The Corrosion Inhibition Mechanism And The Influence On Cement Hydration Of Vitamin Corrosion Inhibitor

With the accelerated layout of China’s marine power strategy and the further promotion of green development goals,it is urgent to develop and apply new and efficient environment-friendly rust inhibitors to achieve long-life operation of large coastal projects.Vitamin corrosion inhibitors have been proved to have excellent performance on steel bar rust inhibition on the premise of green and environmental protection.However,the existing research on the mechanism of rust inhibitor and its effect on cement hydration is not clear,which greatly limits the wide application of vitamin rust inhibitor.In this paper,through the combination of experiment and quantum chemical calculation,the anti rust properties of vitamins B3,B6 and C are tested,the molecular structure models of three kinds of anti rust agents are established,their adsorption mechanism on the passive film of reinforcement is clarified,and the effects of the three kinds of anti rust agents on the macro properties and hydration microstructure of cement are explored.The influence mechanism of rust inhibitor on cement hydration through competitive adsorption with water molecules at the initial stage of hydration is revealed from the molecular scale.The specific research results are as follows:（1）The accurate molecular scale models of three vitamins are established by quantum chemical method.Among them,vitamin B3 has higher molecular reaction activity due to its low HOMO-LUMO energy gap and dipole moment.The electron localization function and van der Waals surface electrostatic potential show that the C-N and COOH functional groups of the three vitamins have higher reaction activity and are easier to bond with metal ions and H ions.Electrochemical test research shows that the three vitamins can better prevent the corrosion damage of reinforcement.The higher the concentration of vitamin B3,the greater the radius of capacitive resistance arc,and the slower the corrosion speed of reinforcement.The phase angle of 0.6%vitamin B6is the largest,and the rust prevention effect is the best.The local acidic environment produced by high concentration vitamin C will destroy the stability of reinforcement passivation film and affect the rust prevention effect.（2）First principles calculations show that vitamin molecules are parallel toγ-FeOOH surface adsorption is the most stable adsorption mode.Hydrogen bond plays an important role in the interaction between vitamin and steel passive film,and the more chemical bonds formed between vitamin and surface,the stronger the adsorption capacity.The results of charge density difference show that the functional groups of vitamin molecules adsorbed on the passive film mainly form chemical bonds with H and O atoms on the surface of the passive film.These chemical bonds are formed by the strong hybridization between N-2p,O-2p and h-1s orbitals on the surface.（3）First-principle calculation shows that the hydroxyl group dissociated in the adsorption process of vitamin molecules on C₃S.The dissociated hydrogen atom occupied the ionic O site of the C₃S surface,which may influence water adsorption on the C₃S surface.The competitive adsorption between vitamin and water molecules was found in the adsorption process;vitamin B3 and C dissociated and held the active site of C₃S surface,influencing the dissociation adsorption of the water molecule.The charge density difference and independent gradient model analysis also show that there are both chemical interactions and Vander Waals force in the competitive adsorption between vitamin and water.（4）The admixture of vitamins affects the cement flow and setting time,and the admixture of vitamin C has a slow setting effect.For the three vitamins,the admixture of 0.24%～0.40%will seriously reduce the early compressive strength.The hydration analysis and microstructural characterization show that vitamin rust inhibitors can delay the pre-induction process of hydration to varying degrees,and 0.40%of vitamin C can significantly reduce the exothermic rate of cement hydration and the exothermic heat of hydration,resulting in a substantial increase in cement setting time and porous,multi-gap hydration products.The addition of vitamin C also hinders the formation of calcium alumina and calcium hydroxide in the early stage of hydration,which is the main reason for the low early strength of cement.