Corrosion protection properties of hydroxamic acid self-assembled monolayer on carbon steel

Self assembled monolayers (SAMs) of hydroxamic acids CH₃(CH₂)_nCONHOH with different alkyl length were formed on the carbon steel electrode surface. The corrosion protection properties of the monolayers were examined and characterized by electrochemical polarization curves, electrochemical impedance spectroscopy, X-ray photoelectron spectroscopy (XPS) and contact angle measurements. XPS results showed that the hydroxamic acid molecules adsorbed on the carbon steel surface, and the contact angle values on the modified surface supported the formation of hydrophobic hydroxamic acid SAMs. The results of electrochemical studies showed that the values of the corrosion potential shift towards the positive direction, and anodic currents of the carbon steel dissolution significantly decreases, indicating that hydroxamic acids are anodic inhibitors. However, the chain length and assembling time influence the protection efficiency.     

Effect of metal ions on corrosion inhibition of pimeloyl-1,5-di-hydroxamic acid for steel in neutral solution

The influence of metal ions on the adsorption process and corrosion inhibition of pimeloyl-1,5-di-hydroxamic acid (C7) on carbon steel surface in neutral solutions has been investigated by surface analytical and electrochemical techniques. Effective corrosion inhibition given by C7 in the presence of Zn²⁺ and Ni²⁺ is believed to be associated with the ability of the hydroxamic acid to form stable slightly soluble complexes with these cations. The influence of the metal ions on the inhibition efficiency is primarily related to the stability constants of C7-cation complexes. Magnesium has no effect on the inhibition performance as it has low stability constant with C7. It was found that the inhibition by C7/cation mixtures depends greatly on the molar ratio and immersion time.