Surface tension of liquid mixtures and metal alloys. Positive and negative temperature coefficients in alloys with remarkably high surface density

The effect of temperature on the surface tension is examined in liquid alloys that combine a positive or negative temperature coefficient with gravity limitation of the surface concentration in the surface-active metal constituent. This is a restriction that is likely to occur in alloys where the metal with lower surface tension is much denser than the other component. Since there is a surface tension increase due to di-minished segregation, the resultant temperature coefficient will depend on the superposition of two in-dependent effects. Working in the framework of Butler's thermodynamics for ideal surface phases, equations and methods of analysis are obtained to describe both effects. These developments are illustrated with alloys where the surface density is likely to attain the bulk density at certain compositions, namely the Al-Zn alloys that exhibits a negative temperature coefficient and the Sn-Bi, Ga-Bi, Ga-Pb and Cu-Pb alloys that present composition ranges with positive temperature coefficients. The specific concave down d gamma/dT curves of liquid alloys are theoretically predicted. Furthermore, good estimates are obtained for systems with positive and negative temperature coefficients, except within a 50 K interval of phase transitions, or for systems showing large deviations from ideal behaviour.(c) 2023 Published by Elsevier B.V.

Automated summary

This study examines the effect of temperature on surface tension in liquid alloys with a positive or negative temperature coefficient and a gravity limitation of the surface concentration in the surface-active metal constituent. It is found that the temperature coefficient depends on the combined effects of increased surface tension due to diminished segregation. The study provides equations and analysis methods based on Butler's thermodynamics for ideal surface phases. The results are illustrated using specific alloys such as Al-Zn, Sn-Bi, Ga-Bi, Ga-Pb, and Cu-Pb. The theoretical prediction of specific concave down d gamma/dT curves of liquid alloys is also made, and good estimates are obtained for systems with positive and negative temperature coefficients. However, deviations may occur during phase transitions or for systems with non-ideal behavior. (c) 2023 Published by Elsevier B.V.