Anticorrosion Activity of a Polyacrylamide with High Molecular Weight on C-Steel in Acidic Media: Part 1

Abstract

The chemical structure of a polyacrylamide (PA), synthesized by inverse emulsion polymerization, was confirmed by FTIR and 1H NMR. The experimental conditions were conducted to produce high molecular weight of 1.4 × 106 g mol−1 determined by both gel permeation chromatography and viscosity average molecular weight methods. The efficiency of PA was evaluated, on corrosion inhibition of C-steel in 1.0 M HCl solution, by means of electrochemical impedance spectroscopy, potentiodynamic polarization (PP), and mass-loss (ML) measurements, and a very good concordance was obtained from the three techniques. The inhibiting efficiency increased up to 4 × 10−6 mol L−1 and dropped down afterward. The PP curves revealed that PA was of mixed-type, influencing predominantly the anodic process. The electrochemical interface was satisfactorily modeled with the electrical circuit (RS + Qdl/Rct) using CPE(α,Q) reflecting one-time constant. This fact, testifying the dominant character of charge transfer control of the C-steel corrosion process, was well described in both Nyquist along with Bode diagrams which take into account the frequency dependence, justifying the suitable choice of the electrical circuit. The adsorption of PA involved both physical and chemical interactions of non-protonated and protonated molecules with a deeper discussion on the suitable sites of protonation. The performance of PA was maintained if not slightly ameliorated in a more aggressive medium such as 0.5 M H2SO4 at 298 K. Two-time constants were needed to model the electrochemical interface (RS + Qdl/(Rct + RL/L)).