Clusters in liquid metals

Abstract

The two divergent approaches to the structure of liquid metals, which regard them as being either condensed-gas or quasi-crystalline, are inadequate to explain the properties and behaviour of liquid metals. In this article the concept of entropy is used to suggest that some form of near-solid association of large numbers of atoms, not amenable to any rigorous mathematical treatment, is retained in the liquid state. The implications of ‘Bernel's concept of the statistical geometrical structure of liquid metals are discussed. This concept regards a liquid as a network of holes or Voronoi polyhedra and suggests that metallic liquids when heated should exhibit a second-order transformation because their thermal expansion is accompanied by a progressive change in atomic coordination. A second-order transformation is indeed suggested by the experimentally determined values of the specific heat of certain liquid metals. Other evidence in support of this contention is also presented. The work of Kumar and his co-workers on the structure of liquid alloys in terms of the dispersion of clusters in monatomic atoms, which behave like true liquids, is discussed. It is shown that the temperature-dependence of viscosity is in conformity with this picture. It is suggested that the clusters may be analogous with the ‘pseudo-nuclei’ of the Bernal concept.