The protection of TDPA deposited from mixed solutions with different water/ethanol ratios for aluminum alloy against corrosion in NaCl solution

Purpose - The purpose of this paper is to investigate the effect of water content of assembly solution on the adsorption behavior and corrosion protection performance of 1-tetradecylphosphonic acid [TDPA, CH3(CH2)13P(O)(OH)2] films on aluminum alloy surface in NaCl solution. Design/methodology/approach - Self-assembled monolayers (SAMs) of TDPA were prepared on the 2024 aluminum alloy surface in TDPA containing ethanol-water solutions with different water contents. The adsorption behavior of the SAMs on the alloy surface and their corrosion protection properties in a 3.5 per cent NaCl solution were characterized by potentiodynamic polarization scan, Fourier-transformed infrared spectroscopy (FTIR) and atomic force microscopy (AFM). Findings - The FTIR results demonstrated that the TDPA molecules were successfully adsorbed on the 2024 aluminum alloy surface, and the density of the SAMs increased with the increasing water content in the assembly solution. The electrochemical studies and corrosion morphologies observed by AFM showed that the optimal condition is 2 h of assembling in solution B or solution C. The corrosion inhibition efficiency values follow the order solution B approximate to solution C > solution A at the first 2 h assembly and solution B > solution C > solution A while the assembly time exceeded 2 h. The dependence of corrosion inhibition performance of the SAMs on the water content and on the assembly time is related to the balancing of competition between TDPA adsorption and dissolution of the alloy oxidation film. Originality/value - It illustrates potential application prospects of TDPA for surface treatment of aluminum alloy. Via the comparison with our previous work, this paper provides useful information regarding the difference of corrosion inhibition properties of organic phosphonic acid for aluminum alloy between in neutral and in acid solution.