Polarization Curves of Carbon Steel in Concentrated LiBr Solutions Containing LiOH and Li₂MoO₄ at Different Temperatures after Short Immersion

Abstract

We have tried to measure polarization curves of SS400 carbon steel in concentrated LiBr solutions over 393 K, and investigated the influence of temperature as well as concentrations of LiOH and Li₂MoO₄ on its corrosion behavior. Test solutions were 65 mass% (mass% is replaced by % hereafter) LiBr solutions containing 0 to 0.2% LiOH and 0 to 0.03% Li₂MoO₄. Test temperatures were 393 and 438 K. The test solutions were deaerated. The specimen was immersed in the test solution for a short time of 0.3 ks and was subjected to measurement of polarization curve in the same solution. As a result, the followings were obtained: The anodic current density in 65% LiBr solution without LiOH increased monotonically with a rise in a potential, and the relation was maintained regardless of Li₂MoO₄ addition and temperature change. In 65% LiBr solutions with LiOH up to 0.2% at 393 and 438 K, the anodic polarization curves showed active dissolution and passivation. When 0.05% LiOH was added to the 65% LiBr solution, the corrosion potential negatively shifted, and the potential was maintained regardless of more addition of LiOH. As a LiOH concentration increased, a pitting potential was raised. The polarization curves at 393 and 438 K showed almost no change regardless of addition of 0.03% Li₂MoO₄, meaning that Li₂MoO₄ had almost no effect on corrosion inhibition to the specimen for the short immersion. The corrosion rate at 393 K was approximately 0.3 A·m⁻² regardless of the addition of LiOH nor Li₂MoO₄. Whereas, the corrosion rate at 438 K slightly decreased with increasing LiOH concentration, regardless of the addition of Li₂MoO₄. Cathodic current density in the solution with 0.2% LiOH and 0.03% Li₂MoO₄ increased with a rise in a temperature on the basis of Arrhenius relation. It is thought that insufficient effect of LiOH and Li₂MoO₄ on corrosion inhibition was observed because of a short immersion time of 0.3 ks before measurement of polarization curves.

Fig. 4 Polarization curves of the specimen in the solutions of 65% LiBr + x% LiOH (x = 0, 0.05, 0.1, 0.2) at 393 K.