The powder of iron nitride, which the research group succeeded in producing by the gram
The powder of iron nitride, which the research group succeeded in producing by the gram
[Click to enlarge image]

A Japanese research group succeeded in producing powder of iron nitride (Fe16N2) by the gram.

The group, which consists of Migaku Takahashi and Tomoyuki Ogawa, professor and associate professor, respectively, at a graduate school of Tohoku University, and researchers at Toda Kogyo Corp, succeeded in generating Fe16N2 powder with a purity of 91% and a reproducibility for the first time in the world.

The group has been researching on Fe16N2 as a candidate for a powerful magnet material that does not use any rare earth element in the "Rare Metal Substitute Materials Development Project" led by New Energy and Industrial Technology Development Organization (NEDO).

The produced Fe16N2 powder has a particle diameter of several tens to several hundreds of nanometers. Its saturation magnetization is 230emu/g at a temperature of 50K and 221emu/g at room temperature, which is higher than that of pure iron (1emu/g =4n x 10-7Wb·m/kg).

Though its magnetic crystalline anisotropy, which is proportionate to coercive field strength, is low, its maximum energy product, which determines the strength of magnet, is expected to be 100MGOe (796kJ/m3), which is more than 30% higher than that of sintered magnets using neodymium-iron-boron (Nd-Fe-B).

The group aims to commercialize a magnet using iron nitride in fiscal 2023 to fiscal 2025 by (1) developing a technology to mass-produce the powder, (2) reducing the number of defects on the powder's boundary surface and variation in size, (3) improving coercive field strength by replacing the iron nitride with other elements such as iron (Fe) and nitrogen (N), (4) developing a technology to align and solidify the nano-sized powder and (5) developing an alignment technology and a solidification technology for enhancing the filling rate of Fe16N2, which decomposes at a temperature higher than 200°C.

This time, it became possible to produce Fe16N2 powder by the gram because the group determined the process conditions and the raw materials that prevent Fe16N2 from turning into Fe4N and Fe in the phase of lowering temperature. As for the production method, the group tried various methods such as using an organometallic complex as a raw material, inorganically producing iron compounds, etc and succeeded in producing the Fe16N2 powder with some of the methods.

For example, in the method of using an organometallic complex as a raw material, the research group optimized the process conditions and controlled the shape and crystal grain size of the raw material. Though the time it takes to produce the powder differs depending on production method, it is possible to produce about 2g of the powder in half a day or one and a half day.

This time, Toda Kogyo synthesized raw materials, and Tohoku University developed a technology to produce Fe16N2 with a high purity by using the materials.