DETERMINATION OF THERMODYNAMIC QUANTITIES OF BINARY METAL SYSTEMS WITH LOW SOLUBILITY OF COMPONENTS IN THE SOLID Α-Phase

Abstract

The method for determining the thermodynamic quantities: the partial enthalpy of dissolution , the activity coefficients and activities of the second component B in binary metallic systems with low solubility in the solid α-phase has been proposed. The algorithm for determining the above values is a sequence of preliminary calculations of the limiting and equilibrium distribution coefficients and construction of saturated solid solution lines for such systems with low solubility of the second component. Preliminarily obtained data are necessary for determining the partial enthalpy of dissolution and other quantities in the systems under study. Such a sequence of calculations is the proposed method for determining the thermodynamic parameters of dissolution. The values and temperature dependences of the dissolution enthalpy of component having a low solubility for such systems as Cd-Na, Cd-Tl, Te-Ga, Te-As, Te-Cu, Zn-Sn, as well as the activity coefficients and the activities of the second component in the saturating α-phase in these systems were determined. An analysis of obtained results on the enthalpy of dissolution shows that a change in the partial enthalpy with a change in the dissolution temperature is observed. When the temperature decreases from the melting point of the pure main component to the eutectic temperature, an increase in the partial enthalpies of dissolution of the second component is observed for studied systems. The Te-Ga system is characterized by a negative value . A negative value indicates an exothermic process of gallium dissolution in tellurium, in contrast to other systems in which the dissolution of the second component occurs with heat absorption. Analyzing the enthalpy of dissolution in the systems under study, it should be noted that the low values of < 2000 J/mol are characterized by the systems Cd-Na and Te-Ga. For systems Te-Cu, Te-As, Te-Tl, Zn-Sn > 15000 J/mol. Systems with a value > 15000 J/mol reveal a tendency to the occurrence of retrograde solubility in them. The difference in values is found to be more than two orders of magnitude for different systems.