanism of wear. © The Author(s), under exclusive license to Springer Nature Switzerland AG 2024.