Acid-Base Reactions of Transition Metal Alloys: Thermochemistry of the Base-Rich End

摘要

The thermodynamics of binary transition metal alloys, stabilized by generalized Lewis acid-base reactions, were studied within the context of the Engel-Brewer Theory. The activity of the base metals was determined from the vapor pressure measurements of the Pd or Rh in the base-rich end of TiPd, VPd, NbPd and VRh alloys. The vapor pressures were determined by thermally induced atomic emission spectroscopy. The composition of the alloys in equilibrium with carbon were determined. From the known thermodynamics of the metal carbides, the activity was calculated for the acid metals. Titration curves from the pure base metal to the compositions in equilibrium with carbon were developed. The data confirmed the general qualitative properties of the acid-base reaction. The 4d metals are better acids than the 3d metals. The effectiveness of the acid-base reaction across a transition series is determined by the number of d electron pairs available for donation, the number of empty d orbitals available to accept electron pairs, the nuclear charge and a crystal field effect. The data was compared to the regular solution model in an attempt to represent the solution behavior. (ERA citation 12:039202)