Corrosion Inhibition Of Brass By Compound Amino Acid In Seawater

Due to the good mechanical properties, excellent thermal and electrical conductivity, corrosion resistance,brass has widely been used in industrial equipment, especially the heat exchange and cooling system. But the corrosion of brass in seawater will cause significant economic losses. Therefore, it is important to develop nontoxic and green compounds as corrosion inhibitors for brass in seawater.In order to find the green and high efficient corrosion inhibitors, corrosion inhibitive performance of two amino acids namely L-cysteine and lysine on brass in seawater was investigated by potentiodynamic polarization and electrochemical impedance spectroscopy(EIS). Then the impact of the addition of different concentrations of sodium gluconate on the corrosion inhibition behavior of amino acids was studied.The results indicate that L-cysteine and lysine are effective corrosion inhibitors for brass corrosion process in seawater at 298 K. The relative maximum inhibition efficiency is 87.5% in the presence of 100mg/L L-cysteine and 89.93% with the concentration of 90mg/L Lysine. After the addition of different concentrations of sodium gluconate, the inhibition efficiency is significantly improved as a result of the synergistic effect and the inhibition efficiency increases with adding the sodium gluconate. The highest inhibition efficiency of 97.35% was obtained with 100mg/L L-cysteine and the addition of 50mg/L sodium gluconate. Meanwhile, the compound inhibition of Lysine with the addition of 45mg/L sodium gluconate on brass achieved the highest inhibition efficiency of 98.62%.Electrochemical experiments showed that the addition of L-cysteine reduced the cathode corrosion current density, changed the corrosion potential negatively and shifted the corrosion potential over 85 mV, which confirms that L-cysteine acts as a cathode inhibitor for brass in seawater. As for cysteine in seawater, the corrosion current density diminished and potential shifted a little which illustrated that cysteine inhibits cathode reaction more and acts as a mixed type inhibitor. It was found that the adsorption of L-cysteine and lysine on brass surface in seawater obeys the Langmuir adsorption isotherms. After the addition of sodium gluconate, the inhibition efficiency increased. Surface observation further confirms the inhibition action using scanning electron microscope(SEM). What's more, there's a thin film generated on the surface of brass.EDS tests indicated that the content of chlorine decreased, but nitrogen, sulfur and oxygen increased with inhibitor addition. The reason is that the adsorption of corrosion inhibitor on brass which retardant the contact between Cl- and brass. In addition to X-ray diffraction tests, almost no corrosion product was detected on the surface of brass.