Corrosion Rates of Mild Steel In NH4NO3-NH3-H2O Solutions★

Abstract

Abstract Corrosion rates of mild steel in mixtures of NH4NO3-NH3-H2O were measured at temperatures of 30, 45 and 60 C. The effects of various sulfur and arsenic-containing inhibitors were studied, with particular emphasis on NH4CNS. The corrosion reaction was found to be markedly affected by stresses in the metal to the extent that completely stress-relieved coupons would not corrode at all. The rate of the uninhibited reaction was much lower at 45 and 60 C than at 30 C, indicating a change in the mechanism of the corrosion reaction. The uninhibited corrosion rate of 3700 mdd at 30 C was decreased to approximately 25 mdd with NH4CNS concentrations greater than 0.1 percent. At 45 C, the most effective inhibitor was found to be 0.05 percent 2-mercapto-ethanol + 0.05 percent sodium arsenite, followed closely by 0.1 percent NH4CNS + 0.05 percent sodium arsenite. Thio-cyanate and thiourea alone at concentrations of 0.1 percent were somewhat less effective. Simple potential measurements using a platinum reference electrode showed the corroding coupons to be about 0.9 volt more anodic than the stress-relieved coupons. 4.3.4