Effectiveness of lanthanum triflate activated silica nanoparticles as fillers in silane films for corrosion protection of low carbon steel

The synergistic effects of lanthanum activated silica nanoparticle fillers in silane films on the corrosion behavior of low carbon steel have been investigated. The silane films were synthesized through hydrolysis and condensation reactions of 3-glycidoxy-propyl-trimethoxy-silane (3-GPTMS) and methyl-triethoxy-silane (MTES) in acid catalyzed condition. A new corrosion inhibitor, lanthanum triflate at 1000 ppm concentration, was used to activate silica nanoparticles before their impregnation into silane sol-gel mixtures. The morphological characteristics and elemental distribution of the coatings were investigated using scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectrometer (EDX), confirming crack-free coatings distributed with silica nanoparticles. The structural characteristics and adhesive properties of the silane coatings on steel substrates were analyzed using Fourier Transform Infrared Spectroscopy (FTIR) with the results suggesting the formation of Si-O-Si network and Si-O-Fe bonding. Furthermore, the wetting properties of the coatings were determined through contact angle measurements; the silane films doped with lanthanum and/or silica nanoparticles exhibited increased hydrophobicity of the coatings. The corrosion resistance of the coated steel was evaluated by using electrochemical impedance spectroscopy (EIS) fitted with electrical equivalent models (EEC). The EIS diagrams obtained for the coatings doped with fillers exhibited higher impedance values by at least an order of magnitude when compared with non-doped coatings, indicating improved barrier properties of the coatings. Moreover, the films doped with both lanthanum inhibitor and silica nanoparticles exhibited the most efficient corrosion resistance - by more than two orders of magnitude for more than 168 h - compared to the films doped with either La3+ or silica nanoparticles alone. The overall system responses from EIS at high and low frequencies confirmed the benefits derived from synergistic roles of lanthanum-silica nanoparticles in silane films for a long term corrosion resistance performance of low carbon steel. (C) 2015 Elsevier B.V. All rights reserved.