Cristobalite-suppressed Al-SiO2 ceramic coatings: DFT guided nanoparticle design for durable oxidation resistance

Ceramic coatings, characterized by their tailored microstructures, exceptional high temperature stability, and engineered functionalities, have been widely explored for extreme environment applications. To protect TiAl alloy from oxidation attack, a variety of silicon-based coatings have been developed by actively or passively forming SiO₂, such as pure SiO₂ coatings, enamel coatings, silicide coatings. Conventional SiO₂ coatings obtained by spraying, spinning, and immersion can improve the oxidation resistance of TiAl alloys to some extent, they still suffer from inadequate adhesion, insufficient densification, and crack sensitivity. Recently, electrodeposition has been proposed to fabricate SiO₂ coatings on TiAl alloys. The electrodeposited SiO₂ coating is well adherent with the TiAl substrate and exhibits excellent densification ability, resulting in significant enhancements to the high temperature oxidation resistance. Due to the use of KNO₃ in the precursor electrolyte, a certain amount of K⁺ ions is contained in the SiO₂ coating, promoting the sintering and densification of the coating. However, the preferential accumulation of alkali metal cations can lead to the precipitation of a large amount of cristobalite. The substantial volume changes of cristobalite during the heating and cooling stages may induce crack formation, adversely impacting the high temperature protective performance of the coating. Thus, controlling the precipitates of cristobalite and promoting the stability of the SiO₂ coating are crucial.

Recently, a team of material scientists led by Lian-Kui Wu from Sun Yat-sen University, China employed Al nanoparticles with high surface activity to modify SiO₂ coatings. Incorporating Al nanoparticles significantly inhibits and optimizes the generation of cristobalite, suppressing the formation of cracks, leading to the improved oxidation resistance of the SiO₂ coating. Moreover, the stabilizing effect of Al on the K⁺ ion migration and coating structure is revealed by this study.

The team published their work in Journal of Advanced Ceramics on May 13, 2025.

“In this study, we develop Al-modified SiO₂ coatings (Al-SiO₂ coatings) via ​co-electrodeposition. Fig. 1a displays the formation mechanism of Al-modified SiO₂ coatings. Through the application of cathodic potential, water molecules and dissolved oxygen at the electrode interface are electrochemically reduced to catalytically generate OH⁻ ions in situ. These OH⁻ ions facilitate the condensation reaction of TEOS, leading to the formation of a SiO₂ coating on the TiAl alloy surface. During this process, the hydroxylated surface of Al nanoparticles adsorbs protons, inducing their cathodic migration, which enables their encapsulation within the SiO₂ coating to form an Al-SiO₂ composite coating.” said Lian-Kui Wu, professor at School of Materials at Sun Yat-sen University (China), a senior expert whose research interests focus on the field of high temperature oxidation.

Compared with TiAl alloy coated with other ceramic coatings in the literature, the Al-SiO₂ ceramic coating developed in this study offers superior performance in high temperature oxidation environment. The researchers explained that the good oxidation resistance of Al-SiO₂ coating comes from two aspects. On the one hand, the reduced proportion of cristobalite reduces the residual stress after 100 h oxidation and inhibits the occurrence of cracks and other defects. “After thermal treatment, the microstructure of SiO₂ coating is regulated by the incorporated Al nanoparticles. The incorporation of Al nanoparticles inhibits the precipitation of cristobalite, so as to reduce the crack initiation and improve the overall compactness of the coating. Therefore, the Al-SiO₂ coating exhibits better oxidation resistance compared with the SiO₂ coating.” said Liankui Wu.

On the other hand, during oxidation, potassium silicate transforms into potassium aluminosilicate with a higher melting point and better stability. “DFT simulation scenario reveals that the doped Al atoms preferentially exist in substitutional positions, generating shorter Al-K bonds, preventing the migration of K, and stabilizing the K@SiO₂ lattice, which is beneficial to reducing the trend of crystallization and promoting the barrier properties of the SiO₂ coatings.” said Liankui-Wu.

Other contributors include Haojie Yan, Xianze Meng, Hao Li, Ruozhan Yin from the School of Materials at Sun Yat-sen University in Shenzhen, China; Xiaofeng Zhang from the Guangdong Provincial Key Laboratory of Modern Surface Engineering Technology in Guangzhou, China; Junbao Chong from School of Materials Science and Engineering, Inner Mongolia University of Science & Technology in Inner Mongolia, China.

This work was financially supported by the National Natural Science Foundation of China (52271084, 51971205, and 92160202), and the Guangdong Basic and Applied Basic Research Foundation (2021B1515020056).

About Author

​​Prof. Liankui Wu (Corresponding Author)​​ is a Full Professor and Doctoral Supervisor at the School of Materials, Sun Yat-sen University. His research primarily focuses on material corrosion and protection, with recent emphasis on high temperature corrosion resistance of TiAl alloys and surface engineering for marine equipment. A recipient of the Shenzhen High-Level Talent award. Prof. Wu has led multiple competitive research projects including National Natural Science Foundation of China, Distinguished Young Scholars Fundation of Guangdong Province. He has authored over 80 first/corresponding-author SCI papers in top-tier journals like Journal of Advanced Ceramics and Corrosion Science, holds more than 20 patents, and has been consistently ranked among the top 2% of scientists from all over the world (2021-2023) by Stanford University.​​

Prof. Xiaofeng Zhang (Corresponding Author)​​ is a Full Professor and Doctoral Supervisor at Guangdong Academy of Sciences, serving as Deputy Director of both the Thermal Spray Research Center and Guangdong Changxing Laboratory. A recipient of the National Excellent Young Fundation and Distinguished Young Fundation of Guangdong Province, he developed innovative aluminum-plating technology for aero-engine thermal/environmental barrier coatings with multiple industrial applications. His honors include China Nonferrous Metals Society's Outstanding Youth Scientist Award and two First Prizes in provincial/national science awards. With 93 first/corresponding-author SCI papers and 43 patents, he was listed in Stanford's Top 2% Scientists 2023.

About Journal of Advanced Ceramics

Journal of Advanced Ceramics (JAC) is an international academic journal that presents the state-of-the-art results of theoretical and experimental studies on the processing, structure, and properties of advanced ceramics and ceramic-based composites. JAC is Fully Open Access, monthly published by Tsinghua University Press, and exclusively available via SciOpen. JAC’s 2023 IF is 18.6, ranking in Top 1 (1/31, Q1) among all journals in “Materials Science, Ceramics” category, and its 2024 CiteScore is 25.9 (5/130) in Scopus database. ResearchGate homepage: https://www.researchgate.net/journal/Journal-of-Advanced-Ceramics-2227-8508