Unveiling the corrosion mechanism of 3-nitro-1,2,4-triazol-5-one (NTO) toward mild steel from ab initio molecular dynamics: how the “nitro-to-amino” reaction matters

Abstract

Although NTO is unquestionably acidic, its potential to corrode weaponry and associated reaction mechanisms remain puzzling. Here, ab initio molecular dynamics (AIMD) with explicit solvation and “slow-growth” sampling approaches are utilized to identify the key steps involved in NTO induced metal corrosion. Our results affirm that the acidity of NTO originates from the lower dehydrogenation barrier of the N4 site compared to the N1 site (0.28 vs. 0.37 eV). Furthermore, NTO has the strongest adsorption on Fe(110) in a nitro-dissociation manner, revealed by using density functional theory (DFT) calculations. Notably, under the catalysis of Fe(110) and hydrogen shuttling, both NTO and its anion can realize the “nitro-to-amino” reaction within 4 ps, but the reduction barrier of the anion is higher. The surface species (*O and *OH) produced by the “nitro-to-amino” reaction serve as corrosion precursors and exacerbate the observed surface iron oxide formation in the experiments. Consequently, the surface corrosion products and azole rings, which are difficult to further decompose under mild conditions, act as a barrier to mitigate the corrosion rate. This work not only unveils a crucial issue in the application of NTO, but also highlights the importance of metal surface and hydrogen bonding in the corrosion process. Our research provides guidance for elaborating the mechanism of NTO induced corrosion at the microscopic level; it may hold for other acidic organic molecules as well. Such understanding can help in establishing corresponding protective measures.