Abstract: Calcium lignosulphonate (CL) was separated into four fractions of different relative molecular weights (M_w) by ultrafiltration and their contents of functional groups were determined. The corrosion-inhibition performances and mechanism of different fractions were studied by weight-loss and electrochemical impedance spectroscopy. Results indicated that contents of carboxyl, phenolic hydroxyl and sulfonic groups decreased with increased M_w. Only the fractions of M_w<5 000 had corrosion-inhibition performance. The fitting results showed that the equivalent circuit models were different with fractions of different M_w. Two time-constants appeared in the electrode system in the solution with M_w between 1 000 and 5 000, which indicated that this fraction could form an inhibitory film on the surface of carbon steel.

Key words: calcium lignosulphonate, corrosion inhibition, electrochemical impedance spectroscopy