How hexagonal boron nitride (h-BN) nanosheets affect protection performance of waterborne epoxy coating

摘要

Advances in nanotechnology stimulates the coating industry to take advantage of the intriguingproperties of nanomaterials. 2D hexagonal boron nitride nanosheets (h-BN) have attracted greatattention as coating pigments, primarily due to their high thermal stability and exceptional barrierproperties. In this study, the effects of the addition of different concentrations of h-BN pigments (0,0.5, 1 and 1.5 wt%) to a waterborne epoxy coating pigmented with zinc phosphate-based corrosioninhibitor are investigated. Leaching measurements and electrochemical impedance spectroscopy(EIS) are complemented with microstructural characterizations to provide insights into the effect ofh-BN pigments on barrier properties, inhibitive-species leaching and anticorrosion performance ofthe primer coatings.It is shown that addition of h-BN always increases the coating resistance compared to that ofcoatings without h-BN. However, at low concentrations, such increase is more relevant that at highconcentrations. The increase in the resistance of the h-BN containing coatings is attributed to: 1-enhanced barrier properties, since h-BN particles lengthen diffusion pathways for reactive speciesand, 2- enhanced polymeric structure, since h-BN reduces the number of intrinsic free volumes andvoids within the matrix. The adverse effect of higher concentrations of h-BN on coating resistancesis attributed to the formation of relatively large agglomerates of h-BN pigments, acting as defectsthat result in preferential transport paths for diffusion of species. The addition of h-BN into thecoatings reduces the leaching rates of inhibitive species released from the inhibitor pigments,which is also supported by the EIS data, indicating higher pore resistances with h-BN pigment. Onthe other hand, EIS data did not reveal any self-healing behaviour for the coatings (regardless ofthe concentration of h-BN), whereas they showed that incorporation of h-BN pigments into thecoating results in an increase in the oxide layer resistance.