Effect of sharp concentration gradients on the nucleation of intermetallics in disordered solids: influence of the embryo shape

A depth-averaged random walk scheme is applied to investigate the process of solute transport, including advection, diffusions and reaction. Firstly, the model is used to solve an instantaneous release problem in a uniform flow, for which analytical solutions exist. Its performance is examined by comparing numerical predictions with analytical solutions. The advantage of the random walk model includes high accuracy and small numerical diffusion. Extensive parametric studies are carried out to investigate the sensitivity of the predictions to the number of particles. The result reveals that the particle number influences the accuracy of the model significantly. Finally, the model is applied to track a pollutant cloud in the Thames Estuary, where the domain geometry and bed elevation are complex. The present model is free of fictitious oscillations close to sharp concentration gradients and displays encouraging efficiency and accuracy in solving the solute transport problems in a natural aquatic environment.

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Metastability at the nanometer scale

MRS Proceedings ◽

10.1557/proc-398-209 ◽

1995 ◽

Vol 398 ◽

Author(s):

P.J. DESRÉ

Keyword(s):

Glass Transition ◽

Metallic Glasses ◽

Liquid Droplet ◽

Parent Phase ◽

Nanometer Scale ◽

Undercooled Liquid ◽

Concentration Gradients ◽

Sharp Concentration ◽

Transitory State ◽

Topological Disorder

ABSTRACTUnder constraints and at the nanometer scale, transitory metastable states can be generated in multicomponents materials. Examples illustrating such specific states are presented. They concern i) The crystalline nucleation in a growing undercooled liquid droplet formed from a liquid parent phase, ii) The suppression of intermetallic nucleation in solid solutions or glasses subjected to sharp concentration gradients, iii) The nanocrystalline transitory state preceding amorphisation by ball milling. In connection with this latter example, a thermodynamic model for the nanocrytal to glass transition, based on an hypothesis of a topological disorder wetting at the nanograin boundaries, is proposed. Thermodynamics - Nucleation - Phase transitions - nanocrystals - metallic glasses

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Reversion of particles possessing sharp concentration gradients

Acta Metallurgica ◽

10.1016/0001-6160(82)90191-2 ◽

1982 ◽

Vol 30 (8) ◽

pp. 1697-1704 ◽

Cited By ~ 4

Author(s):

K. Tsumuraya

Keyword(s):

Concentration Gradients ◽

Sharp Concentration

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FALL3D-8.0: a computational model for atmospheric transport and deposition of particles, aerosols and radionuclides – Part 1: Model physics and numerics

Geoscientific Model Development ◽

10.5194/gmd-13-1431-2020 ◽

2020 ◽

Vol 13 (3) ◽

pp. 1431-1458 ◽

Cited By ~ 1

Author(s):

Arnau Folch ◽

Leonardo Mingari ◽

Natalia Gutierrez ◽

Mauricio Hanzich ◽

Giovanni Macedonio ◽

...

Keyword(s):

Memory Management ◽

Atmospheric Transport ◽

Model Performance ◽

Concentration Gradients ◽

Central Difference ◽

Track Record ◽

And Performance ◽

Extreme Scale ◽

Solving Strategy ◽

Sharp Concentration

Abstract. This paper presents FALL3D-8.0, the last version release of an open-source code with 15+ years of track record and a growing number of users in the volcanological and atmospheric communities. The code has been redesigned and rewritten from scratch in the framework of the EU Centre of Excellence for Exascale in Solid Earth (ChEESE) in order to overcome legacy issues and allow for successive optimisations in the preparation of the code towards extreme-scale computing. However, this baseline version already contains substantial improvements in terms of model physics, solving algorithms, and code accuracy and performance. The code, originally conceived for atmospheric dispersal and deposition of tephra particles, has been extended to model other types of particles, aerosols and radionuclides. The solving strategy has also been changed, replacing the former central-difference scheme for a high-resolution central-upwind scheme derived from finite volumes, which minimises numerical diffusion even in the presence of sharp concentration gradients and discontinuities. The parallelisation strategy, input/output (I/O), model pre-process workflows and memory management have also been reconsidered, leading to substantial improvements on code scalability, efficiency and overall capability to handle much larger problems. All these new features and improvements have implications on operational model performance and allow, among others, adding data assimilation and ensemble forecast in future releases. This paper details the FALL3D-8.0 model physics and the numerical implementation of the code.

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Nucleation Modes in Sharp Concentration Gradients

MRS Proceedings ◽

10.1557/proc-481-113 ◽

1997 ◽

Vol 481 ◽

Author(s):

F. Hodaj ◽

A. M. Gusak ◽

A. O. Kovalchuk ◽

P. J. Desre

Keyword(s):

Aspect Ratio ◽

Reaction Kinetics ◽

Concentration Gradient ◽

Thermodynamic Potential ◽

Critical Concentration ◽

Planck Equation ◽

Amorphous Layer ◽

Mechanism Of Formation ◽

Concentration Gradients ◽

Sharp Concentration

ABSTRACTReaction kinetics in bimetallic multilayers have demonstrated that sharp unidirectional concentration gradient, which develop as interdiffusion proceeds at the interface are able to delay or to suppress nucleation of intermetallics. It has been found that the existence of a critical gradient beyond which nucleation is inhibited is strongly dependent on the mechanism of formation of the embryo [1–7].A mechanism of nucleation under concentration gradient (∇c) is proposed and treated on the basis of the Fokker–Planck equation for the distribution in the size space.The influence of the aspect ratio of the embryo on the critical concentration gradient is also studied. Due to the fluctuations of the embryo shape, it is shown that the minimization of the thermodynamic potential leading to the aspect ratio of the embryo is only significant beyond a certain value of the concentration gradient. Application is presented to the nucleation of the compound Ni10Zr7 in an amorphous layer Ni-Zr.

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FALL3D-8.0: a computational model for atmospheric transport and deposition of particles, aerosols and radionuclides. Part I: model physics and numerics

10.5194/gmd-2019-311 ◽

2019 ◽

Author(s):

Arnau Folch ◽

Leonardo Mingari ◽

Natalia Gutierrez ◽

Mauricio Hanzich ◽

Giovanni Macedonio ◽

...

Keyword(s):

Memory Management ◽

Atmospheric Transport ◽

Source Code ◽

Concentration Gradients ◽

Track Record ◽

And Performance ◽

Extreme Scale ◽

Solving Strategy ◽

Sharp Concentration ◽

The Eu

Abstract. This manuscript presents FALL3D-8.0, the last version release of an open-source code with 15+ years of track record and a growing number of users in the volcanological and atmospheric communities. The code has been redesigned and rewritten from scratch in the framework of the EU Center of Excellence for Exascale in Solid Earth (ChEESE) in order to overcome legacy issues and allow for successive optimisations that are already planned in the preparation of the code towards extreme-scale computing. However, this baseline version already contains substantial improvements in terms of model physics, solving algorithms, and code accuracy and performance. The code, originally conceived for atmospheric dispersal and deposition of tephra particles, has been extended to model other types of particles, aerosols and radionuclides. The solving strategy has also been changed, replacing the former central-differences scheme for a high-resolution central-upwind scheme derived from finite volumes, which minimises numerical diffusion even in presence of sharp concentration gradients and discontinuities. The parallelisation strategy, Input/Output (I/O), model pre-process workflows and memory management have also been reconsidered, leading to substantial improvements on code scalability, efficiency, and overall capability to handle much larger problems. This paper details the FALL3D-8.0 model physics and the numerical implementation of the code.

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