Nd 2 Fe 14 C-based Magnet with Better Permanent Magnetic Properties Prepared by a Simple Mechanochemical Method

Nd2Fe14C-based magnet is prepared by a mechanochemical method, namely high-energy ball-milling Nd2Fe11Bx (x = 0-0.15) alloy in heptane (C7H16), followed by annealing to 850 degrees C in vacuum. Under the action of high-energy ball-milling, Nd2Fe11Bx react with heptane to form NdH2+delta, Fe-(CB), C, etc. H-2 is released and Nd2Fe17, Nd2Fe17Cx (x = 0-3), Nd2Fe14C, Nd carbides and alpha-Fe are formed in the subsequent annealing. C amount depends on ball-milling time t. Long time ball milling or high C content suppresses the formation of 2:17 phase and favors the formation of 2:14:1 phase in the final products. Excessive ball-milling results in the quick increase of alpha-Fe. The maximum of magnetically hard Nd2Fe14C is obtained at t = 4 h. For Nd2Fe11 samples, there exists considerable quantity of Nd carbides and alpha-Fe phase appears earlier and increases rapidly with extending the ball-milling time t. The addition of B element shortens the ball-milling time of the formation of maximum Nd2Fe14C and prominently suppresses the formation of Nd carbide and alpha-Fe. The optimum magnetic properties, coercivity H-i(c) of 1193.7 kA/m, remanence M-r of 580.9 kA/m, maximum magnetic energy product (BH)(max) of 91.7 kJ/m(3) is approaching to its theoretic value of 99.2 kJ/m(3) for isotropic Nd2Fe14C magnet, are obtained in Nd2Fe11B0.06 alloy ball milled for 3.5 h. (C) 2017 Elsevier B.V. All rights reserved.