Acid-modification and praseodymium loading of halloysite nanotubes as a corrosion inhibitor

Abstract This work aimed to study the encapsulation of praseodymium ions (Pr) as a corrosion inhibitor in acid-modified halloysite nanotubes (Hal) in order to increase their corrosion inhibition lifetime. Inhibitor loading in Hal was confirmed by the change of surface area from 46 m2.g−1 in raw Hal to 185 m2.g−1 in acid-treated Hal and 125 m2.g−1 in Pr loaded Hal. Acid-modification not only resulted in an increase in the internal diameter of Hal (from 12.11 nm to 17.41 nm) but also induced structural and chemical changes such as structural peak shift of Hal and variation of Al/Si ratio. Inhibitor encapsulation in Hal in vacuum was confirmed by high-resolution transmission electron microscopy (TEM), and field-emission scanning electron microscopy and energy-dispersive x-ray (FESEM-EDX) techniques. In addition, 0.025 wt% of acid-modified praseodymium loaded in Hal was encapsulated by micro- to nano-size urea-formaldehyde capsules for corrosion-resistant coatings. Hal encapsulated by inhibitor was dispersed in sol-gel hybrid matrix and the resulted coating was then deposited on AZ31 magnesium alloy. EIS experiments were conducted after 24 h immersion in 3.5% NaCl. The results showed that the coating containing inhibitor-encapsulated Hal (IEHAL) has lower corrosion rate in comparison with silane coating (SC) due to the increase of surface polarization resistance. Salt spray tests for 120 h also revealed that the coating containing IEHAL provides superior corrosion resistance.