Thermodynamics of cadmium- and zinc-rich alloys in the Cd−La,Cd−Ce,Cd−Pr,Zn−La,Zn−Ce and Zn−Pr systems

The thermodynamics of the cadmium- and zinc-rich alloys in the Cd?La, Cd?Ce, Cd?Pr, Zn?La, Zn?Ce, and Zn?Pr systems have been studied with a high-temperature galvanic cell method. The values of the standard free energy of formation (kcal per mole) of the intermetallic compounds are given by the equations: $$begin{gathered} (LaCd_{11} ), Delta Gf^ circ = - 72.3 + 43.6 times 10^{ - 3} T (670^ circ to 804^ circ K) hfill (CeCd_{11} ), Delta Gf^ circ = - 70.5 + 44.6 times 10^{ - 3} T (638^ circ to 884^ circ K) hfill (PrCd_{11} ), Delta Gf^ circ = - 69.1 + 44.8 times 10^{ - 3} T (635^ circ to 825^ circ K) hfill (LaZn_{11} ), Delta Gf^ circ = - 92.6 + 48.0 times 10^{ - 3} T (705^ circ to 793^ circ K) hfill (CeZn_{11} ), Delta Gf^ circ = - 87.9 + 45.0 times 10^{ - 3} T (710^ circ to 1018^ circ K) hfill (PrZn_{11} ), Delta Gf^ circ = - 85.3 + 42.7 times 10^{ - 3} T (696^ circ to 875^ circ K) hfill end{gathered} $$ Equations are also given for the partial molar excess free energies of the lanthanide in dilute solutions of the lanthanide in liquid cadmium or zinc. The enthalpy of formation of the intermetallic compounds is discussed in terms of the crystalline structure of these intermetallic compounds. It is shown that the enthalpy of formation is a linear function of the ration/V _c , wheren is the number of zinc or cadmium atoms which are near-neighbors of the lanthanide atom andV _c is the volume of the cage formed by the near-neighbor cadmium or zinc atoms. A linear dependence of the enthalpy of formation onn/V _c is also found for the intermetallic compounds in several other binary systems. These empirical correlations are discussed in terms of a model which involves localized bonds between the lanthanide and zinc or cadmium atoms.