Fabrication And Corrosion Protection Of "Green" And Self-healing Composite Films On Carbon Steel

Corrosion is a metallic material degradation process occurring naturally and commonly,which can cause catastrophic accidents and huge economic losses(3-4%GDP).Corrosion of carbon steel is the main cause brought serious problems of safety and durability,and resulted in huge economic losses in society.Therefore,it is necessary to develop suitable anti-corrosion strategies.However,traditional corrosion protection often causes environmental pollution and health risk.It is thus of considerable importance and urgency to develop alternative environmental friendly corrosion protection technologies.Mussel adhesive protein(MAP)is non-toxic,low-cost and environmental friendly materials,which have been applied in corrosion protection field,and show effective corrosion protection for carbon steel.This thesis aims to develop a facile one-step-dipping method and use industrial’pure MAP(lower in cost)to prepare MAP/CeO2 and MAP/CeO2/Na2HPO4 composite films on carbon steel,which is beneficial in a real industrial application.A series of spectroscopic measurements were conducted to characterize the morphology and microstructure of the MAP-containing composite films.The corrosion protection and self-healing property of the MAP-containing composite films were evaluated by means of electrochemical tests.This thesis contains not only fundamental researches on self-healing and corrosion protection of MAP-containing composite films,but also feasibility of application in real system.The main progress and achievements are listed as follows:(1)A composite film composed of mussel adhesive protein(MAP)and CeO2 nanoparticles had been deposited on carbon steel surface by one-step-dipping method,which is explored as a ’green’ alternative corrosion protection for carbon steel.Combination of scanning reference electrode technique(SRET)and in-situ atomic force microscopy(in-situ AFM)was preformed to evaluate corrosion protection and self-healing property of the MAP/Ceo2 composite film.The mechanism of self-healing process is proposed as follows:when carbon steel with the pre-formed composite film is exposure to the neutral NaCl solution,initial localized corrosion occurs in the defects and releases Fe ions,which can form Fe-catecholato complexes with the pre-deposited MAP/CeO2 nanoparticles in the composite film dffectively inhibited the corrosion process,and then the active defects become passive during prolonged exposure.(2)A MAP/CeO2/Na2HPO4 composite film was successfully prepared on carbon steel using one-step-dipping method,which is suitably used in protection for rebar in concrete.The stable and well-distributed colloid stability of mixture solution usually last for about 1 h,and it can be recovered after stirred/ultrasonic treated when it has powder precipitation.The composite film dried in air contains aggregates and some hole-like defects,and exhibits a certain increasing and excellent corrosion protection for carbon steel in normal,even high local Cl-or high pH simulated concrete pore solution.In neutral 0.1 mol/L NaCl solution,bare carbon steel usually corrode seriously,whereas the composite film can still provide protective corrosion protection and self-healing property for carbon steel.(3)The effect of thermal treatment up to 200 ℃ on the corrosion protection was investigated for a composite film composed of MAP,CeO2 nanoparticles and Na2HPO4 deposited on carbon steel.The results show a certain increase in the corrosion protection with time for the prepared composite film on carbon steel.The analyses reveal that thermal treatment leads to a complete elimination of water molecules in the composite film,and an enhanced cross-linking and cohesion of the film due to a sufficient oxidation of catechols to o-quinones.As a result,the thermal treatment(200 ℃ for 10 minutes)does not cause any negative effects on the functionality of the MAP in the composite film.Instead,it leads to an enhanced corrosion protection of the MAP/CeO2/Na2HPO4 composite film for carbon steel.(4)In the pilot-scale test of thermal spray system,it was demonstrated that the MAP-containing composite films with outer epoxy coating were able to provide a good corrosion protection for steel rebar,and the pretreatment of MAP-containing composite films on rebar significantly enhanced the adhesion of epoxy coating on steel rebar.(5)Bis-[triethoxysilylpropyl]amine(BTSPA),BTSPA/CeO2 and MAP/CeO2/BT-SPA composite film were coated on carbon steel surface by electrodeposition.The results demonstrated that the BTSPA/CeO2 composite film formed on the BTSPA film electrodeposited at-0.8 V vs.SCE,exhibited an enhanced corrosion protection for carbon steel and an improvement of adhesion between substrate and outer epoxy coating.The electrodeposited BTSPA modified MAP/CeO2 composite film showed a good corrosion protection initially,and then provides an increasing corrosion protection for carbon steel with prolonged exposure time.The MAP/CeO2/BTSPA composite film combined the advantages both of BTSPA film and MAP/CeO2 composite film was able to provide excellent and increasing corrosion protection for carbon steel.