Thermodynamik fester Fe ‐Ni Legierungen: Massenspektrometrische Bestimmung der thermodynamischen Mischungseffekte und Berechnung des Schmelzdiagramms

Abstract

AbstractThermodynamic investigations on solid Fe‐Ni alloys (f.c.c.‐phase) have been performed by means of a mass spectrometer in combination with a high temperature Knudsen cell unit. The “Algebraic Intensity‐Ratio”‐method (A.I.R.) has been applied for determing the thermodynamic excess functions. The molar excess Gibbs energies GE, the molar heats of mixing HE, and the molar excess entropies SE are negative over the whole range of composition. At 1623 K the minimum value of GE is ‐2350 J/mol (57.6 at % Ni), the minimum value of HE is ‐3950 J/mol (63.6 at % Ni), and the minimum value of SE is ‐1.04 J/mol K (70.2 at % Ni). The thermodynamic activities aj show slight negative deviations from Raoult's law. Using the results of this work, the thermodynamic results from mass spectrometric studies on liquid Fe ‐Ni alloys, and literature data for the enthalpies and heat capacities of Fe and Ni the phase diagram has been redetermined, using a generally applicable procedure for the calculation of the equilibrium compositions of coexisting phases. The applied procedure is based upon the generalized Newton method for the numerical solution of equations.