Study On Corrosion Inhibition Effect Of Polyaspartic Acid To Carbon Steel In Tap Water

Corrosion has always been one of the major problems in modern industry and manufacture. Adding corrosion inhibitor is a generally applied technique in material protection for its advantage of high efficiency and easy control. With the development of green chemistry, green corrosion inhibitor needs to be nontoxic and biodegradable. Polyaspartic acid (PASP), the environmentally benign corrosion scale inhibitor, which is nontoxic and biodegradable, has become the focus of the present study in the fields of chemistry, water treatment and medicine in the past decade. In this paper, the corrosion inhibition ability and mechanism of PASP on 45~# carbon steel in neutral solution are discussed in detail by potentiodynamic polarization and electrochemical impedance spectroscopy. The primary results are as follows:1 .PASP is prepared by thermal condensation of L-aspartic acid, which is characterized by Infrared Spectrometry.2. Potentiodynamic polarization curves show that, PASP can inhibit the reaction of anode when added into tap water. The anodic polarization curve in solution in the presence of PASP is far different from that in the solution without PASP. All above proves that PASP as the adsorption inhibitor can inhibit the anode reaction primarily. Within the experimental temperature the inhibitor ability of PASP decreases with the rise of the temperature;the inhibitor ability of PASP increases with the rise of the pH;The inhibitor efficiency of PASP is 61.4% when the concentration is 1.0g/L. The maximum is 93.1% (5.0g/L) at 20°C.3. Impedance measurements indicate that the corrosion inhibition efficiency of PASP for carbon steel increases with concentration rise when its concentration is lower than 1.0g/L, and becomes approximately constant when higher than 1.0g/L.4. The corrosion inhibition coefficient shows linear dependence on PASP concentration, and the adsorptive behavior of PASP on carbon steel in solution at different temperatures follows the Freundlich adsorption isotherm. At 20°C,the formula of isotherm is log η =3.309 + 0.456 logC. The free energy of adsorption and adsorption equilibrium constant is obtainedby adsorption isotherm, and the obtained value is -28.35kJ/mol and 2037.04, which indicates the adsorption of PASP on the surface of carbon steel is spontaneous.5. The values of apparent activation energy of various inhibitor concentrations are obtained. The adding of PASP increases the apparent activation energy of the corrosion reaction of carbon steel, which indicates PASP retards the corrosion process within the experimental temperatures.6. The experiment proves that PASP and Molybdate inhibitor have better positive function. When the density is O.lg/LPASP and 0.1 g/L Molybdate, the maximum inhibition efficiency is 73.95 %.7. PASP and CiatfeSC^Na inhibitor have apparent function. When the density is O.lg/LPASP and 0.05g/L Ci2H23SO4Na, the inhibition efficiency is 70.71%, an increase of 44.91 % over that when PASP is used alone.8. In conclusion, as a secure and easily biodegradable green corrosion inhibitor, PASP has certain corrosion inhibition functions when added into water solution. Complex conjunction can further improve the corrosion inhibition efficiency and decrease the dosage. Some parameters obtained from the experiment can offer theoretical basis for the study on the corrosion inhibition ability of PASP in neutral solution.