Corrosion protection for aerospace aluminum alloys by Modified Self-assembled NAnophase Particle (MSNAP) sol–gel

The Air Force Research Laboratory is developing environmentally benign alternatives to the traditional chromated aircraft coating for aircraft corrosion protection, targeted at a 30+ year performance life cycle. The Self-assembled NAnophase Particles (SNAP) process is a new method of forming functionalized silica nanoparticles in-situ from hydrolyzed tetramethoxysilane (TMOS) and glycidoxypropyltrimethoxysilane (GPTMS) in an aqueous sol–gel process, and then cross-linking the nanoparticles to form a thin, fully dense, protective film on Al aerospace alloys. These nanostructured coatings have been shown to provide an excellent barrier to corrosion for aluminum aerospace alloys; and other applications are envisioned. Much work has been done on characterization and performance of these coatings. This paper discusses a modification of SNAP formulation with tetraethoxysilane (TEOS). Films were formulated and developed to produce a dense barrier sol–gel coating on AA2024-T3. Corrosion protection properties of the films were evaluated with potentiodynamic scan (PDS) electrochemical technique, electrochemical impedance spectroscopy (EIS) and Salt Spray test (5% NaCl).