Interrelation of depletion and segregation in decomposition of nanoparticles

Гусак, А. М.; Ковальчук, А. О.; Straumal, Boris B.

doi:10.1080/14786435.2012.753481

Cited by 6 publications

(6 citation statements)

References 24 publications

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“…Equilibrium is then defined as the minimum of the Gibbs energy when varying these parameters. Using these continuous models, the effect of the size and shape of the particles on the equilibrium structure has been demonstrated [5][6][7][8] with, for example, the increase of solubility in nanoalloys and the decrease of melting temperatures. Size and shape dependent phase diagrams have been defined, in which equilibrium compositions after separation and solubility limits do not coincide.…”

Section: Introductionmentioning

confidence: 99%

Thermodynamics of phase-separating nanoalloys: Single particles and particle assemblies

2018

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The aim of this paper is to investigate the consequences of finite size effects on the thermodynamics of nanoparticle assemblies and isolated particles. We consider a binary phase separating alloy with a negligible atomic size mismatch and equilibrium states are computed using off-lattice Monte Carlo simulations in several thermodynamic ensembles. First, semi-grand canonical ensemble is used to describe infinite assemblies of particle with the same size. When decreasing the particle size, we obtain a significant decrease of the solid/liquid transition temperatures as well as a growing asymmetry of the solid state miscibility gap related to surface segregation effects. Second, a canonical ensemble is used to analyze the thermodynamic equilibrium of finite monodisperse particle assemblies. Using a general thermodynamic formulation, we show that a particle assembly may split into two sub-assemblies of identical particles. Moreover, if the overall average canonical concentration belongs to a discrete spectrum, the sub-assemblies concentrations are equal to the semi-grand canonical equilibrium ones. We also show that the equilibrium of a particle assembly with a prescribed size distribution combines a size effect and the fact that a given particle size assembly can adopt two configurations. Finally, we have considered the thermodynamics of an isolated particle to analyze whether a phase separation can be defined within a particle. When studying rather large nanoparticles, we found that the region in which a two-phase domain can be identified inside a particle is well below the bulk phase diagram but the concentration of the homogeneous core remains very close to the bulk solubility limit.

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Section: Introductionmentioning

confidence: 99%

Thermodynamics of phase-separating nanoalloys: Single particles and particle assemblies

2018

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“…Furthermore, as the decomposition of the Au−Ni alloy is related to the concentration change, the 2 nm-sized nanoparticles may not just have a sufficient number of Au or Ni atoms to create the viable nucleus of a new phase. 23,25 The authors of ref 26 supposed the existence of preferred nucleation sites resulting in the substantial decrease of the critical size for nanoscale phase separation. In the case of the Au−Co nanoalloy, theoretical calculations predict the segregation of Au to the surface and subsurface layers of the Co core.…”

Section: ■ Discussionmentioning

confidence: 99%

“…From these results, it is clear that the smaller the size is, the greater the miscibility gap narrowing on the phase diagram occurs; but what happens with the binary phase diagram at ultimately small sizes of components? The theoretical calculations predict that the nanoparticle size at which the miscibility gap disappears completely should exist. − If so, the equilibrium phase diagram of Au–Ni should be transformed into a simpler type, with complete solubility of Au and Ni in the solid-state even at room temperatures. Contrary to this, the authors of ref , based on ab initio and atomistic calculations of AuCo nanoalloys, claim that the phase separation is still possible at equilibrium up to the smallest sizes.…”

Section: Introductionmentioning

confidence: 99%

Mixing of Immiscible Components by the Size Effect: A Case Study of Au–Ni Nanostructures

et al. 2020

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Modern catalysts widely utilize multicomponent nanosized materials and structures, and the interphase interactions in such systems are still unresolved in many aspects. In this work, we present the results of the experimental investigation of interface interactions in Au−Ni bimetallic nanostructures using advanced electron microscopy techniques. Nanoparticles were formed in a vacuum by the sequential condensation of components. The formation of solid solutions was investigated by high-resolution highangle annular dark-field scanning transmission electron microscopy, electron diffraction, Xray energy-dispersive spectrometry, and electron energy loss spectroscopy methods down to the atomic level while heating Au−Ni nanoparticles in a transmission electron microscope. It has been shown that Au and Ni, which are immiscible in bulk, form a homogeneous solid solution at room temperature upon the reduction of size down to ≈2 nm. The resulting solid solution has a random alloy structure and provides longterm stability characteristics to equilibrium alloys. This effect has been analyzed in the framework of available approaches.

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“…The size and composition dependent results have been obtained mainly for melting and solidification of nanoparticles and they demonstrate the increase of solubilities of chemical elements, shift of equilibrium curves at phase diagrams downward in temperatures, etc. [ 8 – 13 ]. Hereby most of investigations have the restriction comparing only the energies of entire solid and entire liquid nanosystems.…”

Section: Introductionmentioning

confidence: 99%

“…Size effects in multicomponent nanomaterials, where the first-order phase transformation starts from a nucleation and includes a change of composition of chemical elements, are accompanied with the less known “chemical depletion” effect: the amount of one of the chemical components may not be sufficient for the formation of a new phase nucleus of the different composition [ 11 – 13 ]. The similar arguments may be applied for the cases of density change during the nucleation in finite systems [ 14 ] and for grain boundary segregation problem as a successful approach to stabilize nanocrystalline materials against grain growth [ 15 – 17 ].…”

Section: Introductionmentioning

confidence: 99%

Two-phase equilibrium states in individual Cu–Ni nanoparticles: size, depletion and hysteresis effects

Shirinyan¹

2015

Beilstein J. Nanotechnol.

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SummaryIn isolated bimetallic nanoscale systems the limit amount of matter and surface-induced size effects can change the thermodynamics of first-order phase transformation. In this paper we present theoretical modification of Gibbs free energy concept describing first-order phase transformation of binary alloyed nanoparticles taking into account size effects as well as depletion and hysteresis effects. In such a way the hysteresis in a form of nonsymmetry for forth and back transforming paths takes place; compositional splitting and the loops-like splitted path on the size dependent temperature–composition phase diagram occur. Our calculations for individual Cu–Ni nanoparticle show that one must differentiate the solubility curves and the equilibrium loops (discussed here in term of solidification and melting loops). For the first time we have calculated and present here on the temperature–composition phase diagram the nanomelting loop at the size of 80 nm and the nanosolidification loop at the size of 25 nm for an individual Cu–Ni nanoparticle. So we observe the difference between the size-dependent phase diagram and solubility diagram, between two-phase equilibrium curves and solubility curves; also intersection of nanoliquidus and nanosolidus is available. These findings lead to the necessity to reconsider such basic concepts in materials science as phase diagram and solubility diagram.

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Interrelation of depletion and segregation in decomposition of nanoparticles

Cited by 6 publications

References 24 publications

Thermodynamics of phase-separating nanoalloys: Single particles and particle assemblies

Thermodynamics of phase-separating nanoalloys: Single particles and particle assemblies

Mixing of Immiscible Components by the Size Effect: A Case Study of Au–Ni Nanostructures

Two-phase equilibrium states in individual Cu–Ni nanoparticles: size, depletion and hysteresis effects

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