Proposal of New Co-Addition Method for α”-Fe₁₆(N, C)₂ Particles by Gas–Solid Reactions

Metastableα '-Fe-N (12 at% N) andα '-Fe-C (12 at% C) are unique materials with a magnetocrystalline constantK₁of +5×106and- 7×106erg/cm3, respectively, according to measurements based on thin films. Therefore, co-additionα ''-Fe₁₆X₂(X= N, C) particles are attractive as potential new soft magnetic materials because their magnetocrystalline constant can be varied by manipulating their N and C concentrations. However, introducing C interstitially intoα-Fe particles by the carbonization process using a C-containing gas such as CO gas is difficult because the equilibrium phase Fe3C is easily generated. Therefore, we investigated various reaction routes of nitridation and carbonization, along with various C-containing gases, to prepare co-additionα ''-Fe16(N, C)2particles. We obtainedα ''-Fe16(N, C)2particles using a route in whichα-Fe was obtained by reduction of Fe3O4particles, followed by nitridation toα ''-Fe16N2and subsequent carbonization toα ''-Fe16(N, C)2. The amount of C particles after carbonization was measured to be 0.8 wt% (3.6 at%). This gas–solid reaction process based on the concept of usingα ''-Fe16N2as a material with an expandedα-Fe lattice is a useful method for the co-addition of interstitial N and C.