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

Abstract

Fine powder of iron oxide has been required in the preparation of ferromagnetic α"-Fe 16 N 2 powder in low temperature nitridation. Its particle size of about 30 nm and less humidity content was crucial in the reproducible α"-Fe 16 N 2 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 -Fe in hydrogen at 400 °C. Particle size of the -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 -Fe particle. After the successive nitridation under ammonia flow at 160 °C, the highest yield of α"-Fe 16 N 2 in 66 wt% was observed on the nitrided product from the latter -Fe because of the smallest α-Fe particle size after the reduction in the present study. The yield and reproducibility of "-Fe 16 N 2 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.

Magnetic softening of Co doped α′′-Fe₁₆N₂ containing residual Fe–Co alloy prepared in low temperature nitridation

“…The particle size around 100 nm has been suitable for nitridation to ¡BB-Fe 16 N 2 phase as reported in our previous study. 14) Saturation magnetization of 195 Am 2 kg ¹1 for the reduced ¡-Fe (x = 0) increased to 206 Am 2 kg ¹1 at x = 0.05 similarly to the Slater-Pauling curve as summarized in Table 1. The magnetic coercivity decreased on the Co doping and the bcc alloy at x = 0.03 showed the smallest magnetic coercivity of 11 mT.…”

“…2),3), 14) The "¡BB-(Fe 1¹x Co x ) 16 N 2 " yield slightly increased with increasing nitridation duration as summarized in Table 2. Maximum yield in 42 wt % of the cobalt doped "¡BB-(Fe 1¹x Co x ) 16 N 2 " appeared at x = 0.03 in 8 h of nitridation duration.…”

“…Results and discussion 3. 14) Their crystallite size estimated from the line broadening of the main diffraction peak decreased from 45 nm (x = 0) to 30 nm (x = 0.05) with increasing Co content. The lattice parameter was a = 0.83885(1) nm at x = 0, which was comparable to the reported value of a = 0.8394 nm.…”

“…14) Co doped Fe 3 O 4 prepared similarly in the hydrolysis reaction of mixed Fe(acac) 3 and Co(acac) 3 in BA solution might be useful to prepare the Co doped "¡BB-Fe 16 N 2 " by low temperature nitridation through its reduced FeCo alloy. In the present study, fine powder of (Fe 1¹x Co x ) 3 O 4 was prepared in BA solution by changing the mixing ratio of Fe(acac) 3 and Co(acac) 3 .…”

Formation and Decomposition of Metastable α′′‐Fe16N2 from in situ Powder Neutron Diffraction and Thermal Analysis

“…It became obvious that 600°C is the maximum reduction temperature from the oxide to iron powder. [63] Finally, the reaction time in ammonia was decreased to 20 h at 160°C yielding 90.7 % αЈЈ-Fe 16 N 2 next to α-Fe. [14] In 2013 two publications dealing with the synthesis of single phase samples of αЈЈ-Fe 16 N 2 [15] and the isothermal decomposition of αЈЈ-Fe 16 N 2 at different temperatures [64] were presented.…”