Synthesis of methyltriethoxysilane-modified calcium zinc phosphate nanopigments toward epoxy nanocomposite coatings: Exploring rheological, mechanical, and anti-corrosion properties

Abstract

In this study, the effects of unmodified calcium zinc phosphate (UCZP) and modified calcium zinc phosphate (MCZP) nanopigments (NPs) on the rheological, mechanical, and corrosion protection performance (CPP) of the epoxy (EP) coatings were investigated. Transmission electron microscopy (TEM) coupled with energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) were used to study morphology and overall chemical structure of synthesized calcium zinc phosphate (CZP) NPs, respectively. The grafting of methyltriethoxysilane (MTES) molecules on the surface of CZP was assessed using Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), and contact angle (CA) measurements. The rheological-mechanical properties and anti-corrosion ability of the prepared coatings were assessed by rheometric mechanical spectroscopy (RMS), tensile test, micro-Vickers hardness (MVH) measurements, salt spray, electrochemical impedance spectroscopy (EIS) and pull-off tests. A 1.3° increase in CA was seen for MCZP NPs after silanization. The total resistance (Rt = coating resistance (Rc) + charge transfer resistance (Rct)) of EP coating increased from 0.4 MΩ cm2 to 50.1 and 25,118.8 MΩ cm2 in the presence of UCZP and MCZP NPs, respectively, after 50 days of immersion in 3.5 wt% NaCl solution. A 32.6 % and 24.6 % reduction in the adhesion loss were observed for the UCZP and MCZP NPs filled EP coatings, respectively.