Initial stage oxidation on nano-trenched Si(1 0 0) surface

Micromechanism of oxygen transport during initial stage oxidation in Si(100) surface: A ReaxFF molecular dynamics simulation study

Crack propagation of Si nanofilm accompanied by initial stage of wet oxidation

Effect of oxidation on crack propagation of Si nanofilm: A ReaxFF molecular dynamics simulation study

In this work, reactive force field molecular dynamics (ReaxFF MD) simulations are performed to study competitive and synergistic effects and their impact on CO, CO2, unburned carbon (UC), and nitrogen oxide (NO) emissions in coal/NH3 cofiring at different conditions. Simulation results show that cofiring results in higher emissions of UC and NO. Increasing the temperature is helpful in reducing UC emissions but has little effect on NO emissions. Although decreasing the O2 equivalent ratio can help in reducing NO emissions, UC emissions increase significantly. The conclusion is that the best O2 equivalent ratio in cofiring is 0.6. Increasing the NH3 cofiring ratio will reduce NO emissions but seriously increase UC emissions. The competition between coal and NH3 for O2 will decrease the coal combustion rate and increase the NH3 combustion rate. The competition effect is further proved by tracing the OH distribution. The synergistic mechanism is revealed. The free radicals and intermediates generated from coal combustion, such as HO2, H2O2, H, and OH, will promote NH3 decomposition and oxidation. The kinetics analysis shows that the competition between NH3 combustion and coal combustion only influences the combustion rate of coal and NH3, while the synergistic effect of coal decreases the activation energy of NH3 combustion. The research results are helpful to further study the mechanism of coal/NH3 cofiring and guide the technology of NH3 blending in coal-fired power plants.

The initial stage oxidation of biaxially strained Si(100) at temperatures ranging from 300 K to 1200 K has been investigated by Reactive Force Field Molecular Dynamics simulations. We reported that the oxidation process involving the reaction rate and the amount of absorbed O atoms could be enhanced by the coupling effect of higher temperatures and larger external tension. By fitting the simulation results, the relationship between absorbed oxygen and the coupling of temperature and strain was obtained. In probing the mechanism, we observed that there was a ballistic transport of O atoms, displaying an enhancement of inward penetration by external tension. Since such an inward transport was favored by thermal actuation, more O atoms penetrated into deeper layers when the 9% strained Si oxidized at 1200 K. Moreover, the evolution of stress in the surface region during the oxidation process was discussed, as well as the related oxide structure and the film quality. These present results may provide a way to understand the thermally-mechanically coupled chemical reactions and propose an effective approach to optimize microscale component processing in the electronic field.

Gasification with supercritical water is an efficient process that can be used for the valorization of biomass. Lignin is the second most abundant biopolymer in biomass and its conversion is fundamental for future energy and value-added chemicals. In this paper, the supercritical water gasification process of lignin by employing reactive force field molecular dynamics simulations (ReaxFF MD) was investigated. Guaiacyl glycerol-β-guaiacyl ether (GGE) was considered as a lignin model to evaluate the reaction mechanism and identify the components at different temperatures from 1000 K to 5000 K. The obtained results revealed that the reactions and breaking of the lignin model started at 2000 K. At the primary stage of the reaction at 2000 K the β-O-4 bond tends to break into several compounds, forming mainly guaiacol and 1,3-benzodioxole. In particular, 1,3-benzodioxole undergoes dissociation and forms cyclopentene-based ketones. Afterward, dealkylation reaction occurred through hydroxyl radicals of water to form methanol, formaldehyde and methane. Above 2500 K, H2, CO and CO2 are predominantly formed in which water molecules contributed hydrogen and oxygen for their formation. Understanding the detailed reactive mechanism of lignin’s gasification is important for efficient energy conversion of biomass.

