Enhancement of the Coercive Force of Sm2Fe17N3 Powders via Surfactant Added Mechanical Milling

The effect of the mechanical milling of Sm2Fe17N3 nitride in a vibratory mill, in particular, the effect of the powder-to-ball mass ratio (m), milling time (t(mill)), milling medium, and concentration of added surfactants, has been systematically studied in order to determine optimum parameters for the high level of hysteresis properties of the magnetically anisotropic powder. It is shown that, as m increases from 15 to 50, the increase in the coercivity H-c of the powder at the beginning milling stages (t(mill) <= 4 h) is substantially accelerated; in this case, about 80% particles are less than 1 mu m in size. As the milling time increases (t(mill) > 4 h), the coercivity continues to increase. However, the specific residual magnetization sigma(r) and maximum energy product (BH)(max) begin to decrease because of the developed process of particle agglomeration, which results in a deterioration of the powder allignment. The addition of a surfactant to the protective medium markedly intensifies the milling process and accelerates the kinetics of the increase of H-c at the beginning milling stages at m = 15. The best complex of magnetic hysteresis properties, sigma(r) >= 135 emu/g, H-c, >= 8 kOe, and (BH)(max) >= 18 MG Oe, is observed for powders milled in 5% solution of oleic acid in acetone, 5% solution of capronic acid in toluene, and 1% solution of methyl caproate in toluene.