Abstract
Pitting corrosion of carbon steel in a new working fluid for absorption heating and refrigeration was studied. The fluid was a concentrated solution of mixed lithium salt consisting of LiBr, LiCl, LiI and LiNO3, which had been developed aiming to increase the performance of the absorption cycle. The fluid contained not only the oxidizing agent, NO3-, but also, the oxidizing agent, I2 which is the oxidized species of I-. When the solution is kept at an elevated temperature of approximately 150°C, it is found that, regardless of the amount of NO3-, a small quantity of I2 raise the spontaneous electrode potential of platinum, ESP (Pt), to +120mV with respect to the saturated calomel electrode kept at room temperature. While, in an environment with no I2 and only one or greater than one percentage of LiNO3, the ESP (Pt) drops to approximately -120mV. Thus, the fluid forms an oxidizing halide environment that tend to induce localized corrosion in steels. The critical pitting potential, VC, PIT, for the carbon steel was determined to be either -340mV or -310mV for all oxidizing solutions with various concentrations of LiNO3 and I2. By comparing VC, PIT and ESP, it became apparent that pitting corrosion occurred violently in solutions containing I2 for the steel with ESP value more noble than VC, PIT. However, it became also apparent that in solutions containing more than 1% of LiNO3, pitting corrosion ceased when I2 is reduced by NaHSO3 completely. Insusceptibility of the carbon steel to localized corrosion is strengthened with a higher concentration of NaHSO3.
