Volume and Surface Properties of Nickel Melts Containing a Lead Impurity

Abstract—Physicochemical properties (surface tension, density) and structure of Ni–Pb melts with low (0.01, 0.025, and 0.05 wt %) lead contents are studied. Critical melting temperatures are determined. As the lead content increases, the melt density is found to increase to values, which exceed those expected for the additivities of heaver lead; this fact assumes the appearance of strong compression effect in the Ni–Pb system. In this case, the converging of temperature dependences measured during heating and cooling and decrease in hysteresis phenomena are observed. Near the melting temperature, the surface tension of the melt is found to decrease proportionally to the lead impurity content; surface active lead-based compounds form at the surface. After metal melting, the adsorption isotherm of lead in nickel is similar to the Langmuir isotherm. In accordance with the melting conditions, the adsorption in the Ni–Pb melts can be either positive or negative. Negative adsorption corresponds to the transition of a constituent from the surface into the volume; positive adsorption corresponds to the transition of the constituent from the volume to the interface. An increase in the lead content in the melts comprising residual oxygen favors suppression of the processes that cause a decrease in the surface tension and adsorption.