Synthesis of Fe₃N by mechano-chemical reactions between iron and organic H_x(CN)₆ ring compounds

Abstract

Novel mechanically activated solid state synthesis reactions between elemental αFe powder and amine compounds-piperazine (Hi₁₀C₄N₂) and pyrazine (H₄C₄N₂) — have been studied. Powder samples prepared after 144 and 228 h of ball milling in vacuum were examined by X-ray diffraction, scanning electron microscopy and thermal analysis methods. After ball milling for a time brief compared to that required for most solid state-gas reactions formation of a crystalline iron nitride (Fe₃N) a predominant phase with nitrogen concentration up to ca. 9.0 wt% was observed. Thermal analysis experiments showed structural stability of the Fe₃N phase up to ca. 720 K. In the final product a small residual fraction was formed from αFe and carbon dispersed during mechanical processing. The concentration of carbon in this fraction, estimated from thermogravimetric analysis was up to 2.5 wt%, dependent on milling conditions and the organic compound used. Mechanochemical synthesis, reaction effectiveness, product composition and particle morphology depends on the milling time and chemical characteristics of the organic compound used. Fine Fe₃N particles at a submicrometre size range were obtained only by milling with pyrazine. Further, the higher chemical reactivity of pyrazine than piperazine was confirmed through the higher level of nitridation achieved in the same preparation time.