Corrosion Inhibition of Mild Steel by Cationic and Anionic Polymers in Cooling Water System

Abstract

The behavior of corrosion inhibition of mild steel by various cationic and anionic polymers, that is, polyethyleneimine (PEI), its derivative (PEID), polyarylamine (PAAm) and polydicyanodiamide derivative (PDCDA) as cationic polymers and polymaleic acid derivative (PMAD), polyacrylic acid derivative (PAAD) and polyacrylic acid (PAA) as anionic polymers, was investigated by corrosion tests and physicochemical measurements. Testing was done in two pseudoconcentrated solutions with low (LC) and high (HC) concentrations of ionic species like Ca2+ and Cl−. The cationic polymers lacked inhibition ability, while the anionic polymers had a more effective inhibition ability. The anionic polymers had a potential to act as corrosion inhibitors of an adsorption‐type in LC solution and as both corrosion inhibitors and scale inhibitors of calcium carbonate . In LC solution, the inhibition efficiency (η) value of anionic polymers was dependent on number‐average molecular weight , content of carboxylic group (‒COOH), and concentration of ‒COOH. In particular, the anionic polymers as inhibitors had an effective range of (103 order). In HC solution, the degree of corrosion of steel was influenced by concentrations of both anionic polymers and solution components such as Ca ion ; the anionic polymers were competitively adsorbed with Ca ion on the steel.