Aluminum-lithium alloys represent a critical class of structural materials in the aerospace sector due to their exceptional strength-to-weight ratio, stiffness, and fatigue resistance. However, their susceptibility to localized corrosion in chloride-containing environments poses a significant limitation to their long-term application, particularly in airframe and wing components exposed to atmospheric conditions. Organic polymer coatings, especially epoxy resins, have been widely adopted for the corrosion protection of metallic substrates by virtue of their strong adhesion, chemical resistance, and barrier properties. Nevertheless, conventional epoxy coatings exhibit inherent shortcomings such as brittleness, proneness to microcracking, and most critically, degradation under ultraviolet (UV) radiation. This photodegradation results in chalking, discoloration, gloss loss, and ultimately a drastic reduction in anti-corrosion performance. Therefore, there exists a compelling need to develop coatings that offer integrated and durable protection against both corrosion and UV aging, without compromising other mechanical or surface properties.
The work aims to present the design, fabrication, and multi-performance evaluation of a novel class of epoxy-based nanocomposite coatings reinforced with surface-modified CeO2 nanosheets, engineered to provide simultaneous corrosion inhibition, UV shielding, and autonomous self-healing functionality. The approach centers on the incorporation of CeO2 into an epoxy matrix in a manner that overcomes typical nanoparticle aggregation issues while enabling multiple protective mechanisms.
The synthesis protocol involved the preparation of sheet-like CeO2 nanoparticles via a reverse precipitation technique, followed by surface functionalization with two silane coupling agents: vinyl triethoxysilane (VTEO) and γ-aminopropyl triethoxysilane (KH550). This step was essential to enhance interfacial compatibility with the epoxy resin and to ensure homogeneous dispersion of the nanofillers. The resulting nanocomposites were systematically compared against control samples including unmodified CeO2/epoxy and pure epoxy coatings. A suite of material characterization techniques, confirmed the successful grafting of silane molecules onto CeO2 surfaces without alteration of its cubic fluorite crystal structure. The modified nanosheets exhibited rougher surface topography and a uniform distribution of Ce, O, and Si, indicative of effective functionalization.
The functional performance of the coatings was rigorously evaluated through spectroscopic, electrochemical, and surface analysis methods. UV-Vis absorption and fluorescence emission spectra demonstrated that silane-modified CeO2 composites possessed significantly enhanced and broadened UV absorption ranges, spanning both UVA and UVB regions. More notably, these composites showed a substantial reduction in fluorescence intensity, suggesting efficient conversion of absorbed UV energy into harmless thermal energy, thereby mitigating photo-oxidative damage to the epoxy matrix. FT-IR analysis of coatings subjected to accelerated UV aging revealed that pure epoxy underwent severe degradation of aromatic ether and aliphatic C-CH3 bonds. In contrast, the composite coatings exhibited minimal changes in these functional groups, underscoring the photostabilizing effect of the nanofillers.
Water contact angle measurements further supported the enhanced durability of the modified coatings. After UV exposure, the VTEO-CeO2/epoxy and KH550-CeO2/epoxy coatings displayed contact angle reductions of only 12.9% and 16.0%, respectively, compared to a 33.7% reduction in pure epoxy. This indicated superior resistance to photo-induced hydrophilic transformation, which was closely linked to loss of barrier performance.
Electrochemical assessments provided compelling evidence of the coatings' corrosion protection capabilities. Following 168 h of UV aging, potentiodynamic polarization tests indicated that the VTEO-CeO2/epoxy coating exhibited the most noble corrosion potential and the lowest corrosion current density, reflecting optimal corrosion resistance. Electrochemical impedance spectroscopy (EIS) results were consistent with these findings, showing that the silane-modified CeO2 composites maintained larger capacitive arcs in Nyquist plots and higher impedance values even after aging, indicative of preserved barrier properties. In contrast, pure epoxy and unmodified CeO2/epoxy coatings suffered significant degradation in performance.
A standout feature of this work is the demonstration of self-healing capability. Artificial scratches introduced into the VTEO-CeO2/epoxy coating are effectively sealed after immersion in a 3.5wt.% NaCl solution. EDS analysis of the healed scratch confirms the presence of Ce but no detectable carbon or substrate elements (Al, Mg), which is evident in the unhealed scratch of pure epoxy. This supports a healing mechanism wherein Ce3+ ions, released from the CeO2 nanostructures, migrate to the defect site and react with hydroxyl ions produced by the cathodic oxygen reduction reaction to form insoluble cerium hydroxide/oxide precipitates.
Key words
cerium dioxide /
silane modification /
UV aging resistance /
corrosion resistance /
self-healing
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Funding
National Natural Science Foundation of China (52171083); Fundamental Research Funds for the Provincial Universities of Zhejiang (2022YW83)
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