1989 Volume 30 Issue 9 Pages 647-659
The cohesive energy of metals in the liquid state can be estimated thermodynamically from the latent heat of vaporization of these liquid metals. The cohesive energy of simple metals such as K, Na, Cd, Zn and Pb in the liquid state near the melting temperature is very close to that in the solid state and even near the boiling temperature the cohesive energy is not so much different from that in the solid state. Thus, the mutual interaction energy between neighbouring atoms in the liquid is considered to be near that in the solid. In the liquid state of metals with the f.c.c., h.c.p. or b.c.c. structure atoms are distributed in random close packed arrangement in which vacancies are included, and it is shown that the mean distance between neighbouring atoms remains unchanged nearly independent of temperature from the measurements of structure factor S(Q) at several temperatures. The larger volume expansion accompanied by the temperature increase in the liquid state of metals does not originate from the increase in the mean distance between neighbouring atoms, but is supposed to be caused by the increase in vacancy concentration α(T) included in the random close packed arrangement of atoms in the liquid. The mobility of a vacancy in random distribution of atoms is exceedingly high compared with that of a vacancy in the ordered arrangement of atoms in the crystal. These vacancies play an essential role in the fluidity problem of liquid. The diffusion constant D and the viscosity coefficient η are evaluated as a function of the vacancy concentration α(T) in good agreement with the observed values for liquid K, Na and Pb.
