A unified equation for the viscosity of pure liquid metals

The following unified equation has been elaborated in the present paper, to describe the viscosity of all liquid metals as a function of temperature: eta(i) = A . M-i(1/2) / V-i(2/3) . T-1/2 . exp( B . T-m,T-i / T ) with N-i, M-i, V-i, T-m,T-i being the dynamic viscosity, atomic mass, molar volume and melting point of the given metal i, and T is temperature. The above equation was tested on 101 measured points of 15 selected liquid metals, and the average values of the generally valid parameters were found as: A = (1.80 +/- 10.39) . 10(-8) (J/Kmol(1/3))(1/2), B = 2.34 +/- 0.20. Based on these parameters, the temperature dependence of viscosity was estimated for 32 liquid metals. The above equation was derived by (i) combining Andrade's equation with the activation energy concept, and (ii) by combining Andrade's equation with the free volume concept. It is shown, that the activation energy and the free volume concepts have identical roots and lead to identical results. The above equation is shown to be valid for liquid semi-metals (Si, Ge, Sb, Bi), if their actual melting points are replaced by their corrected melting points, corresponding to (unstable) metallic solid crystals. The ratio of viscosity to surface tension of pure liquid metals is discussed, as well.