Sodium Polyacrylate Scale Inhibitor, Corrosion Mechanism

The mechanism of scale and corrosion inhibition of sodium polyacrylate (Na-PAAC) has been studied by electron spin resonance (ESR) technique, diffuse reflectance spectroscopy (DRS) FT-ER technique, chemical and electrochemical methods. Na-PAAC of low molecular weight was prepared by polymerizing acrylic acid in water using (NH4)2S208 as initiator and was spin-labelled by reacting with 4-mino-2,2-6,6-iperidinooxy. The ESR spectrum from the labelled polymer in aqueous solution consists of three distinct lines, the one to higher field being more broadened than the other two, reflecting the slower rotation of the nitroxide when attached to the polymer backbone as compared to free in solution. The adsorption of Na-PAAC onto scales from water was mainly induced by the attraction between positive charges on the scales and negative charges of polymer. The configuration of the adsorbed layer was that some segments of the adsorbed molecule were bound to the scale surface, some were dangling in the water. During the growing of scale crystal, the adsorption of the polymer at the active sites of crystal, which results in the repulsion between them, would inhibits the growing of the crystal effectively. Inhibition of Na-PAAC on carbon steel in hard water was investigated in the terms of potentiostatic steady-state polarization and A. C. impedance techniques. The results show that the ~ of the carbon steel did not moved but the transfer resistance (R~) was increased. The mechanism of inhibition was that the adsorption of Na-PAAC on the metal surface reduced the occurring area of corrosion reaction. The results of DRS FT-IR technique show that for different metal oxide, the reason of adsorption were different: on FeOOH, the Fe3~ ions on the surface in the presence of sodium polyacrylate formed a Fe( III )-PAAC complex; on A1203, the main induction was the attraction between positive-negative charges.