Evaluation of polyaniline composites and nanostructures as anti-corrosive pigments for carbon steel

Abstract

Conducting polymers have recently been studied as a new class of materials for the corrosion protection of metals. Polyaniline (PANI) is the best candidate to perform this function due to its high environmental stability and simple preparation. Polyaniline was synthesized by polymerizing aniline monomer with various inorganic oxides and with several ratios of phosphoric acid doping. The prepared samples were characterized by Fourier Transform Infrared Spectroscopy (FTIR) and X-Ray Diffraction Meter (XRD) and the morphology of these samples was examined using Scanning Electron Microscopy (SEM) and Field Emission Scanning Electron Microscopy (FESEM). Electrical conductivity of the samples was measured using a multimeter. Besides, pigments dispersion stability was observed in ethanol medium at six increasing times (0, 1, 3, 6, 12 and 24 hours). The prepared samples were used as anti-corrosive pigments by blending with commercially available acrylic paint. The blended pigments and acrylic paint were then applied on carbon steel panels by simple dip coating method. The coated steel panels were then dried at room temperature for two days. Once the coatings were fully dried, the steel panels were immersed in 5% NaCl solution for 60 days and left in salt spray chamber for 35 days according to standard ASTM G31 and ASTM B117 respectively. The degree of corrosion for full immersion test samples were evaluated by calculating the corrosion rate from weight loss method and by visual observation for samples exposed in salt fog chamber. The adhesion strength was measured according to ASTM D3359 standard. Sample that was most affected by corrosion, has lower adhesion strength with metal. The degrees of corrosion on the steel panel are related to the pigment used in paint and thus the best PANI composite pigment for corrosion protection was PANI-Silicone dioxide (PANI-SiO2) while the best nano form in terms of corrosion protection was PANI nanofiber. This was due to its highest electrical conductivity and good adhesion strength for PANI-SiO2 and better dispersion stability for PANI nanofibers.