日本金属学会誌

J. Japan Inst. Metals, Vol. 60, No. 8 (1996),
pp. 765-774

Preparation of Sm2Fe17NX Powders by Mechanical Grindingin NH3 Atmosphere and Their Magnetic Properties

Mikio Ito, Kazuhiko Majima,Shigeru Katsuyama and Hiroshi Nagai

Department of Materials Science and Engineering, Faculty of Engineering, Osaka University, Suita

Abstract:

Sm2Fe17NX magnetic powders have been prepared by mechanical grinding (MG) in NH3 atmosphere and subsequent nitriding. The influence of the compositional difference of starting material and MG conditions on their magnetic properties have been investigated. The increase of MG time promotes absorption of nitrogen into powders during nitriding because of the activation of powders. However, too long MG treatment causes the decrease of nitrogen concentration and deterioration of their magnetic properties due to the diminution of Sm2Fe17 structure. Therefore, there is an optimum value of MG time. The grain size of about 100 nm being much smaller than the single magnetic domain size of about 270 nm is obtained by MG with a vibration mill. The best value of maximum energy product (BH)max of 50.7 kJ⋅ m-3 (6.34 MGOe) is obtained by MG with the vibration mill and subsequent nitriding.
These powders have been also prepared by MG with a rotary ball mill whose mechanical energy is lower than that of a vibration mill. Though the powders obtained by MG in NH3 for 288 ks with a rotary ball mill have the sufficient nitrogen content of about 35000 ppm without subsequent nitriding, their magnetic properties are extremely deteriorated. The powders prepared by MG for 36 ks with a rotary ball mill and subsequent nitriding in N2 at 723 K for 21.6 ks show good rectangularity in the demagnetization curve and higher magnetization. The maximum energy product (BH)max and remanence are 129 kJ⋅ m-3 (16.1 MGOe) and 1.0 Wb⋅ m-2, respectively.


(Received February 21, 1996)

Keywords:

mechanical grinding, ammonia, nitriding, grain size, magnetization, coercivity, maximum energy product, rectangularity of demagnetization curve, vibration mill, rotary ball mill


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