Addition of transition elements to the phosphate sealing of cerium oxide protective primer deposited on AA2024-T3 alloy
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2016-01-01
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Abstract
A concise investigation was undertaken to determine the impact of transitional elements on the phosphate sealing of cerium oxide primer layers deposited on AA2024-T3 aircraft alloy. The cerium oxide primer layers were deposited electrochemically on preliminary treated alloy specimens under potentiostatic conditions. The subsequent phosphate sealing layer deposition was performed in equimolar solutions of NaMoO4, NaVO3 or ZrO(NO3)2 in (NH4)2HPO4 medium for 30 min at 90°C. The already coated and sealed specimens were submitted to comparative measurements via electrochemical impedance spectroscopy and linear voltammetry after 168 h of exposure to 3.5% NaCl model corrosive medium. The obtained bi-layer coatings were characterized by systematic analyses using scanning electron microscopy, energy dispersion X-ray spectroscopy and X-ray photoelectron spectroscopy. The latter analysis evinced that cerium present in a cerium phosphate coating was predominantly in Ce(III) state, while doping by Mo, V and Zr caused oxidation to Ce(IV) species. The results obtained reveal successful inclusion of these elements inside the phosphate sealing layer.