Synthesis and characterization of iron and iron nitride microtubes obtained from biogenic iron oxide

With the aim to obtain iron tubular microstructures attractive for various applications, we have used a natural biogenic iron ochre as a raw material and explore various procedures and experimental conditions to achieve our goal. Our experiments included reduction, nitridation and characterization of microtubes derived from biogenic iron ochre. Various temperatures of reduction under streams of H₂/N₂ or NH₃ were tested. Our results show that the tubular structure is maintained after reduction of the natural material under H₂/N₂. In addition, ammonia was not produced under our experimental conditions, and as expected, hydrogen reduced the material. However, the treatment under NH₃ reduces the material and allows the incorporation of nitrogen into the structure of the solid yielding iron nitride microtubes. Reduced and nitrided microstructures were successfully obtained from natural biogenic iron ochre. A temperature of 500 °C seems to be suitable to expose the calcined biogenic iron ochre under H₂/N₂ for 4 h or under ammonia for 8 h to obtain reduced or nitrided microtubes, respectively. The stability of the tubular structure during reduction/reduction–nitridation is maintained under both treatments. Further interesting applications of this natural biomaterial could be envisaged.