Environmentally friendly, nano lithium silicate anticorrosive coatings

Abstract

The aim of this study was to develop environmentally friendly, nano-structured inorganic coatings suitable for the protection of metal substrates. The formulation variables included (i) two binders based on lithium silicate of 7.5/1.0 silica/alkali molar ratio (one of them a commercial colloidal solution, and the other a laboratory-prepared nanosolution), (ii) eight pigment compositions based on two spherical microzinc alone (D 50/50 4 and 8 μm) and mixed with spherical nanozinc in three microzinc/nanozinc (w/w) ratios (90/10, 80/20 and 70/30) and finally (iii) six values of pigment volume concentration, PVC (from 47.5 to 70.0%). The electrode potentials were measured in sodium chloride solution at 25 °C and pH 7.0 during 70 days to establish the evolution of cathodic protection; in addition, panels were exposed in salt spray (fog) chamber to determine the degree of rusting and in 100% relative humidity to evaluate the blistering resistance. It was concluded that the variables alkaline silicate type, pigment composition and PVC values exhibited an important influence on the anticorrosive efficiency; very good performance was achieved with the nano-structured inorganic binder (7.5/1.0 SiO 2/Li 2O molar ratio) and the fine spherical microzinc (D 50/50 4 μm) modified with nanozinc (similar efficiency for 80/20 and 70/30 microzinc/nanozinc, w/w, ratios), in a wide range of PVC values (from 52.5 to 65.0% and from 47.5 to 60.0%, respectively).