Preparation Of Composite Fluorescent Probe And Its Application In Detection Of Metal Corrosion Under Coating

Corrosion is a destructive phenomenon caused by the interaction between metal materials and the environment.In order to minimize corrosion hazards,protective measures need to be taken to control the occurrence and development of corrosion.At present,coating protection is still the most important and widely used anti-corrosion technology.The shielding effect produced by the coating temporarily isolates the metal from the corrosive environment and is protected.However,as the use time increases,the corrosive medium will gradually penetrate through the coating/metal interface,thereby inducing corrosion of the metal under the coating.The speed of the above process will directly affect the anti-corrosion performance of the coating and the anticorrosion effect of the metal.If the early corrosion of the metal under the coating can be detected in time,it will play an important role in inhibiting the further deterioration of the corrosion situation.However,due to the lack of in-situ,intuitive and effective technology and methods,the corrosion detection of the metal under the coating is still very difficult.There is an urgent need to carry out relevant research to reveal the behavior of metal corrosion under the coating and provide technical theoretical support for the effective control of corrosion.In recent years,fluorescent probes have been widely and successfully applied in many fields due to their unique photoluminescence properties.Based on the characteristics of fluorescent probes that can produce fluorescence response to corrosion ions,it provides new technical ideas and technical approaches for the rapid,high-sensitivity,non-destructive and in-situ detection of early metal corrosion under the coating.In this paper,in response to the technical needs of early metal corrosion detection under the coating,two composite fluorescent probes were prepared and applied to the coating,and the early corrosion detection of aluminum alloy and carbon steel under the coating was successfully realized.The main research contents and results are as follows:1.In order to reduce the interference of the coating components on the fluorescent probe,the fluorescent probe N'-(4-diethylamino-2hydroxybenzylidene)-2-hydroxybenzohydrazide(NDH)and rhodamine B derivatives(Rxbxja)were coated with nano-silica.By adjusting the synthesis conditions,the surface morphology of the two composite fluorescent probes SiO2/NDH and S-Rxbxja could be adjusted to determine the optimal ingredient ratio and process conditions.SEM,FTIR,XRD,TG and other analysis methods have shown the successful preparation of the coating structure.In the selected solution environment,the fluorescence response behavior of the composite fluorescent probes SiO2/NDH and S-Rxbxja to different concentrations of Al,+and Fe3+was studied.The results show that the composite probes have specificity and stability in the recognition of two metal ions.At the same time,XPS was used to analyze the mechanism of fluorescent probes to identify corrosionions.2.0.2wt%of SiO2/NDH was added to 519w acrylic resin to prepare composite coating 519w+SiO2/NDH,which was applied to the surface of AA 5083 aluminum alloy.In a relatively short period of time,for artificial scratches on the coating and early pitting corrosion under the coating,a clear blue fluorescent indicator could be observed through a fluorescence microscope,and it can indicate the spread of corrosion to a certain extent.It shows that the prepared 519w+SiO2/NDH coating can realize the rapid and early corrosion detection of aluminum alloy.At the same time,the comprehensive mechanical properties of the 519w+SiO2/NDH coating were significantly improved compared to the water-based acrylic resin coating;The results of EIS and PC show that the resistance value of the composite coating increases and the selfcorrosion potential of the metal under the coating shifts positively.The above results are attributable to the good compatibility of SiO2/NDH with water-based coatings,which reduces the number of micro-defects in the coating;In addition,Al3+and NDH can form a chelate,covering a layer of insoluble film-like substance on the surface of the substrate,which increases the shielding of the coating to corrosive media.3.0.5wt%of S-Rxbxja was added to 519w acrylic resin to prepare composite coating 519w+S-Rxbxja,which was applied to the surface of Q235 carbon steel.In a short period of time,for the artificial scratches on the coating surface and the early pitting corrosion under the coating,obvious orange-red fluorescent indications could be observed through a fluorescence microscope;At the same time,the appearance of pink in the corrosion area could be observed with the naked eye.realizing the fluorescence/color dual-channel detection of early corrosion of carbon steel.At the same time,the 519w+S-Rxbxja coating maintains relatively excellent comprehensive mechanical properties;EIS and PC results show that the corrosion resistance of the coating has been significantly improved.The above results are attributable to the good dispersion of S-Rxbxja in the coating,which improves the shielding of the coating and effectively prevents the entry of corrosive ions such as H2O and Cl-;In addition,Fe3+ and Rxbxja can form coordination compounds to cover the substrate surface,delays the process of corrosion.