Molecular Dynamics Study On Passive Film Destruction And Corrosion Inhibition Of Steel Bar Under Stress

Reinforced concrete is one of the most significant basic structures in marine engineering.In today’s world,the biggest challenges facing the civil engineering field are related to durability.The high-salt and high-humidity environment of the ocean will cause serious corrosion to the steel bars in reinforcement,resulting in structural deterioration.The corrosion of reinforced concrete is different from the ordinary environment,and the destruction of the passivation film is a necessary condition for corrosion to proceed.In the marine environment,it is the corrosion of chloride ions that causes structural damage to the steel passivation film.And adding rust inhibitors to concrete can effectively slow down the corrosion of steel bars.However,the passivation film is extremely small and the destruction process is complicated,so it is difficult to study it experimentally.In this paper,the research methods of molecular dynamics simulation(MD)and electrochemical testing are used to reveal the mechanism of chloride ion damage to the passivation film of steel bars and the degradation behavior of the passivation film of steel bars under stress.Thus,the study of rust inhibitors and their mechanisms of action is necessary.On this basis,the study of rust inhibitors in them mechanism of action.The main conclusions are as follows(1)The mechanism of chloride ion destroying the passivation film of steel bar was studied by molecular dynamics simulation.The necessary condition for the degradation of γ-Fe OOH is the presence of both ions and defects.The steps of degradation are.(i)Adsorption: Cl-first adsorbs on the defects of γ-Fe OOH,and then induces Na+ to form Cl-Na pairs.(ii)Vibration: Cl-Na pairs vibrate around the defect area.(iii)Fracture:Vibration weakens the interlayer interaction of γ-Fe OOH,thereby destroying the γ-Fe OOH structure.(2)The effect of different passivation film structure strains on corrosion behavior was examined using molecular dynamics simulations.γ-Fe OOH can only maintain its plastic strain in a small strain range.When the strain exceeds 50%,the failure mode changes from plastic failure to brittle fracture.The Fe-O bond is the key to maintain the interlayer structure.An increase in the distance between two atoms reduces the stability of the interlayer structure.The appearance of the interlayer cross-linking region indicates that γ-Fe OOH can no longer bear stress.(3)The structure degradation of passivation film under different shear stresses and different defects was studied by molecular dynamics simulation.Defects are a necessary condition for passivation film degradation.A perfect passivation film has a strong ability to resist shear stress.Under 0.5MPa stress,only deformation will occur without damage.With increasing stress,the defect passivation film transitions from a partial connection to an overall deterioration between layers.Under low stress conditions,it can maintain its own structural stability through the dislocation sliding effect.Under high stress conditions,the dislocation effect disappears and the structure deteriorates.(4)The anti-chloride ion mechanism of amino-2-thiazoline(ATL)is studied by molecular dynamics simulations.2-ATL binds to the iron surface via van der Waals forces and inhibits chloride ions by active adsorption.(i)monitoring: ATL molecules adsorb;(ii)desorption: ATL molecules desorb from the iron surface;movement: ATL molecules move towards chloride ions to approach chloride ions;(iv)control: ATL molecules capture chloride ions and prevent corrosion.