Mechanochemical Synthesis and Nitrogenation of the Nd(1.1)Fe(10)CoTi Alloy for Permanent Magnet

In this work, the mechanochemical synthesis method was used for the first time to produce powders of the nanocrystalline Nd(1.1)Fe(10)CoTi compound from Nd(2)O(3), Fe(2)O(3), Co and TiO(2). High-energy-milled powders were heat treated at 1000 °C for 10 min to obtain the ThMn(12)-type structure. Volume fraction of the 1:12 phase was found to be as high as 95.7% with 4.3% of a bcc phase also present. The nitrogenation process of the sample was carried out at 350 °C during 3, 6, 9 and 12 h using a static pressure of 80 kPa of N(2). The magnetic properties M(r), µ(0)H(c), and (BH)(max) were enhanced after nitrogenation, despite finding some residual nitrogen-free 1:12 phase. The magnetic values of a nitrogenated sample after 3 h were M(r) = 75 Am(2) kg(–1), µ(0)H(c) = 0.500 T and (BH)(max) = 58 kJ·m(–3). Samples were aligned under an applied field of 2 T after washing and were measured in a direction parallel to the applied field. The best value of (BH)(max) ~ 114 kJ·m(–3) was obtained for 3 h and the highest µ(0)H(c) = 0.518 T for 6 h nitrogenation. SEM characterization revealed that the particles have a mean particle size around 360 nm and a rounded shape.