Preparation of the single phase γ′-(Fe_1−xNi_x)₄N compounds (0 ≤x ≤ 0.6)

Abstract

Single phase γ′-Fe₄N type (Fe_1−xNi_x)₄N compounds (0 ≤ x ≤ 0.6 have been synthesized for the first time by controlled heat treatment of iron-nickel oxalates in a gaseous flow of NH₃ xand H₂. The preparation processes were investigated using differential scanning calorimetry (DSC), X-ray diffraction and Mössbauer spectroscopy. The results confirmed that annealing of oxalates in the NH₃ and H₂ atmosphere included the processes of dehydration, decomposition and reduction, nitrogenation and thermal decomposition of the nitrides. The decomposition and reduction occur simultaneously. The final products depend on the flow rate ratio of NH₃ ∶ H₂ and the annealing temperature. The formation conditions for the single phase γ′-Fe₄N type (Fe_1−xNi_x)₄N compounds are related to the nickel concentration, with increasing nickel content, the nitrogenation temperature decreased, in contrast the flow rate ratio of NH₃∶ H₂ increased.