Inhibition Effect of Polymers Having Carboxylic Acid-Side Chains on Corrosion of Mild Steel in Cooling Water System

Abstract

The relationship between inhibition abilities and characteristics of the polymers having carboxylic acid-side chains on the corrosion of mild steel in a cooling water system was investigated by physicochemical methods. In a low concentrated solution, the inhibition efficiency (η) of these polymers depended on (1) the number average molecular weight (Mn), (2) the content of maleic (MA) and acrylic acid (AA) units and (4) the concentration of these polymers in comparison with (3) the kind of MA and AA units. It was found for the condition of polymers having higher η value that (1) the Mn was 1000 to 3000, (2) the content of MA and AA units was about 50% and (4) the concentration of polymer was 100 to 200ppm. In a high concentrated solution, the η somewhat tended to rest on (2) the content and (3) the kind of MA and AA units and (4) the concentration of these polymers relative to (1) the Mn. It was found for the best condition of polymer in inhibition that (2) (& (3)) the content of AA was about 100% and (4) the concentration of polymer was more than 500ppm. The was also related to the degree of gelation of these polymers and calcium ions in a high concentrated solution. It is thought that these anionic polymers adsorbed on the surface of mild steel to form the layer and depressed the corrosion of mild steel under the condition of low and high concentrated solutions not to cause a scale-inhibition and a gelation.