Coordination cluster model for calculating Sievert’s constant of hydrogen solutions in melts of the Pb-Bi-Li system

The coordination cluster method is used to calculate Sievert’s constant in dilute hydrogen solutions of the Pb-Bi-Li system for alloys in which the concentration ratio X Pb/X Bi is the same as in the binary Pb-Bi alloy (45.5 : 55.5), while the lithium concentration is no higher than 1.5 wt %. The calculations are made at temperatures of 250–700°C. The results of the calculations in terms of the coordination cluster model (CCM) are in satisfactory agreement with the experimental data obtained earlier for the Pb-Li-H system. It is shown for the quaternary Pb-Bi-Li-H system that, at each temperature, the change in the hydrogen pressure with an increase in its concentration of the melt is limited by the equilibrium pressure of the formation of lithium hydride. In the same way as the binary Li17Pb83 eutectic, upon transition to the two-phase range, the hydrogen pressure stops growing as the hydrogen concentration of the system increases. It follows from the calculation results that the thermodynamic characteristics (Sievert’s constant and the limiting solubility X H(Pb-Bi-Li)) of hydrogen solutions in the ternary Pb-Bi-Li system (X Pb = 34.2 at %, X Bi = 42.8 at %, and X Li = 23 at %) approach the corresponding characteristics of the binary Li17Pb83 eutectic.