Crystallization of Supercooled Liquid Elements Induced by Superclusters Containing Magic Atom Numbers

Metals

关键词: thermal properties;    solid-liquid interface energy;    crystal nucleation;    undercooling;    superclusters;    liquid-solid transition;    overheating;    non-metal to metal transition in cluster;    Laplace pressure;   

DOI  :  10.3390/met4030359

来源: mdpi

【 摘 要 】

A few experiments have detected icosahedral superclusters in undercooled liquids. These superclusters survive above the crystal melting temperature T_m because all their surface atoms have the same fusion heat as their core atoms, and are melted by liquid homogeneous and heterogeneous nucleation in their core, depending on superheating time and temperature. They act as heterogeneous growth nuclei of crystallized phase at a temperature T_c of the undercooled melt. They contribute to the critical barrier reduction, which becomes smaller than that of crystals containing the same atom number n. After strong superheating, the undercooling rate is still limited because the nucleation of 13-atom superclusters always reduces this barrier, and increases T_c above a homogeneous nucleation temperature equal to T_m/3 in liquid elements. After weak superheating, the most stable superclusters containing n = 13, 55, 147, 309 and 561 atoms survive or melt and determine T_c during undercooling, depending on n and sample volume. The experimental nucleation temperatures T_c of 32 liquid elements and the supercluster melting temperatures are predicted with sample volumes varying by 18 orders of magnitude. The classical Gibbs free energy change is used, adding an enthalpy saving related to the Laplace pressure change associated with supercluster formation, which is quantified for n = 13 and 55.

【 授权许可】

CC BY   
© 2014 by the authors; licensee MDPI, Basel, Switzerland.