Corrosion Inhibition Performance Of Carboxymethl Chitosan And Phosphonic Chitosan In Seawater

Seawater is an electrolyte solution with good electric capability, and the metals in seawater were destroyed through chemistry and electrochemistry corrosion reactions. The corrosion inhibitors are widely used in the protection of resources and reducing of corrosion of metal materials, so rational use of inhibitors is an effective method in preventing corrosion of metals and alloy.In this paper, two inhibiors were obtained through the carboxymethl and phophonic modification of chitosan. The corrosion inhibition performance and inhibitive mechanism of carboxymethl chitosan (CMC) and phophonic chitosan (PHC) for mild steel and copper were studied by loss-weight method, electrochemical measurement and quantum chemical calculation.The results from the investgation of the corrosion inhibition performance of CMC in seawater indicated that the inhibition efficiency for mild steel increased with the increasing of dosage. The inhibition efficiency for copper increased with the increase of dosage but changed little when the concetration over 400mg/L. The inhibition efficiency increased with the increase of dosage at high temperature, and the inhibition efficiency of low concentration CMC was higher at high temperature than at low temperature.The CMC filmed on mild steel beforehand at high inhibitor concentration was better than un-filmed.The results from the investgation of the corrosion inhibition performance of CMC with other components in seawater indicated that CMC compounded with Na2CrO4 at room temperature produced good synergistic inhibition performance. It was not suitable for compound with Ca(C6H11 O7)2 no matter under normal temperature or at 60℃. It had good synergistic inhibition effect with ZnSO4 at 40℃but lots of floccules appeared at 60℃. The synergistic inhibition effect with (C6H7NaO6)n at 60℃was not obvious. Chelation appeared when compounded with (NH4)2MoO4 at room temperature and 60℃and its was not suitable for synergistic inhibition.The results from the investgation of the corrosion inhibition performance of PHC in seawater indicated that the inhibition efficiency of PHC for mild steel and copper reached the hightest when the concentration was 300mg/L. The inhibition efficiency for mild steel increased with the increasing of temperature, but decreased when the temperature over 50℃. The corrosion inhibitive effects for rusty and dry-wet immersed mild steel were good and the inhibition performance couldn't be affected by dissolved oxygen. The inhibition efficiency kept high for a long time, the inhibition efficiency increased with immersion time and the highest efficiency was 96.23%.The results from the measurements of electrochemical polarization curves, electrochemistry impedance spectrum indicated that the corrosion potentials of mild steel and copper in seawaters with CMC and PHC changed, the inhibitor molecule adsorbing on the surface of the metals, and the charge transfer resistance increased and the double layer capacitance capacitance decreased. The polarization indicated that CMC is a mixed cathodic/anodic corrosion inhibitor, but mainly cathodic corrosion inhibitor, and PHC as a cathodic inhibitor.The optimized geometry structure and HOMO, LUMO were analyzed and calculated through quantum chemical calculation. The contribution ability of electron of the indican ring was strong, and it was very easy to form multi-active adsorbing centers by forming coordination key directly between lone pair electronic elements in–OH or -NH2 and empty track of Fe atom. The forming of chelate key between–OH ond -NH2 and d orbit of metals, especially with Fe2+ and Fe3+. The chelation between meatal atoms and Fe2+ or Fe3+ were stronger because the electronegativity of P element was higher, thus the inhibition efficiency was high.