The effects of cerium ions on the curing, polymerisation and condensation of hybrid sol-gel coatings

The hybrid sol-gel coatings developed in the present work serve as corrosion protection of aluminium alloy AA7075 and are based on (3-glycidyloxypropyl) trimethoxysilane (GPTMS), tetraethyl orthosilicate (TEOS) and silica (SiO2) nanoparticles, with the addition of cerium nitrate as a corrosion inhibitor. However, it is not clear whether this protection results from the corrosion inhibition effect alone or from the cerium effect on the sol-gel network. Thus, the role of cerium addition as well as of curing temperature on the network structure was studied by several techniques. Liquid-state nuclear magnetic resonance spectroscopy (29Si NMR) and solid-state magic angle spinning nuclear magnetic resonance spectroscopy (29Si MAS/NMR) were used to study the chemical composition and degree of polycondensation of inorganic and organic networks as a function of curing temperature and cerium content. The stability of sols was followed by measurements of viscosity and particle size, while the thermal stability of the two sols was determined by differential scanning calorimetry and thermal gravimetric analysis.