Anti-corrosion hybrid coatings based on epoxy–silica nano-composites: Toward relationship between the morphology and EIS data

Abstract

This work reports on design and manufacture of organic–inorganic hybrid coatings based on diglycidyl ether of bisphenol A (DGEBA) epoxy resin pursuing hydrolyzation of tetraethoxysilane (TEOS) through a sol–gel process. The resulting hybrid materials were cured to be used as potential anticorrosive coatings. The assigned materials were modified molecules made of DGEBA and 3-aminopropyl triethoxylsilane (APTES), in which the molar ratio of epoxide group of DGEBA to NH of APTES varied in the order of 2:1, 4:1, 8:1 and 16:1. In the next stage, the APTES-modified DGEBA precursors were added to different amounts of pre-hydrolyzed TEOS, i.e. 7.5, 12.5 and 17.5 wt%, as inorganic part of the resulting hybrid. The mixtures were subsequently cured at room temperature by a cycloaliphatic amine based curing agent to yield transparent epoxy–silica hybrid coatings. Microstructure assessment of the hybrid materials, before and after curing, was performed using FTIR and 29Si NMR spectroscopies. The morphology of the epoxy–silica hybrid coatings has also been studied by scanning electron microscopy (SEM). The anti-corrosive measurements on the resultant coatings were conducted based on electrochemical impedance spectroscopy (EIS). The mechanical properties evaluation such as micro-hardness measurements and pull-off adhesion tests of the cured samples were also carried out. The thermal properties of the cured hybrid coatings were evaluated using thermogravimetric analysis (TGA). The results showed that the concentration of APTES and pre-hydrolyzed TEOS play an important role in determining the morphology as well as the mechanical and thermal properties of coatings. The EIS results corresponding to these effects reaffirmed that the corrosion resistance of the hybrid coatings improved with increasing the inorganic phase content.