Enthalpies of Formation of Niobium Aluminides as Determined by the Knudsen Effusion Method

Abstract

The high temperature thermodynamics and phase diagram of the Nb‐Al system have been studied in the temperature range and the composition interval . A weight‐loss‐mass‐spectrometer apparatus was used to measure the rates of effusion and ion intensities of aluminum during incongruent vaporization from a Knudsen cell. Surface depletion problems were solved by using special intermediate annealing sequences The composition ranges of the and compounds and the niobium‐rich solid solution are reported Enthalpies of the reactions: were determined by the second law and third law methods. Enthalpies of formation for the compounds are: ; , and.