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Physical chemistry, Polymer science, Electrochemistry, Colloid chemistry, Materials engineering, Coating and films
Organic-inorganic polymers formed by hydrolysis/condensation reactions of alkoxide precursors, such as organically modified silanes (Ormosils) have found applications as electronic, optical and protective coatings. Such coatings possess important characteristics such as chemical stability, physical strength and scratch resistance. Further performance improvement is achieved through the incorporation of zirconium and titanium based nanoparticles, also formed through the sol-gel process. However due to the inherent difference in the reactivity of the precursors, the hydrolysis of each precursor must be carried out separately before being combined for final condensation. Zirconium precursors are commonly chelated using acetic acid or acetyl acetonate prior to hydrolysis, to lower the hydrolysis rate. In this body of work, 3,4-diaminobenzoic acid (DABA) and acetyl acetonate (acac) were compared as chelating ligands for controlling the hydrolysis reactions of zirconium n-propoxide to form nanoparticles within a silane sol matrix. The sols were applied as coatings on aerospace grade aluminium alloy AA 2024-T3 and characterised spectroscopically, electrochemically and calorimetrically. The results correlated with neutral salt spray evaluations which indicate that the novel use of DABA as a chelating ligand significantly improved the sol-gel protective performance over the traditional acac equivalent. The data indicates the anticorrosion properties of the nitrogen rich chelate have a key role in protecting the alloy.
Varma, P., et al.: Corrosion Protection of AA 2024-T3 Aluminium Alloys Using 3, 4-Diaminobenzoic Acid Chelated Zirconium-Silane Hybrid Sol-Gels. Thin Solid Films, Volume 518, Issue 20, 2 August 2010, Pages 5753-5761. doi:10.1016/j.tsf.2010.05.088