Hybrid sol–gel coatings based on GPTMS/TEOS containing colloidal SiO2 and cerium nitrate for increasing corrosion protection of aluminium alloy 7075-T6
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One of the promising candidates to replace the chromate conversion coatings for corrosion protection of aluminium alloy AA7075 are the hybrid sol–gel coatings. In the present work hybrid silica sol–gel coatings doped with cerium nitrate were prepared and characterized. Tetraethoxysilane (TEOS) and 3-glycidoxypropyl-trimethoxysilane (GPTMS) were used as precursors. Silica SiO2 (Ludox) particles were added to achieve a barrier properties of coating, while Ce(NO3)3·6H2O was added in order to obtain an active corrosion protection. Optimization of sol synthesis was based on the results of ATR-FTIR spectroscopy and UV–vis–NIR spectroscopy. Opening of epoxy rings and completion of hydrolysis and the condensation reactions during the synthesis process were confirmed. Coatings were characterized through thickness, water contact angle, roughness, adhesion, electrochemical properties (potentiodynamic and electrochemical impedance spectroscopy) and the response to prolonged immersion time in 0.1 M NaCl. The high degree of cross-linking of Si–O–Si network structure and high density was achieved during the synthesis of the sol. Moreover, the results showed that the curing process and the incorporation of cerium nitrate into the hybrid sol–gel coating affected to the corrosion properties of the coating. The observed enhancement in corrosion protection properties is attributed to the combination of the barrier properties of the silica matrix with the active protection of the cerium nitrate.
KeywordsAluminium alloy Sol–gel coatings Corrosion protection Barrier properties SiO2 nanoparticles Cerium inhibitor
The authors acknowledge financial support from the Slovenian Research Agency (research core funding No. P2-0393 and the project 'Lightweight alloys based on aluminium as materials with increasing potential in transportation industry', ID J1-6734). The authors thank Aritz Iglesias, Desiré Ruiz and Eva Peiteado for the technical help at ICV (CSIC). The authors also thank Sheila Omar for all helpful advices. The measurements of sol viscosity were performed at the Nanotesla Institute Ljubljana. The authors thank Dr. Branka Mušič and Adis Šahinović for discussion and comments. The authors thank Prof. R.H. Pain for proof reading the manuscript.
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Conflict of interest
The authors declare that thay have no conflict of interest.
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