Hybrid sol–gel coatings based on GPTMS/TEOS containing colloidal SiO2 and cerium nitrate for increasing corrosion protection of aluminium alloy 7075-T6

• Published in: Journal of sol-gel science and technology 2018-03, Vol.85 (3), p.546-557
• Main Authors: Tiringer, Urša, Milošev, Ingrid, Durán, Alicia, Castro, Yolanda
• Format: Article
• Language: English
• Subjects: Aluminum base alloys; Ceramics; Cerium nitrate; Chemical synthesis; Chemistry and Materials Science; Chromate coatings; Composites; Contact angle; Conversion coatings; Corrosion; Corrosion prevention; Crosslinking; Electrochemical analysis; Electrochemical impedance spectroscopy; Fourier transforms; Glass; Inorganic Chemistry; Ludox (trademark); Materials Science; Nanotechnology; Natural Materials; Nitrates; Optical and Electronic Materials; Optimization; Original Paper: Industrial and technological applications of sol-gel and hybrid materials; Properties (attributes); Protective coatings; Silica gel; Silicon dioxide; Sol-gel processes; Spectrum analysis; Submerging; Tetraethyl orthosilicate
• ISSN: 0928-0707; 1573-4846
• DOI: 10.1007/s10971-017-4577-7

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 SiO 2 (Ludox) particles were added to achieve a barrier properties of coating, while Ce(NO 3 ) 3 ·6H 2 O 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.