Simulations of oxidation of metal nanoparticles with a grain boundary inside

Zhdanov, Vladimir P.

doi:10.1007/s11144-020-01818-4

Cited by 3 publications

(5 citation statements)

References 60 publications

(105 reference statements)

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“…Regarding morphological aspects, during the oxidation process, the tungsten nanoparticles tend to lose their nano-scale dimension ( Figure 3 ), fusing in crystalline micro sized particles ( Figure 4 ). The oxidation of the WNPs is favored by the diffusion of oxygen along the paths defined by the facets of the nanocrystallites present in the structure of the flower like nanoparticles [ 17 ] and by the possible crystalline defects [ 34 ]. Apart from the oxidation effect, further heating of the sample (up to 900 °C) leads to the recrystallization of the oxidized particles and the fusion of particles that are in contact.…”

Section: Resultsmentioning

confidence: 99%

Hybrid Nanostructures Obtained by Transport and Condensation of Tungsten Oxide Vapours onto CNW Templates

et al. 2021

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We present hybrid nanomaterial architectures, consisting of carbon nanowalls (CNW) templates decorated with tungsten oxide nanoparticles, synthesized using a mechanism based on tungsten oxide sublimation, vapor transport, followed by vapor condensation, in the absence or presence of plasma. The key steps in the decoration mechanism are the sublimation of tungsten oxides, when are exposed in vacuum at high temperature (800 °C), and their redeposition on colder surfaces (400–600 °C). The morphology and chemical composition of the hybrid architectures, as obtained from Scanning Electron Microscopy and X-ray Photoelectron Spectroscopy, are discussed with respect to substrate nature and the physical conditions of synthesis. We pointed out that the decoration process is strongly dependent on the temperature of the CNW templates and plasma presence. Thus, the decoration process performed with plasma was effective for a wider range of template temperatures, in contrast with the decoration process performed without plasma. The results are useful for applications using the sensing and photochemical properties of tungsten oxides, and have also relevance for fusion technology, tungsten walls erosion and material redeposition being widely observed in fusion machines.

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Section: Resultsmentioning

confidence: 99%

Hybrid Nanostructures Obtained by Transport and Condensation of Tungsten Oxide Vapours onto CNW Templates

et al. 2021

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“…The reaction becomes of first-order because, if the cell drawn from A contains a particle, it is sure that in the same position in B, there will also be a particle. Then, the rates of change in the concentrations of A and B end up depending only on a random number, and in the corresponding deterministic model, they are governed by Equation (6). In this scenario, the two models (stochastic and deterministic) coincide-see the first set of curves on the left in Figure 4-with the deterministic analytical solution for first order with k n = 1/N represented by the green curve.…”

Section: Stochastic Methods Without Diffusion and Small Neighborhoodmentioning

confidence: 97%

“…In this condition, particle A reacts with particle B upon direct contact. The ODE for this case is given by Equation (6).…”

Section: Deterministic Modelmentioning

confidence: 99%

“…For the other cases (with diffusion and K n ≥ 1/N), the deterministic description is made with Equation (5). The solutions for Equations (5) and (6) are analytical.…”

Section: Deterministic Modelmentioning

confidence: 99%

“…Thus, in very viscous media, the rate of change in reagent concentrations may decrease dramatically or even cease at the low concentration limit, when the reaction occurs only between neighboring molecules. Stochastic models [6][7][8][9][10][11][12] based on Ehrenfest Urn Model (EUM) 13 and the Stochastic Simulation Algorithm (SSA) proposed by Gillespie 14 can take into account that the reaction occurs between neighboring molecules, and then help to understand the behavior of solutions at the limit of low concentrations. Piersall and Anderson 15 describe that "Since its beginning, the science of chemical kinetics has been the science of differential equations, but chemical reactions occur as a result of collisions between molecules, being inherently stochastic processes.…”

Section: Introductionmentioning

confidence: 99%

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The role of the diffusion process in bimolecular reactions with neighborhood

Filho

López‐Castillo

2020

Int J of Chemical Kinetics

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We performed stochastic and deterministic calculations to study simple bimolecular chemical kinetics with a neighborhood, necessary for solid-state and viscous medium reactions. Regarding the standard deterministic method using ordinary differential equations (ODEs) to describe a bimolecular reaction with the neighborhood, we established a comparison that indicates, in this method, an implicit diffusion process. For example, the reaction is processed in a homogeneous medium, differently from the stochastic method without diffusion. The two methods coincide at the thermodynamic limit (containing little relative fluctuation) when added with the explicit diffusion process on the stochastic model. The irreversible reaction without diffusion was emulated using the ODEs of a reversible reaction, and the inherent residual concentration of the reactions with low or no diffusion occurring in solids or strong viscous media was obtained from pseudochemical equilibrium.

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Simulation of reduction of oxidized metal nanoparticles

Zhdanov

2023

Reac Kinet Mech Cat

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I analyze theoretically the spatio-temporal kinetics of reduction of oxidized metal nanoparticles by hydrogen (or methane). The focus is on the experimentally observed formation of metal and oxide domains separated partly by pores. The interpretation of such multiphase processes in nanoparticles at the mean-field level is hardly possible primarily due to complex geometry, and accordingly I use the lattice Monte Carlo technique in order to tackle this problem. The main conclusions drawn from the corresponding generic simulations are as follows. (i) The patterns predicted are fairly sensitive to the metal-metal and metal-oxygen interactions. With decreasing the former interaction and increasing the latter interaction, there is transition from the formation of metal aggregates and voids to the formation of a metal film around the oxide core. (ii) During the initial phase of these kinetics, the extent of reduction can roughly be described by using the power law, and the corresponding exponent is about 0.3. (iii) With decreasing the hydrogen (or methane) pressure and/or increasing the oxide nanoparticle size, as expected, the kinetics are predicted to become longer. (iv) The dependence of the patterns on the presence of the support and/or Kirkendall void in an oxide nanoparticle is shown as well.

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Simulations of oxidation of metal nanoparticles with a grain boundary inside

Cited by 3 publications

References 60 publications

Hybrid Nanostructures Obtained by Transport and Condensation of Tungsten Oxide Vapours onto CNW Templates

Hybrid Nanostructures Obtained by Transport and Condensation of Tungsten Oxide Vapours onto CNW Templates

The role of the diffusion process in bimolecular reactions with neighborhood

Simulation of reduction of oxidized metal nanoparticles

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