Protection of low-carbon steel in aqueous solutions by lignosulfonate inhibitors

The corrosion and electrochemical behavior of low-carbon steel and iron in a neutral aqueous solution containing ZnHEDP, lignosulfonates LS1 and LS2, and their mixtures was studied. Corrosion tests showed that these lignosulfonates stimulate corrosion at room temperature but act as weak inhibitors at 80 degrees C. However, adding LS1 and LS2 to ZnHEDP enhanced the steel protection by the latter; a synergism of their protective effects was observed at certain ratios of the complexonate and polymers. Although LS1 and LS2 are compounds of the same type, their effects on steel corrosion in a neutral aqueous solution containing ZnHEDP differ substantially: LS1 favors the inhibition by ZnHEDP of the cathodic reaction only, while LS2 affect both electrode reactions.