Preparation of Iron Nitrides with Ultrahigh Magnetization by MA in NH_3

以电解铁粉和羰基铁粉为原料，采用氨气机械合金化(MA)法制备了氮化铁。后者的渗氮进展要好于前者。例如，电解铁粉在NH_3中MA 160h后的样品中含有12at%N和2.0at%O，同样MA时间后的羰基铁粉样品中含有11.5 at%N和2.7at%O。NH_3加压下的MA工艺具有良好的抗氧化性，在14-15at%N以下为过饱和体心立方结构，18-19at%N以上为Fe_3N结构，而用MG工艺制备的11.1at%N样品不能获得Fe_3N。NH_3中的MA工艺也用于制备Sm_2Fe_(17)&Gt；N_x样品。用该工艺制备的Sm_2Fe_&lt；17&Gt；N_X样品具有高于2.0T的超高矫直力。本实验将继续获得由Fe_2Fe_&lt；16&gt；N_2和Sm_2Fe_&lt；17&gt；N_X组成的纳米复合磁性材料。

Mechanical alloying (MA) in NH_3 has been applied to prepare iron-nitride where two different kinds of iron powders, i.e., electrolytic iron powder and carbonyl iron powder, were used as the starting materials. Nitriding has proceeded better in the latter than in the former. For example, 12at%N and 2.0at%O were contained in the specimen of the electrolytic iron powder after MA in NH_3 for 160h, and 11.5at%N and 2.7at%O in the specimen of the carbonyl iron powder after the same MA time. The MA process under higher pressure of NH_3 has shown an effect on preventing oxidation.The specimen obtained by the above mentioned MA process showed a supersaturated bcc structure below 14-15at%N,and Fe_3N structure above 18-19at%N.Fe_<16>N_2 could not obtained by the MG process for the 11.1at%N specimen prepared by the MA process. Fe_4N,however, obtained by the annealing treatment.The MA process in NH_3 has been also applied for the preparation of Sm_2Fe_<17>N_X specimen. The Sm_2Fe_<17>N_X specimen obtained by this process has been confirmed to show the ultra high coercivity higher than 2.0T.This experiment would be continued to get the nano-composite magnetic materials composed of Fe_<16>N_2 and Sm_2Fe_<17>N_X.