The standard molar gibbs energy of formation of YbPt₃ and LuPt₃ intermetallics

Abstract

The standard molar Gibbs energies of formation of YbPt3 and LuPt₃ intermetallic compounds have been measured in the temperature range 880 K to 1100 K using the solid-state cells:View the MathML source and View the MathML source The trifluoride of Yb is not stable in equilibrium with Yb or YbPt₃. The results can be expressed by the equations: View the MathML source View the MathML source The standard molar Gibbs energy of formation of LuPt₃ is −41.1 kJ·mol⁻¹ more negative than that for YbPt₃ at 1000 K. Ytterbium is divalent in the pure metal and trivalent in the intermetallic YbPt₃. The energy required for the promotion of divalent Yb to the trivalent state is responsible for the less negative Δ_fGmo of YbPt₃. The enthalpies of formation of the two intermetallics are in reasonable agreement with Miedema's model. Because of the extraordinary stability of these compounds it is possible to reduce oxides of Yb and Lu with hydrogen in the presence of platinum at View the MathML source. The equilibrium chemical potential of oxygen corresponding to the reduction of Yb₂O₃ and Lu₂O₃ by hydrogen in the presence of platinum is presented in the form of an Ellingham diagram.