Chamber protection of zinc by individual compounds. Ethylhexanoic acid

Chamber protection is a promising and rapidly developing method of vapor-phase protection of metals from atmospheric corrosion by inhibitors. Corrosion screening of individual organic inhibitors has shown that chamber treatment (CT) with 2-ethylhexanoic acid (EHA) efficiently inhibits the initiation of zinc corrosion. A set of accelerated corrosion, electrochemical and physical methods was used to study the specific features of zinc chamber protection and mechanisms of EHA action. It was shown that: – as the temperature of zinc CT increases, the EHA efficiency first increases and then decreases. The growth of the protective effect is associated with an increase in the inhibitor’s vapor pressure that favors adsorption. The descending branch of the temperature dependence is due to a decrease in adsorption as the adsorbent (zinc) is heated. The optimal temperature of zinc CT with EHA is 100°C. – the efficiency of EHA increases as the CT time is increased to 1 hour. This is the optimal duration for this system. Longer CT does not provide a positive effect and is inexpedient. – CT of zinc under the optimal conditions results in the formation of surface adsorption films of EHA up to 100 nm thick. The acid reacts with the metal and the surface oxide to form the C4H9-CH(C2H5)-COO-Zn-OH basic salt. Once zinc is removed from the chamber and exposed to open air, the basic salt is dehydrated and converted to a compound with the formula CH(C2H5)-COO-Zn-O-Zn-OOC-СН(C2H5)-C4H9 that is responsible for metal protection. This process determines the growth in the protection efficiency during the first day of metal exposure outside the chamber at room temperature. – the surface layers formed on zinc during CT followed by exposure to air passivate the metal and stabilize its passive state. Their action is associated with both shielding of the surface from the corrosive environment and inhibition of corrosion processes on the active metal surface. The EHA efficiency in zinc protection was confirmed by field tests.