Inhibition mechanism of CHF3 on hydrogen–oxygen combustion: Insights from reactive force field molecular dynamics simulations

We have investigated the initial stage of oxidation of Si (001) surface by water (H2O) molecules using reactive molecular dynamics (MD) simulation at 300 K and 1200 K without any external constraint on the water molecules. Previously, reported water reaction behaviors on silicon surface by ab initio calculations or experimental observations were reproduced by the present MD simulation. The present simulation further revealed that the hydrogen atom in H2O is more attractive than oxygen atom in O2 to bond with Si, such that it accelerates the dissociation process of H2O. It was also observed that the oxidation reaction was enhanced with increased number of the supplied water molecules. It was suggested that the repulsion between water molecules and their fragments facilitates the dissociation of both water molecules and hydroxyl decomposition on the Si surface. Therefore, the wet oxidation behavior appeared to have more temperature dependence even in the early stage of oxidation.

The carburization of transition metals in hydrocarbon pyrolysis is a common corrosion phenomenon in the petrochemical industry. Nevertheless, early events of carburization mechanism remain still unclear. The present work reveals the details at earlier stages of the Fe nanoparticles carburization in ethylene (C2H4) pyrolysis with reactive ReaxFF force field molecular dynamics simulations. Our results show that the chemisorption and dissociation of C2H4 on Fe surfaces are crucial steps to the carburization corrosion. First of all, C2H4 molecules are chemically adsorbed on the surface of the Fe nanoparticle. Afterward, continuous dehydrogenation of C2H4 occurs by C–H bond break to form C2Hx (x = 0–3). And finally, an amorphous C-rich carbide FeC3.39 is obtained. The carbide formation proceeds in four sequential and repetitive stages, including chemisorption and dehydrogenation of C2H4 on the surface of the Fe nanoparticle, diffusion and polymerization of C2Hx to form short C chains on the surface and in the ...

The high-temperature reaction pathways of bio-oil oxidation were investigated by simulations of a 24-component bio-oil model using reactive force field (ReaxFF) molecular dynamics. Evolution profiles of fuel, O2, and major products, including radicals, with time and temperature during the initial stage of bio-oil oxidation were obtained. Major products generated during the simulations are consistent with observations reported in the literature. A kinetic model obtained from the simulated bio-oil oxidation is able to predict a long-time evolution trend of fuel consumption. Reaction networks of five representative components of the bio-oil model were revealed. The bio-oil oxidation is initiated by a series of homolysis and H-abstraction reactions and then propagation reactions involving H-shift, H-abstraction, and β-scission reactions. Oxidation of the unsaturated C–C bond, ring reduction of the phenolic radical, and abscission of the −CO structure (decarbonylation) appear frequently. Reaction pathways obtained from the comprehensive observations of simulation results employing VARxMD are in broad agreement with the literature. This work demonstrated a methodology that ReaxFF molecular dynamic simulations combined with the capability of VARxMD for reaction analysis can provide useful insights into the reaction pathway of bio-oil combustion.

Initial oxidation of Si(100) and Si(111) surfaces has been investigated by XANES (X-ray absorption near-edge structure) spectroscopy using synchrotron radiation. At room temperature, oxidation of Si(111) surfaces proceeds much faster than that for Si(100) surfaces. The XANES spectra indicate that oxygen is atomically adsorbed onto the Si surfaces in initial stages of oxidation at room temperature. As oxidation on the surface proceeds, the XANES spectra exhibit the formation of a continuum shape resonance. The local electronic states and the local site structure for the progressive oxidation process are discussed.

Molecular representation and atomic-level coking evolution investigation of modified coal tar pitch via 13C NMR, MALDI-TOF-MS, SAXS, and ReaxFF MD

Atomic oxygen erosion mechanism of polyimide via reactive molecular dynamics simulation and density functional theory calculation

Production mechanism of single excessive hydrogen in current transformers: A reactive molecular dynamics simulation study

Insight into the thermal conversion of corn stalk gasification in supercritical water based on reactive molecular dynamics simulations