A HARD-SPHERE MODEL IN ANALYTIC FORM FOR ATOMIC TRANSPORT-PROPERTIES OF LIQUID-METALS

Simple analytical forms of hard sphere model are presented for atomic transport properties of liquids, that is the self-diffusion coefficien t, D-s, and the shear viscosity, eta. The D-s and the back scattering factor have been evaluated based on a recent analytical expression of D-s for hard spheres presented by Speedy, which was obtained by compil ing D-s data from many computer simulations for hard spheres. This har d sphere model was applied to test the reliability of recent epoch-mak ing experiment of diffusion in liquids, the measurement of D-s in spac e for liquid Sn due to Frohberg et al.; values of D-s in space are low er than those obtained on earth particularly at higher temperatures th an the melting temperature and whose temperature dependence obeys a T- 2 law. The former fact seems to indicate that the previous experimenta l data of D-s on earth may be suffered from gravitational (and thermal ) convection effects and the latter fact provides some insights into t he mechanism of diffusion in liquids. The result of this space experim ent was well reproduced by this hard sphere model. In addition, the ex perimental data of D-s and eta of liquid Hg was also well reproduced b y this hard sphere model, in which an universal reduced relation for t he temperature dependence of the hard sphere diameter, sigma, was dete rmined by fitting the calculated D-s to the experimental one under mic rogravity for liquid Sn. The liquid Hg was selected because its experi mental values of D-s and eta on earth are very reliable. Therefore, a new experimental technique for diffusion coefficients in liquids, the measurement of D, in liquids under microgravity: seems to be very reli able and should be exploited further.