Magnetite/maghemite mixture prepared in benzyl alcohol for the preparation of α'-Fe16N2 with α-Fe

摘要

Fine powder of iron oxide has been required in the preparation of ferromagnetic α"-Fe16N2 powder in low temperature nitridation. Its particle size of about 30 nm and less humidity content was crucial in the reproducible α"-Fe16N2 preparation in high yield. Magnetite and maghemite mixture with about 40 nm particle size was obtained by the reaction of iron acetylacetonate Fe(acac)3 of more than 4 g dissolved in 40 mL benzyl alcohol. It was reduced to α-Fe in hydrogen at 400 ℃. Particle size of the α-Fe was 300 nm in the reduction of iron oxides obtained from 2 g of Fe(acac)3. It decreased to 100 nm in the preparation using 8 g of Fe(acac)3 because smaller iron oxide was easily reduced sintering to larger α-Fe particle. After the successive nitridation under ammonia flow at 160℃, the highest yield of α"-Fe16N2 in 66 wt% was observed on the nitrided product from the latter α-Fe because of the smallest α-Fe particle size after the reduction in the present study. The yield and reproducibility of α"-Fe16N2 formation in low temperature nitridation was improved by using the iron oxide prepared in non-aqueous benzyl alcohol compared to the use of magnetite obtained from aqueous solution. Benzyl alcohol was a useful solvent to obtain iron oxide fine powder having less humidity because of its very small water solubility.