Issue 21, 2015

Phase stability in nanoscale material systems: extension from bulk phase diagrams

Abstract

Phase diagrams of multi-component systems are critical for the development and engineering of material alloys for all technological applications. At nano dimensions, surfaces (and interfaces) play a significant role in changing equilibrium thermodynamics and phase stability. In this work, it is shown that these surfaces at small dimensions affect the relative equilibrium thermodynamics of the different phases. The CALPHAD approach for material surfaces (also termed “nano-CALPHAD”) is employed to investigate these changes in three binary systems by calculating their phase diagrams at nano dimensions and comparing them with their bulk counterparts. The surface energy contribution, which is the dominant factor in causing these changes, is evaluated using the spherical particle approximation. It is first validated with the Au–Si system for which experimental data on phase stability of spherical nano-sized particles is available, and then extended to calculate phase diagrams of similarly sized particles of Ge–Si and Al–Cu. Additionally, the surface energies of the associated compounds are calculated using DFT, and integrated into the thermodynamic model of the respective binary systems. In this work we found changes in miscibilities, reaction compositions of about 5 at%, and solubility temperatures ranging from 100–200 K for particles of sizes 5 nm, indicating the importance of phase equilibrium analysis at nano dimensions.

Graphical abstract: Phase stability in nanoscale material systems: extension from bulk phase diagrams

Associated articles

Supplementary files

Article information

Article type
Paper
Submitted
09 Mar 2015
Accepted
15 Apr 2015
First published
22 Apr 2015
This article is Open Access
Creative Commons BY-NC license

Nanoscale, 2015,7, 9868-9877

Phase stability in nanoscale material systems: extension from bulk phase diagrams

S. Bajaj, M. G. Haverty, R. Arróyave, W. A. Goddard III FRSC and S. Shankar, Nanoscale, 2015, 7, 9868 DOI: 10.1039/C5NR01535A

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