Abstract
Thiourea, (Inh I), N-allylthiourea, (Inh II), and 3-allyl-1-[(2-methoxyphenyl)methyl]thiourea (Inh III) were used to mitigate the pitting corrosion of Ni in 0.01 M H2SO4 by the galvanostatic polarization technique. The used compounds decrease the pitting corrosion by displacement of the pitting potential, E-pit into more positive values, with decreasing the amount of electricity, Q(inh), required to reach E-pit. The inhibition efficacy, eta, was found to increase with raising the inhibitor concentration and depend on its kind. The inhibition efficacy, eta, increases in the sequence Inh I < Inh II < Inh III. The inhibitive action of these compounds is discussed in terms of blocking the electrode surface through an adsorption process following the Temkin isotherm. The calculated values of Delta G(ads)degrees are found to be -48.63, -50.18, and -51.84 kJ/mol for Inh I, Inh II, and Inh III, successively. These values are compatible with a chemisorption process including the transfer of electrons from the inhibitor molecule to the Ni metal surface.