Influence of amino functionalised POSS additive on the corrosion properties of (3-glycidoxypropyl)trimethoxysilane coatings on AA 2024 alloy

The influence of the addition of a mixture of POSS compounds substituted equally by 3-aminopropyl and isobutyl groups (AP4IB4 POSS) on sol–gel coatings prepared from (3-glycidoxypropyl)trimethoxysilane (GPTMS) was evaluated from the point of view of their anticorrosion properties. AP4IB4 POSS belong to a group of polyhedral oligomeric silsesquioxanes and their functionalisation with amino groups enables cross-linking with the epoxy groups of GPTMS. Additionally, GPTMS molecules react among themselves through hydrolysis and condensation processes of trimethoxysilane groups when catalysed by 0.1 M KF. The results of the Raman and IR measurements revealed that a molar ratio of GPTMS:H2O = 1:3 is more beneficial than a molar ratio of 1:1.5 for the preparation of sol–gel coatings. The anticorrosion properties of the mixed GPTMS/POSS coatings deposited on AA 2024 aluminium alloy were tested using potentiodynamic electrochemical measurements and a salt-spray chamber test. It was found that the mixed GPTMS/POSS coatings showed improved corrosion protective properties vs. either pure GPTMS or POSS coatings.

► Sol–gel (3-glycidoxypropyl)trimethoxysilane (GPTMS) anticorrosion coatings were made.
► POSS additive improved the anticorrosion properties of GPTMS coatings.
► Amino-functionalised POSS reacted with epoxy rings of GPTMS.
► The most condensed films: one H-atom of amino-POSS per one epoxy ring of GPTMS.
► Mixed GPTMS/POSS coatings survived 368 h in salt-spray chamber.