Vaporization study on M 2Zr ( M = FeandCr) by a mass-spectrometric method

Abstract

The vapor pressures over Fe 2Zr and Cr 2Zr were measured by means of mass spectrometry in the temperature ranges of 1550–1756 K and 1476–1704 K, respectively. The thermodynamic activity of iron (or chromium) in Fe 2Zr(s) (or Cr 2Zr(s)) was determined from the vapor pressure of Fe(g) (or Cr(g)), which was the only gaseous species observed over each intermetallic compound. Applying the regular solution model with Kaufman and Bernstein parameters to the thermodynamic activity of iron (or chromium) determined experimentally, the thermodynamic activity of zirconium in Fe 2Zr (or Cr 2Zr) was calculated as a function of temperature. Thermodynamic quantities such as the partial molar enthalpy and entropy, the partial molar free energy of formation (mixing) and the excess partial molar free energies of iron (or chromium) and zirconium in Fe 2Zr (or Cr 2Zr) were calculated. The integral molar Gibbs free energies, enthalpies and entropies of formation of Fe 2Zr and Cr 2Zr were also calculated from the partial molar quantities. The enthalpy of formation of Fe 2Zr obtained in this study was in good agreement with a previous experimental value by high temperature calorimetry and fell between two predicted values by model calculation. The enthalpy of formation of Cr 2Zr determined in this study was close to one of the two calculated values reported previously. The stabilities (or formations) of Fe 2Zr and Cr 2Zr were briefly discussed in comparison with that of U-Zr solid solution.