Response Characteristics Of Chromogenic Agent And Fluorescent Agent To Metallic Ions And Their Application In Corrosion Monitoring

Fluorescent indicators are widely used as a kind of important detection materials.In recent years,people pay more attention to the corrosion and protection of metals.Fluorescent indicators play an important role in early corrosion monitoring of metals and have a broad market prospect.In this thesis,three kinds of chromogenic agents(sulfosalicylic acid,potassium thiocyanate,phenanthroline)and five kinds of fluorescent agents(rhodamine hydrazide,rhodamine ethylenediamine,8-hydroxyquinoline,morin,coumarin)were added into the epoxy paint coated on Q235 carbon steel,2A12 aluminum alloy and B10 white copper substrates,and the color or fluorescence response characteristics to iron,copper and aluminum ions were studied.Fluorescence spectrophotometry and ultraviolet spectrophotometry were used to investigate the color developments and fluorescence responses of different chromogenic agents and fluorescent agents to the metallic ions;FTIR was employed to explore the complexation mechanisms of the different fluorescent agents and the metallic ions;electrochemical impedance technique and metallographic fluorescence microscope measurements were carried out to study the relationship between the impedance values at different time,coating fluorescence intensity and matrix corrosion morphology.The main conclusions are as follows:1.Sulfosalicylic acid and potassium thiocyanate have strong response characteristics to ferric ions,and phenanthroline has strong response characteristics to ferrous ions.It can be used in the water-based epoxy resin to monitor the corrosion of carbon steel under the coating.2.Rhodamine hydrazide has strong fluorescence response and fluorescence selectivity to ferrous and ferric ions(Fe2+and Fe3+).Rhodamine hydrazide has strong anti-interference ability to some metallic ions such as Na+,K+,Mg2+,Zn2+,Ca2+,Cu2+and Al3+ions.Adding 1wt%rhodamine hydrazide and 1wt%polyacrylamide into the water-based epoxy resin has a certain warning effect on the initial corrosion state of carbon steel.3.Rhodamine ethylenediamine has good complexation ability to cupric ions and obvious fluorescence response.It can be seen from the fluorescence and FTIR results that rhodamine ethylenediamine has good selectivity for cupric ions and is not easy to be interfered when mixed with other common metallic ions(Na+,K+,Mg2+,Zn2+,Ca2+,Cr3+and Al3+).Electrochemical impedance test and corrosion sensitivity test results showed that rhodamine ethylenediamine with 0.8 wt%content in the water-based epoxy coating is effectively able to monitor the initial corrosion state of white copper.4.8-hydroxyquinoline,morin and coumarin all have strong response characteristics to aluminum ions.8-hydroxy quinoline,morin and coumarin with 1 wt%content in the water-based epoxy coating,respectively,is effectively able to monitor the initial corrosion state of white copper monitor the early corrosion state of aluminum alloy.The ratio of fluorescent color area in the coating which contains coumarin to the corrosion area of the substrate is larger than those containing 8-hydroxyquinoline and morin.This indicated that coumarin has higher sensibility to the corrosion of the above several metallic ions.