Visualising the adsorption behaviour of sodium dodecyl sulfate corrosion inhibitor on the Mg alloy surface by a novel fluorescence labeling strategy

Corrosion inhibitors, have the characteristics of environmental friendly and high efficient, are widely used to inhibit the corrosion of alloys; however, their corrosion inhibition mechanism and adsorption behavior is still unclear. Herein, a cationic dye (1,8-naphthalenimide, NP) is synthesized for fluorescent visualisation of the sodium dodecyl sulfate (SDS) adsorption behavior on the alpha-Mg and beta-Li phases. In-situ observation showed that obvious fluorescence adsorption preferentially appeared on the alpha-Mg phase via physicochemical adsorption. Moreover, stronger fluorescence intensity was observed on the local corrosion sites due to the precipitation of Mg-SDS complex. Micro-scale in situ observation under electrochemical control is applied to explain the inhibition mechanism from the perspective of corrosion kinetics. The inhibition efficiency is evidently improved (>90%) after the addition of SDS, and the optimum value reaches 95.1% at the SDS concentration of 0.04 M. Surface characterizations are conducted to validate the adsorption behaviour of SDS on the Mg alloy surface. The inhibition mechanism of SDS is proposed by experimental and theoretical calculations. This work advances the development and application of specific fluorescence tracking to elucidate the adsorption behaviour of corrosion inhibitors at the micro-level and provides a new idea for the development of efficient corrosion inhibitors.