ReaxFF-Based Molecular Dynamics Study of the Mechanism of the Reaction of N₂O₄ with H₂O

Abstract

During long-term storage of the liquid propellant N 2 O 4 , it absorbs H 2 O to form the N 2 O 4 (H 2 O) n system, and this in turn generates HNO 3 , HNO 2 , and other substances in the storage tank because of corrosion, which seriously affects the performance of weaponry. In this work, we carried out computational simulations of N 2 O 4 with different masses of water based on ReaxFF, analyzed the reaction intermediates and products, and investigated the mechanism of the reaction of N 2 O 4 with H 2 O and of N 2 O 4 (H 2 O) n . The results show that the reaction product ω(HNO 3 +HNO 2 ) undergoes a rapid growth in the early stage of the reaction and then tends toward dynamic equilibrium; the potential energy of the system decreases with the increase of ω(H 2 O), the reaction rate increases, and the rate of decomposition of HNO 2 to form HNO 3 increases. When ω(H 2 O) is 0.2 or 1.0%, the intermediate products are N 2 O 4 H 2 O or N 2 O 4 (H 2 O) 2 , respectively, and the reaction proceeds along two paths; when ω(H 2 O) ≥ 2.0%, N 2 O 4 (H 2 O) 3 appears as the intermediate product, HNO 3 and HNO 2 are directly produced in one step, and a stable current loop can be formed within the whole system.