Oxyhydroxide of metallic nanowires in a molecular H₂O and H₂O₂ environment and their effects on mechanical properties

Abstract

To avoid unexpected environmental mechanical failure, there is a strong need to fully understand the details of the oxidation process and intrinsic mechanical properties of reactive metallic iron (Fe) nanowires (NWs) under various aqueous reactive environmental conditions. Herein, we employed ReaxFF reactive molecular dynamics (MD) simulations to elucidate the oxidation of Fe NWs exposed to molecular water (H2O) and hydrogen peroxide (H2O2) environment, and the influence of the oxide shell layer on the tensile mechanical deformation properties of Fe NWs. Our structural analysis shows that oxidation of Fe NWs occurs with the formation of different iron oxide and hydroxide phases in the aqueous molecular H2O and H2O2 oxidizing environments. We observe that the resulting microstructure due to pre-oxide shell layer formation reduces the mechanical stress via increasing the initial defect sites in the vicinity of the oxide region to facilitate the onset of plastic deformation during tensile loading. Specifically, the oxide layer of Fe NWs formed in the H2O2 environment has a relatively significant effect on the deterioration of the mechanical properties of Fe NWs. The weakening of the yield stress and Young modulus of H2O2 oxidized Fe NWs indicates the important role of local oxide microstructures on mechanical deformation properties of individual Fe NWs. Notably, deformation twinning is found as the primary mechanical plastic deformation mechanism of all Fe NWs, but it is initially observed at low strain and stress level for the oxidized Fe NWs.

Atomistic insights on the influence of pre-oxide shell layer and size on the compressive mechanical properties of nickel nanowires

“…Previous theoretical studies indicated that plastic deformation always starts mechanically through emission of initial dislocations from the free surface, oxide shell layer, and/or the interface of the NW for the pristine and oxide-coated NWs that affect the overall mechanical properties. 2,23,31 However, it is difficult to identify exactly the location of initiation of initial dislocations. Generally, initial dislocation sources activated from these sites to initiate plastic deformation is associated with the combined effects of the geometry, the presence of local defects, the local atomic structure, the thickness of the oxide shell layer, the interface, surface morphologies, the size of the NW, and the applied strain rate.…”

“…Generally, initial dislocation sources activated from these sites to initiate plastic deformation is associated with the combined effects of the geometry, the presence of local defects, the local atomic structure, the thickness of the oxide shell layer, the interface, surface morphologies, the size of the NW, and the applied strain rate. 2,21,22,31 Therefore, the basic driving force for size-dependent mechanical deformation is believed to arise from the free surface, the oxide region, and/or the interface. Therefore, the low yield strength value of the oxide-coated NWs compared to their pristine counterparts and the softening as a function of diameter can be explained by the local structural analysis at the vicinity of oxide region and the free surface of NWs.…”

Role of Dissolved Oxygen in Iron Oxidation in Supercritical Water: Insights from Reactive Dynamics Simulations

“…There are several ReaxFF studies on metal oxidation with water or oxygen at the ambient environment or under the supercritical state. − In 2012, Aryanpour et al developed the first set of ReaxFF parameters for iron (Fe)–oxyhydroxide systems based on density functional theory calculations and the parameter set has been widely applied in subsequent ReaxFF studies. Pan et al , studied the process of iron oxidation under a typical moist condition and reported that a triplex structure was formed at the end of a three-stage oxidation process to reduce the overall oxidation speed.…”

“…Pan et al , studied the process of iron oxidation under a typical moist condition and reported that a triplex structure was formed at the end of a three-stage oxidation process to reduce the overall oxidation speed. Aral et al , investigated the effect of oxidation on the deformation of iron nanowires, and in their ReaxFF MD simulations, the iron nanowires were rapidly surface-oxidized in the atmosphere of either O 2 or H 2 O. DorMohammadi et al studied the initial stages of iron corrosion in pure water and reported the critical stages of the iron corrosion process identified as dissociation of water to OH – and H + , adsorption of OH – on the iron surface, penetration of oxygen into iron to form iron oxides, and dissolution of iron into solution. In 2015, Assowe et al developed a set of ReaxFF parameters for the nickel (Ni)–oxyhydroxide system, simulated the reaction of Ni in aqueous solution at room temperature (300 K) with an external electric field, and reported the generation of Ni composite on the surface.…”

Oxide shell layer influences on size-dependent tensile and compressive mechanical properties of iron nanowires: A ReaxFF molecular dynamics study

“…Surface oxidation occurs readily as reactive metallic pristine materials are exposed to a variety of different reactive oxidizer environments. [1][2][3][4][5][6][7] As a consequence of the oxidation process, the inevitable formation of a continuous oxide shell layer naturally covers the free surface of metallic reactive materials, depending mostly on the elapsed time, the oxygen pressure, and the temperature of the environment during manufacturing, processing, and working conditions. [1][2][3][4][5][6][7] Thereby, physical, chemical, electronic, and mechanical properties of metallic nanomaterials are modified by the oxidation at the free surface.…”