ReaxFF Reactive Molecular Dynamics Study of Orientation Dependence of Initial Silicon Carbide Oxidation

Abstract

We analyze the early stage of the highly anisotropic silicon carbide oxidation behavior with reactive force field molecular dynamics simulations. The oxidation of a-, C,- m-, and Si-crystallographic faces is studied at typical industry-focused temperatures in the range from 900 to 1200 °C based on the time evolution of the oxidation mechanism. The oxide thicknesses and the growth rates are obtained from these simulation results. In addition, an investigation of the silicon and carbon emission is performed with respect to various orientations in order to support further development of macroscopic physical models that aim to predict initial silicon carbide oxidation.

Sensitivity of SiC Grain Boundaries to Oxidation

“…This transition in the growth rate is consistent with previous simulations of oxidation of single-crystal SiC with different temperatures and oxygen concentrations. ,, It can be attributed to the fact that oxide layer formed on top of the crystal affects the in-diffusion of O 2 and out-diffusion of gas products. The gas products block the SiC surface from chemically reacting with oxygen, and thereby they decelerate the oxidation process . After about 100 ps, the growth rate decreases, and the dependence of oxide growth on time becomes close to linear.…”

“…Similar pressures were used in earlier MD simulations of SiC oxidation, ,,, where it was shown that such simulations give a reasonable description of chemical reactions. The surfaces of SiC were initially not passivated, as the passivation of surfaces could potentially affect the investigation of orientation dependence of oxidation growth rates. , Periodic boundary conditions were applied along all three directions. We placed a reflective boundary at the top of the simulation box (the top z boundary) to prevent oxygen from leaving the simulation cell and from interacting with the bottom surface of SiC.…”

“…For example, a number of first-principle calculations ,, have been carried out to identify the energetics and reaction pathways for oxygen adsorption and carbon desorption on different SiC surfaces during the early stages of oxidation. Simulations using classical molecular dynamics (MD) − have also been reported where formation and breaking of atomic bonds was tracked during the growth of the first few nanometers of oxide, providing a deeper understanding of the dependence of the oxidation rate on crystal orientation, surface atomic composition, and crystal structure. Experiments have been conducted both in dry and wet environments to evaluate oxidation rate under a wide range of conditions. ,,, In general, it was found that GBs and interfaces in SiC were more vulnerable to oxidation. ,− In cases where preferential corrosion of GBs was observed, it was also found that such corrosion could result in detachment of entire grains and in acceleration of the oxidation rate.…”

“…Experiments have been conducted both in dry and wet environments to evaluate oxidation rate under a wide range of conditions. 19,20,31,32 In general, it was found that GBs and interfaces in SiC were more vulnerable to oxidation. 21,32−34 In cases where preferential corrosion of GBs was observed, it was also found that such corrosion could result in detachment of entire grains and in acceleration of the oxidation rate.…”

ReaxFF Force Field Development and Application for Toluene Adsorption on MnMOx (M = Cu, Fe, Ni) Catalysts

“…Following the established protocol to train the parameters involved in the ReaxFF potential functions, these have to be parametrized against experimental results and high-level ab initio calculations. 9 For a complete description of the ReaxFF field, all of the factors in expansion should be optimized during the force-field optimization process. 10 The ReaxFF potential is written as where E system is the overall interaction energy of the system; E bond is the bond energy, the two-body attractive term that is dynamically dependent on bond orders of specific bond type, σ, π, or ππ; E val and E tor are the three-body valence angle terms and the four-body torsion terms, respectively, describing angle and torsion strain energy; E lp and E over/under are the energy contributions from lone-pair electrons, and the penalty energy coming from overcoordination and undercoordination; E conj represents the conjugation energy term; E vdWaals is the energy of van der Waals interactions; E Coulomb is the electrostatic contribution; E H-bond represents hydrogen bond; and E Coulomb and E vdWaals are the nonbonded interactions between all pairs irrespective of the connectivity in the system.…”